The specific identity of electrolyte cations has many implications in various electrochemical reactions. However, the exact mechanism by which cations affect electrochemical reactions is not agreed upon in the literature. In this report, we investigate the role of cations during the electrochemical reduction of CO2 by chelating the cations with cryptands, to change the interaction of the cations with the components of the electric double layer. As previously reported we do see the apparent suppression of CO2 reduction in the absence of cations. However, using in situ-SEIRAS we see that CO2 reduction does indeed take place albeit at very reduced scales. We also observe that cations play a role in tuning the absorption strengths of not only CO2 as has been speculated, but also that of reaction products such as CO.

The field of electrochemical CO₂ reduction has been transitioning to industrially relevant scales by changing the architecture of the electrochemical cells and moving away from the traditional aqueous H-cells to membrane electrode assemblies (MEA). The reaction environments in MEAs vary drastically from that of aqueous H-cells, which could result in significantly different catalytic activity. In this paper, we test AgPd alloys, one of the most promising CO producing catalysts reported, at industrially relevant scales (50 to 200 mA/cm²) in a MEA configuration. We report that, with increasing Pd composition in the electrode, the CO selectivity reduces from 99 % for pure Ag to 73 % for pure Pd at 50 mA/cm². The MEA configuration helps attain a high CO partial current density of 123 mA/cm². We find that catalytic activity reported in aqueous H-Cells does not translate at higher current densities and that cell architecture must play an important role in benchmarking catalytic activity.

X-ray absorption spectroscopy (XAS) offers the unique possibility to study metal electrocatalysts such as silver and copper while they are performing electrochemical carbon dioxide (CO2) reduction. In this work, we present an approach to perform operando XAS experiments on an electrochemical cell performing CO2 reduction with a gas diffusion electrode (GDE) as cathode. The experimental set-up, advantages and drawbacks, XAS data analysis, and XAS theory are discussed. Results on copper and silver GDEs obtained through the presented procedures are then presented and discussed. Structural and compositional catalyst data acquired under operando conditions can help further density functional theory calculations, and catalytic, and systems studies on CO2 reduction. Structural and compositional data including crystallite size were obtained while performing high current density (up to 200 mA cm-2) CO2 reduction. On the silver catalysts at higher than 100 mA cm-2 applied current density, a Ag-X contribution was found and is ascribed to Ag-O. For both silver and copper, the XAS experiments revealed that the crystallite size of the ex situ samples is smaller than the samples during CO2 reduction. Furthermore, metal particle size polydispersity was found in the silver catalysts by comparing the obtained coordination numbers with theoretical values. The operando EXAFS data was of such high quality (k: 3-14 Å-1) that four shells could be fitted. The value of combining ex situ material characterisation and electrocatalyst performance data with operando XAS experiments is discussed and found to be of great importance to further CO2 reduction research.

Carbon dioxide can be electrochemically converted into feedstocks for many industrial processes, such as the manufacturing of synthetic fuels and chemicals. This work focuses on the structure-functionality relationship between Au, Sn, and bimetallic AuSn catalysts and their CO2 reduction performance in an H-Cell at varying current densities. X-Ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), and atomic force microscopy (AFM) were used to determine the crystal structure, surface morphology, and composition of compositionally variant bimetallic thin films of Au-Sn before and after electrolysis. The electrochemical activity for each bimetallic film was measured in terms of electrode current and product selectivity as a function of applied current density and catalyst composition. The results of this work show that not all combinations of metals for CO2 reduction can improve catalyst activity toward a desired product and that a detailed material characterization can help in drawing structure-functionality relationships between a catalyst and its activity.