Convoluted selectivity trends and a missing link between reaction product distribution and catalyst properties hinder practical applications of the electrochemical CO2 reduction reaction (CO2RR) for multicarbon product generation. Here we employ operando X-ray absorption and X-ray diffraction methods with subsecond time resolution to unveil the surprising complexity of catalysts exposed to dynamic reaction conditions. We show that by using a pulsed reaction protocol consisting of alternating working and oxidizing potential periods that dynamically perturb catalysts derived from Cu2O nanocubes, one can decouple the effect of the ensemble of coexisting copper species on the product distribution. In particular, an optimized dynamic balance between oxidized and reduced copper surface species achieved within a narrow range of cathodic and anodic pulse durations resulted in a twofold increase in ethanol production compared with static CO2RR conditions. This work thus prepares the ground for steering catalyst selectivity through dynamically controlled structural and chemical transformations.

Bimetallic CuZn catalysts have been recently proposed as alternatives in order to achieve selectivity control during the electrochemical reduction of CO2 (CO2RR). However, fundamental understanding of the underlying reaction mechanism and parameters determining the CO2RR performance is still missing. In this study, we have employed size-controlled (∼5 nm) Cu100–xZnx nanoparticles (NPs) supported on carbon to investigate the correlation between their structure and composition and catalytic performance. By tuning the concentration of Zn, a drastic increase in CH4 selectivity [∼70% Faradaic efficiency (F.E.)] could be achieved for Zn contents from 10 to 50, which was accompanied by a suppression of the H2 production. Samples containing a higher Zn concentration displayed significantly lower CH4 production and an abrupt switch in the selectivity to CO. Lack of metal leaching was observed based on quasi in situ X-ray photoelectron spectroscopy (XPS). Operando X-ray absorption fine structure (XAFS) spectroscopy measurements revealed that the alloying of Cu atoms with Zn atoms takes place under reaction conditions and plays a determining role in the product selectivity. Time-dependent XAFS analysis showed that the local structure and chemical environment around the Cu atoms continuously evolve during CO2RR for several hours. In particular, cationic Zn species initially present were found to get reduced as the reaction proceeded, leading to the formation of a CuZn alloy (brass). The evolution of the Cu–Zn interaction with time during CO2RR was found to be responsible for the change in the selectivity from CH4 over Cu-ZnO NPs to CO over CuZn alloy NPs. This study highlights the importance of having access to in depth information on the interplay between the different atomic species in bimetallic NP electrocatalysts under operando reaction conditions in order to understand and ultimately tune their reactivity.

In this study, we have taken advantage of a pulsed CO 2 electroreduction reaction (CO 2 RR) approach to tune the product distribution at industrially relevant current densities in a gas-fed flow cell. We compared the CO 2 RR selectivity of Cu catalysts subjected to either potentiostatic conditions (fixed applied potential of −0.7 V RHE ) or pulsed electrolysis conditions (1 s pulses at oxidative potentials ranging from E an = 0.6 to 1.5 V RHE , followed by 1 s pulses at −0.7 V RHE ) and identified the main parameters responsible for the enhanced product selectivity observed in the latter case. Herein, two distinct regimes were observed: (i) for E an = 0.9 V RHE we obtained 10% enhanced C 2 product selectivity (FE C 2 H 4 = 43.6% and FE C 2 H 5 OH = 19.8%) in comparison to the potentiostatic CO 2 RR at −0.7 V RHE (FE C 2 H 4 = 40.9% and FE C 2 H 5 OH = 11%), (ii) while for E an = 1.2 V RHE , high CH 4 selectivity (FE CH 4 = 48.3% vs 0.1% at constant −0.7 V RHE ) was observed. Operando spectroscopy (XAS, SERS) and ex situ microscopy (SEM and TEM) measurements revealed that these differences in catalyst selectivity can be ascribed to structural modifications and local pH effects. The morphological reconstruction of the catalyst observed after pulsed electrolysis with E an = 0.9 V RHE , including the presence of highly defective interfaces and grain boundaries, was found to play a key role in the enhancement of the C 2 product formation. In turn, pulsed electrolysis with E an = 1.2 V RHE caused the consumption of OH – species near the catalyst surface, leading to an OH-poor environment favorable for CH 4 production.

Direct conversion of carbon dioxide into multicarbon liquid fuels by the CO 2 electrochemical reduction reaction (CO 2 RR) can contribute to the decarbonization of the global economy.H ere,w ell-defined Cu 2 On anocubes (NCs, 35 nm) uniformly covered with Ag nanoparticles (5 nm) were synthesized.W hen compared to bare Cu 2 ONCs,t he catalyst with 5at% Ag on Cu 2 ONCs displayed atwo-fold increase in the Faradaic efficiency for C 2+ liquid products (30 %a t À1.0 V RHE), including ethanol, 1-propanol, and acetaldehyde, while formate and hydrogen were suppressed. Operando X-ray absorption spectroscopyrevealed the partial reduction of Cu 2 O during CO 2 RR, accompanied by ar eaction-driven redispersion of Ag on the CuO x NCs.D ata from operando surfaceenhanced Raman spectroscopyf urther uncovered significant variations in the CO binding to Cu, whichw ere assigned to AgÀCu sites formed during CO 2 RR that appear crucial for the C À Ccoupling and the enhanced yield of liquid products.

Water electrolysis is a key technology to establish CO2-neutral hydrogen production. Nonetheless, the near-surface structure of electrocatalysts during the anodic oxygen evolution reaction (OER) is still largely unknown, which hampers knowledge-driven optimization. Here using operando X-ray absorption spectroscopy and density functional theory calculations, we provide quantitative near-surface structural insights into oxygen-evolving CoOx(OH)y nanoparticles by tracking their size-dependent catalytic activity down to 1 nm and their structural adaptation to OER conditions. We uncover a superior intrinsic OER activity of sub-5 nm nanoparticles and a size-dependent oxidation leading to a near-surface Co–O bond contraction during OER. We find that accumulation of oxidative charge within the surface Co3+O6 units triggers an electron redistribution and an oxyl radical as predominant surface-terminating motif. This contrasts the long-standing view of high-valent metal ions driving the OER, and thus, our advanced operando spectroscopy study provides much needed fundamental understanding of the oxygen-evolving near-surface chemistry.