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. An excellent‐performance, alkaline‐solution‐available, and highly porous urchin‐like Co and Fe codoped WO2.72 OER electrocatalyst is synthesized. The electronic structure and surface circumstance of alkaline‐solution‐labile WO2.72 are subtly modified by homogenously ion codoping. The optimized catalyst is used as oxygen evolution electrode in a photovoltaic water splitting system to achieve very durable and high‐efficiency solar‐to‐hydrogen conversion.