Insights into the spontaneous formation of hybrid PdOx/PEDOT films: electroless deposition and oxygen reduction activity

Abstract

Hybrid palladium oxide/poly(3,4-ethylenedioxythiophene) (PdO_x/PEDOT) films were prepared through a spontaneous reaction between aqueous PdCl₄²⁻ 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% Pd⁰, 64 ± 3 at% Pd²⁺, and 18 ± 4 at% Pd⁴⁺ by X-ray photoelectron spectroscopy) and the formation of stable, electrochemically reversible Pd⁰/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.