Shanghai silicate institute has made progress in the research of BiVO4 based photoanode materials

Solar photoelectric chemistry (PEC) cracking water is an effective method to convert solar energy into hydrogen energy. Among many semiconductor photoanodes, BiVO4 is an excellent photoanode material due to its suitable conduction band, valence band position and forbidden band width. BiVO4 has a light absorption edge of 515nm and a theoretical maximum photocurrent density (Jmax) of 7.5ma cm-2 under AM1.5 sunlight. However, the actual photodecomposition hydroelectricity current density (JH2O) is much lower than its theoretical value, mainly because BiVO4 has energy loss in each process of photopec decomposition of water. According to previous reports, JH2O can be expressed as JH2O = Jmax * eta abs * eta sep x eta trans eta of abs is absorption efficiency, eta sep is charge separation efficiency, eta is trans surface hole transfer efficiency. The BiVO4 light anode eta sep and eta trans is low, and relatively wide band gap and the instability limits its further photoelectric conversion efficiency and practical application.
Recently, Shanghai institute of silicate, Chinese academy of sciences, in cooperation with Peking University and fudan university, has made new progress in the design of bivo4-based photoanode and its application in photocatalytic cracking water. The team prepared the BiVO4 photoanode with a reduced black nanostructure at room temperature using the typical method of preparing BiVO4 photoanode with nanostructure. The BiVO4 photoanode with black nanostructure can not only improve the efficiency of charge transmission and separation, but also greatly expand the absorption spectrum of visible light (band gap reduced by 0.3 eV). However, the surface catalytic efficiency of the BiVO4 photoanode with black nanostructure is not significantly improved, and its stability is not good. In addition, the charge recombination between photoanode and catalyst is very serious with the traditional oxygen producing catalyst (OEC) load. Therefore, through further experimental design, the team used ALD technology to load amorphous TiO2 on the surface of BiVO4 photoanode with nano-structure, and then further reduced it. EELS results showed that the BiVO4 supporting TiO2 also achieved the same reduction degree as the black nano-structure BiVO4 in the reduction process, while the invisible TiO2 was reduced to amorphous tio2-x. The charge transfer and separation characteristics of the reduced BiVO4 (b-bivo4 / tio2-x) photoanode coated with amorphous tio2-x are basically consistent with those of the BiVO4 photoanode with black nano-structure. The resulting b-bivo4 / tio2-x-ray anode achieves a relatively high current density at low voltage (3.85 mA cm-2 at 0.6 VRHE), thus achieving a bias conversion efficiency of 2.5% (ABPE). Further study found that amorphous tio2-x not only acted as OEC catalyst, but also played a role of stable reduced BiVO4 photoanode, so as to achieve long-term stable and efficient water cracking of b-bivo4 / tio2-x anode. Relevant research results were published in Advanced Energy Materials 2019 (DOI: Novel black-bivo4 /TiO2-x Photoanode with Enhanced Photon Absorption and Charge Separation for Efficient and Stable Solar Water Separation) as the title of “Novel black-bivo4 /TiO2 Photoanode with Enhanced Photon Absorption and Charge Separation for Efficient and Stable Solar Water Separation” 10.1002/aenm.201901287), Dr. Zhang zhangliu of Shanghai institute of silicate and zhang pengfei of fudan university are the co-first authors, and professor huang fuqiang of Shanghai institute of silicate, academician of Chinese academy of sciences and professor zhao dongyuan of fudan university are the co-corresponding authors.
The research has been funded by the national key research and development program, the national natural science foundation of China, the Chinese academy of sciences and the Shanghai municipal science and technology commission.

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