5.7% Efficiency Si Photoanodes for Solar Water Splitting Catalyzed by Vertically Grown and Oxygen‐Vacancy‐Rich NiFe Hydroxides

Abstract The sluggish oxygen evolution reaction (OER) kinetics and adverse charge transfer and stability at the multi‐interfaces from Si to electrolyte severely impede the application of Si photoanodes. Herein, oxygen vacancy (OV)‐rich NiFe‐layered hydroxides (NiFe‐OH) nanosheet arrays are vertically orientated on Ni‐protected Si photoanodes by a facile solvothermal method followed by a hot Fe ion‐exchange treatment. By virtue of the formation of OVs on NiFe‐OH nanosheets and the vertical contact between the NiFe‐OH and Si substrate, the as‐prepared Si photoanode not only enables abundant active sites for OER but also boosts charge and mass transfer when compared to traditional electro‐deposit samples. Moreover, the vertical contact of NiFe‐OH on Ni/Si benefits to release the interfacial stress and thereby promotes the electrode stability. Consequently, the optimal Si photoanode shows an ultrahigh applied bias photon‐to‐current efficiency of 5.7% and a good stability of over 200 h, outdoing almost all of the recently reported Si photoanodes.