Interfacing CuO, CuBi ₂ O ₄ , 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 <i>in situ</i> transient absorption spectroscopy.