关键词: Cu/Pd界面, 亚硝酸盐还原, 钯膜反应器, 质子耦合电子转移, 反应位点选择

Abstract: Nitrite-to-ammonia conversion is a multistep reduction that requires hydrogen delivery together with a suitable interfacial electrochemical environment. Palladium membrane reactors (PMRs) spatially separate hydrogen supply from the substrate, but whether a hydrogen-rich membrane interface alone can sustain this deep reduction remains unclear. Here, we systematically compared the hydrogenation and electrolysis sides of a Cu/Pd PMR. On the hydrogenation side, NH₃ was barely formed; representative Cu/Pd samples gave only 1.90-2.16 μg h^-1 cm^-2 after 9 h, with apparent Faradaic efficiencies below 2%. The weak response persisted under sustained electrochemical hydrogen charging and in direct-H₂ open-circuit controls, although differences in interfacial hydrogen availability may still contribute. On the electrolysis side, Cu modification gave markedly higher activity with clear dependences on potential, Cu loading, and pH. Under optimized electrolysis-side conditions, 0.5 mg cm^-2 Cu in alkaline electrolyte at -1.2 V vs. RHE gave an NH₃ yield rate of 1140.38 μg h^-1 cm^-2. In the three-compartment PMR open-circuit controls, the NH₃ yield rate was only 0.24-1.61 μg h^-1 cm^-2, more than two orders of magnitude lower. We therefore propose a “spatial-mechanistic compatibility” model: the reaction site in a PMR is not governed solely by hydrogen flux, but by how well the interfacial functionality matches the mechanistic demands of the target reaction.

Key words: Cu/Pd interface, Nitrite reduction, Palladium membrane reactor, Proton-coupled electron transfer, Reaction-site selection