The electrodeposition of Pt100-xCux alloys is demonstrated using an electrolyte comprised of 1mol/L H2SO4, 0.001 mol/L K2PtCl4 and 0.1 mol/L CuSO4. Film growth proceeds by facile Cu underpotential deposition (upd) occurring in parallel with Pt overpotential deposition with the latter controlling the overall rate of alloy deposition. Pt and Pt100-xCux deposition was monitored in real time using an electrochemical quartz crystal microbalance (ECQM). Pt deposition from 1mol/L H2SO4 + 0.001 mol/L K2PtCl42- is diffusion limited at potentials below -0.150 V SSE and occurs with close to 100% current efficiency. In the added presence of CuSO4, Pt100-xCux alloy deposition occurs and monitoring the steady-state mass/charge ratio enables the composition of the growing film to be evaluated with sub-monolayer precision. For a given potential the film composition so determined was in excellent agreement with the alloy composition determined for 1 m thick films using a combination of ex-situ methods. Alloy formation is supported by the exothermic enthalpy of mixing. The potential dependence of the alloy composition is described by an asymmetric regular solution model with an extrema for alloying enthalpy of -18.9 ± 0.2 kJ/mol.
Citation: Journal of the Electrochemical Society
Pub Type: Journals
electrocatalysis, electrodeposition, Pt-Cu alloys, quartz crystal microbalance, underpotential deposition