Enhancement of catalytic performance by controlling the type of junctions in metal/oxide catalysts for the urea oxidation reaction

Abstract

The urea oxidation reaction (UOR) is a vital process for both hydrogen fuel production and the treatment of environmental contaminants. Metal/oxide catalysts, widely used not only in the UOR but also in various other catalytic processes, are highly regarded for their ability to enhance catalytic performance by increasing surface area and utilizing strong metal–support interactions (SMSIs). Despite their extensive use, the role of electronic properties at the metal/oxide interface, particularly the influence of junction type (ohmic vs. Schottky), has not been thoroughly investigated. This study aims to address this gap by examining the impact of junction type on the catalytic performance of metal/oxide systems in the UOR. Ni/ZnO systems with varying Ga doping concentrations (0–10 at% Ga) on the ZnO were synthesized to modulate the junction type between ohmic and Schottky. Comprehensive analyses revealed a transition from Schottky to ohmic junctions at 2 at% Ga, followed by a return to Schottky behavior at 8 at% Ga. Ga-doped ZnO with ohmic junctions, (i.e., 2 at% and 4 at%) exhibited significantly higher catalytic activity, generating higher current at lower overpotentials compared to systems with Schottky junctions (undoped ZnO and Ga (8–10 at%)-doped ZnO). This enhancement is attributed to the formation of oxidative strong metal–support interaction (O-SMSI). Furthermore, ohmic junction systems demonstrated improved electrochemical durability due to the inherently low interfacial resistance. These findings highlight the critical role of junction type in optimizing the performance of metal/oxide catalysts for the UOR and provide valuable insights for the rational design of more efficient catalytic systems.