CO2 Electrolysis: From Model Metal Foams to Gas Diffusion Electrodes Using Dynamic Hydrogen Bubble Templation

Abstract

On the road to a clean and sustainable energy production, reducing our greenhouse gas emissions is of utmost importance. It is already well known that the electrochemical reduction reaction of carbon dioxide (CO2RR) to valuable products can contribute to this goal by power-to-X technology1, 2. Hereby, amongst other factors, the choice of the electrocatalyst material defines the final product spectrum. For instance, the noble metal Ag shows very high selectivities in the conversion of carbon dioxide to carbon monoxide and achieves faradaic conversion efficiencies close to 100 %. High conversion rates and the efficiency of the reduction process itself are necessary to make the process industrially viable. To enhance the conversion, highly catalytically active porous electrodes with increased surface area are required. A fast and simple way to produce these electrodes without the use of solvents is the hydrogen bubble templating (DHBT) method3, 4. This technique takes advantage of the hydrogen evolution reaction (HER). By applying sufficiently high overpotentials, metal ions are reduced and electrochemically deposited, while simultaneously the bubbles originating from HER work as a dissolving negative template for the metal to grow around, thereby forming macro-porous layers and nanoscale interconnecting foam walls.To find out the optimal manufacturing parameters, the activity of electrochemically deposited metal foams for the CO2RR is determined in model systems using an H-cell first. Combining the characterization of such intricate foam electrodes using physicochemical and microscopic techniques in conjunction with electrochemical analyses provides us with an in-depth insight into the structure of the carefully tailored electrodes. By elucidating the morphology, we were able to link the electrochemical deposition at higher current densities to a more homogenous and denser structure, which in turn achieved better performances in the conversion of CO2 to valuable products.Although catalyst design and its effects on the CO2RR performance can be studied in H-cells very easily, the transfer of these model foam electrodes towards gas-fed electrodes is necessary to take the next development step towards industrial application and to approach higher TRLs. By avoiding solvation limits of CO2 in aqueous electrolytes and thereby decreasing its diffusion length, gas diffusion electrodes can accomplish industrially required current densities by intense contact between the liquid and the gas phase with the catalytically active surfaces within the metallic electrodes. Herein, we will demonstrate how the DHBT method can be used to produce gas diffusion electrodes for application in the CO2RR within minutes. A. Bagger, W. Ju, A. S. Varela, P. Strasser and J. Rossmeisl, Chemphyschem : a European journal of chemical physics and physical chemistry, 18(22), 3266–3273 (2017).S. Vesztergom, A. Dutta, M. Rahaman, K. Kiran, I. Zelocualtecatl Montiel and P. Broekmann, ChemCatChem, 13(4), 1039–1058 (2021).K. Klingan, T. Kottakkat, Z. P. Jovanov, S. Jiang, C. Pasquini, F. Scholten, P. Kubella, A. Bergmann, B. Roldan Cuenya, C. Roth and H. Dau, ChemSusChem, 11(19), 3449–3459 (2018).T. Kottakkat, K. Klingan, S. Jiang, Z. P. Jovanov, V. H. Davies, G. A. M. El-Nagar, H. Dau and C. Roth, ACS applied materials & interfaces, 11(16), 14734–14744 (2019).