Activating catalytically inert Janus diamane for efficient water splitting via 2D type-II C4HF/ h -BN heterostructures

We propose a two-dimensional (2D) type-II van der Waals heterostructure by vertically stacking Janus diamane C4HF with monolayer h-BN for efficient photocatalytic water splitting. While C4HF is catalytically inert due to fully saturated surfaces, h-BN suffers from an ultra-wide bandgap and low carrier mobility. The heterostructure leverages complementary functionality: h-BN provides chemisorption sites for reaction intermediates, while C4HF induces a pronounced red shift in optical absorption and enhances carrier mobility, achieving light-hole mobility up to 91.74 × 103 cm2 V−1 s−1. Type-II band alignment and an intrinsic out-of-plane built-in electric field drive spatial separation of photogenerated carriers, suppressing recombination. First-principles calculations predict spontaneous hydrogen evolution under illumination and near-spontaneous oxygen evolution, with corrected solar-to-hydrogen efficiency exceeding 20%. Through the quasihorizontal projectile motion model of the photogenerated carrier, we predict that the migration time of photogenerated carriers to the heterostructure surface is on the femtosecond scale, enabling them to participate rapidly in catalytic reactions. The heterostructure exhibits significant out-of-plane piezoelectricity, enabling strain-amplified carrier separation. These results establish C4HF/h-BN as a robust piezo-photocatalytic platform and provide a design paradigm for 2D carbon-based photocatalytic materials.