Synthesis of Au-Nanoparticles on Carbon using Lysine as a Capping Agency in a Gas Diffusion Electrodes Cell for Electrocatalytic CO₂ Reduction

We have prepared a membrane electrode assembly (MEA) consisting of Au nano particles (AuNPs) dispersed on Ketjen black (a carbon conductor: C) and Nafion (a proton conductor) as a cathode catalyst and IrO₂ as an anode catalyst for electrocatalytic CO₂ reduction in a gas diffusion electrodes cell. With using lysine as a capping agency, we have succeeded to make MEA first time. MEA with the area of 1 cm² showed good performance in electrocatalytic CO₂ reduction giving the CO production rate of 78.5 μmol/h with a Faraday efficiency of 81.3% and a current density of 5.2 mA/cm² at maximum under the cell voltage of −2.2 V. The particle sizes of synthesized Au-NPs were divided into two groups of around 30 nm and a few nm. The formation of the latter was assisted by the capping effect of lysine and enhanced the electrocatalytic activity. However, at the present condition for AuNPs synthesis, appearance of 50 nm sized particles was unavoidable. Suppression of their formation would significantly enhance the catalytic activity and the present type of membrane assembly has great potential for a practical use.