Surface charge as activity descriptors for electrochemical CO2 reduction to multi-carbon products on organic-functionalised Cu

Abstract

Intensive research in electrochemical CO2 reduction reaction has resulted in the discovery of numerous high-performance catalysts selective to multi-carbon products, with most of these catalysts still being purely transition metal based. Herein, we present high and stable multi-carbon products selectivity of up to 76.6% across a wide potential range of 1 V on histidine-functionalised Cu. In-situ Raman and density functional theory calculations revealed alternative reaction pathways that involve direct interactions between adsorbed histidine and CO2 reduction intermediates at more cathodic potentials. Strikingly, we found that the yield of multi-carbon products is closely correlated to the surface charge on the catalyst surface, quantified by a pulsed voltammetry-based technique which proved reliable even at very cathodic potentials. We ascribe the surface charge to the population density of adsorbed species on the catalyst surface, which may be exploited as a powerful tool to explain CO2 reduction activity and as a proxy for future catalyst discovery, including organic-inorganic hybrids.

The importance of a charge transfer descriptor for screening potential CO2 reduction electrocatalysts

“…This is in line with the low-PZC branch of the selectivity volcano predicted from analyzing the experimental Cu facets data in Figs. 4 b and c. This also agrees with recent experimental data on organic molecule-functionalized Cu surfaces showing higher surface charge density to enhance the C 2 product selectivity 92 . At even higher PZC values, the selectivity is predicted by this analysis to go down at some point, likely due to an over-stabilization of *OCCO and the next step becoming rate-limiting.…”

“…To prepare materials with optimal PZC, structural design concepts need to be developed. Such concepts are relatively well known for the work function: Halide adsorption 98 or the adsorption of organic molecules 92 , 99 are just a few examples, of how the work function can be tuned in addition to the substrate effect presented above. Employing work function design strategies the future task should thus be to find materials with the optimal CO adsorption energy and PZC.…”

Understanding the complexity in bridging thermal and electrocatalytic methanation of CO2

“…They influence the local electric field (see later) and provide additional electrostatic interaction near the catalyst surface. 237 This effect is similar to that from cations in the electrolyte, as discussed in the previous section. 228,238–240 However, a major difference between the cation effect and organic surface functionalities, such as histidine, 237 is that the latter can adsorb specifically on the electrocatalyst surface under cathodic bias.…”

“…237 This effect is similar to that from cations in the electrolyte, as discussed in the previous section. 228,238–240 However, a major difference between the cation effect and organic surface functionalities, such as histidine, 237 is that the latter can adsorb specifically on the electrocatalyst surface under cathodic bias. Further, the hydration shell of the organic moiety is much larger than alkali cations but softer, thus enabling higher surface charge accumulation than alkaline metal cations.…”

Organic-moiety-engineering on copper surface for carbon dioxide reduction

“…Organic molecules possess tunable and defined chemical structure, unique chemical properties, and can be immobilized onto Cu surface via bonding and interaction, which have been applied for Cu modification to tune the local microenvironment and catalytic activity. 38–40 In particular, the nitrogen-containing molecules are most widely applied and studied, including N-substituted pyridinium additives, N , N ′-ethylene-phenanthrolinium dibromide, thiol pyridine, amino acid, organosuperbases, and ionic liquids etc. Pyridine based molecules with abundant lone pairs and affinity to CO 2 show great promise in CO 2 RR.…”