Oxygen reduction at sparse arrays of platinum nanoparticles in aqueous acid: hydrogen peroxide as a liberated two electron intermediate

Abstract

Electrodeposition methods are used to generate a sparse array of platinum nanoparticles on a glassy carbon electrode. Specifically electrodeposition from a 1 mM solution of H₂PtCl₆ in 0.5 M H₂SO₄ leads to surface coverages of 0.46% to 1.96% and nanoparticles of size 29 nm to 136 nm in diameter, using deposition times of 30 and 15 seconds. The reduction of oxygen at an array of 29 nm nanoparticles with a surface coverage of 0.46% showed voltammetric signals with a scan rate dependence consistent with a two electron reduction of O₂ to H₂O₂ with the rate proportional to and formal potential (E⁰_f) of −0.058 V vs. SHE, a standard electrochemical rate constant (k₀) of ∼10 cm s⁻¹ and a transfer coefficient (α) of 0.23. At higher Pt nanoparticle coverages, a scan rate dependence consistent with the partial further reduction of H₂O₂ to water becomes evident.