•Al2O3-coated LiCoO2 was prepared via simple method.•The cyclic stability was investigated by CV method.•The cyclic stability was studied in different potential ranges.•The electrode is suitable for application in the potential range of 3.70–4.50 V.•It has still 113 mAh/g discharge capacity even after 500 cycles.In this article, Al2O3-coated LiCoO2 cathode is synthesized by high-temperature solid-state reaction method, i.e. sintering the mixture of Al2O3 and LiCoO2 powder. X-ray diffraction (XRD) analysis shows that there is no Al2O3 impurity being found in the final product. Scanning electron spectroscopy (SEM) and transmission electron spectroscopy (TEM) measurements show that the micro-morphology of pristine LiCoO2 grains is sustained after coating Al2O3. We analyze the surface chemistry of the pristine and Al2O3-coated LiCoO2 by X-ray photoelectron spectroscopy (XPS) technique. The electrochemical behavior is systematically investigated. The cathodes are cycled in different potential ranges (3.70 V–4.30, 4.35, 4.40, 4.45, 4.50, 4.55 and 4.60 V). The charge-discharge, cyclic voltammetry (CV) and Electrochemical impedance spectroscopy (EIS) measurements show that coating Al2O3 can obviously improve the cyclic stability and decrease the total interfacial resistance. We could conclude that Al2O3-coated LiCoO2 cathode is suitable for practical application in the potential range of 3.70–4.50 V vs. Li/Li+. The discharge capacity can reach 113 mAh/g after 500 cycles. It is very possible that the LiCo1 − xAlxO2-like surface phase, formed on the surface of LiCoO2, prevents Co-dissolution. As results, the operation potential range is extended and the cyclic stability is improved.

•Hierarchical, freestanding bowl-like NiCo2O4 have been designed and prepared on the carbon fiber papers directly.•The synthesis approach is electrochemical deposition combined with hard template.•The NiCo2O4@CFPs could be applied as air electrode directly without binder and conductive agents.•This novel air electrode exhibits excellent cell performances for Lithium-O2 batteries.In this paper, hierarchical, freestanding bowl-like NiCo2O4 growing directly on carbon fiber paper (NiCo2O4@CFPs) are designed and synthesized through a controllable and facile electro-deposition combined with hard template method, and then applied as air electrode for long-life Lithium-O2 batteries. This novel air electrode could deliver a high discharge capacity of 9624.2 mAh g−1, low discharge/charge over-potentials (over-potential gap < 1.0 V), excellent cycleability (∼100 cycles). Moreover, it exhibits extraordinarily rate capability and reversibility. Specifically, amorphous nanosheet-like Li2O2 have been observed as the main discharge products, which might be tailored by the special bowl-like catalyst. The excellent cell performances could be ascribed to the special open structure of the synthesized bowl-like catalyst, which could provide large specific surface area, enough space for accommodating the discharge products and facilitate the transport of oxygen and electrolyte in the Lithium-O2 batteries. This facile, low-cost synthesis approach further sheds light on fabrication of various hierarchical bowl-like air electrodes including metal oxides, metals or their hybrids, and possesses promising applications on metal-air batteries and fuel cells.Hierarchical, freestanding bowl-like NiCo2O4 has been designed and synthesized on the carbon fiber papers directly and applied as air electrodes for Lithium-O2 batteries, which exhibits excellent cell performances with a high discharge capacity of 9624.2 mAh g−1, low discharge/charge over-potentials (over-potential gap < 1.0 V, charge potential < 4.0 V), excellent cycleability (100 cycles), superior rate capability and reversibility.Download high-res image (321KB)Download full-size image

•α-Fe2O3@PPy and α-Fe2O3@NC pseudo-nanocubes composites have been synthesized.•The composite catalysts own lower intrinsic and charge transfer resistances.•The composites exhibit more pyridinic-N/FeN, graphitic-N and oxygen vacancy.•The composite catalysts display enhanced ORR catalytic performances.•α-Fe2O3@NC shows promising applications on metal-air batteries and fuel cells.Exploring of high-efficient, low-cost and eco-friendly catalysts for oxygen reduction reaction (ORR) is one of the vital issues for fuel cells and metal-air batteries. Herein, α-Fe2O3 pseudo-nanocubes have been synthesized with a facile solvothermal method, and then α-Fe2O3@NC composite catalysts were prepared through chemical polymerization of pyrrole on α-Fe2O3, following with pyrolyzed in nitrogen atmosphere. The synthesized composite catalysts display enhanced ORR catalytic performances, including the positive shifting of the onset potential, improving of the limited current density with long-term stability compared to those of the pristine α-Fe2O3. The enhanced electrocatalytic performances could be ascribed to the low intrinsic and charge transfer resistances, the high content of pyridinic-N and/or FeN, the emergence of graphitic-N and abundant oxygen vacancy on the composite surface. This study here implies that the catalytic activity and stability of metal oxides with poor conductivity could be controlled and improved by simply coating with a nanoscale conductive layer, which shows promising potential applications as precious-metal free catalysts for various metal-air batteries and fuel cells.Download high-res image (218KB)Download full-size image

•Au-based catalyst as bi-functional catalyst for ORR and OER was reported firstly.•The three dimensional self-supported AuCuCo was synthesized in one step.•AuCuCo exhibits excellent catalytic activity and stability for ORR and OER.The sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) have been one of the bottlenecks hindering the commercial application of rechargeable metal-air batteries. This report describes the viability of synthesis of self-supported Au-based alloy (AuCuCo) by a facile one-pot hydrothermal method and their use as highly efficient catalysts for ORR and OER. The obtained AuCuCo exhibits comparable electrocatalytic activity and better stability toward both the ORR and OER in alkaline media as compared with commercial Pt/C and IrO2/C catalyst. The improved electrocatalytic activity of AuCuCo is attributed to its unique three-dimensional nanostructure, the abundance of twin crystals, and change in the electronic structure of Au by alloying.Au-based alloy as bi-functional electrocatalyst for ORR and OER is reported for the first time. The as-synthesized AuCuCo exhibits excellent electrocatalytic activity and stability toward both the ORR and OER. The improved electrocatalytic activity of AuCuCo is attributed to its unique 3D nanostructure, the abundance of twin crystals and change in the electronic structure of Au by alloying.Download high-res image (225KB)Download full-size image

Nitrogen-doped carbon hollow cubes (NCHCs) are fabricated from biomass L-lysine monohydrochloride via a facile and low-cost NaCl template process, showing efficient bifunctional electrocatalytic activities towards the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The resultant lysine-derived carbon hollow cubes with hierarchical pores on the wall are conducive to mass transport and high utilization of nitrogen dopant-induced active sites during the electrocatalytic process. When used as electrocatalysts for the ORR, an onset potential of 0.92 V vs. RHE has been achieved for NCHCs. A negative shift of only 61 mV exists in the half-wave potential of NCHCs compared to that of the commercial Pt/C (20 wt%). Moreover, the NCHCs show high activity for the OER comparable to that of commercial RuO2/C (20 wt%). The sustainable conversion of biomass lysine to heteroatom-doped carbon hollow cubes and the recyclability of the NaCl template allow a scalable production and practical application of carbon materials for energy storage and conversion.

Advanced cathode catalysts are crucial to the promotion of aprotic Li–O2 batteries for practical applications. Carbon is usually used as a cathode catalyst, but it reacts with the discharge products (Li2O2, LiO2) to form an insulating layer of lithium carbonate and prevents further reaction. To resolve this issue, the development of non-carbon cathode catalysts is of great demand. Herein, for the first time, we designed and fabricated a MnCo2O4 (MCO) spinel oxide decorated Magnéli phase Ti4O7 as a carbon-free cathode for Li–O2 batteries. The sub-stoichiometric Ti4O7 oxide serves as an electronic conductive network. The MCO spinel oxide along with the synergistic effect between Ti4O7 and MCO facilitate the kinetics of both oxygen reduction and decomposition of Li2O2. Furthermore, uniform anchoring of MCO nanoparticles on Ti4O7 surface provides a stable lithium peroxide–cathode interface during the discharge/charge process. The resulting Ti4O7/MCO hybrid proves to be a highly effective cathode catalyst. The discharge/charge voltage gap of the Ti4O7/MCO hybrid is about 0.75 V, which is significantly lower than that of pure carbon, C + MCO and pristine Ti4O7 cathode. A high specific capacity (5400 mA h g−1 at 100 mA g−1) and excellent cycling performance (100 cycles at a capacity of 500 mA h g−1 under 200 mA g−1) were obtained for this hybrid. The high catalytic activity and durability renders the Ti4O7/MCO hybrid a highly promising carbon-free cathode for Li–O2 batteries.

The sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) has been one of the bottlenecks hindering the commercial application of rechargeable metal–air batteries. It is urgent and necessary to develop non-noble bifunctional catalysts for both the ORR and the OER with high catalytic activity. Herein, an in situ synthetic route to obtain Mo2C–C hybrid microspheres as bifunctional catalysts has been reported. In this route, the synchronously prepared C microspheres act not only as the template, but also as the reactant. Interestingly, SEM, TEM and XPS results show that core–shell, yolk–shell and pierced structured microspheres could be formed by increasing the content of Mo2C in the Mo2C–C hybrids. Additionally, the formation of a non-crystalline amorphous MoOx (MoO2 and MoO3) nano-film appears to improve the conductivity of the as-prepared Mo2C–C hybrids. Rotating-ring-disk electrode (RRDE) results show that the Mo2C–C hybrids exhibit enhanced catalytic activity for the ORR and OER compared with that of the C microspheres and Mo2C. In particular, Mo2C–C-5 displays excellent bifunctional activity and stability, which is close to the behavior of a commercial Pt/C electrocatalyst for the ORR and a RuO2 electrocatalyst for the OER.

To expedite the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in electrochemical systems, efficient nonprecious electrocatalysts are highly desired. In this work, a hybrid of CoFe2O4 nanoparticles supported on nitrogen/sulfur dual-doped three-dimensional (3D) reduced graphene oxide networks (CFO/NS-rGO) has been designed and fabricated. The doping of N and S provide the graphene networks with a large amount of defects. Moreover, both N and S doped in reduced graphene oxide play important roles in engineering the covalent coupling between CoFe2O4 and the 3D graphene networks. The covalent coupling between CoFe2O4 and NS-rGO along with the hierarchical porous structure and 3D networks endow the hybrid with a pronounced ORR activity (4-electron pathway), superior OER activity (comparable to that of the state-of-the-art RuO2/C catalyst) and high durability toward both ORR and OER.

•NCO@LSM core-shell structured nanorods have been fabricated.•NCO@LSM nanorods exhibit enhanced bifunctional catalytic activities.•NCO@LSM nanorods based LiO2 batteries show improved performances.•Both catalytic activity and core-shell structure contribute to high performance.La1–xSrxMnO3 perovskite oxides are promising electrocatalysts for LiO2 batteries because of their excellent intrinsic catalytic activity for oxygen reduction reaction (ORR). However, the relatively inert catalytic activity for oxygen evolution reaction (OER) suppresses their practical applications in LiO2 battery. Here, nanoscale NiCo2O4 (NCO) layer with high OER catalytic activity has been homogenously incorporated into the surface of La0.8Sr0.2MnO3 (LSM) nanorods to form a core-shell structure. In this typical structure, the ORR mainly occurred on the LSM core, while the OER mainly occurred on the nanoscale NCO shell, and structure damage of catalysts coming from gas evolution can be greatly avoided. The synergy of high catalytic activity and core–shell structure results in the LiO2 battery with good rate capability and excellent cycle stability, which sustains 80 cycles without capacity attenuation at a high current density of 200 mA g−1.

Ni-doped spinel oxides NixCo1-xFe2O4 (x = 0, 0.25, 0.5, 0.75) hollow nanospheres electrocatalysts are synthesized with a simple hydrothermal approach. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) results reveal that the morphology, hollow and spinel structures of the cobalt ferrites remain unchanged with doping. The electrocatalytic activity of the Ni-doped CoFe2O4 with different doping contents has been studied and compared with the pure CoFe2O4 hollow nanospheres in alkaline solution by using rotating ring-disk electrode (RRDE) technique. For ORR, the Ni0.5Co0.5Fe2O4 (x = 0.5) exhibits as the most active catalyst with the highest diffusion limited current density and more positive onset potential. Whereas, the Ni0.75Co0.25Fe2O4 (x = 0.75) shows the best catalytic activity for OER with more negative onset potential (0.27 V vs. Ag/AgCl) and maximum current density (36.0 mA/cm2 at 1.0 V). X-ray photoelectron spectra (XPS) measurements reveal that the oxygen vacancy on the oxide surfaces increases, while the cations occupied ratio on octahedral/tetrahedral sites in spinel structures decreases along with the increasing of the Ni doping content. Combining with the charge transfer resistance measured by electrochemical impedance spectroscopy (EIS), these three factors work synergistically on the catalytic activities of the Ni-doped CoFe2O4 hollow nanospheres.

Efficient nonprecious electrocatalysts with fast kinetics for the the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are critical to improve the efficiency of electrochemical systems such as fuel cells and metal-air battereies. Here, Co9S8 embedded in porous nitrogen-doped carbon (N-C) matrix has been designed and fabricated. The as-fabricated Co9S8/N-C hybrid shows an excellent ORR activity, which is comparable to that of the commercial Pt/C (20 wt.%). Notably, the OER activity of Co9S8/N-C hybrid is superior to that of the RuO2/C (20 wt.%), a benchmark electrocatalyst for OER. The stabilities of Co9S8/N-C hybrid toward ORR and OER are significantly improved as compared to that of Pt/C (20 wt.%) and RuO2/C (20 wt.%), respectively. The synergistic effect of the covalent coupling between Co9S8 and N-C and the porous structure of N-C is responsible for the enhanced catalytic activity and durability of Co9S8/N-C hybrid.Co9S8 embedded in porous nitrogen-doped carbon (N-C) matrix has been designed and fabricated. The synergistic effect of the covalent coupling between Co9S8 and N-C and the porous structure of N-C is responsible for the enhanced catalytic activity and durability of Co9S8/N-C hybrid for ORR and OER.

Phosphorus (P) and cobalt (Co) co-doped reduced graphene oxide (P-Co-rGO) has been developed and studied through a facile electrostatic assembly followed by a pyrolysis process. The prepared P-Co-rGO catalyst shows a great enhancement in the electrocatalytic activity and stability towards the oxygen reduction reaction (ORR) in alkaline solution, characterized with a positive onset potential of 0.89 V (vs. RHE), a negative shifting of only about 12.8 mV of the half-wave potential and the closest diffusion limiting current density (−5.5 mA cm−2) as compared to those of the commercial Pt/C (20 wt%). More interestingly, the prepared P-Co-rGO also exhibits excellent catalytic activity and stability for the oxygen evolution reaction (OER), with a low potential of 1.62 V (vs. RHE) at the current density of 10 mA cm−2 and a maximum current density of almost 30 mA cm−2 at 1.66 V (vs. RHE). Specifically, the prepared P-Co-rGO shows much higher activity and stability than the mono-doped reduced graphene oxide either with P or Co, respectively. This could be ascribed to the modification of the charge and spin densities and the edge and defect effects of the rGO after the co-doping of P and Co, thus resulting in a remarkable enhancement of the electrocatalytic properties for both the ORR and OER.

Boron-doped ordered mesoporous carbons (B-OMCs) with a tunable and high level of doping content (>1 wt%) have been synthesized via a one-pot solvent evaporation induced self-assembly (EISA) process. The as-prepared B-OMCs show a highly ordered 2D hexagonal mesostructure with an average pore size of 3.4–4.0 nm, which could facilitate an efficient mass transport of O2 and electrolyte during the oxygen reduciton reaction (ORR) process. The electrochemical investigations demonstrate that B-doping could significantly enhance the electrocatalytic activity of the carbon materials for the ORR in alkaline media. Specifically, the B-OMCs with a boron doping content of 1.17 wt% show the highest electrocatalytic activity and best long-term durability for ORR as compared to the non-doped OMCs and the B-OMCs with other doping contents. Combined with various physical characetrizations including X-ray diffraction, small angle X-ray scattering, N2 physisorption, Raman spectroscopy and X-ray photoelectron spectroscopy, the enhanced catalytic performance of the B-OMCs could be ascribed to the synergistic effects of the ordered mesostructure, specific surface area and moderate boron doping. This work not only helps the fundamental understanding of the correlation between the catalytic performance and the morphology, structure of the OMCs and the doping extent of heteroatoms, but also shows the promising potential applications of the B-OMCs as efficient, low-cost catalysts in metal-air batteries and fuel cells.

Monodispersed porous spinel-type cobalt ferrite oxide (CoFe2O4) nanospheres (CFO-ns) directly grown on reduced graphene oxide (rGO) sheets are fabricated by a one-pot solvothermal method. With this special structure of CFO-ns and the covalent coupling between CFO-ns and rGO in the CFO-ns/rGO hybrid, more active sites are exposed and the transport of O2 and electrolyte is faciliated when the CFO-ns/rGO hybrid is employed as an electrocatalyst for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The CFO-ns/rGO hybrid demonstrates high catalytic activity for both the ORR and OER. It shows a more positive onset potential of −0.11 V (vs. Ag/AgCl) for the ORR, which is 50 mV higher than that of CFO-ns + rGO physical mixture (−0.16 V). Meanwhile, the onset potential of CFO-ns/rGO hybrid (0.56 V) for the OER is 40 mV lower than that of CFO-ns + rGO mixture (0.60 V). The high activity of the CFO-ns/rGO hybrid is attributed to the special structure of CFO-ns, the covalent coupling between CFO-ns and rGO as well as the suppressed agglomeration of CFO-ns and restacking of rGO in the hybrid. Moreover, the covalent coupling between CFO-ns and rGO endows the hybrid with excellent electrochemical stabilities for both the ORR and OER.

•Hierarchical NiCo2O4 hollow nanospheres have been prepared via a hard template method.•The synthesized NCO hollow consists of ultrathin nanosheets.•The NCO hollow exhibits excellent catalytic activity for both ORR and OER.•The NCO hollow also owns superior long-term stability.High efficient, cost-effective catalysts for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are the key issue of the rechargeable lithium-air batteries. Herein, we report the facile synthesis of hierarchical NiCo2O4 (NCO) hollow nanospheres via a hard template method and following heat treatment. The synthesized hollow NCO consists of ultrathin nanosheets, which could provide larger specific surface area, more active sites and easy access channels for oxygen and electrolyte transport. The electrochemical studies reveal that the NCO hollow owns excellent ORR and OER catalytic activities, characterized with lower onset potential, higher diffusion limiting current density. Moreover, the NCO hollow shows superior stability compared to that of NCO urchin, Pt/C and RuO2 for ORR and OER, respectively. The excellent electrocatalytic activities, long-term stability for both the ORR and OER and the facile synthesis procedure make the NCO hollow a potential promising bi-functional catalyst for the metal-air batteries and fuel cells.

•Bacterial-cellulose-derived CNF-supported CFO has been facilely synthesized.•The as-prepared CFO/CNF is an efficient electrocatalyst for both ORR and OER.•The covalent coupling between CFO and CNF contributes to the high activity.•Improved electronic conductivity and mass transport contribute to the high activity.Exploration of cost-effective electrocatalysts with high catalytic activity toward the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) remains a key challenge in the development of metal-air batteries. In this study, bacterial-cellulose-derived carbon nanofiber-supported CoFe2O4 (CFO/CNF) has been prepared via a facile and green method. The three dimensional (3D) interconnected CNF network support with high surface area not only provides high electronic conductivity but also promotes the mass transfer of O2 and electrolyte during the ORR and OER. Furthermore, the strong coupling between CFO and CNF allows for fast charge transfer, facilitating the electrocataltyic processes. These lead to the high electrocatalytic activity of as-prepared CFO/CNF nanocomposite toward both the ORR and OER, outperforming CFO and CNF, respectively. Meanwhile, the stability of CFO/CNF nanocomposite toward the ORR and OER is much higher than that of benchmark Pt/C (20 wt.%) and RuO2/C (20 wt.%), respectively.

LiCoO2-based cathode does still have a powerful competition in high-end mobile electronics due to its relatively high true density (about 5.2 g/cm3). When the operation potential range is extended, the improvement in its cycle stability has attracted more attention. The extension of its operation potential can be realized by partial replacement of Co by Ni and Mn or by surface modification. However, Ni and Mn replacing partial Co results in decreased true density; for example, the true density of LiNi0.5Mn0.3Co0.2O2 is about 4.6 g/cm3. In this case, the increase in its practical energy density is impossible. As a result, the surface modification technology becomes very important to extend its operation potential range. In this article, an Al2O3-coated LiCoO2 cathode was synthesized. X-ray diffraction test did not show any impurity. Scanning electron spectroscopy measurements showed that the basic microstructure of pristine LiCoO2 grain is sustained after coating Al2O3. The surface characteristic of pure and Al2O3-coated LiCoO2 was also analyzed using an X-ray photoelectron spectroscopy (XPS) technique. Unusual XPS peaks of O 1s, Al 2p, and Co 2p binding energy were found and may be caused by the possible H existence in crystal structure. The electrochemical behavior was systematically investigated, and the cathode was cycled at different charge cutoff voltages (4.30∼4.60 V). The charge-discharge and cyclic voltammetry measurements showed an obviously improved cyclic performance after coating Al2O3. The electrocatalytic activity is not clearly changed before and after coating Al2O3. From our systematical investigation, it could be concluded that the Al2O3-coated LiCoO2 cathode is suitable for practical application in the potential range of 3.70∼4.50 V vs. Li/Li+.

Efficient electrocatalyst for oxygen reduction reaction (ORR) is crucial for the performance improvement of fuel cells and metal-air batteries. However, catalyst with high activity, easy fabrication process, and low cost is still a daunting challenge. In this work, low-cost BaCO3 nanorods have been demonstrated as efficient electrocatalysts toward the ORR in alkaline media for the first time. The activity of BaCO3 nanorods can be further enhanced by hybridizing with reduced graphene oxide (BaCO3/rGO). The mechanism of ORR on the surface of BaCO3 catalyst was investigated via in situ electrochemical Raman spectroscopy (in situ EC-Raman). Our findings suggest that the barium ions on the surface of catalyst play a key role in the adsorption of oxygen molecules and the formation/decomposition of intermediates. This work provides an important insight into the catalytic activity of BaCO3 for ORR, which can serve as a guide for the design of alkali-earth metal-carbonate-based catalyst.

The design and synthesis of MnCo2O4 anchored on P-doped hierarchical porous carbon (MCO/P-HPC) is reported. Without harsh oxidative treatment, creating anchoring sites for MnCo2O4 on the surface of carbon is realized by P-doping in carbon. The chemical coupling between P-HPC and MCO induced by P-doping provides pathways for fast charge transport. This hybrid with a hierarchical porous structure favors efficient electrolyte penetration, oxygen transport, and effective accommodation of insoluble discharge product Li2O2. When employed as an electrocatalyst in rechargeable Li–O2 batteries, the MCO/P-HPC hybrid delivers a high discharge capacity (13 150 mAh g–1 at 200 mA g–1), excellent rate capability (7028 mAh g–1 at 1000 mA g–1), and long cycle stability (200 cycles at a capacity of 1000 mAh g–1 under 200 mA g–1).Keywords: chemical coupling; electrocatalyst; Li−O2 battery; MnCo2O4; P-doped carbon

The oxygen reduction reaction (ORR) at the cathode of fuel cells and metal–air batteries requires efficient electrocatalysts to accelerate its reaction rate due to its sluggish kinetics. Nitrogen- and phosphorus-doped biocarbon has been fabricated via a simple and low-cost biosynthesis method using yeast cells as a precursor. The as-prepared biocarbon exhibits excellent electrocatalytic activity for the ORR. An onset potential of −0.076 V (vs Ag/AgCl) and a negative shift of only about 29 mV in the half-wave potential of the biocarbon as compared to commercial Pt/C (20 wt % Pt on Vulcan XC-72, Johnson Matthey) is achieved. The biocarbon possesses enhanced electron poverty in carbon atoms and a decreasing amount of less electroactive nitrogen and phosphorus dopants due to the biomineralization during the synthesis. The surface gap layer along with the mesopores in the biocarbon increases accessible active sites and facilitates the mass transfer during the ORR. These factors correlate with the high ORR activity of the biocarbon. The results demonstrate that biomineralization plays a critical role in tailoring the structure and the electrocatalytic activity of the biocarbon for ORR.Keywords: bioarbon; electrocatalytic activity; nitrogen- and phosphorus-doped; oxygen reduction reaction; yeast cells

Efficient electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) play a critical role in the performance of fuel cells and metal–air batteries. In this work, we report a one-pot fabrication pathway to prepare yolk–shell structured La0.9Sr0.1CoO3 perovskite microspheres as highly active electrocatalysts for the ORR. The shell number could be controlled by using different solvents. Compared with regular La0.9Sr0.1CoO3 particles, yolk–shell structured La0.9Sr0.1CoO3 oxides have larger specific surface area. Catalytic activities of the as-prepared catalysts for the ORR and OER in 0.1 M KOH media have been studied by using a rotating ring-disk electrode (RRDE) technique. RRDE results show that multi-shelled La0.9Sr0.1CoO3 exhibits better catalytic activity for the ORR and OER with durabilities superior to commercial Pt/C catalysts.

An efficient catalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is the most critical factor influencing the performance of lithium–air batteries. We present MnOx decorated CeO2 nanorods as a highly active cathode catalyst for lithium–air batteries fabricated via an in-situ redox reaction. Lithium–air batteries based on MnOx@CeO2 catalysts show enhanced electrochemical performances, including high first discharge specific capacity (2617 mA h g−1 at 100 mA g−1), low overpotential, good rate capability (up to 400 mA g−1), and cycle stability (only 1.1% voltage loss after 30 cycles of specific capacity limit of 1000 mA h g−1 tested at 200 mA g−1). The improved performance might be attributed to the high catalyst efficiency.

•LSM nanorods have been synthesized by a soft templates method.•LSM nanorods have unique microporous structure with numerous defects.•LSM nanorods exhibit enhanced bifunctional catalytic activities.•LSM nanorods based Li–air batteries show enhanced electrochemical performances.Efficient electrocatalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is the most critical factor to influence the performance of lithium–air batteries. We present La0.8Sr0.2MnO3 (LSM) perovskite nanorods as high active electrocatalyst fabricated via a soft template method for lithium–air batteries. The as–prepared LSM nanorods are microporous with numerous defects and large surface area (20.6 m2 g−1), beneficial to the ORR and OER in the discharge and charge processes, respectively. Lithium–air batteries based on the microporous LSM nanorods electrocatalysts show enhanced electrochemical performances, including high first discharge specific capacity (6890 mAh g−1(electrode) at 200 mA g−1), low overpotential, good rate capability (up to 400 mA g−1), and cycle stability (only 1.1% voltage loss after 30 circles of specific capacity limit of 1000 mAh g−1 tested at 200 mA g−1). The improved performance might be due to the synergistic effect of the unique microporous and one–dimensional structure and numerous defects of the prepared LSM catalyst.

Efficient bi-functional electrocatalysts with high durability are essential to the development of metal–air batteries, the performance of which is limited by the slow kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at the cathode. In this work, a covalently coupled FeCo2O4/hollow reduced graphene oxide spheres (FCO/HrGOS) hybrid with a 3D architecture has been fabricated step by step via an electrostatically induced assembly method. The covalent coupling between FCO and HrGOS along with the 3D architecture of FCO/HrGOS not only provides an efficient electron transport path but also facilitate the transport of electrolyte and O2 during the ORR and OER process in 0.1 M KOH aqueous solution. The ORR on FCO/HrGOS is mainly dominated by a 4e− reaction pathway. The as-prepared FCO/HrGOS exhibits comparable ORR activity and superior OER activity as compared to commercial Pt/C (20 wt.% Pt). Meanwhile, the stabilities of FCO/HrGOS toward both the ORR and OER are significantly higher than those of commercial Pt/C. The high electrocatalytic activity and durability of FCO/HrGOS hybrid are attributed to the covalent coupling between FCO and HrGOS as well as the 3D architecture of FCO/HrGOS built from the hollow graphene sphere.

Phosphorus-doped carbon hollow spheres (P-CHS) have been synthesized by a hydrothermal method using glucose as a carbon source, tetraphenylphosphonium bromide as a P source and anionic surfactant sodium dodecyl sulfate as a soft template. The as-prepared P-CHS have microporous shell structure with high specific surface area of >500 m2 g−1. The electrocatalytic activity of P-CHS for oxygen reduction reaction (ORR) in alkaline media has been studied by using a rotating ring-disk electrode (RRDE) technique. The RRDE results reveal that the as-prepared P-CHS containing 1.61 at.% of P exhibits high electrocatalytic activity and superior long-term stability for the ORR. The content of P in carbon is found to have a great influence on the microstructure and therefore the ORR activity of P-CHS. The high electrocatalytic activity and durability of P-CHS for the ORR are primarily ascribed to highly active catalytic sites induced by P doping in the carbon lattice and the efficient mass transfer of reactants and products facilitated by hollow spherical structure of P-CHS during the ORR.

•A non-rare-earth element based perovskite BaMnO3 nanorods as an active electrocatalyst for the ORR and OER have been prepared and investigated for the first time.•A thin carbon-coating layer with thickness of approximately 10 nm has been successfully introduced to enhance the electrical conductivity and the electrocatalytic activities of the bare perovskite for both ORR and OER.•The stabilities of bare BaMnO3 nanorods for both ORR and OER have also been improved dramatically with the help of carbon coating, especially for the OER process.Highly efficient, low-cost catalysts, especially with bifunctional electrocatalytic capabilities for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are vital for the wide commercialization of fuel cells and metal-air batteries. In this study, BaMnO3 - a non-rare-earth element based perovskite nanorods have been prepared and investigated for the first time, and a thin carbon-coating with a thickness of approximately 10 nm has been successfully introduced to enhance the electrical conductivity of the bare perovskite. Electrochemical tests reveal that bare BaMnO3 nanorods exhibit very good catalytic activity. More interestingly, a remarkably enhanced ORR activity for the perovskite BaMnO3 nanorods was observed after coating with a thin layer of carbon, which dominated with a direct four-electron pathway. Meanwhile, the OER process has also been enhanced extraordinarily with the carbon-coating, reaching a maximum of 14.8 mA cm−2 at 1.0 V (vs. Ag/AgCl), which is far superior to both the bare BaMnO3 nanorods and commercial Pt/C (20 wt%) catalysts. Furthermore, the stabilities of bare BaMnO3 nanorods for both ORR and OER have also been improved dramatically with the help of carbon coating. These results shed light on the significant potential application of the carbon-coated perovskite BaMnO3 porous nanorods on fuel cells and metal-air batteries as an efficient bi-functional catalyst.A thin carbon layer has been introduced to coat on the perovskite BaMnO3 nanorods by a facile method, which exhibit significantly enhanced electrocatalytic activity for both the ORR and OER with excellent stability.

Lithium-air battery has attracted extensively attention and now developing catalysts with high electrocatalytic activity is one of the challenges for lithium-air battery. In this paper, 3D hierarchical porous spinel CoFe2O4 hollow nanospheres were first prepared by a facile hydrothermal method. The hollow CoFe2O4 nanospheres have unique bimodal porous structure which consists of micropores and mesopores. The catalytic activity of the CoFe2O4 hollow nanospheres for oxygen reduction reaction (ORR) has been studied and compared with the acetylene black, the solid CoFe2O4 nanospheres and the commercial Pt/C by using rotating ring-disk electrode (RRDE) technique. The spinel CoFe2O4 hollow nanospheres exhibit superior catalytic activity for the ORR compared to the acetylene black and the solid CoFe2O4 nanospheres. Besides, the spinel CoFe2O4 hollow nanospheres also afford high catalytic activity for the oxygen evolution reaction (OER). Furthermore, the hollow CoFe2O4 nanospheres show the smallest overpotential between ORR and OER. The chronoamperometric studies show that the CoFe2O4 hollow nanospheres exhibit excellent stability for both the ORR and OER. The high ORR and OER activities and stabilities of CoFe2O4 hollow nanospheres could be attributed to their special 3D hierarchical porous structure. This material shows a significant potential application on lithium-air battery.

Efficient electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial for improving the performance of metal–air batteries. In this study, CoFe2O4/biocarbon (CFO/BC) nanocomposites have been synthesized via a facile biosynthesis method by using yeast cells as carbon sources and structural templates. The as-prepared CFO/BC nanocomposites possess a hierarchical structure with a high surface area (79.84 m2 g−1). The rotating ring-disk electrode (RRDE) and rotating disk electrode (RDE) measurements revealed that CFO/BC nanocomposites exhibit excellent catalytic activity for both the ORR and OER. The onset potential of CFO/BC for the ORR is −0.14 V (vs. Ag/AgCl), which is higher than that of CoFe2O4 (−0.29 V) and that of biocarbon (−0.25 V), respectively. Meanwhile, the CFO/BC nanocomposites show much higher activity for the OER as compared to CoFe2O4 and biocarbon. The chronoamperometric tests show that the CFO/BC catalyst shows high durability for both the ORR and OER, outperforming the commercial Pt/C (20 wt% Pt on Vulcan XC-72, Johnson Matthey). The high electrocatalytic activity and durability of the CFO/BC nanocomposite are mainly attributed to the strong coupling between CoFe2O4 nanoparticles and biocarbon as well as the hierarchical structure of CFO/BC.

We demonstrated a facile method to synthesize gold-nanoparticle-decorated Gd0.3Ce0.7O1.9 (Au-GDC) nanotubes. X-ray diffraction, transmission electron microscopy, X-ray photoelectron microscopy, and energy-dispersive X-ray measurements were performed to characterize their structure and composition. In this unique structure, gold nanoparticles were uniformly decorated in the inner wall of Gd0.3Ce0.7O1.9 (GDC) nanotubes with high gold loading. The catalytic activity of a Au-GDC nanotube catalyst for oxygen reduction reaction (ORR) in a 0.1 M KOH solution was studied using a rotating ring-disk electrode (RRDE) technique. RRDE results show that the ORR mainly favors a direct four-electron pathway, and a maximum cathodic limiting current density of −6.70 mA cm–2 at 2500 rpm was obtained, which is much bigger than that of gold bulk electrode and as-reported gold/rGO hybrid catalysts and close to the behavior of a commercial Pt/C catalyst below −0.8 V. Most importantly, the as-prepared Au-GDC nanotube catalyst exhibits excellent stability for the ORR because of the maximum interaction between gold nanoparticles and GDC nanotube supports.Keywords: catalytic activity; Gd0.3Ce0.7O1.9 nanotube; gold nanoparticle; oxygen reduction reaction;

The electrocatalyst for oxygen reduction reaction (ORR) plays an important role in determining the performance, cost and durability of fuel cells and metal–air batteries. In this study, low-cost and highly active phosphorus (P)-doped carbon xerogel electrocatalyst for the ORR was facilely synthesized. The catalytic activity of P-doped carbon xerogel for the ORR in 0.1 M KOH solution has been studied by using a rotating ring-disk electrode (RRDE) technique. The RRDE results show that P-doped carbon xerogel exhibits excellent catalytic activity for the ORR and long-term stability in basic media. The ORR on P-doped carbon xerogel with optimized amount of P mainly favors a direct four electron pathway. The high electrocatalytic activity and durability of P-doped carbon xerogel are primarily attributed to the P-doping in the carbon lattice. Furthermore, the amount of P incorporated into carbon instead of the specific surface area of the P-doped carbon xerogel is found to play a critical role in the ORR activity enhancement and the ORR pathway modification.

•P-Co-MC was synthesized with a soft template for the first time;•P-Co-MC exhibits high catalytic activity for the ORR comparable to Pt/C;•High activity of P-Co-MC arises from synergistic effect of P and Co doping in carbon.Phosphorus and Co co-doped mesoporous carbon (P–Co-MC) has been prepared using a soft template. The P–Co-MC exhibits high catalytic activity comparable to commercial Pt/C and long-term stability for the oxygen reduction reaction (ORR) in basic media. The high activity of P–Co-MC for the ORR is mainly attributed to the synergistic effect of P and Co doping in carbon.

Hierarchical NiCo2O4 spinel nanowire array (H-NCO-NWA) electrocatalysts have been prepared through a facile template-free co-precipitation route. The as-prepared H-NCO-NWA exhibits a mesoporous (ca. 8 nm) structure and a high specific surface area of 124 m2 g−1. The assembled Li–air batteries presented lower overpotentials, reasonable specific capacity, and enhanced cyclability.

•BCFN was evaluated as bifunctional catalyst in alkaline media.•The ORR mainly favors a direct four electron pathway.•BCFN had better catalytic activity for the OER than that of pure C electrode and commercial Pt/C electrode.•The electrochemical performances of Li–air batteries with BCFN as cathode catalyst were tested.Ba0.9Co0.5Fe0.4Nb0.1O3 (BCFN) perovskite has been synthesized by a solid-state reaction method, and characterized by XRD, SEM, BET. This oxide has a porous structure and a specific surface area of 10.24 m2 g−1 after ball-milled 24 h. The catalytic activity of the oxide for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) in 0.1 M KOH solution has been studied by using a rotating ring-disk electrode (RRDE) technique. RRDE results show that the ORR mainly favors a direct four electron pathway, and a maximum cathodic current density of −5.70 mA cm−2 at 2500 rpm was obtained, which is close to that of Pt/C (20 wt.% Pt on carbon) electrocatalyst in the same testing conditions. Compared with behaviors of pure C and Pt/C electrode, a lower onset potential of BCFN for OER is observed, and a bigger anodic current at the same applied potential is obtained. Considering small surface area of the BCFN catalyst, a big overpotential is given in the discharge–charge curves. However, the outputs of 2032 coin Li–air batteries in a dry gas mixture composed of 80 vol.% pure N2 and 20 vol.% pure O2 demonstrated that BCFN could be a potential bifunctional catalyst for the Li–air battery.

Efficient electrocatalysts for the oxygen reduction reaction (ORR) play a critical role in the performance of fuel cells and metal–air batteries. In this study, we report a facile synthesis of phosphorus (P)-doped porous carbon as a highly active electrocatalyst for the ORR. Phosphorus-doped porous carbon was prepared by simultaneous doping and activation of carbon with phosphoric acid (H3PO4) in the presence of Co. Both phosphorus and cobalt were found to play significant roles in improving the catalytic activity of carbon for the ORR. The as-prepared phosphorus-doped porous carbon exhibited considerable catalytic activity for the ORR as evidenced by rotating ring-disk electrode studies. At the same mass loading, the Tafel slope of phosphorus-doped porous carbon electrocatalysts is comparable to that of the commercial Pt/C catalysts (20 wt% Pt on Vulcan XC-72, Johnson Matthey) with stability superior to Pt/C in alkaline solutions.

Developing catalysts with high electrocatalytic activity for an oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) has recently attracted much attention because the sluggish kinetics of these two reactions limits the performance and commercialization of fuel cells and metal–air batteries. Herein, a facile template-free co-precipitation route was reported for the design and fabrication of well-ordered NiCo2O4 (NCO) spinel nanowire arrays. The as-prepared NCO spinel nanowire arrays are characterized by XRD, SEM, TEM, BET and XPS. BET results show that NCO spinel nanowire arrays have a mesoporous (ca. 8 nm) structure and a high specific surface area of 124 m2 g−1. The catalytic activity of NCO spinel nanowire arrays for the ORR and the OER in 0.1 M KOH solution has been studied by using a rotating ring-disk electrode (RRDE) technique. RRDE results show that the NCO spinel nanowire array catalyst exhibits excellent catalytic activity for the ORR. The ORR mainly favors a direct four electron pathway, which is close to the behavior of the Pt/C (20 wt% Pt on carbon) electrocatalyst under the same testing conditions. Anodic linear scanning voltammogram results show that the NCO spinel nanowire array catalyst is more active for the OER. The chronoamperometric and cyclic voltammogram tests show that the NCO spinel nanowire array catalyst exhibits excellent stability and reversibility for the ORR and the OER.

•Urchin-like La0.8Sr0.2MnO3 (LSM) perovskite oxide has been synthesized.•Mechanism of the ORR on urchin-like LSM perovskite oxide has been studied.•Urchin-like LSM perovskite oxide is a bifunctional catalyst for the ORR and the OER.•Urchin-like LSM perovskite oxide could be used as a potential catalyst for a lithium-air battery.An urchin-like La0.8Sr0.2MnO3 (LSM) perovskite oxide has been synthesized through a co-precipitation method with urea as a precipitator, and characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and BET analysis. SEM results show that a micro/nanocomposite with an urchin-like morphology has been obtained. The as-synthesized LSM perovskite oxide has a high specific surface area of 48 m2 g−1. The catalytic activity of the oxide for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) in 0.1 M KOH solution has been studied by using a rotating-ring-disk electrode (RRDE). In the ORR test, a maximum cathodic current density of 5.2 mA cm−2 at −1.0 V (vs. Ag/AgCl) with 2500 rpm was obtained, and the ORR mainly favors a direct four-electron pathway. The results of anodic linear scanning voltammograms indicate that the urchin-like LSM perovskite oxide exhibits an encouraging catalytic activity for the OER. All electrochemical measurements suggest that the urchin-like LSM perovskite oxide could be used as a bifunctional catalyst for the ORR and the OER.

The catalytic activity of electrochemically dealloyed PdCu3 thin films for oxygen reduction reaction (ORR) in acidic media has been studied by using a rotating disk electrode (RDE). The dealloyed PdCu3 thin films show a ∼2.0 fold increase in the specific oxygen reduction activity over pure Pd thin films. The structure of electrochemically dealloyed PdCu3 thin films has been investigated at an atomic scale by synchrotron-based anomalous X-ray diffraction (AXRD). AXRD reveals that a Pd enriched surface layer is formed in the dealloyed film and a compressive lattice strain exists in this Pd surface layer. The enhanced catalytic activity of dealloyed Pd–Cu films for the ORR is primarily due to the compressive strain in the surface layer. We compare the structure–composition–catalytic activity relationships in dealloyed Pd–Cu thin films to related results on dealloyed Pt–Cu thin films. These studies show that dealloying and the resulting structure and the ORR activity are dependent on the nature of the noble component of alloy.Highlights► Dealloyed Pd–Cu thin films show higher ORR activity compared to pure Pd. ► Enhancement of ORR activity is attributed to the strain in the Pd surface layer. ► Dealloying and the ORR activity are dependent on the noble component of alloy. ► The relationship between the structure and ORR activity is better understood.

•BSCF was evaluated as bifunctional catalyst in alkaline media.•A maximum current density of 6.25 mA cm−2 at 2500 rpm was obtained for the ORR.•The ORR mainly favors a direct four electron pathway.•BSCF had better catalytic activity for the OER than that of the pure C electrode.Ba0.5Sr0.5Co0.8Fe0.2O3 perovskite oxide has been synthesized by a sol–gel method, and characterized by XRD, SEM, BET. This oxide has a porous structure and a specific surface area of 2.78 m2 g−1. The catalytic activity of the oxide for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) in 0.1 M KOH solution has been studied by using a rotating ring-disk electrode (RRDE) technique. RRDE results show that the ORR mainly favors a direct four electron pathway, and a maximum cathodic current density of 6.25 mA cm−2 at 2500 rpm was obtained, which is close to the behavior of Pt/C (20 wt% Pt on carbon) electrocatalyst in the same testing conditions. Compared with pure C electrode, BSCF is more active for OER, a lower onset potential for OER and a bigger anodic current at the same applied potential are observed.

A robust bifunctional electrocatalyst for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is highly desired for the application in rechargeable metal air batteries. Here, we report a new strategy to in-situ prepare La2O3-nitrogen doped carbon tubes (NCNTs) hybrids by one step calcination treatment with LaNi0.9Fe0.1O3 perovskite oxides as precursors, sugar as carbon sources and urea as nitrogen sources. The contents of applied LaNi0.9Fe0.1O3 oxides affect the formation of NCNTs, and the obtained NCNTs have abundant wrinkles on the surface. In alkaline solution, the LO-NF-NCNTs-1.0 sample catalyzes the ORR with an onset potential of 0.896 V (vs. RHE) and a half-wave potential (E1/2) of 0.772 V (vs. RHE), which is only an E1/2 gap of 65 mV compared with commercial Pt/C catalyst. Meanwhile, the LO-NF-NCNTs-1.0 sample exhibits better OER activities than the commercial RuO2 catalyst. Significantly, we demonstrate that the LO-NF-NCNTs-1.0 sample possesses surprisingly catalytic stabilities, and an outstanding tolerance towards methanol crossover. The excellent bifunctional activities may be attributed to the typical morphology of NCNTs, coupling effect between NCNTs and La2O3 because of the formation of active LaO and CO bonds.La2O3-NCNTs hybrids in-situ derived from LaNi0.9Fe0.1O3-C composite have been prepared by one step calcination treatment. The as-prepared La2O3-NCNTs hybrids exhibit robust bifunctional electrocatalytic activities and stabilities for both the ORR and the OER.

Efficient electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) play a critical role in the performance of fuel cells and metal–air batteries. In this work, we report a one-pot fabrication pathway to prepare yolk–shell structured La0.9Sr0.1CoO3 perovskite microspheres as highly active electrocatalysts for the ORR. The shell number could be controlled by using different solvents. Compared with regular La0.9Sr0.1CoO3 particles, yolk–shell structured La0.9Sr0.1CoO3 oxides have larger specific surface area. Catalytic activities of the as-prepared catalysts for the ORR and OER in 0.1 M KOH media have been studied by using a rotating ring-disk electrode (RRDE) technique. RRDE results show that multi-shelled La0.9Sr0.1CoO3 exhibits better catalytic activity for the ORR and OER with durabilities superior to commercial Pt/C catalysts.

Efficient electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial for improving the performance of metal–air batteries. In this study, CoFe2O4/biocarbon (CFO/BC) nanocomposites have been synthesized via a facile biosynthesis method by using yeast cells as carbon sources and structural templates. The as-prepared CFO/BC nanocomposites possess a hierarchical structure with a high surface area (79.84 m2 g−1). The rotating ring-disk electrode (RRDE) and rotating disk electrode (RDE) measurements revealed that CFO/BC nanocomposites exhibit excellent catalytic activity for both the ORR and OER. The onset potential of CFO/BC for the ORR is −0.14 V (vs. Ag/AgCl), which is higher than that of CoFe2O4 (−0.29 V) and that of biocarbon (−0.25 V), respectively. Meanwhile, the CFO/BC nanocomposites show much higher activity for the OER as compared to CoFe2O4 and biocarbon. The chronoamperometric tests show that the CFO/BC catalyst shows high durability for both the ORR and OER, outperforming the commercial Pt/C (20 wt% Pt on Vulcan XC-72, Johnson Matthey). The high electrocatalytic activity and durability of the CFO/BC nanocomposite are mainly attributed to the strong coupling between CoFe2O4 nanoparticles and biocarbon as well as the hierarchical structure of CFO/BC.

Efficient electrocatalysts for the oxygen reduction reaction (ORR) play a critical role in the performance of fuel cells and metal–air batteries. In this study, we report a facile synthesis of phosphorus (P)-doped porous carbon as a highly active electrocatalyst for the ORR. Phosphorus-doped porous carbon was prepared by simultaneous doping and activation of carbon with phosphoric acid (H3PO4) in the presence of Co. Both phosphorus and cobalt were found to play significant roles in improving the catalytic activity of carbon for the ORR. The as-prepared phosphorus-doped porous carbon exhibited considerable catalytic activity for the ORR as evidenced by rotating ring-disk electrode studies. At the same mass loading, the Tafel slope of phosphorus-doped porous carbon electrocatalysts is comparable to that of the commercial Pt/C catalysts (20 wt% Pt on Vulcan XC-72, Johnson Matthey) with stability superior to Pt/C in alkaline solutions.

Developing catalysts with high electrocatalytic activity for an oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) has recently attracted much attention because the sluggish kinetics of these two reactions limits the performance and commercialization of fuel cells and metal–air batteries. Herein, a facile template-free co-precipitation route was reported for the design and fabrication of well-ordered NiCo2O4 (NCO) spinel nanowire arrays. The as-prepared NCO spinel nanowire arrays are characterized by XRD, SEM, TEM, BET and XPS. BET results show that NCO spinel nanowire arrays have a mesoporous (ca. 8 nm) structure and a high specific surface area of 124 m2 g−1. The catalytic activity of NCO spinel nanowire arrays for the ORR and the OER in 0.1 M KOH solution has been studied by using a rotating ring-disk electrode (RRDE) technique. RRDE results show that the NCO spinel nanowire array catalyst exhibits excellent catalytic activity for the ORR. The ORR mainly favors a direct four electron pathway, which is close to the behavior of the Pt/C (20 wt% Pt on carbon) electrocatalyst under the same testing conditions. Anodic linear scanning voltammogram results show that the NCO spinel nanowire array catalyst is more active for the OER. The chronoamperometric and cyclic voltammogram tests show that the NCO spinel nanowire array catalyst exhibits excellent stability and reversibility for the ORR and the OER.

The sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) has been one of the bottlenecks hindering the commercial application of rechargeable metal–air batteries. It is urgent and necessary to develop non-noble bifunctional catalysts for both the ORR and the OER with high catalytic activity. Herein, an in situ synthetic route to obtain Mo2C–C hybrid microspheres as bifunctional catalysts has been reported. In this route, the synchronously prepared C microspheres act not only as the template, but also as the reactant. Interestingly, SEM, TEM and XPS results show that core–shell, yolk–shell and pierced structured microspheres could be formed by increasing the content of Mo2C in the Mo2C–C hybrids. Additionally, the formation of a non-crystalline amorphous MoOx (MoO2 and MoO3) nano-film appears to improve the conductivity of the as-prepared Mo2C–C hybrids. Rotating-ring-disk electrode (RRDE) results show that the Mo2C–C hybrids exhibit enhanced catalytic activity for the ORR and OER compared with that of the C microspheres and Mo2C. In particular, Mo2C–C-5 displays excellent bifunctional activity and stability, which is close to the behavior of a commercial Pt/C electrocatalyst for the ORR and a RuO2 electrocatalyst for the OER.

An efficient catalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is the most critical factor influencing the performance of lithium–air batteries. We present MnOx decorated CeO2 nanorods as a highly active cathode catalyst for lithium–air batteries fabricated via an in-situ redox reaction. Lithium–air batteries based on MnOx@CeO2 catalysts show enhanced electrochemical performances, including high first discharge specific capacity (2617 mA h g−1 at 100 mA g−1), low overpotential, good rate capability (up to 400 mA g−1), and cycle stability (only 1.1% voltage loss after 30 cycles of specific capacity limit of 1000 mA h g−1 tested at 200 mA g−1). The improved performance might be attributed to the high catalyst efficiency.