Facilitated Electro-Oxidation of Formic Acid at Nickel Oxide Nanoparticles Modified Electrodes

This study addresses the electrocatalytic oxidation of formic acid (FA) at nickel oxide nanoparticles (nano-NiOx) modified Pt, Au, GC anodes. FA oxidation proceeds at the unmodified Pt electrode with the appearance of two oxidation peaks at 0.25 and 0.65 V corresponding to the direct oxidation of FA to CO2 and the oxidation of the poisoning intermediate, CO, to CO2 with a current ratio of the two peaks less than 0.2. Interestingly, this ratio jumps up to more than 50, upon modifying Pt with nano-NiOx. This highlights the essential role of NiOx in enhancing the direct oxidation of FA (at 0.25 V) at Pt substrate. On the other hand, unmodified GC and Au anodes as well as those modified with nano-NiOx exhibit no catalytic response toward FA oxidation. This highlights the essential role of the underlying substrate and depicts also that nano-NiOx behaves as a catalytic mediator which facilitates the charge transfer during the oxidation of FA at Pt anode. Optimization of the surface coverage of nano-NiOx at Pt is achieved, aiming at maximizing the rate of the direct oxidation pathway of FA while suppressing the indirect oxidation route producing the poisoning CO. Moreover, nano-NiOx/Pt anode maintains its high catalytic activity for a prolonged time of continuous oxidation of FA.