Dynamic Changes in the Structure, Chemical State and Catalytic Selectivity of Cu Nanocubes during CO₂ Electroreduction: Size and Support Effects

Abstract

In situ and operando spectroscopic and microscopic methods were used to gain insight into the correlation between the structure, chemical state, and reactivity of size- and shape-controlled ligand-free Cu nanocubes during CO electroreduction (CO RR). Dynamic changes in the morphology and composition of Cu cubes supported on carbon were monitored under potential control through electrochemical atomic force microscopy, X-ray absorption fine-structure spectroscopy and X-ray photoelectron spectroscopy. Under reaction conditions, the roughening of the nanocube surface, disappearance of the (100) facets, formation of pores, loss of Cu and reduction of CuO species observed were found to lead to a suppression of the selectivity for multi-carbon products (i.e. C H and ethanol) versus CH . A comparison with Cu cubes supported on Cu foils revealed an enhanced morphological stability and persistence of Cu species under CO RR in the former samples. Both factors are held responsible for the higher C /C product ratio observed for the Cu cubes/Cu as compared to Cu cubes/C. Our findings highlight the importance of the structure of the active nanocatalyst but also its interaction with the underlying substrate in CO RR selectivity.

In‐Situ Nanostructuring and Stabilization of Polycrystalline Copper by an Organic Salt Additive Promotes Electrocatalytic CO2 Reduction to Ethylene

“…The resulting electrocatalysts show higher current densities and selectivities for ethylene (20 % < FE < 45 %) and oxygenated products compared to a planar electrode, although hydrogen is still the predominant product (40 % < FE <60 %). Unfortunately, these systems suffer from fast structural reconstruction/degradation and performance decay during catalysis, possibly due to the applied electrochemical bias . As a consequence, the sustained influence of Cu morphology on the resulting products still remains elusive.…”

“…These structural observations contrast with previous reports on nanostructured copper electrodes . This is the first example of stable copper nanocubes under electrocatalytic conditions over prolonged reaction times (>40 h, Figure S16).…”

On the Oxidation State of Cu2O upon Electrochemical CO2 Reduction: An XPS Study

“…On the other hand, and in clear conflict with those works, a greater number of recent studies implementing in situ or post‐mortem X‐ray absorption, photoelectron or electron energy loss spectroscopies (XAS, XPS, EELS) have concluded that the initial oxide does not get completely reduced in the course of the CO 2 ‐reduction process. Moreover, those same works additionally assigned the enhanced selectivity for ethylene/alcohols production displayed by these catalysts to the presence of remnant oxide within their (sub‐)surface …”

“…The validation of these conflicting lines of thought is complicated by the high surface roughness intrinsic to these Cu 2 O catalysts, since their eventual reduction to Cu 0 would translate into an abundance of [100](‐stepped) analogous domains and/or in a high surface pH that would justify the CO 2 ‐to‐ethylene selectivity displayed by these materials. Additionally, their correspondingly large content of surface grain boundaries prone to re‐oxidation upon contact with trace amounts of oxygen (e. g., during sample transfer for post‐mortem characterization) could cause the apparent presence of remaining (sub‐)surface oxides asserted in the above studies . Thus, to suppress the ambiguous effects of the surface roughness on the oxide's selectivity and post‐mortem oxidation state, in this work we prepared quasi‐planar, low‐roughness Cu 2 O thin films (TFs) and used them as CO 2 ‐reduction electrocatalysts.…”

Selective CO2 Electroreduction to Ethylene and Multicarbon Alcohols via Electrolyte‐Driven Nanostructuring

“…Previous experimental and theoretical studies demonstrated that Cu(100) is the most favorable crystal orientation for the C−C coupling process . However, the surface of Cu electrodes under electrochemical environments often undergoes reconstructions induced by applied potentials, the intermediates formed during CO 2 RR, as well as specifically adsorbed anions . On the other hand, some anions either present in the electrolyte or adsorbed on the electrode surface, have been shown to play a vital role in the dynamic evolution of the catalyst structure under reaction conditions as well as the activity and selectivity of CO 2 RR.…”