A carbon-based hybrid catalytic-protective overlayer for kesterite photocathodes for solar water splitting

Abstract

Developing stable and efficient photocathodes with low-cost components is crucial for advancing the commercialization of photoelectrochemical (PEC) water splitting devices, specifically for the hydrogen evolution reaction (HER). In this work, we present a cost-effective solution-processed hybrid layer composed of fullerene (C₆₀) grafted onto nitrogen and sulfur-doped graphene (NSG), which serves as a catalytic-protective overlayer for the earth-abundant kesterite Cu₂ZnSn(S,Se)₄ (CZTSSe) photocathode in an acidic environment. The resulting CZTSSe/CdS/C₆₀-NSG/Pt photocathode exhibits a current density of −27.7 mA cm⁻² at 0 V vs. the reversible hydrogen electrode (RHE), a half-cell solar-to-hydrogen efficiency exceeding 3%, and an onset potential of 0.51 V, while retaining 80% of its initial current density after 10 h of operation. Spectroscopic analyses and density functional theory studies indicate that the C₆₀-NSG hybrid layer improves carrier lifetime, facilitates efficient charge transfer, and provides catalytic sites with Gibbs free energy close to thermoneutral for adsorbed H species, leading to higher HER activity and operational stability. Our findings highlight the potential of employing a cost-effective solution-processed ‘carbon-based’ hybrid catalytic-protective layer on photocathodes for solar water splitting.