Yang Shihe, team of Ji Hongbing, Sun Yat sen University / Shenzhen Institute of Peking University, published NAT. Commun. Paper: work function regulation and heterostructure construction to promote photoelectrochemical decomposition of water for hydrogen production

The photoelectrochemical cell is one of the key technologies for hydrogen production in the future, and bismuth vanadate (BiVO 4) as a kind of photoanode material which can utilize visible light and has a suitable energy band position is widely concerned Scientists have successively enhanced the absorption efficiency, electron hole pair separation efficiency and catalytic water decomposition efficiency of BiVO 4 to improve its water decomposition performance At present, most of the research focuses on the photocurrent density and photoelectric conversion efficiency of BiVO 4 photoanode under high bias voltage, which will lead to its work efficiency limited by high bias voltage Therefore, if we find a way to relieve the limitation of the photocurrent density of BiVO 4 under low voltage, it will greatly improve the efficiency of water decomposition of BiVO 4 photocatalyst, and provide reference for the future design of photocatalyst Through the work function regulation and heterojunction construction of BiVO 4 photoelectric anode material, the photocurrent density of decomposition water of BiVO 4 electrode under low bias voltage is improved, and the efficiency of decomposition water of BiVO 4 electrode is greatly improved In this method, firstly, the photoelectrochemical study of the synthesized BiVO 4 electrode is carried out It is found that the existence of the surface defect energy level will lead to the appearance of Fermi pinning effect, which limits the photovoltage (VPH) of BiVO 4 electrode and restricts its current density at low voltage Therefore, the micro Mo doping can reduce the influence of the surface defect energy level without significantly changing the position of the Fermi energy level of BiVO 4, so as to improve the V pH of BiVO 4 (as shown in Fig 1) Fig 1 (source: Nat Commun.) in order to further improve the photocurrent density of BiVO 4 electrode at low bias voltage, the heterojunction of carbon nitride (C3N4) and BiVO 4 was constructed However, it is found in the research process that after the carbon nitride is compounded with the modified BiVO 4 electrode doped with Mo, the band shift will make the recombination of electron hole pairs intensified, thus reducing the photoelectric performance of the entire electrode (Fig 2 A, b) Therefore, in this paper, the boron (b) doping of C 3N 4 makes the Fermi energy level of C 3N 4 move to the valence band, and ingeniously transforms the heterostructure that originally intensifies the electron hole recombination of electrode into the heterostructure that can promote the electron hole separation, thus effectively improving the electron hole separation ability of bismuth vanadate at low voltage (Fig 2E, f) Fig 2 (source: Nat Commun.) finally, nifeo x electrocatalyst was used as a cocatalyst, which was grown on b-c3n4 / Mo BiVO 4 photocatalyst through photoelectrochemical deposition to improve the catalytic efficiency of photocatalyst in catalytic decomposition water This method can make the electrocatalytic agent grow on the photo active site of the electrode material first, which can significantly improve the ability of the material to decompose water After the improvement of nifeo x electrocatalytic agent, the half cell efficiency (ABPE) of the whole electrode reached 2.67%, and the bias voltage needed to achieve this efficiency was only 0.54 V vs rhe (Fig 3) Fig 3 (source: Nat Commun.) according to the unique characteristics of different optoelectronic materials, find the defects of different optoelectronic materials, and design the solution of "suit the case", so as to realize the substantial improvement of optoelectronic catalytic performance and in-depth understanding of mechanism, which is an inevitable process in the study of optoelectronic catalysis The innovation of the research results is to find and solve the common problem that BiVO 4 reduces the photovoltage limiting photocurrent due to the existence of surface defect electrons At the same time, through the analysis and regulation of the surface work function, the heterojunction energy band structure is changed from the structure of intensifying the electron hole pair composite to the structure of enhancing the electron hole pair separation, which provides a reference basis and a new idea for the design and construction of the next generation of photovoltaics in the future Professor Ji Hongbing of the school of chemistry of Sun Yat sen University and Professor Yang Shihe of the Shenzhen Research Institute of Peking University are co correspondents The research progress has been supported by the National Natural Science Foundation, the national key research and development plan, the Guangdong Provincial Natural Science Fund, the Guangdong Pearl River talent plan local innovation team project and the Guangdong Provincial Department of education characteristic innovation plan.