Solar Fuel Generation on Semiconductors: Photo-Assisted H2 Evolution on A Novel Delafossite AgRhO2 and A p-Gap (111) Surface With {110} Faces Revealed by Etching For CO2 Reduction

Abstract

Solar fuel generation is a fascinating approach to alleviating our imminent crises of energy shortage and environmental issues caused by excessive fossil fuel combustion, and has attracted an enormous amount of research interest. The primary studies in this field focus on H2 evolution from water and CO2 reduction to carbonaceous fuels. To date, there are still several obstacles that need to be addressed to realize a genuine solar-driven artificial photosynthesis system.

Inspired by the work on CuRhO2, AgRhO2 has been synthesized and tested for photo-assisted H2 evolution. AgRhO2 has exhibited a superior photocatalytic capability of reducing protons or water to H2 across a swath of pH levels with nearly 100% faradaic efficiencies. In addition, this compound possesses advantageous properties, such as suitable absorption of visible light, a large photocurrent density, and a decent photo-stability in terms of minimal reduction of Ag(I) to Ag(0). Compared to CuRhO2, the improved photo-stability of AgRhO2 has been ascribed to the significantly smaller involvement of Ag in the band-to-band transition, since the transition takes place predominantly between Rh d bands. Therefore, in comparison to Cu(I) in CuRhO2, Ag(I) is considerably less subject to photo-reduction.

As an extension of work on the pyridinium-catalyzed CO2 reduction on p-GaP (111) surface, a new etchant made of sulfuric acid, hydrogen peroxide and water (3H) has been employed to create novel features on a p-GaP (111) surface prior to photoelectrochemistry, which effectively reveals the electrochemically interesting {110} faces. The 3H etchant sculpts trifold-shaped grooves along the directions of a set of {110} planes perpendicular to the (111) substrate. The key player of the intriguing chemistry is the P-deficient sites on the matte p-GaP (111) surface. In comparison to a pristine p-GaP (111) surface, the freshly etched surface demonstrates much enhanced photocurrent density and faster kinetics for interfacial charge transfer in terms of CO2 reduction. The improved photocatalytic capability on the 3H-etched p-GaP (111) surface suggests that the electron transfer is facilitated by the hydride-like species formed on the P terminations of the p-GaP {110} planes.