Novel and highly durable air cathode electrocatalyst with three dimensional (3D)-clam-shaped structure, MnO2 nanotubes-supported Fe2O3 (Fe2O3/MnO2) composited by carbon nanotubes (CNTs) ((Fe2O3/MnO2)3/4-(CNTs)1/4) is synthesized using a facile hydrothermal process and a following direct heat-treatment in the air. The morphology and composition of this catalyst are analyzed using scanning electronic microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX). The morphology characteristics reveal that flower-like Fe2O3 particles are highly dispersed on both MnO2 nanotubes and CNT surfaces, coupling all three components firmly. Electrochemical measurements indicate that the synergy of catalyst exhibit superior bi-functional catalytic activity for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) as well as stability than Pt/C and IrO2 catalysts. Using these catalysts for air-cathodes, both primary and rechargeable zinc-air batteries (ZABs) are assembled for performance validation. In a primary ZAB, this 3D-clamed catalyst shows a decent open circuit voltage (OCV, ∼1.48 V) and a high discharge peak power density (349 mW cm−2), corresponding to a coulombic efficiency of 92%. In a rechargeable ZABs with this bifunctional catalyst, high OCV (>1.3 V) and small charge-discharge voltage gap (<1.1 V) are achieved along with high specific capacity (780 mAh g−1 at 30 mA cm−2) and robust cycle-life (1,390 cycles at cycle profile of 20 mA/10 min).Download high-res image (113KB)Download full-size image

•Fe/N/S-composited hierarchically porous carbon materials are realized with PAD as enriched N source.•FeSO4/PDA ratio plays a promotion role on improving Fe(x)/N/S-PAD’s ORR activity.•Fe(1.5)/N/S-PAD with a trace Fe content down to 1.0 wt.% shows the best catalytic ORR activity.•The stability during ORR in corrosive alkaline/acidic media for 5000 continuous cycles is achieved.•The porous structure and surface functionality influences ORR performance greatly.Non-precious Fe/N/S-composited hierarchically porous carbon materials (Fe(x)/N/S-PAD, PAD: poly(acrylamide-co-diallyldimethyl ammonium chlor), x: the weight ratio of FeSO4 7H2O/PAD) are synthesized using a facile silica colloid template approach with FeSO4 7H2O as Fe and S sources, and PAD as N source, respectively. A simultaneous creation of porous structures and surface functionalities (Fe, N and S) of such catalysts is realized just by simply tuning the weight ratio of FeSO4 7H2O and PAD in the synthetic precursors. As a result, a series of catalyst samples with high oxygen reduction reaction (ORR) activity/stability are obtained, demonstrating the promotion role of FeSO4/PAD ratio in synthesizing high-performing catalysts. Particularly, a catalyst (Fe(1.5)/N/S-PAD) with a trace Fe content down to 1.0 wt.% is tested to be superior to a commercial Pt/C catalyst in alkaline media and exhibits impressive ORR performance in acidic media. Combined with characterization results such as TEM, Raman spectra, BET and XPS analysis, it is found that the well-defined micro- and meso-porous structure play the key role in enhancing catalytic ORR performance rather than the final total N contents in the carbon. Regarding the stability of such a catalyst, test using cyclic voltammetry for 5000 cycles in O2-saturated solution shows a negligible degradation rate when compared with Pt/C one, suggesting that this catalyst could be used for catalyzing the high-performing cathode ORR in proton-exchange membrane fuel cells, alkaline fuel cells and metal–air batteries.Download high-res image (78KB)Download full-size image

•How addition agents affect the electrodeposition preparation of CTSS electrode was studied.•The carboxylic groups in addition agents affected the morphology of electrode surface.•The CTSS electrode by glucose exhibited highly porous coralline-like structure.•The CTSS electrode promoted the electrochemical oxidation of methylene blue in water.This paper describes assembling Ce-doped Ti/SnO2-Sb (CTSS) electrodes via electrodeposition by using glucose, citric acid, tartaric acid, oxalic acid and nothing (for comparison) as addition agent, respectively, for highly efficient organic wastewater treatment. The physicochemical properties of five CTSS electrodes were characterized by using the scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscope and electrochemical measurements. The measurement using SEM exhibited the highly porous coralline-like surface morphology of CTSS(glucose) electrode. It is attributed to fewer carboxylic groups in glucose than in other four addition agents. LSV curves showed that the oxygen evolution overpotentials were 2.36 V, 2.29 V, 2.35 V, 2.25 V, and 2.14 V for CTSS(glucose), CTSS(citric acid), CTSS(tartaric acid), CTSS(oxalic acid) and CTSS(nothing), respectively, indicating that using glucose as addition agent is conductive to electrode preparation for efficient electrocatalytic oxidation of organic wastewaters. The electrocatalytic oxidation removal of methylene blue (MB) was investigated in a 0.5 M H2SO4 and 0.1 M Na2SO4 aqueous solution. The color removal efficiencies after one-hour electrolysis treatment with CTSS(glucose) electrode in this aqueous medium at the current densities of 20, 40, 60 mA cm−2 were all more than 99%. It was found that the CTSS(glucose) electrode has more sufficient active catalytic sites and a service life of 23 h in an accelerated life test, which is longer than the other CTSS ones. Adding glucose into the electroplate liquid to assemble CTSS electrode did achieve more obvious decolorization.Download high-res image (146KB)Download full-size image

•Linear structured aliphatic chain helps to BET area and N/S content of HPCs.•Only pyridinic-N and graphitic-N are found, which happens to be active sites.•HPCs-PAADDA gives ORR performance in alkaline medium (E1/2 = 0.85 V).•HPCs-PAADDA shows high ORR performance even in acidic (E1/2 = 0.72 V) medium.•Long-term stability (CV, 5000) with high power density (516.3 mW cm−2) is realized.Electrochemical reduction of oxygen is the heart of the next-generation energy technologies to fuel cells and metal-air batteries, of which the reference catalysts suffer from two critical bottlenecks lying in their insufficient electroactivities and unclear active site structures. Herein, we introduce the effectively hierarchically porous carbons (HPCs) as the active-sites enriched platform for oxygen electroreduction. Three quaternized copolymers (PUB, PAADDA and PICP) with different chemical structures are used to pursue Fe/N/S-tailored ORR electrocatalysts. The most efficient one prepared by PAADDA gives the onset potential of 0.94 V and a half-wave potential of 0.85 V in basic solution, as well as superb electroactivities of low H2O2% and high electron transfer number in both alkaline and acidic medium. Surprisingly, they all display high discharge power density as applied to Zn-air fuel cells, and the HPCs-PAADDA catalyst thrillingly reaches 516.3 mW cm−2 when catalyst loading is optimized to 5.0 mg cm−2. The results elucidate that the polymer with long aliphatic chain is propitious to trap metals to create active sites and enwrap silica template to construct uniform pore structure. Only two kinds of nitrogen configuration (pyridinic-N and graphitic-N) are found with distinct structure in these HPCs, which happens to be active sites.Download high-res image (300KB)Download full-size image

Although both laboratory and large-scale studies have demonstrated the technological feasibility of electrochemical CO2 reduction (ERC) for producing useful low-carbon fuels, there are still challenges that hinder the practical use of Sn-based catalysts and electrodes in terms of both catalytic activity and stability. In this study, we discuss the design and engineering of several nanostructured SnO2 catalysts via a simple, safe, and low-emission hydrothermal method, targeted at solving low yield, insufficient electrode stability, and specifically high over-potential problems. SnO2 with a novel urchin-like microstructure was developed, which showed high catalytic ERC performance in a CO2-saturated 0.5 M KHCO3 aqueous electrolyte. The composition, morphology, crystal structure, and active surface area of the SnO2 nanocatalysts synthesized at different conditions were thoroughly characterized using SEM, TEM-based selected area electron diffraction (SAED), and XRD. Cyclic voltammetry and linear sweep voltammetry measurements demonstrated that the urchin-like nanostructured SnO2-180-5 (obtained at 180 °C for 5 h) possessed the optimal ERC performance in terms of onset potential, electron transfer, and current density. Such a catalyst exhibited highly selective CO2 reduction to formate, achieving ∼62% Faradaic efficiency at −1.0 V (vs SHE), which is among the lowest overpotentials reported to date for Sn(SnOx)-based catalysts.

With aminopyrine as a nitrogen-enriched small molecule precursor, a series of nitrogen doped carbon materials have been fabricated and explored as electrocatalysts for oxygen reduction reaction (ORR). The most active catalyst is a nitrogen doped carbon, which was prepared through a facile template-mediated pyrolyzing method using ferric nitrate (Fe(NO3)3·9H2O) as an activation reagent along with nanoscaled silica as a sacrificial support (hereafter referred to as AP/SiO2). The AP/SiO2 is confirmed and identified as having highly active molecule catalytic centers for ORR, due to its possessing a porous, sponge-like and uniform structure with a super-large specific surface area of 932.68 m2 g−1. The AP/SiO2 catalyst exhibited a high onset potential of 0.98 V, a half-wave potential of 0.82 V, and a high number of exchanged electrons (>3.8, close to four) in alkaline media. After 5000 continuous cycles, the material showed almost no negative shift with respect to the Pt/C material. Even in acidic medium, the AP/SiO2 catalyst still showed much higher durability than Pt/C and a low yield of HO2−. This work may have provided a new and simple route in the design and batch-synthesis of highly active and durable carbonaceous electrocatalysts for ORR.

High-temperature solid oxide electrolysis cells (SOECs) are advanced electrochemical energy storage and conversion devices with high conversion/energy efficiencies. They offer attractive high-temperature co-electrolysis routes that reduce extra CO2 emissions, enable large-scale energy storage/conversion and facilitate the integration of renewable energies into the electric grid. Exciting new research has focused on CO2 electrochemical activation/conversion through a co-electrolysis process based on the assumption that difficult CO double bonds can be activated effectively through this electrochemical method. Based on existing investigations, this paper puts forth a comprehensive overview of recent and past developments in co-electrolysis with SOECs for CO2 conversion and utilization. Here, we discuss in detail the approaches of CO2 conversion, the developmental history, the basic principles, the economic feasibility of CO2/H2O co-electrolysis, and the diverse range of fuel electrodes as well as oxygen electrode materials. SOEC performance measurements, characterization and simulations are classified and presented in this paper. SOEC cell and stack designs, fabrications and scale-ups are also summarized and described. In particular, insights into CO2 electrochemical conversions, solid oxide cell material behaviors and degradation mechanisms are highlighted to obtain a better understanding of the high temperature electrolysis process in SOECs. Proposed research directions are also outlined to provide guidelines for future research.

There has been a continuous need for high active, excellently durable and low-cost electrocatalysts for rechargeable zinc-air batteries. Among many low-cost metal based candidates, transition metal oxides with the CNTs composite have gained increasing attention. In this paper, the 3-D hollow sphere MnO2 nanotube-supported Co3O4 nanoparticles and its carbon nanotubes hybrid material (Co3O4/MnO2-CNTs) have been synthesized via a simple co-precipitation method combined with post-heat treatment. The morphology and composition of the catalysts are thoroughly analyzed through SEM, TEM, TEM-mapping, XRD, EDX and XPS. In comparison with the commercial 20% Pt/C, Co3O4/MnO2, bare MnO2 nanotubes and CNTs, the hybrid Co3O4/MnO2-CNTs-350 exhibits perfect bi-functional catalytic activity toward oxygen reduction reaction and oxygen evolution reaction under alkaline condition (0.1 M KOH). Therefore, high cell performances are achieved which result in an appropriate open circuit voltage (∼1.47 V), a high discharge peak power density (340 mW cm−2) and a large specific capacity (775 mAh g−1 at 10 mA cm−2) for the primary Zn-air battery, a small charge–discharge voltage gap and a high cycle-life (504 cycles at 10 mA cm−2 with 10 min per cycle) for the rechargeable Zn-air battery. In particular, the simple synthesis method is suitable for a large-scale production of this bifunctional material due to a green, cost effective and readily available process.

•PVA/PUB copolymer linear anion-exchange sites membranes are prepared.•The OH– conductivity reaching ~ 0.01 S cm− 2 is obtained for the membrane.•The membranes show perfect extensibility (200–400%) and tensile stress (15–30 MPa).•The membrane can retain the alkaline stability in tough condition (8 M KOH at 80 °C > 240 h).•MEAs fabricated with the membrane shows power density of 28.6 mW cm− 2 and an OCV of 1.0 V at 25 °C.This study focused on the design and fabricating of a new type of hydroxyl anion conducting membranes employing the interpenetrating polymer network (IPN) comprising poly (vinyl alcohol) (PVA) and linear structured poly bis(2-chloroethyl) ether-1,3-bis [3-(dimethylamino)propyl] urea copolymer (PUB). The membranes are synthesized through blending assisted by a simple chemical cross-linking process. Various characterizations are conducted including Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), gravimetric analysis (TG), X-ray photoelectron spectroscopy (XPS) and AC impedance. Results revealed that by simply tuning the mass fraction of PUB (the content of PUB changed from 20%–50%) in the membrane, the OH– conductivity (10− 2 S cm− 1 at 80 °C, fully hydrated membranes) with high extensibility (at break in the range of 200–400%) and tensile stress (at break around 15–30 MPa, ∼ 50% relative humidity) are achieved. XPS analysis reveals that a slight degradation occurs when the membrane is exposed to exceedingly tough conditions such as 8 M KOH at 80 °C for 240 h, but the OH– conductivity is changed insignificantly. When assembled in a real H2/O2 alkaline fuel cell, the initial peak power densities in the range of 5.7–28.6 mW cm− 2 and an open circuit potential reaching to 1.0 V are obtained for MEAs fabricated with these membranes at 25 °C.

•The paper provides an overview of transition metal macrocyclic (TMM) complex-based electrocatalysts used in ORRs in PEMFCs.•Performances of TMM catalysts, including both ORR activity rates and stabilities, are discussed.•The effects of different types and natures of metals, macrocyclic ligands, and so on are analyzed and reviewed.•Required improvements of TMM catalysts in ORR activity, stability and commercial viability are identified.•Potential research directions to overcome current challenges are suggested.This paper provides a comprehensive overview of the current state of development of transition metal macrocyclic (TMM) complex-based electrocatalysts used in oxygen reduction reactions (ORRs) in polymer electrolyte membrane fuel cells (PEMFCs).Up to date performances of carbon material-supported TMM catalysts, including both ORR activity rates and stabilities are, discussed. The effects of different types and natures of metals, macrocyclic ligands, ligand substitutions, catalyst supporting materials, electrode preparation, and various acid/alkaline solutions are thoroughly analyzed and reviewed based on the published literature. The ORR mechanisms facilitated by these TMM catalysts are discussed from both a theoretical and experimental observation point of view. Required improvements in ORR activity, stability and commercial viability in order for TMM complex-based electrocatalysts to be utilized in PEMFCs are identified. Potential research directions to overcome current challenges are also suggested to facilitate future efforts in this area.

A new type of Fe, N-doped hierarchically porous carbons (N–Fe-HPCs) has been synthesized via a cost-effective synthetic route, derived from nitrogen-enriched polyquaternium networks by combining a simple silicate templated two-step graphitization of the impregnated carbon. The as-prepared N–Fe-HPCs present a high catalytic activity for the oxygen reduction reaction (ORR) with onset and half-wave potentials of 0.99 and 0.86 V in 0.1 M KOH, respectively, which are superior to commercially available Pt/C catalyst (half-wave potential 0.86 V vs. RHE). Surprisingly, the diffusion-limited current density of N–S-HPCs approaches ∼7.5 mA cm−2, much higher than that of Pt/C (∼5.5 mA cm−2). As a cathode electrode material used in Zn–air batteries, the unique configuration of the N–Fe-HPCs delivers a high discharge peak power density reaching up to 540 mW cm−2 with a current density of 319 mA cm−2 at 1.0 V of cell voltage and an energy density >800 Wh kg−1. Additionally, outstanding ORR durability of the N–Fe-HPCs is demonstrated, as evaluated by the transient cell-voltage behavior of the Zn–air battery retaining an open circuit voltage of 1.48 V over 10 hours with a discharge current density of 100 mA cm−2.

•Using N-S-MPC as cathode catalyst, the effects of catalyst/bonding layer on the power generation are investigated.•The power density increased with increasing N-S-MPC loading, and reached the maximum when loading is 3 mg cm−2.•The local hydroxyl ion concentration is important, which was favorably for the process of ORR.•The bonding layer has a great influence on the MEA performances.•The MEA using 30 μL bonding layer produced a maximum power density of AMFC.In this study, nitrogen and sulfur co-doped mesoporous carbon (N-S-MPC) materials are selected as the platform to demonstrate the potential of N-S-MPC to replace precious metal catalyst for fuel cell cathode oxygen reduction. Using both N-S-MPC and commercial available 40%Pt/C as cathode catalysts, the effects of catalyst and bonding layer in the catalyst layer (CL) on the power generation performances are thoroughly investigated for alkaline membrane fuel cells (AMFCs). Through single cell tests, several observations are reached as follows: (1) For N-S-MPC cathode, with increasing N-S-MPC loading from 1.00 to 5.00 mg cm−2, the power density reached the maximum (21.7 mW cm−2) when the catalyst loading is 3 mg cm−2. However, for Pt/C cathode the power density reached the maximum (21.3 mW cm−2) for a catalyst loading of 0.5 mg cm−2, with increasing loading from 0.3 to 0.5 mg cm−2; (2) Increasing the thickness of catalyst layer resulted in an increase in power density. Thus, raising the local hydroxyl ion concentration was in favor of the process of oxygen reduction reaction. (3) The bonding layer also has a significant influence on the MEA fabrications, where the MEA using 30 μL bonding layer produced a maximum power density of 20.8 mW cm−2.

•One-pot synthesis of NiCo2O4 nanosphere and carbon nanotubes hybrid catalysts is reported.•NiCo2O4-CNTs hybrid exhibited highly catalytic activity for both ORR and OER.•The primary Zn–air battery reached a discharge peak power density of 320 mW cm−2.•The rechargeable Zn–air battery showed a stability of 100 h at 10 mA cm−2 with 10 min per cycle.Developing low-cost non-precious metal catalysts for high-performance oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is highly desirable. In this work, both the primary and rechargeable Zn–air batteries with NiCo2O4 nanosphere and carbon nanotubes hybrid (NiCo2O4-CNTs) as cathode catalyst are reported. The catalysts are synthesized through a facile one-pot precipitation reaction and hydrothermal process, which exhibited highly active bi-functional catalytic activity for both ORR and OER. Using NiCo2O4-CNTs hybrid as a cathode catalyst, the resulting practical primary and electrochemically rechargeable Zn–air batteries give a promising discharge peak power density as high as 320 mW cm−2, and a high current density 210 mA cm−2 at 1.0 V. Also, the rechargeable Zn–air batteries in a two-electrode configuration exhibits an unprecedented small charge–discharge voltage polarization of ∼0.75 V at 10 mA cm−2, high reversibility and stability over long charge and discharge cycles. The high performance is believed to be induced by the hybrid effect (coupling effect) among NiCo2O4 and CNTs, which can produce a synergy enhancement for both catalytic ORR and OER.

Nitrogen-doped graphene materials have been demonstrated as promising alternative catalysts for the oxygen reduction reaction (ORR) in fuel cells and metal–air batteries due to their relatively high activity and good stability in alkaline solutions. However, they suffer from low catalytic activity in acid medium. Herein, we have developed an efficient ORR catalyst based on nitrogen doped porous graphene foams (PNGFs) using a hard templating approach. The obtained catalyst exhibits both remarkable ORR activity and long term stability in both alkaline and acidic solutions, and its ORR activity is even better than that of the Pt-based catalyst in alkaline medium. Our results demonstrate a new strategy to rationally design highly efficient graphene-based non-precious catalysts for electrochemical energy devices.

•A comprehensive reviews on radiation-grafted alkaline membranes (RGAMs).•Alkaline polymer electrolyte fuel cells.•RGAM synthesis/fabrication/characterization, membrane material selection, and theoretical approaches.•Alkaline polymer electrolyte fuel cells.•RGAM challenges and possible research directions.The past two decades have witnessed many efforts to develop radiation-grafted alkaline membranes for alkaline PEM fuel cell applications, as such membranes have certain advantages over other kinds of alkaline membranes, including well-controlled composition, functionality, and other promising properties. To facilitate research and development in this area, the present paper reviews radiation-grafted alkaline membranes. We examine their synthesis/fabrication/characterization, membrane material selection, and theoretical approaches for fundamental understanding. We also present detailed examinations of their application in fuel cell in terms of the working principles of the radiation grafting process, the fabrication of MEAs using radiation-grafted membranes, the membranes' corresponding performance in alkaline PEM fuel cells, as well as performance optimization. The paper also summarizes the challenges and mitigation strategies for radiation-grafted alkaline membranes and their application in PEM fuel cells, presenting an overall picture of the technology as it presently stands.

•The yolk-shell Co and N codoped porous carbon microspheres have been synthesized.•The formation process of the yolk-shell precursor is discussed in-depth.•YS-Co/N-PCMs display high ORR and OER performance in alkaline medium.•The integrated yolk-shell and porous structure ensures superior ORR performance.•The YS-Co/N-PCMs outperform Pt/C in methanol resistance ability and stability.The structures and compositions of materials have important influences on their performance. Herein, hierarchically structured yolk-shell Co and N codoped porous carbon microspheres (YS-Co/N-PCMs) have been successfully synthesized by using low-cost melamine, formaldehyde and cobalt acetate as raw materials via a facile template-free hydrothermal method and a subsequent pyrolysis. The formation process of the yolk-shell precursor is systematically investigated, involving a morphological evolution process from solid microspheres, ultrathin and wrinkled shells wrap, to yolk-shell structure formation. More importantly, the unique structure combines the favorable features towards oxygen reduction reaction (ORR), such as high surface area, sufficient Co-Nx and graphitic N active sites and suitable pore structures. As a result, the YS-Co/N-PCMs catalyst shows high catalytic activity for ORR in alkaline media for fuel cells, which not only outperforms commercial Pt-based catalysts in terms of resistance to methanol crossover and long-time stability, but is also better than many non-precious metal doped carbon-based catalysts reported previously. In addition, the YS-Co/N-PCMs catalyst also has high catalytic activity toward oxygen evolution reaction (OER). Therefore, the YS-Co/N-PCMs catalyst may serve as a promising alternative to Pt/C catalyst for ORR and OER in alkaline media.

Non-precious metal oxygen reduction reaction (ORR) catalysts were prepared by pyrolyzing a carbon supported complex consisting of iron acetate coordinated with 1,2,4,5-tetracyanobenzene (TCNB) in an iron phtalocyanine-like polymer arrangement. The effect of heat treatment temperature is systematically investigated from 700 to 1000 °C, with ORR activity investigated by half-cell electrochemical evaluation in 0.1 M HClO4. The highest ORR performance is obtained for the sample heat treated at 1000 °C, with this sample demonstrating high (>98%) selectivity towards the efficient 4 electron reduction mechanism, comparable with some of the best non-precious metal catalysts reported to date. The physical and surface properties of the prepared catalysts were investigated by high-resolution transmission electron microscopy (TEM), fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and BET surface area analysis. After heat treatment, a thin (<10 nm) coating was observed on the surface of the carbon supports, attributed to residual species remaining from the heat treated precursor complex that provide the source of ORR activity.

Nitrogen and sulfur dual-doped mesoporous carbons (NSMCs) have been fabricated through a facile template-mediated pyrolyzing method using poly(ethyleneimine) (PEI) as sources of nitrogen (N) and carbon (C), ferrous sulfate(FeSO4 7H2O) as both precursor of sulfur (S) and activation reagent along with nanoscaled silica as sacrificial supports. The composition, morphology, and microstructure of the products are characterized using X-ray diffraction, scanning electron microscopy, nitrogen sorption analysis and X-ray photoelectron spectroscopy. It reveals that these NSMCs possess a BET surface area over 1064 m2 g−1and abundant mesoporous structure with pore size ranged from 4 to 20 nm. The atomic percentages of N and S functionalities are found to be 4.00 at.% N and 0.83 at.% S, indication of successful incorporation of both nitrogenand sulfur into carbon network. Benefiting from the aforementioned characteristics, these NSMCs show perfect supercapacitive performances, which have been demonstrated by cyclic voltammetry and constant-current charge/discharge cycling techniques. In 0.5 M H2SO4 electrolyte, the specific capacitance (SC) of the as-prepared NSMCs electrode can reach 280 F/g at a current density of 1 A/g. Even at a high rate capability of 100 A/g, the NSMCs electrode still shows the SC value as high as 232 F/g, retaining 83% of that at 1 A/g. Also, the electrode exhibits excellent charge/discharge cycling stability, and no measurable capacitance losses is observed even after 5000 cycles, making them potentially promising for high-performance energy storage devices.

Novel alkaline anion-exchange membranes composed of chitosan (CS) and 1-Ethenyl-3-methyl-1H-imidazoliumchloride polymer with 1-ethenyl-2-pyrrolidone (abbreviated as EMImC-Co-EP) are prepared by a combined thermal and chemical cross-linking technique. The hydroxide conductivity (σOH-), water uptakes, ion exchange capacity (IEC), thermal stability, mechanical property, oxidative stability and alkaline stabilities of CS/EMImC-Co-EP membranes are measured to evaluate their applicability in H2/O2 alkaline fuel cells (FC). The effects of thermal cross-linking temperature and membrane composition on membrane OH− conductivity are studied using AC impedance technique. FTIR, SEM and TG analysis are used for structural characterization of these membranes. It is found that the OH− conductivity of the membranes increases with temperature and exceeds 10−2 S cm−1 at 80 °C. The CS/EMImC-Co-EP membranes show excellent thermal stability with onset degradation temperature high above 200 °C. In particular, the high alkaline stability is achieved for the CS/EMImC-Co-EP membranes in hot 8.0 M KOH at 85 °C without losing their integrity and OH− conductivity during 300 hours of evaluation, and also a relatively high oxidative stability. The membrane electrode assembly (MEA) fabricated with CS/EMImC-Co-EP (1:0.5 by mass) gives an initial power density of 21.7 mW cm−2 using H2 as the fuel and O2 as oxidant at room temperature, on a low metal loading on both the anode and the cathode of 0.5 mg (Pt) cm−2 at ambient temperature.

•Ppy hollow nanospheres support provides new ways to develop catalyst materials as a result of its distorted structure and large surface area.•Ppy hollow nanospheres with uniform size have been successfully prepared through chemical oxidative polymerization of pyrrole in the presence of PS microspheres.•Pa nanoparticles have been successfully assembled on the surface of hollow ppy nanospheres.•Pd/H-ppy exhibits good electrocatalytic activity and stability for ethanol electrooxidation.A facile and low-cost preparation of Pd nanoparticles on the surface of hollow polypyrrole (ppy) nanospheres was introduced in this paper through solvothermal reaction. Herein, uniform polystyrene (PS) microspheres as sacrificial templates were rapidly prepared through a emulsion polymerization method, and then the hollow ppy nanospheres were obtained through chemical oxidative polymerization of pyrrole in the presence of PS microspheres. According to X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements, the novel Pd nanoparticles are well-dispersed on the surface of hollow ppy nanospheres with a relatively narrow particle size distribution. The diameters of hollow ppy nanospheres range from 240 to 280 nm, and the average shell thickness is about 15 nm. Electrochemical analysis results indicate that the as-prepared Pd nanoparticles on the surface of hollow ppy nanospheres (Pd/H-ppy) exhibit good electrocatalytic activity and stability for ethanol electrooxidation.Ppy hollow nanospheres with uniform size have been successfully prepared and employed as the supports for Pd nanoparticles with smaller particle size and better dispersion. Electrochemical measurements demonstrate that the obtained Pd/H-ppy exhibits good electrocatalytic activity and stability for ethanol electrooxidation.

This study reports novel kinds of high tensile strength alkaline anion-exchange membranes composed of imidazolium-functionalized anion exchange polymer electrolytes. The membranes were prepared by a combined thermal and chemical cross-linking of poly (vinyl alcohol) and poly (3-methyl-1-vinylimidazolium chloride)-co-(1-vinylpyrrolidone) (PMVIC-co-VP). Characterizations by AC impedance technique, mechanical property, FTIR spectroscopy, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), along with the water uptake, alkaline resistance and oxidation stability were carried out on the membranes consisting of different PVA/PVA-PMVIC-co-VP mass ratios to evaluate their applicability in alkaline fuel cells. The membrane in a mass ratio of 1:0.4 exhibited high tensile stress at break in the range of 59.3∼76.6 MPa, and the elongation at break around 9.2∼14.9%, depending on the annealing temperature from 130∼190 °C. The OH− conductivity of the membranes was found to be increased with increasing annealing temperature and mass ratio, and reached high up to 1.7 × 10−2 S cm−1. Besides, the membranes showed perfect oxidation stability in 30% H2O2 for 250 hours with no obvious weight loss was observed. XPS analysis indicated that some degradation occurred when the membrane was exposed to 8 M KOH at 85 °C for 312 h, but no lessened OH− conductivity was detected. SEM pictures revealed an ordered microvoid structure with pore size ca. 100∼150 nm uniformly dispersed on the membrane surface, which imparted the PVA/PVA-PMVIC-co-VP membrane with good OH− conductivity.

This research aims to outline a simple but effective way combining orthogonal array design (OAD), experiments and characterization to produce desirable activated carbons (AC) from agricultural wastes. OAD, and experiments including carbonization, KOH impregnation and activation were combined to optimize the preparation of AC derived from coffee residues with high specific surface areas. Results suggest that the optimized parameters are a carbonization temperature (Tc) of 450 °C (30 min), a KOH impregnation ratio (Rkc) of 3:1, and an activation temperature (Ta) of 750 °C (60 min). Extensive experiments further showed that a 100-min (ta) activation with Ta of 900 °C achieved AC with a specific surface area of 2111 m2/g, a high value that has not been reported previously in the production of AC from coffee wastes. Such high specific surface areas are favorable for use in water treatment, but will lead to a reduced yield of AC. N2 adsorption–desorption isotherms, scanning electron microscopy and Fourier transform infrared spectroscopy were shown to be useful tools for investigating the specific surface area, surface functional groups and pore size distribution of AC. Capacitance performance that may indicate the electrosorption capability of AC being used as electrode materials in capacitive deionization was examined by cyclic voltammetry and galvanostatic charge–discharge curves, and the consistency with specific surface areas was confirmed.

Gas diffusion electrodes (GDEs) modified with N,Nʹ-Bis(salicylidene)-ethylenediamine-cobalt(II) (Cosalen) and conductive carbon black (BP) have been prepared. It is demonstrated that modified BP-Cosalen/GDE electrode is able to catalyze CO2 reduction in a more efficient and selective manner than that of bulk Cosalen/GDE in 0.5 M KHCO3 solution. In the presence of 60 wt% of BP, the as-prepared BP-Cosalen/GDE electrode exhibits the highest activity for catalyzing CO2 reduction reaction, wherever increase or decrease the amount of BP do not benefit to CO2 reduction. Compared to other BP-Cosalen/GDE electrodes, the BP-Cosalen/GDE60 shows the most positive onset potential, and the maximum current density reaches 21 mA cm−2. The improved catalytic activity is largely due to the excellent electrical conductivity and the developed pore structure of BP which provides more active phases for the electrochemical reduction of CO2. Further analysis of reduction product reveals that the product on BP-Cosalen/GDE60 electrode is formate in 0.5 M KHCO3 electrolyte. The highest faradaic efficiency reached 27 % along with the production rate of formate as much as 0.44 mM.

•A spontaneous formation of Cu–N–S/C catalysts was realized using a one-step pyrolysis.•The obtained catalysts exhibit high catalytic activity for ORR in alkaline media.•The pyrolysis process can change the ORR parthway from a 2e− transfer process to a 4e− one.•Increasing the catalyst loading can efficiently improve the ORR activity.•Cu-bonded graphitic–N, pyridinic–N and C–Sn–C serve as the ORR catalytic sites.In this work, we report a spontaneous formation of copper (Cu–N–S/C) catalysts containing both nitrogen (N) and sulfur (S) elements using a one-step pyrolysis of carbon supported copper phthalocyanine tetrasulfonic acid tetrasodium salt (CuTSPc/C). The obtained catalysts exhibit high catalytic activities for oxygen reduction reaction (ORR) in alkaline media. Through electrochemical measurements and physical characterizations, several observations are reached as follows: (1) different pyrolysis temperatures can result in different catalyst structures and performances, and the optimum pyrolysis temperature is found to be 700 °C; (2) the electron transfer number of the ORR process catalyzed by the unpyrolyzed catalyst is about 2.5, after the pyrolysis, this number is increased to 3.5, indicating that the pyrolysis process can change the ORR pathway from a 2-electron transfer dominated process to a 4-electron transfer dominated one; (3) increasing catalyst loading from 40 μg cm−2 to 505 μg cm−2 can effectively improve the catalytic ORR activity, under which the percentage of H2O2 produced decreases sharply from 39.5% to 7.8%; and (4) the Cu ion can bond on pyridinic–N, graphite–N and C–Sn–C to form Cu–N–S/C catalyst active sites, which play the key role in the ORR activity.

Nitrogen and sulfur co-doped mesoporous carbon materials are synthesized by pyrolyzing FeSO4 + poly(ethyleneimine) + template SiO2 mixture at a high temperature without additional dopant precursors. For post-treatment, acid leaching is used to remove the metal, and the heat-treatment is tailored to optimize the catalytic activity of the catalysts toward the oxygen reduction reaction (ORR) in acidic solution. Scanning electron microscopy, X-ray diffraction, low-temperature N2 adsorption, X-ray photoelectron spectroscopy and inductively coupled plasma are used to characterize the catalysts' morphologies, structures, and compositions. Rotating disk electrode and rotating ring-disk electrode techniques are employed to quantitatively obtain the ORR kinetic constants and determine the reaction mechanisms. The ORR activity is highly improved by reheating the catalyst after H2SO4 leaching with improved half-wave potential of 0.68 V vs. RHE, and ORR electron number larger than 3.76. Moreover, increasing the catalyst loading of 800 μg cm−2 exhibits only ∼36 mV deviation from Pt/C. It is believed that the synergetic effect between the Fe-, N- and S-containing active sites and the modified carbon matrix structure due to H2SO4 leaching and reheating should make contribution to the high ORR activity.

•An effective fibrous Cu electrode surface was proposed.•The Cu electrode surface contained a layered nanosphere–nanofiber structure.•A surface area of 458.1 cm2/cm2 was achieved.•The fibrous Cu electrode surface was high active for CO2 electroreduction.•A Faradaic efficiency of HCOO- yield reached 43% at low overpotentials.•The electrode surface is stable over 19 hours electrolysis compared to smooth Cu.An effective fibrous Cu electrode surface, created using a procedure combining high-temperature annealing and electroreduction, is explored for CO2 reduction to produce useful fuels. The nanostructure of this Cu electrode surface contains a layer of nanofibers or nanofibers surrounded by kernels with 30–100 nm diameters. With a specific surface area as high as 458 cm2 per geometric electrode surface area, this nanostructured electrode is found to have a high activity toward CO2 reduction, indicated by its more positive reduction potentials and higher catalytic current density than a smooth Cu electrode. The Faradaic efficiency for HCOO− production is 43%, and the electrode surface remains stable during 19 h of electrolysis — better results than with smooth Cu under identical conditions.

Various CuxO catalysts with different special microstructures were synthesized using a simple one-step hydrothermal method by controlling the reaction time and temperature conditions. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) were used to observe the morphologies of the received catalysts. The 3-dimensional (3D) hierarchical nanospheres (500 nm) comprised of secondary structured nanorods (50 nm) are formed at 180 °C for 2 hours. However, when increasing the hydrothermal reaction temperature to 220 °C, solid microspheres with a large size of 2.5 μm begin to appear instead of flabby hierarchical nanospheres. To further investigate the effect of morphologies on the activity and production selectivity of CuxO catalysts, cyclic voltammetry (CV) was used to evaluate the onset potential and current density of catalyzed CO2 reduction combining linear sweep voltammetry (LSV) in 0.5 M KHCO3 solution. The effect of catalyst loading was also tested by applying the gas diffusion layer (GDL) to make up a working electrode for CO2 electroreduction. The results indicate that the synthesized temperature of 180 °C for 2 h is the optimal condition for CuxO nanospheres and the optimal loading is about 3 mg cm−2, under which the onset potential for CO2 electroreduction reaches −0.55 V vs. SHE. By ion chromatography measurement, the faradaic efficiency and production rate of produced formate was found to be 59%, which is much higher than most reported Cu-based catalysts at the same electrolysis conditions, indicating the high selectivity of the CuxO nanospheres due to their controlled special surface morphology.

•A novel series of proton-exchange membranes from partially fluorinated SPAESs were synthesized.•The membranes show excellent dimensional stability and oxidative stability.•A maximum proton conductivity of 0.35 S cm−1 at 90 °C is achieved for SPAES membrane with 50% SDCDPS.•A H2/O2 fuel cell reaches the power density of 120.6 mW cm−2 at 30 °C and 224.3 mW cm−2 at 80 °C.A novel series of sulfonated poly(arylene ether sulfone)s (SPAESs) containing fluorophenyl pendant groups are successfully developed and their membranes are evaluated in low-temperature proton exchange membrane fuel cells. The SPAESs are synthesized from 4,4′-dichlorodiphenylsulfone (DCDPS), 3,3′-disulfonate-4,4′-dichlorodiphenylsulfone (SDCDPS), and (4-fluorophenyl)hydroquinone by nucleophilic aromatic substitution polycondensation. The structure and properties of SPAESs membranes are characterized using 1H-NMR, EA, FT-IR, TG, and DSC, along with the proton conductivity, water uptake, ion exchange capacity and chemical stability. A maximum proton conductivity of 0.35 S cm−1 at 90 °C is achieved for SPAES membrane with 50% SDCDPS. These SPAES membranes display high dimensional stability and oxidative durability, due to the introduction of fluorophenyl pendant groups on the polymer backbone. The fuel cell performances of the MEAs with SPAES reaches an initial power density of 120.6 mW cm−2 at 30 °C, and greatly increases to 224.3 mW cm−2 at 80 °C using H2 and O2 gases.

Carbon nanotubes are believed to be powerful materials for constructing novel hybrid composites with desirable functionalities and applications in many fields. Therefore, a better understanding of the functionalization of multiwalled carbon nanotubes (MWCNTs) holds the key to a better performance of the hybrid properties. In this paper, with a series of aromatic bifunctional molecule additives, modified MWCNTs were used as composite supports for synthesizing nanostructured palladium catalysts for formic acid oxidation. The additives contain anthranilic acid, o-phenylenediamine, salicylic acid, catechol, and phthalic acid. The influence of the different bifunctional groups (such as –NH2, –OH, –COOH, and their mixed groups) on the morphologies, particle sizes, and electrical properties of Pd nanocrystals was intensively studied. Transmission electron microscopy measurement demonstrates that the palladium nanoparticles were well dispersed on the surface of MWCNTs with a relatively narrow particle size distribution in the presence of the additives. Cyclic voltammetry and chronoamperometry tests demonstrate that the functional groups of the additives play an important role in electrocatalytic activity and stability for formic acid oxidation, and the influence law of various functional groups on electrocatalytic activity and stability is also investigated in this paper. We hope it can provide certain theoretical guidance meaning and practical reference value in future studies.

In this review, we examine the most recent progress and research trends in the area of alkaline polymer electrolyte membrane (PEM) development in terms of material selection, synthesis, characterization, and theoretical approach, as well as their fabrication into alkaline PEM-based membrane electrode assemblies (MEAs) and the corresponding performance/durability in alkaline polymer electrolyte membrane fuel cells (PEMFCs). Respective advantages and challenges are also reviewed. To overcome challenges hindering alkaline PEM technology advancement and commercialization, several research directions are then proposed.

A facile one-step and low-cost preparation of Pd–Co bimetallic hollow nanospheres on the surface of multi-walled carbon nanotubes (MWCNTs) is introduced in this paper through a solvothermal reaction. Herein, spherical micelles composed of hexadecyl trimethyl ammonium bromide (CTAB) were employed as soft templates and ethylene glycol (EG) was used as both a solvent and as a reducing agent. According to the X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements, the novel Pd–Co bimetallic hollow nanospheres are well-dispersed on the surface of the MWCNTs with a relatively narrow particle size distribution. The diameters of the hollow nanospheres range from 77 to 89 nm, and the average shell thickness is about 10 nm. The electrochemical analysis results indicate that the as-prepared bimetallic hollow nanospheres exhibit a superior electrocatalytic activity and stability for ethanol electrooxidation than the pure palladium catalyst.

Hydroxyl anion conducting membranes have been developed using poly(vinyl alcohol) (PVA) as polymer matrix by incorporation of poly(diallyldimethylammonium chloride) (PDDA) as anion charge carriers. PDDA of four different molecular weight (namely PDDA-HMw, PDDA-MMw, PDDA-LMw and PDDA-ULMw) was incorporated in order to clarifying the effect of molecular weight on membrane performances. The membranes are characterized in detail by FTIR spectroscopy, scanning electron microscopy (SEM), thermal gravity analysis (TG), mechanical property, AC impedance technique, water uptake, swelling ratio, oxidation and alkaline stability to evaluate their applicability in alkaline fuel cells. The OH− conductivity of the membranes was found to be increased with increasing molecular weight of PDDA, and the maximum OH− conductivity of 0.027 S cm−1 was achieved for PVA/PDDA-HMw membrane. The PVA/PDDA-HMw membrane also showed the best mechanical property and excellent thermal stability due to the most compact and dense network structure. All the membranes showed relatively high oxidative stability in 30% H2O2 and strong alkaline stability in 2 M KOH for 624 h at room temperature. The fuel cell performances of the MEAs with these membranes were 18.2, 23.4, 28.5 and 35.1 mW cm−2 using H2 and O2 gases at 25 °C. The long-term stability of single-cell performance showed that the PVA/PDDA membrane could approximately last 80 h on the fuel cell with only a slight decrease of 0.1 V in cell potential.

Development of high-performance cost-effective electrocatalyts that can replace Pt catalyst have been a central theme in polymer electrolyte membrane fuel cells (PEMFCs) including direct methanol fuel cells (DMFCs). Here we show that carbon-supported pyridine–cobalt nanoparticles (CoPy/C) can generate a high catalytic activity toward the oxygen reduction reaction (ORR). The catalysts are synthesized using cobalt sulfate heptahydrate (CoSO4·7H2O) and pyridine (Py) as the Co and N precursors via a solid state reaction by heat-treatment in an inert atmosphere at 800 °C. In particular, the ORR kinetics on these catalyst materials are evaluated using rotating disk electrode (RDE) technique in electrolytes of various KOH concentrations, ranging from 0.05 to 12 M. The Koutecky–Levich equation analyses indicate that the transferred electron number, n, per oxygen molecule on CoPy/C electrode depend on the low negative ovevrpotentials in low KOH concentrations, whereas in high KOH concentrations the values of n for oxygen reduction depend on the high negative overpotentials, and varies between 3.5 and 4.0. These catalysts exhibit the superior methanol tolerance to commercial 40%Pt/C catalyst, and the negative effect of high KOH concentration is much less for CoPy/C than for Pt/C, suggesting the promising utilization of CoPy/C as electrocatalysts for alkaline polymer electrolyte membrane fuel cells.

This study reports a novel alkaline anion-exchange membrane from poly(vinyl alcohol)/poly(acrylamide-co-diallyldimethylammonium chloride) by incorporating poly(ethylene glycol) as a plasticizer and modified by chemical cross-linking method (PVA/PAADDA/PEG). The membranes are characterized by infrared spectra (FT-IR), scanning electron microscope (SEM) and thermogravimetric analysis (TG). The conductivity, water uptake, ion exchange capacity (IEC), and chemical stability of membranes are determined to evaluate their applicability in alkaline direct methanol alkaline fuel cells (DMAFC). The anionic conductivity (OH−-conductivity) is found to be greatly dependent on the content of PAADDA and PEG in the PVA matrix. The conductivities of up to 1.53 × 10−3 S cm−1 at 25 °C and 8.5 × 10−3 S cm−1 at 80 °C are achieved for PVA/PAADDA/PEG in a mass ratio of 1:0.25:0.25. The membranes also show good alkali and oxidative stability. An open-circuit voltage of 0.85 V and an initial power density of 15.4 mW cm−2 of ADMFC with the membrane (=1:0.25:0.25 by mass), 2 M methanol, 2 M KOH, and humidified oxygen are achieved at room temperature.Highlights► PVA/PAADDA/PEG alkaline membranes were prepared. ► OH− conductivity was found to be greatly dependent on the content of PAADDA and PEG in the PVA matrix. ► The membrane display conductivities of 1.53 mS cm−1 at 25 °C and 8.5 mS cm−1 at 80 °C. ► Performance of DMAFC showed a peak power density of 15.9 mW cm−2.

Carbon-supported copper phthalocyanine (CuPc/C) nanoclusters, as a novel suitable cathode catalyst in polymer electrolyte membrane fuel cells, have been synthesized via a combined solvent impregnation and milling procedure along with high-temperature treatment. For optimizing the electrocatalytic activity of the catalyst obtained, the electrode with varying Nafion ionomer contents in the catalyst layer was screened by cyclic voltammetry and linear sweep voltammetry employing a rotating disk electrode technique to investigate the effect of Nafion ionomer as for alkaline electrolyte. For comparative purposes, electrode with various contents of available anion-ionomer was also investigated. The results revealed that the content of Nafion ionomer can affect the oxygen reduction reaction activity of the CuPc/C catalyst and an optimal content of Nafion ionomer was around 3.5 × 101 μg cm−2, which corresponds well with the electrode prepared using available anion-ionomer. The electrode prepared using Nafion ionomer can produce a comparable performance to that of using available anion-ionomer, giving an onset potential at 0.1 V with a half-wave potential of −0.03 V. Furthermore, Koutechy–Levich analysis showed that the value of electron transfer number is in the range of 3.40 to 3.74 when using electrode with varying Nafion ionomer contents from 2.5 × 101 to 1.6 × 102 μg cm−2. The membrane electrode assembly fabricated with the CuPc/C cathode catalyst with a loading of 3.6 mg cm−2 and a Nafion membrane immersed in 3 M KOH for 48 h produced a power density of 3.8 mW cm−2 at room temperature.

Novel proton-conducting polymer electrolyte membranes have been prepared from bacterial cellulose by incorporation of phosphoric acid (H3PO4/BC) and phytic acid (PA/BC). H3PO4 and PA were doped by immersing the BC membranes directly in the aqueous solution of H3PO4 and PA, respectively. Characterizations by FTIR, TG, TS and AC conductivity measurements were carried out on the membrane electrolytes consisting of different H3PO4 or PA doping level. The ionic conductivity showed a sensitive variation with the concentration of the acid in the doping solution through the changes in the contents of acid and water in the membranes. Maximum conductivities up to 0.08 S cm−1 at 20 °C and 0.11 S cm−1 at 80 °C were obtained for BC membranes doped from H3PO4 concentration of 6.0 mol L−1 and, 0.05 S cm−1 at 20 °C and 0.09 S cm −1 at 60 °C were obtained for BC membranes doped from PA concentration of 1.6 mol L−1. These types of proton-conducting membranes share not only the good mechanical properties but also the thermal stability. The temperature dependences of the conductivity follows the Arrhenius relationship at a temperature range from 20 to 80 °C and, the apparent activation energies (Ea) for proton conduction were found to be 4.02 kJ mol−1 for H3PO4/BC membrane and 11.29 kJ mol−1 for PA/BC membrane, respectively. In particular, the membrane electrode assembly fabricated with H3PO4/BC and PA/BC membranes reached the initial power densities of 17.9 mW cm−2 and 23.0 mW cm−2, which are much higher than those reported in literature in a real H2/O2 fuel cell at 25 °C.Highlights► Two proton-conducting membranes were prepared by immersing bacterial cellulose (BC) into H3PO4 and PA. ► H3PO4/BC membrane showed a high proton conductivity of 0.15 S cm−1. ► PA/BC membrane showed a high proton conductivity of 0.08 S cm−1. ► The MEA fabricated with H3PO4/BC showed an initial power density of 17.9 mW cm−2. ► The MEA fabricated with PA/BC showed an initial power density 23.0 mW cm−2.

The active, carbon-supported copper phthalocyanine (CuPc/C) nano-catalyst, as a novel cathode catalyst for oxygen reduction reaction, is synthesized via a combined solvent-impregnation along with the high temperature treatment. The catalytic activities of both pyrolyzed and unpyrolyzed catalysts are screened by linear sweep voltammetry (LSV) employing a rotating disk electrode (RDE) technique to quantitatively obtain the oxygen reduction reaction (ORR) kinetic constants and the reaction mechanisms. The results show that heat-treatment can significantly improve the ORR activity of the catalyst, and the optimal heat-treated temperature is around 800 °C, under which, an onset potential of 0.10 V and a half-wave potential of −0.05 V are achieved in alkaline electrolyte. Besides the ORR kinetic rate is increased, the ORR electron transfer number is also increased from 2.5 to 3.6 with increasing heat-treatment temperature from 600 to 800 °C. Also, the effect of catalyst loading in the catalyst layer on the corresponding ORR activity is also studied, and finds that increasing the catalyst loading, the catalyzed ORR kinetic current density can be significantly increased. For a fully understanding of this heat-treatment temperature effect, XRD, TEM, SEM–EDX, TG and XPS are used to identify the catalyst structure and composition. TG results demonstrated that the presence of Cu prevents phthalocyanine from thermal decomposition, thus contribute to higher nitrogen content which can form more Cu–Nx activity sites for the ORR. XPS analysis indicates that both pyridinic-N and graphitic-N may be responsible for the enhanced ORR activity.Highlights► Carbon-supported CuPc/C exhibits high catalytic activity for the ORR in alkaline solution. ► The catalytic activity strongly depends on the heat-treatment temperature for the catalyst synthesis. ► An onset potential of 0.10 V and a half-wave potential of −0.05 V are achieved in 0.1 M KOH. ► The ORR electron transfer number is increased from 2.5 to 3.6 with increasing heat-treatment temperature from 600 to 800 °C. ► Cu species contribute to a high N content forming more Cu–Nx activity sites for the ORR.

Highly stable hydroxyl anion conducting membranes have been developed using poly(vinyl alcohol) (PVA) as matrix by incorporation of poly(acrylamide-co-diallyldimethylammonium chloride) (PAADDA) as anion charge carriers. In order to clarifying the cross-linking effect on membrane performances, two series of PVA/PAADDA membranes were prepared by direct and indirect chemical cross-linking ways, and have been characterized in detail at structural and hydroxyl ion (OH−) conducting property by FTIR spectroscopy, thermal gravity analysis (TG), scanning electron microscopy (SEM), water sorption, ion exchange capacity and alkaline resistance stability. The OH− conductivity of the membranes increased with increasing the content of PAADDA in polymer and temperature, and reached 0.74–12 mS cm−1 with direct cross-linking way and 0.66–7.1 mS cm−1 with indirect cross-linking way in the temperature range 30–90 °C. The membranes are found to have the same IEC values but the membranes with direct cross-linking way showed higher water uptake than that with indirect cross-link one. Both membranes showed the thermal stability above 200 °C, and can integrity in 100 °C hot water and methanol solution, where the swelling are better suppressed as high dense chemical cross-linkages in PVA network. Very low methanol permeability (from 1.82 × 10−7 to 3.03 × 10−7 cm2 s−1) in 50% methanol solution was obtained at 30 °C. Besides, the chemical stability in 80 °C, 6 M hot alkali conditions and long-term stability of 350 h in 60 °C hot water revealed that the PVA/PAADDA membranes are promising for potential application in alkaline fuel cells.Highlights► PVA/PAADDA hydroxyl anion conducting membranes was developed. ► Two chemical cross-linking ways are proposed. ► PVA/PAADDA membranes show very low methanol permeability. ► They are from 1.82 × 10−7 to 3.03 × 10−7 cm2 s−1 in 50% methanol solution. ► A chemical stability in 80 °C, 6M hot alkali conditions was achieved.

Alkaline anion-exchange membranes were prepared from poly(vinyl alcohol) and poly(acrylamide-co-diallyldimethylammonium chloride) by blending, then chemical cross-linking using glutaraldehyde as the cross-linking agent (PVA–PAADDA–GA). Membranes were characterized by Fourier-transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). OH− conductivities in the range of 7.7 × 10− 4–3.03 × 10− 3 S cm− 1 were obtained for PVA–PAADDA–GA membranes at room temperature (23 ± 2 °C) along with the IEC values changed from 0.91 to 1.63 mequiv g− 1. The temperature dependences of OH− conductivities followed the Arrhenius relationship at a temperature range from 20 to 90 °C. The apparent activation energy for OH− conduction was in the range of 15–19 kJ mol− 1 depending on PAADDA content in the polymer. High alkaline stability of PVA–PAADDA–GA membranes was retained after conditioning in 6.0 M KOH at 80 °C for 24 h. Also, the membranes showed excellent dimensional stability in both hot water and hot methanol solutions at 90 °C. Although a relatively high water uptake (more than 2-fold of Nafion 115), the PVA–PAADDA–GA membranes showed excellent methanol resistance with the methanol permeability ranged from 2.85 to 4.16 × 10− 7 cm2 s− 1, which were 5 ~ 6 times lower than that of the Nafion 115.Highlights►Alkaline anion-exchange membranes from PVA-PAADDA-GA were prepared. ► Glutaraldehyde (GA) was used as an efficient cross-linking agent.► OH− conductivities in the range of 7.7×10−4–3.03×10−3 S cm−1 were obtained. ► The membranes showed excellent dimensional stability in both hot water and hot methanol solutions at 90 °C. ► High alkaline stability was retained after conditioning in 6.0 M KOH at 80 °C for 24 h.

Active, carbon-supported Ir–V nanoparticle catalysts have been synthesized by an ethylene glycol reduction method under controlled conditions at pH 10–13 and 120 °C, then further reduced at elevated temperature from 150 to 500 °C using IrCl3 and NH4VO3 as the Ir and V precursors. The nanostructured catalysts have been characterized by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (TEM). Ir nanoparticles, after modification with V, show a narrow particle size distribution in the range 0.5–4.5 nm, centered at 1.8 nm, and are uniformly dispersed on Vulcan XC-72. No particle agglomeration was observed, not even at high V loadings (V:Ir = 4:1 in atomic ratio). Investigation of the catalytic activity of the Ir–V/C by means of cyclic voltammetry (CV) and linear sweep voltammetry (LSV) employing a rotating disk electrode (RDE) has revealed that the presence of V may suppress the electrochemical oxidation of Ir and stabilize the Ir active centers. About six times higher kinetic current density was obtained for Ir–V/C compared to that of the pure Ir/C catalyst at 0.8 V versus RHE for the oxygen reduction reaction (ORR). The ORR in acid solution proceeds by an approximately four-electron pathway, through which molecular oxygen is directly reduced to water. The performance of a membrane electrode assembly (MEA) prepared with the most active 40% Ir–10% V/C as the cathode catalyst in a single proton-exchange membrane fuel cell (PEMFC) generated a maximum power density of 517 mW cm−2 at 0.431 V and 70 °C, and 100 h of stable cell operation due to no loss of catalyst sites on the cathode.

Novel alkaline solid polymer electrolyte membranes that can conduct anions (OH−) have been prepared from poly(vinyl alcohol)/poly(vinylpyrrolidone) (PVA/PVP) by blending and chemical cross-linking, followed by doping in aqueous KOH solution. The physicochemical properties of these membranes have been studied in detail by FTIR, TG, and SEM analyses. The ionic conductivity was found to be greatly dependent on the concentration of KOH and the interpenetrated PVP in the PVA matrix. A maximum conductivity of up to 0.53 S cm−1 at room temperature was achieved for PVA/PVP in a mass ratio of 1:0.5 after doping in 8 m aqueous KOH solution. The membrane showed perfect alkaline stability without losing its integrity even upon exposure to 10 m KOH solution at up to 120 °C. Scanning electron micrographs revealed a highly ordered microvoid structure uniformly dispersed on the membrane surface with a pore size of ca. 200 nm after heat-curing, which imparted the membrane with good liquid electrolyte (KOH) retention ability. FTIR spectra showed that these high ionic conductivities may be attributed to the presence of excess free KOH in the polymer matrix in addition to KOH bound to the polymer. Almost constant, highly stable, ionic conductivity while maintaining mechanical integrity was retained at room temperature for more than one month.

Nitrogen-doped graphene materials have been demonstrated as promising alternative catalysts for the oxygen reduction reaction (ORR) in fuel cells and metal–air batteries due to their relatively high activity and good stability in alkaline solutions. However, they suffer from low catalytic activity in acid medium. Herein, we have developed an efficient ORR catalyst based on nitrogen doped porous graphene foams (PNGFs) using a hard templating approach. The obtained catalyst exhibits both remarkable ORR activity and long term stability in both alkaline and acidic solutions, and its ORR activity is even better than that of the Pt-based catalyst in alkaline medium. Our results demonstrate a new strategy to rationally design highly efficient graphene-based non-precious catalysts for electrochemical energy devices.

A facile one-step and low-cost preparation of Pd–Co bimetallic hollow nanospheres on the surface of multi-walled carbon nanotubes (MWCNTs) is introduced in this paper through a solvothermal reaction. Herein, spherical micelles composed of hexadecyl trimethyl ammonium bromide (CTAB) were employed as soft templates and ethylene glycol (EG) was used as both a solvent and as a reducing agent. According to the X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements, the novel Pd–Co bimetallic hollow nanospheres are well-dispersed on the surface of the MWCNTs with a relatively narrow particle size distribution. The diameters of the hollow nanospheres range from 77 to 89 nm, and the average shell thickness is about 10 nm. The electrochemical analysis results indicate that the as-prepared bimetallic hollow nanospheres exhibit a superior electrocatalytic activity and stability for ethanol electrooxidation than the pure palladium catalyst.

A new type of Fe, N-doped hierarchically porous carbons (N–Fe-HPCs) has been synthesized via a cost-effective synthetic route, derived from nitrogen-enriched polyquaternium networks by combining a simple silicate templated two-step graphitization of the impregnated carbon. The as-prepared N–Fe-HPCs present a high catalytic activity for the oxygen reduction reaction (ORR) with onset and half-wave potentials of 0.99 and 0.86 V in 0.1 M KOH, respectively, which are superior to commercially available Pt/C catalyst (half-wave potential 0.86 V vs. RHE). Surprisingly, the diffusion-limited current density of N–S-HPCs approaches ∼7.5 mA cm−2, much higher than that of Pt/C (∼5.5 mA cm−2). As a cathode electrode material used in Zn–air batteries, the unique configuration of the N–Fe-HPCs delivers a high discharge peak power density reaching up to 540 mW cm−2 with a current density of 319 mA cm−2 at 1.0 V of cell voltage and an energy density >800 Wh kg−1. Additionally, outstanding ORR durability of the N–Fe-HPCs is demonstrated, as evaluated by the transient cell-voltage behavior of the Zn–air battery retaining an open circuit voltage of 1.48 V over 10 hours with a discharge current density of 100 mA cm−2.

High-temperature solid oxide electrolysis cells (SOECs) are advanced electrochemical energy storage and conversion devices with high conversion/energy efficiencies. They offer attractive high-temperature co-electrolysis routes that reduce extra CO2 emissions, enable large-scale energy storage/conversion and facilitate the integration of renewable energies into the electric grid. Exciting new research has focused on CO2 electrochemical activation/conversion through a co-electrolysis process based on the assumption that difficult CO double bonds can be activated effectively through this electrochemical method. Based on existing investigations, this paper puts forth a comprehensive overview of recent and past developments in co-electrolysis with SOECs for CO2 conversion and utilization. Here, we discuss in detail the approaches of CO2 conversion, the developmental history, the basic principles, the economic feasibility of CO2/H2O co-electrolysis, and the diverse range of fuel electrodes as well as oxygen electrode materials. SOEC performance measurements, characterization and simulations are classified and presented in this paper. SOEC cell and stack designs, fabrications and scale-ups are also summarized and described. In particular, insights into CO2 electrochemical conversions, solid oxide cell material behaviors and degradation mechanisms are highlighted to obtain a better understanding of the high temperature electrolysis process in SOECs. Proposed research directions are also outlined to provide guidelines for future research.

In this review, we examine the most recent progress and research trends in the area of alkaline polymer electrolyte membrane (PEM) development in terms of material selection, synthesis, characterization, and theoretical approach, as well as their fabrication into alkaline PEM-based membrane electrode assemblies (MEAs) and the corresponding performance/durability in alkaline polymer electrolyte membrane fuel cells (PEMFCs). Respective advantages and challenges are also reviewed. To overcome challenges hindering alkaline PEM technology advancement and commercialization, several research directions are then proposed.