Co and Fe Codoped WO2.72 as Alkaline-Solution-Available Oxygen Evolution Reaction Catalyst to Construct Photovoltaic Water Splitting System with Solar-To-Hydrogen Efficiency of 16.9.

Oxygen evolution electrode is a crucial component of efficient photovoltaic-water electrolysis systems. Previous work focuses mainly on the effect of electronic structure modulation on the oxygen evolution reaction (OER) performance of 3d-transition-metal-based electrocatalyst. However, high-atomic-number W-based compound with complex electronic structure for versatile modulation is seldom explored because of its instability in OER-favorable alkaline solution. Here, codoping induced electronic structure modulation generates a beneficial effect of transforming the alkaline-labile WO2.72 (WO) in to efficient alkaline-solution-stable Co and Fe codoped WO2.72 (Co&Fe-WO) with porous urchin-like structure. The codoping lowers the chemical valence of W to ensure the durability of W-based catalyst, improves the electron-withdrawing capability of W and O to stabilize the Co and Fe in OER-favorable high valence state, and enriches the surface hydroxyls, which act as reactive sites. The Co&Fe-WO shows ultralow overpotential (226 mV, J = 10 mA cm-2), low Tafel slope (33.7 mV dec-1), and good conductivity. This catalyst is finally applied to a photovoltaic-water splitting system to stably produce hydrogen for 50 h at a high solar-to-hydrogen efficiency of 16.9%. This work highlights the impressive effect of electronic structure modulation on W-based catalyst, and may inspire the modification of potential but unstable catalyst for solar energy conversion.