In this study, theoretical calculations and experiments have been carried out to investigate the photoelectric performance of (2Al, S) co-doped rutile SnO2. The electronic structures are studied by density functional theory (DFT). It is found that the metal Al can assist the bonding of the incorporated S with the neighboring O in SnO2, introducing new energy levels in the forbidden band of SnO2, which enhance the photoelectric performance. Meanwhile, the experiments are conducted to verify this. The (2Al, S) co-doped SnO2 with different doping ratios are prepared by a hydrothermal method. The samples are characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Results show that all the samples have rutile structure without any extra phase, and the dopant S2− ion was implanted into the crystalline lattice of (2Al, S) co-doped SnO2 and Al dopants replaced Sn atoms. The photoelectric performance tests show Al and S co-doping can improve the photoelectric performance, especially with a doping ratio of 5%, when the photocurrent reaches maximum of 3.0 μA cm−2 which is almost twice as much as pure SnO2, and the impedance is the smallest. The experiments results are consistent with our theoretical calculations. These findings are expected to be helpful for the design of highly active tin oxide-based photoelectric materials.

•Porous nanostructure carbon quantum dots/polypyrrole composite film was successfully synthesized by direct electrochemical method.•A flexible all-solid-state supercapacitor device was fabricated using the carbon quantum dots/polypyrrole composite electrode.•The flexible supercapacitor exhibits high specific capacitance, excellent reliability and long cycling life.Recently, carbon quantum dots (CQDs) as a new zero-dimensional carbon nanomaterial have become a focus in electrochemical energy storage. In this paper, flexible all-solid-state supercapacitors (ASSSs) were electrochemically synthesized by on-step co-deposition of appropriate amounts of pyrrole monomer and CQDs in aqueous solution. The different electrodeposition time plays an important role in controlling morphologies of stainless steel wire meshes (SSWM)-supported CQDs/PPy composite film. The morphologies and compositions of the obtained CQDs/PPy composite electrodes were characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), Raman spectrum and X-ray photoelectron spectroscopy (XPS). Furthermore, a novel flexible ASSS device was fabricated using CQDs/PPy composite as the electrode and separated by polyvinyl alcohol/LiCl gel electrolyte. Benefiting from superior electrochemical properties of CQDs and PPy, the as-prepared CQDs/PPy composite ASSSs exhibit outstanding electrochemical performance with the areal capacitance 315 mF cm−2 (corresponding to specific capacitance of 308 F g−1) at a current density of 0.2 mA cm−2 and long cycle life with 85.7% capacitance retention after 2 000 cycles.Download high-res image (148KB)Download full-size image

An Ag2O/Ag electrode was prepared through the electrochemical oxidation of sterling silver. This electrode was used as a cathodic electron acceptor in a microbial fuel cell (MFC). The Ag2O/Ag electrode was characterized by scanning electron microscopy, X-ray powder diffraction and linear sweep voltammetry. The maximum voltage output of the MFC with the Ag2O/Ag cathode was maintained at between 0.47 and 0.5 V in 100 cycles, indicating the good regenerative capacity of the Ag2O/Ag electrode. The overpotential loss for silver oxide was 0.021–0.006 V, and the maximum power output, open circuit potential and short circuit current of the MFC were 1.796 W m−3, 0.559 V and 9.3375 A m−3, respectively. The energy required for electrochemical reoxidation ranged from 40% to 55% of the energy produced by the MFC. Results indicated that the Ag2O/Ag electrode could be used as a cathodic electron acceptor in MFCs with excellent stability.

Graphene quantum dots–Cu2O (GQDs–Cu2O) is introduced to a bipolar membrane (BPM) interlayer and shown to be a novel, efficient water dissociation catalyst. This paper reports the use of the GQDs–Cu2O/BPM composite as a separator to prevent the crossover of hydrogen and oxygen. Under reverse bias and sunlight irradiation conditions, GQDs–Cu2O/BPM exhibits lower membrane resistance than BPM. GQDs–Cu2O/BPM also minimizes pH gradient formation, resulting in a decreased potential loss with respect to that of BPM. The efficiency of GQDs–Cu2O/BPM as a diaphragm in H2 generation and energy conservation was assessed. GQDs–Cu2O/BPM was found to be 88.6% and 14.5% more efficient than BPM in H2 generation at the current density of 90 mA cm−2 and under sunlight irradiation, respectively. The composite also saved about 22.6% energy with respect to that of BPM at 90 mA cm−2.

Photoconductive BiOCl has been introduced into a bipolar membrane (BPM) interlayer to prepare a BiOCl/BPM. This paper reports the use of the BiOCl/BPM composite to regenerate NaOH. Under reverse bias and sunlight irradiation conditions, the BiOCl/BPM resistance and cell voltage can be significantly decreased due to the photoconductivity of the BiOCl photocatalyst, which lead to the energy consumption decline in regenerating NaOH. Moreover, the electric field in the interlayer of the BiOCl/BPM contributes in separating the photo-generated electron–hole pairs of the BiOCl photocatalyst, thereby increasing the current efficiency of regenerating NaOH.

The effects of inoculum species, substrate concentration, temperature, and cathodic electron acceptors on electricity production of microbial fuel cells (MFCs) were investigated in terms of start-up time and power output. When inoculated with aeration tank sludge, this MFC outperformed the cell that was inoculated with anaerobic sludge in terms of start-up time and power output. After running for a certain time period, the dominant populations of the two MFCs varied significantly. Within the tested range of substrate concentration (200–1800 mg L−1), the voltage output increased and the time span of the electricity generation lengthened with increasing substrate concentration. As the temperature declined from 35 to 10 °C, the maximum power density reduced from 2.229 to 1.620 W m−3, and anodic polarization resistance correspondingly dropped from 118 to 98 Ω. The voltage output of MFC–Cu2+ was 0.447 V, which is slightly lower than that achieved with MFC–[Fe(CN)6]3− (0.492 V), thereby indicating that MFCs could be used to treat wastewater containing Cu2+ pollutant in the cathode chamber with removal of organics in anode chamber and simultaneous electricity generation.

A series of nano-Mg(OH)2/graphene (Gr) composites was synthesized via simple hydrothermal method using MgSO4·7H2O and graphene oxide (GO) as precursors, hydrazine hydrate as additive. Linear sweep voltammetry tests showed that the 2# composite synthesized from 50 wt.% MgSO4·7H2O and 50 wt.% GO with a surface density of 1.5 mg cm−2 exhibited the best catalytic activity for hydrogen evolution reaction. The 2# composite was utilized as the cathodic catalyst in a microbial electrolysis cell (MEC) to facilitate hydrogen production. In the MEC tests, the nano-Mg(OH)2/Gr cathode was comparable with the Pt/C cathode in terms of current densities and energy efficiency. The hydrogen recovery, cathodic hydrogen recovery and hydrogen production rate obtained with nano-Mg(OH)2/Gr MEC were 71 ± 12%, 83 ± 9% and 0.63 ± 0.11 m3 H2 m−3 d−1, slightly higher than those obtained with the Pt/C cathode MEC. The nano-Mg(OH)2/Gr cathode exhibited good stability, and it was inexpensive (less than 1.7% of the cost of the Pt/C cathode). These results demonstrated that the nano-Mg(OH)2/Gr composite was an effective HER catalyst because of its good catalytic capacity, durability, and low price.

A novel photoelectrocatalytic approach for water splitting through an I-BiOCl/bipolar membrane sandwich structure with photoelectro-synergistic catalysis is proposed in this study. The I-BiOCl/bipolar membrane sandwich structure could facilitate separation of photoexcited electrons and holes, thereby promoting the splitting of water, increasing the efficiency of H2 generation and saving energy consumption.

An important functional material, MOF-5, with unique flower shaped morphology, which is usually synthesized through hydrothermal or solvothermal methods at high temperature and pressure with high energy consumption, was successfully prepared by a mild in situ electrochemical synthesis method in a tunable ionic liquid (IL) system. In the reaction, H2BDC (BDC = 1,4-benzene-dicarboxylate) was chosen as the organic ligand, and the ionic liquid was Bmim (Bmim = 1-butyl-3-methylimidazole) bromine which functioned as a templating agent. The π–π stacking interaction between the imidazole groups, and the ionic band between the Zn2+ and Cl−, cause the directional arrangement of the MOF-5 crystal. Results show that the reaction results in a more perfect MOF-5 crystalline phase in comparison to other methods. The product, MOF-5(IL), presents a distinctive flower shaped morphology with a diameter of about 10 microns, and possesses a homogeneous morphology, stable structure and high thermal stability (up to 380 °C in N2 atmosphere). The electrochemical reaction in the ionic liquid Bmim bromine is a quasi-reversible redox reaction. The cyclic voltammetric curve of the MOF-5(IL) modified carbon paste electrode (CPE) illustrates that the flower shaped MOF-5(IL) has a better ability to catalyze the hydrogen evolution reaction than cubic MOF-5 prepared by other methods. The electrochemical method in the ionic liquid system can also be used to synthesize other MOF materials and nanomaterials by changing the metal ions, ligands and ionic liquid types.

This study successfully synthesised magnesium borate (Mg2B2O5) whiskers using a simpler electrochemical method and lower energy consumption compared with traditional methods. Metallic magnesium was anodised under low-voltage conditions in a borate solution containing ethanol/water mixtures and poisoning agents. The composition and morphology of the magnesium borate whiskers were determined by X-ray diffraction and scanning electron microscope measurements, respectively. The magnesium borate whiskers were 6–8 μm long, each with a diameter of 500 nm. The ratio of the length to the diameter ranges from 12:1 to 16:1. The average current efficiency was 72.6%.

A Ti/SnO2 + RuO2 + MnO2 electrode was prepared by thermal decomposition of their salts. Results from SEM and XPS analyses, respectively, indicate that the coating layer exhibits a compact structure and the oxidation state of Mn in the coating layer is +IV. The experimental activation energy for the oxygen evolution reaction, which increased linearly with increasing overpotential, is about 8 kJ⋅mol−1 at the equilibrium potential (η=0). The electrocatalytic characteristics of the anode are discussed in terms of ligand substitution reaction mechanisms (Sn1 and Sn2). It was found that the transition state for oxygen evolution at the anode in acidic solution follows a dissociative mechanism (Sn1 reaction). The Ti/SnO2 + RuO2 + MnO2 anode in conjunction with UV illumination was used to degrade phenol solutions, where the concentration of phenol remaining was determined by high-performance liquid chromatography (HPLC). The results indicate that the degradation efficiency of phenol on the anode can reach 96.3% after photoelectrocatalytic oxidation for 3 h.

A new method of synthesis 2,2-dimethylolpropionic acid from 2,2-dimethylolpropionaldehyde was put forward. The electrochemical oxidation behavior of 2,2-dimethylolpropionaldehyde has been investigated on a Ti/SnO2 + Sb2O4/PbO2 electrode by cyclic voltammetry (CV) and stable polarization curves in sulfuric acid. The results showed that it was an irreversible reaction controlled by diffusion. The formation mechanism of 2,2-dimethylolpropionic acid in the sulfuric acid was then proposed and the transfer coefficients of the reaction were calculated. It was concluded that RCHO+ỌHads→RCHOỌHads was the rate-determining step in the electrolysis process. The rate of this step obtained from the assumed process agrees well with experiment.

Electrochemical removal of ammonia is a new and effective method in coking wastewater. The reaction mechanism of ammonia removal was proved by stable polarization curve in this paper. First, the supposing of reaction steps of the electrode were proposed. And then reaction parameter of the electrode was measured by Tafel curve. Finally, the reaction mechanism was determined by quasi-equilibrium approach. The results showed that Cl2+H2O→HOCl+H++Cl− was the rate-determining step, the calculated apparent transfer coefficient was uniform to the experimental value.