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

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.