The efficiency of hydrogen peroxide evolution reaction (H 2 O 2 ER) by photoanodic water oxidation is normally limited by low yield and poor selectivity. In this work, the surfaces of Mo doped BiVO 4 are modified by Co 2+ and PO 4 3- ions (CPMB), which has been used as the photoanode with improved H 2 O 2 yield and selectivity. The optimal evolution rate of the CPMB is ca. 0.23 µmol·min −1 ·cm −2 , corresponding to 2.5 times to the pristine BiVO 4 photoanode, and the faradaic efficiency of CPMB photoanode for H 2 O 2 ER is ca. 26%. In this study, the mechanism for the improved H 2 O 2 evolution performance of CPMB has been investigated, indicating that PO 4 3- ions mainly promote the formation of the •OH by dissociation of H 2 O, while Co 2+ ions accelerate the conversion of the •OH for the subsequent H 2 O 2 evolution. This study offers the strategy for designing an efficient photoelectrochemical system with optimized solar conversion efficiency for H 2 O 2 production.
Electrochemical treatment is a popular and efficient method for improving the photoelectrochemical performance of water-splitting photoelectrodes. In our previous study, the electrochemical activation of Mo-doped BiVO 4 electrodes was ascribed to the removal of MoO x segregations, which are considered to be surface recombination centers for photoinduced electrons and holes. However, this proposed mechanism cannot explain why activated Mo-doped BiVO 4 electrodes gradually lose their activity when exposed to air. In this study, based on various characterizations, it is suggested that electrochemical treatment not only removes partial MoO x segregations but also initiates the formation of H y MoO x surface defects, which provide charge transfer channels for photogenerated holes. The charge separation of the Mo-doped BiVO 4 electrode was significantly enhanced by these charge transfer channels. This study offers a new insight into the electrochemical activation of Mo-doped BiVO 4 photoanodes, and the new concept of surface charge transfer channels, a long overlooked factor, will be valuable for the development of other (photo)electrocatalytic systems.
Yuan Guan,Xinyi Gu,Qiankun Deng,Shaomang Wang,Zhongyu Li,Shicheng Yan,Zhigang Zou
Bismuth vanadate is a promising material for photoelectrochemical water oxidation. However, it suffers from a low quantum efficiency, poor stability, and slow water oxidation kinetics. Here, we developed a novel photoanode of CoS/Mo-BiVO4 with excellent photoelectrochemical water oxidation performance. It achieved a photocurrent density of 4.5 mA cm–2 at 1.23 V versus the reversible hydrogen electrode, ∼4 times that of BiVO4. The CoS/Mo-BiVO4 photoanode also exhibited good stability, and the photocurrent density generated by the CoS/Mo-BiVO4 photoanode did not significantly decrease after light irradiation for 2 h. Upon replacement of part of the V with Mo doping in BiVO4, the local electric field around the Mo–O bond was enhanced, thus promoting carrier separation in BiVO4. The CoS was deposited on the surface of Mo-BiVO4, forming a built-in electric field at the interface. Under the action of the bias electric field and the built-in electric field, the carriers of CoS/Mo-BiVO4 were efficiently separated in the direction of the inverse type II heterojunction. In addition, CoS improved the light absorption and charge injection efficiency of the CoS/Mo-BiVO4 photoanode.
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