Electroreduction of Carbon Dioxide to Formic Acid and Methanol over a Palladium/Polyaniline Catalyst in Acidic Solution: A Study of the Palladium Size Effect

Abstract

We controlled the reaction temperature and feeding rate of the reducing agent to show that Pd nanoparticles (NPs) with different sizes can be synthesized from the reduction of their precursor on polyaniline (PANI) as a solid support. We used UV/Vis spectroscopy, 1H NMR spectroscopy, and IR spectroscopy to identify the electronic and catalytic interactions between Pd NPs and PANI. For the first time, that the unique redox properties of Pd/PANI display a high overpotential for hydrogen evolution, which suppresses this competitive reaction for the electroreduction of CO2 in an acidic solution. As a result, two main liquid products (HCOOH and CH3OH) can be produced selectively with only trace amounts of CO in the gas phase. The current efficiencies for HCOOH and CH3OH increase with the decreasing Pd NP size within the potential range of −0.5 to −0.9 V. The highest current efficiencies for HCOOH (22.8 %) and CH3OH (5.4 %) are thus obtained over Pd(1.31 nm)/PANI at −0.9 V.