(560bf) Synthesis and Characterization of Bimetallic Core@Shell Structured Nanoparticles for Electrochemical Reduction of CO2 into Formic Acid

Wei Jyun Wang^a, Su Ha^a, Louis Scudiero^b

^a The Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, WA 99164

^b Chemistry Department and Material Science and Engineering Program, Washington State University, WA 99164

The electrochemical reduction of CO₂ is considered as an attractive strategy to convert CO₂ into formic acid that can be directly used as the energy carriers in a direct formic acid fuel. However, there is still a need to develop novel cathode materials with high catalytic activity and stability for this technology to be viable. Currently, Palladium (Pd) is one of the most efficient electrocatalysts that is able to convert CO₂ into formic acid at low overpotential (< 0.2 V), but it is very expensive and its surface is susceptible to CO poisoning. One strategy to improve the electrocatalytic performance, reduce CO poisoning, and reduce the amount of Pd needed for catalyst synthesis is to produce new bimetallic core@shell nanocatalysts. Those novel bimetallic materials can decrease the bonding strength of key intermediate species on the Pd surface improving its catalytic activity and long-term stability. This was achieved by modifying the electronic properties of Pd shell of Cu@Pd core@shell structured nanoparticle. Synthesized samples of nanoparticles in this work were characterized by UV-Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), Transmission electron microscopy (TEM), cyclic voltammetry (CV) and controlled potential electrolysis (CPE). The core@shell structure of the bimetallic nanoparticles was verified by UV-Vis and TEM results. XPS and CV data suggest that the transfer of charges from the Pd shell to the Cu core decreases the bonding strength of key intermediate species on the surface of Pd. This electronic perturbation of the catalyst surface lowers the energy barrier for CO₂ hydrogenation into formic acid and make the formation of CO on the surface of Pd less favorable. The CV shows that the CO₂ reduction current density is 0.21 mA/cm² on the surface of Cu@Pd, which is about 6.2 times higher than the current density on commercial Pd when overpotential is 0.15 V. The CPE data shows the long-term stability of the Cu@Pd catalyst is higher than commercial Pd. The production of formate/formic acid will be quantified by a titration method.