Ai Guanjie, Mo Rong, Li Hongxing, Zhong Jianxin
Hunan Key Laboratory for Micro-Nano Energy Materials and Devices, School of Physics and Optoelectronics, Xiangtan University, Hunan 411105, P. R. China.
Nanoscale. 2015 Apr 21;7(15):6722-8. doi: 10.1039/c5nr00863h.
Cobalt phosphate (Co-Pi) is photo-electrodeposited on TiO2 nanowire arrays in Co(2+) containing phosphate buffer. The resulting composite photoanode shows a generally enhanced photocurrent near the flat band potential region, and represents a 2.3 times improved photoconversion efficiency compared to that of pristine TiO2 in a neutral electrolyte. A negative effect on the photocurrent generation is also observed when loading TiO2 with a relatively thick Co-Pi layer, which is demonstrated to be due to the poor photohole transfer kinetics in the Co-Pi layer. Moreover, we find that Co-Pi can facilitate the photoelectrochemical performance of TiO2 over a wide pH range from 1-14. This improved activity is studied in detail by optical and electrochemical analyses. It is suggested that the mechanism of the overpotential-demanding water oxidation reaction is changed to a facile pathway by the Co-based electrocatalyst. At the same time, the more significant band bending is induced by the Co-Pi catalyst decreasing the charge recombination. This work provides a feasible route to reduce the external power needed to drive water splitting by coupling an electrocatalyst with a photocatalyst, as well as mechanistic insights important for other Co-Pi modified photoelectrodes for solar-driven water splitting.
磷酸钴（Co-Pi）在含Co(2+)的磷酸盐缓冲液中通过光电沉积法负载于TiO2纳米线阵列上。所得复合光阳极在平带电位区域附近通常表现出增强的光电流，并且在中性电解质中，其光转换效率相较于原始TiO2提高了2.3倍。当TiO2负载相对较厚的Co-Pi层时，也观察到对光电流产生的负面影响，这被证明是由于Co-Pi层中光生空穴转移动力学较差所致。此外，我们发现Co-Pi在pH值为1至14的宽范围内均可促进TiO2的光电化学性能。通过光学和电化学分析对这种改善的活性进行了详细研究。研究表明，基于Co的电催化剂将需要过电位的水氧化反应机制转变为了一条简便的途径。同时，Co-Pi催化剂诱导了更显著的能带弯曲，减少了电荷复合。这项工作提供了一条可行的途径，通过将电催化剂与光催化剂耦合来降低驱动水分解所需的外部功率，同时也为其他用于太阳能驱动水分解的Co-Pi修饰光电极提供了重要的机理见解。
