Silicon Decorated with Amorphous Cobalt Molybdenum Sulfide Catalyst as an Efficient Photocathode for Solar Hydrogen Generation

The construction of viable photoelectrochemical (PEC) devices for solar-driven water splitting can be achieved by first identifying an efficient independent photoanode for water oxidation and a photocathode for hydrogen generation. These two photoelectrodes then must be assembled with a proton exchange membrane within a complete coupled system. Here we report the preparation of a Si/a-CoMoS_x hybrid photocathode which shows impressive performance (onset potential of 0.25 V vs RHE and photocurrent j_sc of 17.5 mA cm^-2 at 0 V vs RHE) in pH 4.25 phosphate solution and under simulated AM 1.5 solar illumination. This performance is among the best reported for Si photocathodes decorated with noble-metal-free catalysts. The electrode preparation is scalable because it relies on a photoassisted electrodeposition process employing an available p-type Si electrode and [Co(MoS₄)₂]^2- precursor. Investigation of the mechanism of the Si/a-CoMoS_x electrode revealed that under conditions of H₂ photogeneration this bimetallic sulfide catalyst is highly efficient in extracting electrons from illuminated Si and subsequently in reducing protons into H₂. The Si/a-CoMoS_x photocathode is functional over a wide range of pH values, thus making it a promising candidate for the construction of a complete solar-driven water splitting PEC device.