Solar fuels photoanodes prepared by inkjet printing of copper vanadates

Abstract

Widespread deployment of solar fuel generators requires the development of efficient and scalable functional materials, esp. for photoelectrocatalysis of the oxygen evolution reaction. Metal oxides comprise the most promising class of photoanode materials, but no known material meets the demanding photoelectrochem. requirements. Copper vanadates have recently been identified as a promising class of photoanode materials with several phases exhibiting an indirect band gap near 2 eV and stable photoelectrocatalysis of the oxygen evolution reaction in a pH 9.2 electrolyte. By employing combinatorial inkjet printing of metal precursors and applying both caldnation and rapid thermal processing, we characterize the phase behavior of the entire CuO-V2O5 compn. space for different thermal treatments via automated anal. of approx. 100 000 Raman spectra acquired using a novel Raman Imaging technique. These results enable the establishment of structure-property relationships for optical absorption and photoelectrochem. properties, revealing that highly active photoelectrocatalysts contg. alpha-Cu2V2O7 or alpha-CuV2O6 can be prepd. using scalable soln. processing techniques. An addnl. discovery results from the formation of an off-stoichiometric beta-Cu2V2O7 material that exhibits high photoelectroaclivity in the presence of a ferri/ferrocyanide redox couple with excellent stability in a pH 13 electrolyte, demonstrating that copper vanadates may be viable photoanodes in strong alk. electrolytes.