More than 10% efficiency and one-week stability of Si photocathodes for water splitting by manipulating the loading of the Pt catalyst and TiO2 protective layer

Abstract

Si has been studied as a photocathode for water splitting; however, its commercial application is hindered by its poor stability and low solar-to-hydrogen conversion efficiency (η), where the effective loading of catalysts on the Si surface is one of the key factors. Herein, we report that uniform and small Pt nanoparticles (NPs) were successfully prepared on an n⁺p-Si pyramid surface by a cheap electroless deposition method using Pt salt, based on the hydrophilic character of SiO₂. A high η of 10.5% was obtained under 100 mW cm⁻² simulated solar illumination with a Pt loading of only 1 μg cm⁻², due to the fact that the Pt NPs are small enough to avoid the optical loss of Si, are distributed uniformly on the light-trapping pyramid Si surface to ensure a large number of reaction sites for H₂ production, and establish intimate contact with Si to facilitate carrier transfer. Finally, an ∼15 nm amorphous TiO₂ layer covered on the Pt/n⁺p-Si using atomic layer deposition results in a superior stability over more than one week of continuous photoelectrochemical testing, while increasing its η to a high value of 10.8% due to the improvement of charge transfer from Pt to the electrolyte. Our findings emphasize the importance of the effective loading of the catalyst and protective layer on the Si photocathode, which subsequently makes the photoelectrochemical process both efficient and stable.