Modulating the Electronic Structure and Basal-Plane Adsorption of Janus CrSSe through Mechanochemical Activation

Mechanochemical activation offers a reversible and chemically noninvasive route to tune the basal-plane reactivity of two-dimensional catalysts. Here, spin-polarized density functional theory calculations are employed to investigate strain- and curvature-engineered Janus CrSSe for the hydrogen evolution reaction, comparing H* adsorption on the CrSSe-S and CrSSe-Se surfaces and extending the analysis to zigzag CrSSe-NT-(n,0) nanotubes. HER-relevant H adsorption thermodynamics are evaluated within the computational hydrogen electrode framework using the adsorption free energy, ΔG _ads, and the H* binding energy, E _b. Pristine 2D CrSSe exhibits strongly non-thermo-neutral H* adsorption with a pronounced polarity dependence. In-plane strain markedly reconstructs the electronic structure, with biaxial tension inducing metallicity and spin polarization and driving ΔG _ads close to thermo-neutral values. Curvature introduces an additional polarity-dependent degree of freedom: S-terminated nanotubes exhibit spin-polarized metallic behavior, whereas Se-terminated nanotubes remain semiconducting and converge to zero-net-spin states. A pronounced structural-magnetic crossover between CrSSe-NT-S-(20,0) and (21,0) is accompanied by an abrupt change in H* binding, revealing a direct coupling between curvature, magnetism, and chemisorption. Moderate axial tensile strain of 3-5% further tunes this curvature-dependent adsorption response and brings ΔG _ads closer to the thermo-neutral regime over a broad range of nanotube diameters. Overall, these results establish strain, curvature, and Janus polarity as coupled physical descriptors for controlling the electronic, magnetic, and hydrogen adsorption properties of CrSSe nanostructures.