Electrocatalysis by design: Enhanced electrooxidation of formic acid at platinum nanoparticles–nickel oxide nanoparticles binary catalysts

Abstract

This study addresses the electrocatalytic oxidation of formic acid (FA) at binary catalysts composed of Pt nanoparticles (nano-Pt) and nickel oxide nanoparticles (nano-NiOx) electrodeposited onto glassy carbon (GC) electrodes. Pt electrode shows two oxidation peaks at ca. 0.25 and 0.65V vs. Ag/AgCl/KCl (sat.) corresponding to the direct (Ipd, favorable) and indirect (Ipind, unfavorable) oxidation pathways of FA, respectively. Nano-Pt/GC electrode shows a significantly higher catalytic activity toward FA oxidation than the bulk Pt electrode. Interestingly, further modification of the nano-Pt/GC electrode with nano-NiOx leads to a superb enhancement of Ipd with a concurrent suppression of Ipind. The catalytic activity of the various modified GC electrodes is probed by the ratio of Ipd/Ipind. This ratio increases from 0.2 at bulk Pt to 1.4 at nano-Pt/GC (i.e., ca. 7 times higher), and jumps up to more than 20 at the binary nano-NiOx/nano-Pt modified GC electrode, reflecting the superiority of the latter electrode toward FA oxidation to CO2. While nano-Pt furnishes a suitable base for FA adsorption, nano-NiOx acts as a catalytic mediator which facilitates the charge transfer during the direct oxidation of FA. The influence of the deposition sequence and the loading level of both species (i.e., Pt and NiOx) on the catalytic activity of the binary catalyst are investigated.