Structural Origin for Efficient Photoelectrochemical Water Splitting over Fe-Modified BiVO<sub>4</sub>
Yifan Hu, Yefei Li, Zhi‐Pan Liu
Abstract
Fe-modified BiVO 4 represents a promising anode material for the photoelectrochemical (PEC) oxygen evolution reaction in neural electrolytes, the bottleneck reaction in PEC water splitting. To reveal the catalytic role of Fe in this composite catalytic system, here we utilize combined theoretical and experimental techniques to identify the location and structure of FeO x phases and optimize the catalytic performance. By using the machine-learning interface search method, we screen out a coherent ε-FeOOH 1.5 (011)/BiVO 4 (001) interface from thousands of likely interface candidates. The interface has a low formation energy (0.74 J/m 2 ), a narrow band structure (∼1.6 eV), and desirable catalytic activity (reaction barrier ∼ 0.64 eV) when the ε-FeOOH 1.5 overlayer is two atomic layers thick. Guided by the theoretical findings, our orthogonal PEC experiments are performed to identify the optimal synthetic conditions. The best PEC activity reaches 5.4 mA/cm 2 (1.23 V vs reversible hydrogen electrode) when using FeSO 4 as the precursor with the chemical bath method at 40 °C for 4 h, which is ∼0.9 mV/ cm 2 higher compared to the previous experiment. By analyzing transmission electron microscopy (TEM) pictures and performing TEM simulations, we confirm that the grass-like FeO x structures grown on BiVO 4 are ε-FeOOH crystals as predicted by theory.