Zachäus Carolin, Abdi Fatwa F, Peter Laurence M, van de Krol Roel
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH , Institute for Solar Fuels , Hahn-Meitner-Platz 1 , 14109 Berlin , Germany . Email:
Department of Chemistry , University of Bath , Bath BA2, 7AY , UK.
Chem Sci. 2017 May 1;8(5):3712-3719. doi: 10.1039/c7sc00363c. Epub 2017 Mar 9.
Bismuth vanadate is one of the most promising photoanode materials for photoelectrochemical water splitting. In order to achieve high photocurrents the surface of BiVO always has to be modified with water oxidation catalysts, such as cobalt phosphate (CoPi), FeOOH, or NiFeO . While this has generally been attributed to the poor intrinsic catalytic activity of BiVO, detailed insight into the fate of the photogenerated charge carriers at the surface is still lacking. We used intensity modulated photocurrent spectroscopy (IMPS) to investigate the surface carrier dynamics of bare and CoPi-modified spray-deposited BiVO films. Using a model developed by Peter , it was possible to distinguish the reaction rate constants for surface recombination and charge transfer to the electrolyte. We found that modification with CoPi reduced the surface recombination of BiVO with a factor of 10-20, without significantly influencing the charge transfer kinetics. Control experiments with RuO , one of the best known OER electrocatalysts, did not affect surface recombination and led to an actual decrease of the photocurrent. These results show that the main role of the CoPi is to passivate the surface of BiVO and that, contrary to earlier assumptions, the photocurrent of BiVO is limited by surface recombination instead of charge transfer. The importance of surface recombination is well recognized for conventional semiconductors in the field of photovoltaics; these findings show that it may also play a crucial role in oxide-based semiconductors for photoelectrochemical energy conversion.
钒酸铋是用于光电化学水分解的最有前途的光阳极材料之一。为了实现高光电流，BiVO的表面总是需要用水氧化催化剂进行修饰，例如磷酸钴（CoPi）、FeOOH或NiFeO 。虽然这通常归因于BiVO固有的催化活性较差，但仍缺乏对表面光生载流子命运的详细了解。我们使用强度调制光电流光谱（IMPS）来研究裸的和CoPi修饰的喷雾沉积BiVO薄膜的表面载流子动力学。使用彼得开发的模型，可以区分表面复合和向电解质的电荷转移的反应速率常数。我们发现，用CoPi修饰可使BiVO的表面复合降低10到20倍，而不会显著影响电荷转移动力学。用最著名的析氧反应（OER）电催化剂之一RuO 进行的对照实验不会影响表面复合，实际上还导致光电流下降。这些结果表明，CoPi的主要作用是使BiVO的表面钝化，并且与早期的假设相反，BiVO的光电流受表面复合而非电荷转移的限制。表面复合的重要性在光伏领域的传统半导体中已得到充分认识；这些发现表明，它在用于光电化学能量转换的氧化物基半导体中也可能起着关键作用。
