Out-of-plane polarization engineering: Optimizing exciton dissociation and solar-to-hydrogen efficiency in photocatalytic water splitting.

This article focuses on the role of out-of-plane polarization in enhancing photocatalytic water splitting using two-dimensional (2D) chromium-based Janus monolayers. The intrinsic dipole and out-of-plane piezoelectricity in these 1H-phase CrXY (X, Y = S, Se, Te) monolayers optimize band edge alignments to match water redox potentials across a wide pH range (0–14), overcoming traditional bandgap limits and enabling efficient solar-to-hydrogen (STH) conversion. Constructing Janus homojunctions from these monolayers naturally forms type-II band alignments that promote spatial separation of photogenerated carriers, further improving photocatalytic efficiency. Notably, CrSSe and CrSeTe homojunctions achieve STH efficiencies up to 38.1% and 34.3% at pH = 0, while strained CrSeTe homojunctions maintain about 37% efficiency across neutral pH conditions, highlighting out-of-plane polarization as a promising strategy for designing high-performance photocatalysts for sustainable hydrogen production.