Emphasis within the CO2 reduction research field has been centered on the 1 dimensional line between the cathode and anode. Scientific advancements are made within the gas-diffusion layers, catalyst structure and morphology, electrolyte engineering, membranes and the interactions of these components. During operation the catalytic activity is then however assumed to be homogenous over the surface area of measurement (e.g. 1 cm2, 5cm2, 100 cm2), with each 1D pathway from the cathode to the anode being considered as equal. As research moves to elevated current densities, higher single pass conversions and larger electrode areas as a default mode of operation, the likelihood of homogenous spatio-activity is decreasing. In brief, spatial variations in feed concentration and current density are impacting the operation of our electrochemical devices, which discounts the activities and selectivities of our developed catalysts. Within this work we discuss three research directions that highlight spatial variations in two common CO2 electrolysis cells. In one work we discuss the limitations of 'black box' measurement techniques during high CO2 utilization experiments. Namely, single GC measurements of a lab-scale electrochemical cell group Faradaic efficiencies into a bulk measurement, instead of spatial one, potentially discounting catalytic activity on novel materials. In a second example, the relatively high resistivity of common gas-diffusion layers is discussed. Here, the distance between current collection points is shown to result in voltage variations across a catalyst surface, causing unwanted current density distributions that dampen peak Faradaic efficiencies of desired C2+ products. Being conscious of the above spatio-active effects during high current density CO2 reduction is then important for not only maximizing device selectivity, but also the potential for device scale-up.

Spatial variations during high current density CO2 reduction: impacts of current density and feed distributions on selectivity

ACS Fall 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.