Mechanistic Study of Hydrogen Production Based on the Formate Decomposition with Platinum Nanoparticles Dispersed by Polyvinylpyrrolidone

Abstract

Formic acid is a potential hydrogen carrier with low toxicity and easy handling in aqueous solution. The mechanism of hydrogen production based on formate decomposition with platinum nanoparticles dispersed by polyvinylpyrrolidone (Pt-PVP) was investigated by measuring the kinetic isotope effect (KIE) using isotope-labelled formate, the pH dependence of activation energy on hydrogen production, and carbon monoxide production from formate dehydration. Experiments using isotope-labelled formate found KIE of OD-formate (HCOOD) is larger than that of d1-formate (DCOOH) in hydrogen production with Pt-PVP, suggesting that the rate-determining step in formate decomposition is hydrogen production from hydride species adsorbed on platinum nanoparticles and protons in the solution. The Arrhenius plot for hydrogen production based on formate decomposition catalyzed by Pt-PVP in various pH regions showed no significant difference in activation energy for hydrogen production between pH 2.5 and 3.5. In contrast, the activation energy decreased at pH 1.8, suggesting that Pt-PVP-catalyzed hydrogen production based on formate decomposition is strongly dependent on formate concentration. Therefore, the rate-determining step for Pt-PVP-catalyzed formate decomposition was hydrogen production from hydride species adsorbed on platinum nanoparticles and protons at pH 2.5 or 3.5 region but was adsorption of formate ion or cleaving C–H of formate adsorbed on platinum nanoparticles at pH 1.8. Pt-PVP only catalyzes the selective decomposition of formate into hydrogen and carbon dioxide without formate dehydration. Our clarification of the hydrogen production mechanism provides useful guidelines to develop new catalysts with high activity for formate decomposition.