Electrochemical reduction of CO₂ to organic acids by a Pd-MWNTs gas-diffusion electrode in aqueous medium.

Pd-multiwalled carbon nanotubes (Pd-MWNTs) catalysts for the conversion of CO₂ to organic acids were prepared by the ethylene glycol reduction and fully characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV) technologies. The amorphous Pd particles with an average size of 5.7 nm were highly dispersed on the surface of carbon nanotubes. Functional groups of the MWNTs played a key role in the palladium deposition. The results indicated that Pd-MWNTs could transform CO₂ into organic acid with high catalytic activity and CO₂ could take part in the reduction reaction directly. Additionally, the electrochemical reduction of CO₂ was investigated by a diaphragm electrolysis device, using a Pd-MWNTs gas-diffusion electrode as a cathode and a Ti/RuO₂ net as an anode. The main products in present system were formic acid and acetic acid identified by ion chromatograph. The selectivity of the products could be achieved by reaction conditions changing. The optimum faraday efficiencies of formic and acetic acids formed on the Pd-MWNTs gas-diffusion electrode at 4₂V electrode voltages under 1 atm CO₂ were 34.5% and 52.3%, respectively.