Ching-Fang Liu

Bio: Ching-Fang Liu is an academic researcher from National Tsing Hua University. The author has contributed to research in topics: Reversible hydrogen electrode & Epitaxy. The author has an hindex of 4, co-authored 5 publications receiving 63 citations.

Effects of Anions and pH on the Stability of ZnO Nanorods for Photoelectrochemical Water Splitting

Abstract: This work demonstrates the improved stability of zinc oxide nanorods (ZnO NRs) for the photoanode of solar water splitting under voltage biases by the addition of borate or carbonate ions in the aqueous electrolyte with suitable pH ranges. The ZnO NRs prepared by the hydrothermal method are highly active and stable at pH 10.5 in both borate and carbonate buffer solutions, where a photocurrent higher than 99% of the initial value has been preserved after 1 h polarization at 1.5 V (vs reversible hydrogen electrode) under AM 1.5G. The optimal pH ranges with a minimum morphological change of ZnO NRs for photoelectrochemical (PEC) water splitting in borate and carbonate buffer solutions are 9-13 and 10-12, respectively. The working pH range for PEC water splitting on ZnO NR photoanodes can be extended to 8.5-12.5 by the combination of borate and carbonate anions. The lifetime of ZnO NR photoanodes can be synergistically prolonged for over an order of magnitude when the electrolyte is the binary electrolyte consisting of borate and carbonate in comparison with these two anions used individually. On the basis of the experimental results, a possible mechanism for the protective behavior of ZnO in borate and carbonate solutions is proposed. These findings can be used to improve the lifetime of other high-performance ZnO-based catalysts and to understand the photocorrosive and protective behaviors of ZnO NRs in the borate and carbonate solutions.

How to achieve the desired performance of solar water splitting with voltage biases

Abstract: This work demonstrates how to set efficiency benchmarks in photo-electrochemical measurements for solar water splitting with assistance of voltage biases. We modify the applied bias photon-to-current efficiency to circumvent the existing limitations for precisely estimating the energy transformation efficiency under valid conditions. The light sources, surface area of counter electrodes, and oxygen content in electrolytes, and photo-anode materials are changed to investigate their impact on the energy transformation efficiency. This work clarifies that a larger counter electrode surface area results in the enhancement of the oxygen reduction reaction, reducing the applied bias voltage but also reducing the hydrogen generation rate. Furthermore, positive potential biases on the photo-anode and removal of dissolved oxygen molecules in the electrolyte are effective to promote the hydrogen generation rate because of efficient electron/hole separation and the ORR elimination. Due to the high photocurrent generated by the ultraviolet light source, the consumption of photocurrents by the ORR is generally negligible. Therefore, a balance between photocurrent and applied potential bias on the photo-electrochemical cell is proposed to achieve the desired energy transformation efficiency.

ZnO As an Active and Selective Catalyst for Electrochemical Water Oxidation to Hydrogen Peroxide

Abstract: Electrochemical synthesis of hydrogen peroxide (H2O2) via two-electron water oxidation reaction (2e-WOR) is an ideal process for delocalized production for water cleaning and other applications. Pr...

Effects of Anions and pH on the Stability of ZnO Nanorods for Photoelectrochemical Water Splitting

Abstract: This work demonstrates the improved stability of zinc oxide nanorods (ZnO NRs) for the photoanode of solar water splitting under voltage biases by the addition of borate or carbonate ions in the aqueous electrolyte with suitable pH ranges. The ZnO NRs prepared by the hydrothermal method are highly active and stable at pH 10.5 in both borate and carbonate buffer solutions, where a photocurrent higher than 99% of the initial value has been preserved after 1 h polarization at 1.5 V (vs reversible hydrogen electrode) under AM 1.5G. The optimal pH ranges with a minimum morphological change of ZnO NRs for photoelectrochemical (PEC) water splitting in borate and carbonate buffer solutions are 9-13 and 10-12, respectively. The working pH range for PEC water splitting on ZnO NR photoanodes can be extended to 8.5-12.5 by the combination of borate and carbonate anions. The lifetime of ZnO NR photoanodes can be synergistically prolonged for over an order of magnitude when the electrolyte is the binary electrolyte consisting of borate and carbonate in comparison with these two anions used individually. On the basis of the experimental results, a possible mechanism for the protective behavior of ZnO in borate and carbonate solutions is proposed. These findings can be used to improve the lifetime of other high-performance ZnO-based catalysts and to understand the photocorrosive and protective behaviors of ZnO NRs in the borate and carbonate solutions.