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

By controlling reaction temperature and feeding rate of reducing agent, it is shown that Pd nanoparticles with different sizes can be synthesized from reduction of their precursor on polyaniline (PANI) as solid carrier. Using UV-Vis spectroscopy, 1H-NMR, and ATR-IR as characterization tools, electronic and catalytic interactions between Pd NPs and PANI can be clearly identified. It is shown that for the first time that the unique redox properties of Pd/PANI display a high over-potential for hydrogen evolution, suppressing this competitive reaction from electro-reduction of CO2 in acidic solution. As a result, two main liquid products (HCOOH and CH3OH) can be selectively produced with only trace amount of CO in gas phase. The current efficiencies for HCOOH and CH3OH are found to increase with decreasing Pd NPs sizes within the potential range of -0.5 to -0.9 V. The highest current efficiency for HCOOH (22.8 %) and for CH3OH (5.4%) are thus obtained over Pd(1.31 nm)/PANI at -0.9 V.