A novel particulate photocathode composed of CdTe–ZnTe solid solutions with a composition gradient for solar hydrogen evolution from water

Particulate photoelectrodes are promising for the development of innovative unbiased water-splitting devices by combining a photoanode and a photocathode. This configuration relaxes the requirements for band edge potentials of oxygen- and hydrogen-evolution systems while enhancing the solar-to-hydrogen conversion efficiency. However, particulate photocathodes often exhibit lower performance than thin-film-based photocathodes because of the difficulty of implementing functional structures. In this study, a novel CdTe-based particulate photocathode prepared <i>via</i> the modified particle transfer method, along with a ZnTe contact layer introduced <i>via</i> the close-spaced sublimation method, is presented. A Zn _<i>x</i> Cd_1-<i>x</i> Te (0 ≤ <i>x</i> ≤ 1) solid solution with a composition gradient is produced under appropriate preparation conditions, and the conduction-band minimum gradient introduced by the composition gradient suppresses charge recombination and shifts the onset potential of the cathodic photocurrent to +0.7 V_RHE. The introduction of a Cu layer to the back contact and post-deposition rapid thermal annealing further enhances the photocurrent, which reaches -7 mA cm^-2 at 0 V_RHE and a half-cell solar-to-hydrogen efficiency of 1.1% at 0.28 V_RHE. The photocathode also exhibits an incident photon-to-current conversion efficiency (IPCE) of 36% at 520 nm and greater than 10% IPCE across the wavelength range 440-800 nm, which is the highest IPCE reported thus far for a particulate photocathode. These findings demonstrate the potential of the method of introducing a composition gradient for enhancing photoelectrochemical and photocatalytic hydrogen evolution.