Smart selection of fuel blends: Robust oxidation of formic acid in its blend with urea at NiOx/Pd nanoparticles-based binary anodes

Abstract

Enhanced oxidation of formic acid (FAO) is observed at NiOx/Pd/GC anodes in the presence of urea as a blending fuel. FAO is noticeably enhanced (in the presence of urea as a blending fuel) as demonstrated by CV measurements where a five-fold increase of the direct FAO peak (Ipd), and a favorable negative shift of its onset potential (Eonset) are observed. Additionally, a six-fold increase of the fuel utilization (FU), expressed in the amount of charge consumed during FAO is markedly enhanced in FA-urea fuel blend (0.3 M FA and 0.2 M urea) compared to that obtained in the absence of urea (i.e., 0.3 M FA only) at the NiOx/Pd/GC electrode. Additionally, capacitance measurements of the electrode/electrolyte interface increases in line with FAO activity. Urea molecules are thought to form a bridged H-bonding with formate anions thus facilitating a favorable adsorption geometry allowing for a facile C–H scissoring, thus promoting the oxidative dehydrogenation pathway of FA to CO2. A plausible explanation assumes the formation of 6- and/or 8-membered rings between formate anion and urea (via hydrogen bonding). These findings emphasize the importance of the proper design of the catalyst together with the smart selection of the blending fuel with FA.