Highly selective Ag foam gas diffusion electrodes for CO2 electroreduction by pulsed hydrogen bubble templation†

Abstract

The electrochemical reduction of carbon dioxide to valuable fossil-free products opens up a way to close the carbon cycle, if based solely on renewable energy sources. Making the process industrially viable, however, needs high CO₂ conversion rates, efficient electrodes, and high selectivity for desired products. To reach this goal, highly catalytically active porous electrodes with maximized surface areas are required. We combined pulsed electrochemical deposition of the Ag foam catalyst with ionomer infiltration of the electrode to produce Ag-based gas diffusion electrodes (GDEs) in a facile and fast production process. Using the dynamic hydrogen bubble templation method (DHBT), we utilized the parasitic hydrogen evolution reaction (HER) to aid the solvent free structuring of the 3D catalyst network and directly manufacture a GDE. Different deposition parameters and in particular pulse-to-pause ratios increased the amount of deposited catalyst and successfully reduced the overpotential during CO₂RR operation. To inhibit electrode flooding and decrease CO₂ mass transport limitations during CO₂RR, we further infiltrated the electrode with a suitable perfluorosulfonic acid ionomer. SEM and EDS analyses showed a homogeneous Ag/F distribution along the cross section of the electrodes. These electrodes catalyzed the conversion of CO₂ to CO at industrially viable current densities of 500 mA cm⁻² with an unprecedented faradaic efficiency up to 76% in 1 M KHCO₃.