Surveying Metal Antimonate Photoanodes for Solar Fuel Generation

Ternary antimonate (X-Sb-O) materials are surveyed as photoanodes aimed at solar-driven evolution of dioxygen from water to enable solar generation of fuels and chemicals. Exploring this class of materials is motivated by their recent proliferation as operationally stable electrochemical materials as well as the prior demonstration of X-Sb-O photocatalysts. The survey was conducted via combinatorial materials science methods with a high throughput workflow including parallel synthesis via cosputter deposition and annealing, combinatorial characterization via X-ray diffraction and fluorescence, and automated photoelectrochemistry using a scanning droplet cell. The resulting 5608 measurements of external quantum efficiency span X-Sb-O composition systems with 14 different elements (X = Mg, Al, Cr, Fe, Co, Ni, Cu, Zn, Y, Ag, In, La, Pb, Bi) as well as a variation in annealing temperature, electrolyte pH, and illumination sources ranging from 2.1 to 3.2 eV. Automated analysis of the resulting wealth of data enabled the discovery of 19 photoanode phases, including 9 with broad spectral response. The discoveries include transition metal antimonates, metal oxides comprising only main group elements, and amorphous photoanodes. The general Pourbaix stability of the ternary antimonates creates opportunities for continued development of operationally stable photoanodes, and the lack of open d-orbital character at the band edges of the main group oxides makes them particularly compelling for future study.