UC Berkeley

Cu/ZnO/Al 2 O 3 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 2 , CO 2 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 2 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 2 and H 2 -free N 2 or CO 2 argues against persistent Cu–Zn alloying or oxygen-vacancy formation and supports reversible hydrogen doping of ZnO. CO 2 slows H insertion into ZnO relative to N 2 , while water strongly suppresses it. Junction electrical measurements thus inform how such catalytic interfaces evolve under reactive conditions.