Dynamic Metal-Semiconductor Electrical Interfaces in Model Cu|ZnO Hydrogenation Catalyst Structures

<jats:p> Cu/ZnO/Al <jats:sub>2</jats:sub> O <jats:sub>3</jats:sub> catalysts are commonly used for methanol synthesis, yet the chemical state of the Cu|ZnO interface remains debated. We probe Cu|ZnO interfacial chemistry by measuring junction electrical characteristics under N <jats:sub>2</jats:sub> , CO <jats:sub>2</jats:sub> and gas mixtures from 50 to 250 °C and up to 10 bar(a). The pristine interface behaves as a nonideal rectifying Schottky diode, and H <jats:sub>2</jats:sub> exposure drives a reversible transition toward ohmic behavior, with increased apparent n-type donor density in the ZnO and lower Schottky-barrier height. This result implies the electric potential at the putative active-catalyst interface decreases under reactive conditions. Recovery of rectifying behavior under O <jats:sub>2</jats:sub> and H <jats:sub>2</jats:sub> -free N <jats:sub>2</jats:sub> or CO <jats:sub>2</jats:sub> argues against persistent Cu–Zn alloying or oxygen-vacancy formation and supports reversible hydrogen doping of ZnO. CO <jats:sub>2</jats:sub> slows H insertion into ZnO relative to N <jats:sub>2</jats:sub> , while water strongly suppresses it. Junction electrical measurements thus inform how such catalytic interfaces evolve under reactive conditions. </jats:p>