Tungsten oxide-coated copper gallium selenide sustains long-term solar hydrogen evolution

This work demonstrates that ultrathin (4 nm) tungsten oxide (WO 3 ) coatings on copper gallium selenide (CuGa 3 Se 5 ) photocathodes have the potential for long-term solar hydrogen evolution. With a combination of a robust 1.84 eV CuGa 3 Se 5 absorber layer, a WO 3 protective coating, and a Pt catalyst, we obtain a new durability milestone for any non-silicon photoelectrochemical hydrogen-producing device by passing 21 490 C cm −2 of charge across six weeks of continuously-illuminated chronoamperometric testing under applied bias. Employs ultrathin WO 3 coatings on CuGa 3 Se 5 photocathodes to achieve a new durability milestone for solar hydrogen evolution on a non-silicon absorber.