Photo-assisted decoration of Ag-Pt nanoparticles on Si photocathodes for reducing overpotential toward enhanced photoelectrochemical water splitting

Abstract

Developing new catalysts to decorate photoelectrodes has been widely used to enhance the performance of photoelectrochemical (PEC) cells. However, the high cost, complex synthesis, and poor stability of catalyst decoration strongly hinder its practical application. Here, we report a facile and low-cost decoration of Ag-Pt nanoparticles (Ag-Pt NPs) on Si photocathodes with TiO2/Ti sacrificial overlayers. Such a decoration does not rely on any metallic-ion precursor solution since it is formed automatically via galvanic replacement reactions during PEC measurements; that is, Ti is displaced by Ag+ and Pt2+ ions, which are from the employed reference and counter electrodes, respectively. The as-decorated Ag-Pt NPs are verified to significantly enhance the hydrogen evolution reduction kinetics without substantially degrading the optical performance of Si photocathodes. Owing to optoelectronic advantages, the overpotential required to maintain a photocurrent density of 10 mA cm−2 (under AM 1.5G illumination) is reduced from −0.8 VRHE (for the bare planar Si photocathode) to −0.1 VRHE (for the planar Si photocathode with Ag-Pt NP decoration). Moreover, a further anodic shift (to 0 VRHE) is visible for the Si nanowire array photocathode with Ag-Pt NP decoration, along with high long-term stability of the PEC response in acidic and neutral electrolytes. This study opens a new opportunity for the photo-assisted decoration of various alloy NPs on the morphology-varying photoelectrodes with different applications.