The effect of vanadium substitution in polyoxometalates on the electrocatalytic oxidation of formic acid

Abstract

Direct formic acid fuel cells (DFAFCs) can directly convert chemical energy into electrical energy with high energy efficiency and low carbon and nitrogen oxide emissions. They could be promising clean energy devices for the replacement of generators based on combustion. It is essential to develop effective electrocatalysts for the development of DFAFCs. Polyoxometalates (POMs) and transition metal substituted polyoxometalates (TMSPs) have been used as additives for anodic Pd catalysts owing to their excellent redox properties, which target enhancing resistance against CO poisoning of Pd catalysts. In this paper, vanadium-substituted polyacids (VSPs) are successfully synthesized via ether acidification. A VSPs/rGO support is prepared through electrochemical self-assembly, and then, palladium is deposited on the substrate using electrodeposition. The results show that the prepared VSPs could still maintain the Keggin structure after vanadium substitution in polyacids. The prepared Pd/VSPs/rGO composites are characterized by employing TEM and XPS tests, which prove that GO is successfully reduced to rGO and the Pd nanoparticles are uniformly supported on the substrate. The electrocatalytic activity of the prepared Pd/VSPs/rGO complex for formic acid oxidation is tested through CV. It is found that the current density of the prepared Pd/PW₁₀V₂/rGO complex for formic acid oxidation is 4.83 mA cm⁻², which is 2.06 times that of Pd/C (2.35 mA cm⁻²), 1.07 times that of Pd/PW₁₂/rGO (4.53 mA cm⁻²), 1.31 times that of Pd/PW₁₁V/rGO (3.68 mA cm⁻²) and 1.70 times that of Pd/PW₉V₃/rGO (2.84 mA cm⁻²). I–T test and CO stripping voltammetry show that the Pd/PW₁₀V₂/rGO composite catalytic material exhibits better stability and toxicity resistance than commercial Pd/C and Pd/PW₁₂/rGO. EIS shows that Pd/PW₁₀V₂/rGO displays optimal electronic conductivity. Subsequent research may focus on exploration of the catalytic active sites and reaction mechanisms of Pd/VSPs/rGO composite catalysts.