Electrocatalysis of formic acid oxidation on Pt–Ru alloys modified with Pb adatoms

Abstract

Abstract Catalytic effect of lead adatoms, deposited at under-potentials, in the oxidation of formic acid on platinum ruthenium alloys was discovered. With increasing the degree of coverage with the lead adatoms, the catalytic activity of Pt–Ru electrodes increases, reaches its maximum and subsequently decreases. No firmly adsorbed intermediates at the Pt–Ru surface were observed at the optimal coverage degree. Then, its catalytic activity is about 200 mV higher than that on pure Pt in the current density range of 10−4 mA cm−2 to 10−1 mA cm−2. Two effects are responsible for the catalysis of formic acid oxidation. The lead adatoms decrease the number of assemblies of few adjacent free atoms of Pt, on which firmly bound intermediates should form. Positive residual charge of lead adatoms improves their interaction with oxy species, placed on the adjacent atoms of ruthenium. The established interaction stabilizes the energetic state of these oxy species causing the increase in their concentration. A larger concentration of the oxy species accelerates oxidation of firmly bound intermediates and thus releases the Pt atoms for the oxidation of subsequent molecules of formic acid.