High throughput optimisation of PdCu alloy electrocatalysts for the reduction of nitrate ions

A high-throughput methodology was used to synthesise compositional gradient thin films of PdCu alloys. The expected equilibrium phases of the PdCu alloys as a function of composition were identified using XRD. The electrochemical behaviour of the alloys in NaOH base electrolyte was measured simultaneously on a micro-fabricated array of 100 electrodes. Small concentration of Pd addition to the Cu resulted in a reversible Cu derived surface redox, and higher concentrations decreased its equilibrium potential (a destabilisation of the surface oxide). The former is due to the mediation of the redox reaction by Pd and the latter due to electronic interaction between Pd and Cu. The most active reduction catalyst (rate at constant overpotential or minimum overpotential for a fixed rate) is in a narrow compositional region around 84%(at) Cu. The trend in reactivity can be understood by the promotion of nitrate reduction through hydrogen spillover from Pd at low concentrations in the alloy. The reduction in activity as the palladium concentration increases further is concomitant with the destabilisation of oxygen on copper, and therefore likely to be due to the inability to stabilise the nitrate ion at the surface, or extract the first oxygen atom to produce nitrite. (C) 2013 Elsevier Inc. All rights reserved.