Theoretical insights on hydrogen activation and diffusion behaviour on ZnO (101 ̅0) surface

Abstract

ZnO is an important component in many catalysts for hydrogenation of carbon monoxide and dioxide, upcycling of plastics and hydrodeoxgenation of biomass, which exhibits a strong capacity for H2 activation. This work examines eleven distinct H2 activation pathways on pristine and defective ZnO (101 @#x0305;0) surfaces, demonstrating that the OV-Zn3 ensemble is not a spectator site. Instead, OV-Zn3 acts as an electron reservoir with strong electron-donating ability albeit with limited electron-storage capacity. This region interacts with surface H adsorbates and, while modulating the behavior of the adsorbed H species, undergoes lattice distortion and electronic rearrangement as the adsorption site varies. Furthermore, the tendency of the H atoms to adsorb on the Zn-O pairs drives the growth of an one-dimensional H-chain along the [0001] direction, leading to distinct diffusion behavior along the [0001] and [12 @#x0305;10] directions. The existence of multiple H2 activation routes and H diffusion pathways provides a rational explanation for the experimentally observed variations in the OV concentration as well as the hydrogen coverage at the OV sites. By correlating these atomic-scale insights with available experimental observations, we propose how defect engineering and thermal control could be synergistically employed to tune H₂ activation on ZnO surfaces, thus providing a fresh perspective for rational catalyst design of ZnO-based hydrogenation catalysts.