Bingyan Zhang

Active catalysts based on cobalt oxide@cobalt/N-C nanocomposites for oxygen reduction reaction in alkaline solutions

Over the past few years, electrocatalysis for the oxygen reduction reaction in alkaline solutions has undergone tremendous advances, and non-precious metal catalysts are of prime interest. In this study, we present a highly promising CoO@Co/N-C (where N-C represents a N-doped carbon material) catalyst, achieving an onset potential of 0.99 V (versus the reversible hydrogen electrode (RHE)) and a limiting current density of 7.07 mA·cm−2 (at 0.3 V versus RHE) at a rotation rate of 2,500 rpm in an O2-saturated 0.1 M KOH solution, comparable to a commercial Pt/C catalyst. The H2-O2 alkaline fuel cell test of CoO@Co/N-C as the cathode reveals a maximum power density of 237 mW·cm−2. Detailed investigation clarifies that a synergistic effect, induced by C-N, Co-N-C, and CoO/Co moieties, is responsible for the bulk of the gain in catalytic activity.

Efficient p-type dye-sensitized solar cells based on disulfide/thiolate electrolytes

Herein, an organic redox couple 1-methy-1H-tetrazole-5-thiolate (T(-)) and its disulfide dimer (T2) redox shuttle, as an electrolyte, is introduced in a p-type dye-sensitized solar cell (DSC) on the basis of an organic dye (P1) sensitizer and nanocrystal CuCrO2 electrode. Using this iodide-free transparent redox electrolyte in conjunction with the sensitized heterojunction, we achieve a high open-circuit voltage of over 300 mV. An optimal efficiency of 0.23% is obtained using a CoS counter electrode and an optimized electrolyte composition under AM 1.5 G 100 mW cm(-2) light illumination which, to the best of our knowledge, represents the highest efficiency that has so far been reported for p-type DSCs using organic redox couples.

A perovskite solar cell-TiO2@BiVO4 photoelectrochemical system for direct solar water splitting

Converting solar energy into hydrogen via photoelectrochemical water splitting has attracted significant attention during the past decades. Herein, we design a novel core/shell TiO2@BiVO4 photoanode in combination with a CH3NH3PbI3-based perovskite solar cell for unassisted solar water splitting. Compared to pristine TiO2 NRs, the resulting TiO2@BiVO4 film exhibits a 3.25-fold enhanced photocurrent density (∼1.3 mA cm−2) under irradiation (xenon lamp coupled with an AM 1.5 G filter, 100 mW cm−2). This significant enhancement is attributed to the excellent light absorption properties of BiVO4 and a fast electron transfer process in the single crystalline TiO2 NRs. Especially, the type-II band alignment between the BiVO4 and rutile TiO2 NRs provides a large driving force for electron injection from the BiVO4 to the TiO2. The perovskite solar cell-TiO2@BiVO4 photoelectrochemical tandem device exhibits an overall solar-to-hydrogen efficiency of 1.24%, comparable to other TiO2-based PV/PEC systems.

Electrochemically reduced graphene oxide multilayer films as metal-free electrocatalysts for oxygen reduction

In this work we report on functional multilayer films containing electrochemically reduced graphene oxide (ERGO) by the alternating layer-by-layer (LBL) assembly of negatively charged graphene oxide (GO) and positively charged poly (diallyldimethylammonium chloride) (PDDA) in combination with an electrochemical reduction procedure. As a metal-free catalyst, the resulting [PDDA@ERGO] multilayer film possesses a remarkable electro-catalytic activity toward the oxygen reduction reaction (ORR) with superior methanol tolerance in alkaline media. Further research indicates that the unusual catalytic activity of the prepared hybrid films arises from synergetic chemical coupling effects between PDDA and ERGO. Importantly, the [PDDA@ERGO] multilayer film as a metal free oxygen reduction catalyst reported here is easy to build up with the advantages of fine control of the film thickness, being energy effective, fast and green without using dangerous and corrosive substances.

N/Si co-doped oriented single crystalline rutile TiO2 nanorods for photoelectrochemical water splitting

Chemical modification of the aligned single crystalline TiO2 nanorods provides possibilities to improve their photoelectrochemical (PEC) activity under visible light. This work reports on the N/Si co-doped single crystal rutile TiO2 nanorods fabricated by a flexible one-step hydrothermal procedure for PEC water splitting, exhibiting a photocurrent of 1.77 mA cm−2 at 1.23 V vs. RHE and a noticeable visible-light response under standard testing conditions (xenon lamp with an AM 1.5 G filter, 100 mW cm−2). The excellent PEC activity can be attributed to the synergetic effect of N and Si co-dopants, which enhances the incident photon to current conversion efficiency both in ultraviolet and visible regions, and improves the charge transfer at the photoanode/electrolyte interface. A solar-powered water splitting device has been designed by combining an efficient perovskite solar cell with the N/Si co-doped TiO2 NRs-based PEC system, achieving an overall solar-to-hydrogen efficiency of 1.1%. This has been the highest value reported for TiO2-based PEC systems so far.

Hydrogen peroxide biosensor based on microperoxidase-11 immobilized on flexible MWCNTs-BC nanocomposite film.

In the present work, we report on an experimental study of flexible nanocomposite film for electrochemical detection of hydrogen peroxide (H2O2) based on bacterial cellulose (BC) and multi-walled carbon nanotubes (MWCNTs) in combination with microperoxidase-11 (MP-11). MWCNTs are used to functionalize BC and provide a flexible conductive film. On the other hand, BC can improve MWCNTs׳ biocompatibility. The investigation shows that MP-11 immobilized on the flexible film of MWCNTs-BC can easily present a pair of well-defined and quasi-reversible redox peaks, revealing a direct electrochemistry of MP-11 on the nanocomposite film. The apparent heterogeneous electron-transfer rate constant ks is estimated to be 11.5s(-1). The resulting flexible electrode presents appreciated catalytic properties for electrochemical detection of H2O2, comparing to traditional electrodes (such as gold, glassy carbon electrode) modified with MP-11. The proposed biosensor exhibits a low detection limit of 0.1 µM (at a signal-to-noise ratio of 3) with a linear range of 0.1-257.6 µM, and acquires a satisfactory stability.

Photoelectrochemical Water Splitting System—A Study of Interfacial Charge Transfer with Scanning Electrochemical Microscopy

Fast charge transfer kinetics at the photoelectrode/electrolyte interface is critical for efficient photoelectrochemical (PEC) water splitting system. Thus, far, a measurement of kinetics constants for such processes is limited. In this study, scanning electrochemical microscopy (SECM) is employed to investigate the charge transfer kinetics at the photoelectrode/electrolyte interface in the feedback mode in order to simulate the oxygen evolution process in PEC system. The popular photocatalysts BiVO4 and Mo doped BiVO4 (labeled as Mo:BiVO4) are selected as photoanodes and the common redox couple [Fe(CN)6](3-)/[Fe(CN)6](4-) as molecular probe. SECM characterization can directly reveal the surface catalytic reaction kinetics constant of 9.30 × 10(7) mol(-1) cm(3) s(-1) for the BiVO4. Furthermore, we find that after excitation, the ratio of rate constant for photogenerated hole to electron via Mo:BiVO4 reacting with mediator at the electrode/electrolyte interface is about 30 times larger than that of BiVO4. This suggests that introduction of Mo(6+) ion into BiVO4 can possibly facilitate solar to oxygen evolution (hole involved process) and suppress the interfacial back reaction (electron involved process) at photoanode/electrolyte interface. Therefore, the SECM measurement allows us to make a comprehensive analysis of interfacial charge transfer kinetics in PEC system.

Investigation on regeneration kinetics at perovskite/oxide interface with scanning electrochemical microscopy

Scanning electrochemical microscopy (SECM) is a powerful technique for quantitative and qualitative investigation of interfacial charge transfer processes. This work presents an SECM investigation on the regeneration kinetics of an organo-metal halide perovskite (CH3NH3PbI3) sensitized onto various semiconductor oxide nanocrystals, including n-type titanium dioxide and p-type nickel oxide. We found for the first time that the regeneration rate constant, and absorption cross section of CH3NH3PbI3 are significantly higher than the conventional sensitizers.

Band gap engineering of MnO2 through in situ Al-doping for applicable pseudocapacitors

Band gap engineering was achieved by in situ doping method for high electrical conductivity and chemical activity of MnO2. By in situ releasing and adsorption during electrodeposition, Al3+ with close ion radius to Mn4+ could replace the position of Mn4+ in MnO2. The in situ doping process brings impurity level in MnO2 and changes the energy band structure. The narrower band gap of MnO2 after Al doping with higher electron concentration on conduction band could improve the conductivity of MnO2. The specific capacitance of Al-doped MnO2 achieves 430.6 F g−1 which is almost 2.5 times of the capacitance of initial MnO2 (177 F g−1), shedding light on its practical applications.

Co9S8 hollow spheres for enhanced electrochemical detection of hydrogen peroxide

This work reports on an experimental investigation of Co9S8 hollow spheres with excellent interfacial charge transfer ability for the electrochemical detection of hydrogen peroxide and glucose in alkaline environment. The result reveals that the Co9S8 hollow spheres exhibit excellent electrocatalytic activity for the reduction of hydrogen peroxide. An electrochemical sensor based on Co9S8 can be further realized, exhibiting a linear response range from 0.0001 to 11.11mM for hydrogen peroxide with a low detection limit of 0.02μM, and a high sensitivity of 267.2mA mol(-1)cm(-2), which is one of the highest values among the non-enzymatic sensors based on inorganic oxides. The Co9S8 sensor also exhibits good response toward glucose at different concentrations. These results demonstrate that the as-prepared Co9S8 hollow spheres have a potential application in the development of sensors for enzyme-free detection of H2O2 and glucose.