Ultrasound-assisted synthesis of copper-based catalysts for the electrocatalytic CO2 reduction: Effect of ultrasound irradiation, precursor concentration and calcination temperature

Abstract

The reduction of high CO2 concentrations in the atmosphere is an imperative task to reduce the consequences of the greenhouse effect on our planet. Developing active and selective materials for electrochemical CO2 reduction towards value-added products is mandatory to bring this technology to a practical application. This work studied the effect of assisting Cu and Zn oxides co-precipitation with sonochemistry. Different factors were investigated: the ultrasounds (US) amplitude, the effect of US irradiation time during either precipitation or ageing processes, the precursor concentration and calcination temperature. The synthesised catalysts were tested for the electrocatalytic CO2 reduction reaction in a Rotating Disk Electrode (RDE) system. Faradaic efficiencies >14% towards alcohols were obtained using US-assisted synthesised Cu-based catalysts. Instead, with the US-prepared Cupper-Zinc-based catalysts, the selectivity towards H2 and C1 products (CO and formate) was improved, and the syngas productivity was increased by > ⁓1.4-fold compared to the non-sonicated one. The alcohols production of the best Cu-catalyst was also confirmed on scalable electrodes. Controlling the synthesis conditions allowed to tune the physicochemical properties of the nanoparticles, including specific surface area, porosity, crystallite size and phases. Mesoporous materials with a mean pores size of around 25 nm were found to induce a better CO2 diffusion and CO retention time in the porous network, improving the *CO intermediate adsorption at active sites, promoting its dimerisation and thus enhancing the selectivity towards C2+ alcohols. The here reported results open the way for new electrocatalysts designs with properly tuned porosity for the selective CO2 conversion to different valuable products.