Interfacing CuO, CuBi2O4, and protective metal oxide layers to boost solar-driven photoelectrochemical hydrogen evolution

This article reports the development of CuO|CuBi2O4 photocathodes stabilized by protective layers of TiO2, MgO, or NiO, with Pt or MoS2 nanoparticles serving as co-catalysts to facilitate H2 evolution. Most notably, this work demonstrates the first application of MgO as a protection/passivation layer for photocathodes in a water-splitting cell. All configurations of photocathodes were studied structurally, morphologically, and photoelectrochemically revealing that CuO|CuBi2O4|MgO|Pt photocathodes achieve the highest stable photocurrent densities of −200 μA cm−2 for over 3 hours with a Faradaic efficiency of ∼90%. Bias-free tandem water splitting was then performed by pairing this photocathode with a dye-sensitized TiO2 photoanode, producing H2 from neutral water without an external bias. This paper demonstrates key stability findings and proposes the use of spin-coated MgO, TiO2, and NiO as feasible earth-abundant protective materials to aid in the formation of a cheap and scalable tandem water splitting system. Charge transfer dynamics have also been probed by combining spectroelectrochemistry and in situ transient absorption spectroscopy.