Insights into the spontaneous formation of hybrid PdO(x)/PEDOT films: electroless deposition and oxygen reduction activity

Hybrid palladium oxide/poly(3,4-ethylenedioxythiophene) (PdO(x)/PEDOT) films were prepared through a spontaneous reaction between aqueous PdCl(4)(2−) ions and a nanostructured film of electropolymerized PEDOT. Spectroscopic and electrochemical characterization indicate the presence of mixed-valence Pd species as-deposited (19 ± 7 at% Pd(0), 64 ± 3 at% Pd(2+), and 18 ± 4 at% Pd(4+) by X-ray photoelectron spectroscopy) and the formation of stable, electrochemically reversible Pd(0)/α-PdO(x) active species in alkaline electrolyte and furthermore in the presence of oxygen. The elucidation of the Pd speciation as-deposited and in solution provides insight into the mechanism of electroless deposition in neutral aqueous conditions and the electrocatalytically active species during oxygen reduction in alkaline electrolyte. The PdO(x)/PEDOT film catalyses 4e(−) oxygen reduction (n = 3.97) in alkaline electrolyte at low overpotential (0.98 V vs. RHE, onset potential), with mass- and surface area-based specific activities competitive with, or superior to, commercial 20% Pt/C and state-of-the-art Pd- and PEDOT-based nanostructured catalysts. The high activity of the nanostructured hybrid PdO(x)/PEDOT film is attributed to effective dispersion of accessible, stable Pd active sites in the PEDOT matrix.