Highly Active and Durable Cu _xAu_{(1- x)} Ultrathin-Film Catalysts for Nitrate Electroreduction Synthesized by Surface-Limited Redox Replacement

Cu_xAu_(1-x) bimetallic ultrathin-film catalysts for nitrate electroreduction have been synthesized using electrochemical atomic layer deposition by surface-limited redox replacement of Pb underpotentially deposited layer. Controlled by the ratio of [Cu²⁺] ions and [AuCl₄ ^-] complex in the deposition solution, the alloy film composition (atomic fraction, x in the range of 0.5-1) has been determined by X-ray photoelectron spectroscopy and indirectly estimated by anodic stripping voltammetry. The catalytic activity and durability of Cu_xAu_(1-x) thin films, Cu thin film, and bulk Cu have been studied by one- and multiple-cycle voltammetry. The synthesized Cu_xAu_(1-x) thin films feature up to two times higher nitrate electroreduction activity in acidic solution compared to bulk and thin-film Cu counterparts. Highest activity has been measured with a Cu_0.70Au_0.30 catalyst. Durability tests have demonstrated that Cu thin films undergo rapid deactivation losing 65% of its peak activity for 92 cycles, whereas Cu_0.70Au_0.30 catalysts lose only 45% of their top performance. The significantly better durability of alloy films can be attributed to effective resistance to poisoning and/or hindered dissolution of Cu active centers. It has been also found that both Cu_xAu_(1-x) and pure Cu thin films show best electroreduction activity at lowest pH.