Enhanced Performance of Si MIS Photocathodes Containing Oxide-Coated Nanoparticle Electrocatalysts

Electrodepositing low loadings of metallic nanoparticle catalysts onto the surface of semiconducting photoelectrodes is a highly attractive approach for decreasing catalyst costs and minimizing optical losses. However, securely anchoring nanoparticles to the photoelectrode surface can be challengingespecially if the surface is covered by a thin insulating overlayer. Herein, we report on Si-based photocathodes for the hydrogen evolution reaction that overcome this problem through the use of a 2–10 nm thick layer of silicon oxide (SiO_<i>x</i>) that is deposited on top of Pt nanoparticle catalysts that were first electrodeposited on a 1.5 nm SiO₂|p-Si­(100) absorber layer. Such insulator–metal–insulator–semiconductor (IMIS) photoelectrodes exhibit superior durability and charge transfer properties compared to metal–insulator–semiconductor (MIS) control samples that lacked the secondary SiO_<i>x</i> overlayer. Systematic investigation of the influence of particle loading, SiO_<i>x</i> layer thickness, and illumination intensity suggests that the SiO_<i>x</i> layer possesses moderate conductivity, thereby reducing charge transfer resistance associated with high local tunneling current densities between the p-Si and Pt nanoparticles. Importantly, the IMIS architecture is proven to be a highly effective approach for stabilizing electrocatalytic nanoparticles deposited on insulating overlayers without adversely affecting mass transport of reactant and product species associated with the hydrogen evolution reaction