WOx-Carbon nanorods catalyzed photoelectrochemical hydrogen evolution reaction of silicon-photocathode in acidic media

Abstract

Silicon (Si) photocathode with surface decoration of co-catalysts is a promising material for green hydrogen production. The surface of the Si is often further etched into pyramids for optical absorption. However, the photon-generated charges tend to concentrate on the pyramid peaks, whilst the catalyst of nanoparticles generally aggregate in the valley, where less charges are available. In this work, one-dimensional tungsten oxide (WOx) with an ultra-thin layer of carbon species have been used as the cocatalyst, which preferentially stay on the upperpart of the pyramids with intimate contact. WOx has great potential in catalysis for hydrogen evolution reaction (HER) due to its ideal proton adsorption/desorption behavior. However, WOx, especially in form of nanorods, has rarely been reported as cocatalysts for photo(electro)catalysis, due to the challenges in the preparation and stabilities during long-term HER catalysis. Herein, the formation of WOx-C nanorods was induced, leading to improved conductivity and stability as co-catalysts. The density functional theory (DFT) calculations revealed the low reaction free energy of WOx-C co-catalysts and the smooth electrons transfer from W to protons. The Si photocathodes deposited with the optimized WOx-C hybrids nanorods showed high performance in PEC reaction, achieving a current density of −21.3 mA·cm−2 at 0 VRHE and an onset potential of +0.218 VRHE under acidic conditions. The catalytic mechanism of WOx-C nanorods for the pyramidal Si-photocathode is investigated and proposed.