Highly Efficient NiFe Nanoparticle Decorated Si Photoanode for Photoelectrochemical Water Oxidation

n-Si is a narrow band gap semiconductor that has been demonstrated as an excellent photoabsorber material for photoelectrochemical (PEC) water splitting. Depositing a thin layer of Ni film on n-Si can form a Schottky junction at the interface, which offers a simple and useful route toward light-driven water oxidation. However, the relatively low catalytic activity of the Ni layer and the presence of interface states limit the application of this structure. Herein, we prepared a high-performance NiFe nanoparticle decorated Si photoanode for efficient solar-driven water oxidation to O2. NiFe nanoparticles were dispersed on a Si substrate surface homogeneously to form an inhomogeneous metal–insulator–semiconductor (MIS) junction, which increased the photovoltage of the photoanode. In addition, the oxide/oxyhydroxide layer on the deposited NiFe layer formed during the evaporation deposition acted as a highly efficient electrocatalyst, which also contributed to the high PEC performance of the photoanode. The photoanode covered with a 2 nm NiFe film exhibited the best PEC performance with a low onset potential of 1.09 V versus reversible hydrogen electrode (RHE) (the potential required to reach the photocurrent of 1 mA/cm2), a high photocurrent of 25.2 mA/cm2 at 1.23 V versus RHE, and a stable output over 50 h under AM 1.5G illumination due to the high-performance inhomogeneous MIS junction and a thick oxide/oxyhydroxide catalytic shell formed on the NiFe nanoparticle via an aging process.