In catalysis science stability is as crucial as activity and selectivity. Understanding the degradation pathways occurring during operation and developing mitigation strategies will eventually improve catalyst design, thus facilitating the translation of basic science to technological applications. Herein, we reveal the unique and general degradation mechanism of metallic nanocatalysts during electrochemical CO2 reduction, exemplified by different sized copper nanocubes. We follow their morphological evolution during operation and correlate it with the electrocatalytic performance. In contrast with the most common coalescence and dissolution/precipitation mechanisms, we find a potential-driven nanoclustering to be the predominant degradation pathway. Grand-potential density functional theory calculations confirm the role of the negative potential applied to reduce CO2 as the main driving force for the clustering. This study offers a novel outlook on future investigations of stability and degradation reaction mechanisms of nanocatalysts in electrochemical CO2 reduction and, more generally, in electroreduction reactions.

Despite substantial progress in the electrochemical conversion of CO 2 into value-added chemicals, the translation of fundamental studies into commercially relevant conditions requires additional efforts. Here, we study the catalytic properties of tailored Cu nanocatalysts under commercially relevant current densities in a gas-fed flow cell. We demonstrate that their facet-dependent selectivity is retained in this device configuration with the advantage of further suppressing hydrogen production and increasing the faradaic efficiencies toward the CO 2 reduction products compared to a conventional H-cell. The combined catalyst and system effects result in stateof-the art product selectivity at high current densities (in the range 100−300 mA/cm 2 ) and at relatively low applied potential (as low as −0.65 V vs RHE). Cu cubes reach an ethylene selectivity of up to 57% with a corresponding mass activity of 700 mA/mg, and Cu octahedra reach a methane selectivity of up to 51% with a corresponding mass activity of 1.45 A/mg in 1 M KOH.

Electrochemical reduction of CO 2 using renewable energy is a promising strategy to mitigate the CO 2 emissions and to produce valuable chemicals. However, the lack of highly selective, highly durable, and nonpreciousmetal catalysts impedes the applications of this reaction. In this work, coppernanowire-supported indium catalysts are proposed as advanced electrocatalysts for the aqueous electroreduction of CO 2 . The catalysts are synthesized by a facile method, which combines In 3+ deposition on Cu(OH) 2 nanowires, mild oxidation, and in situ electroreduction procedures. With a thin layer of metallic In deposited on the surface of the Cu nanowires, the catalyst exhibits a CO Faradaic efficiency of ∼93% at −0.6 to −0.8 V vs RHE; additionally, an unprecedented stability of 60 h is achieved. The characterization results combined with density functional theory (DFT) calculations reveal that the interface of Cu and In plays an essential role in determining the reaction pathway. The calculation results suggest that the Cu−In interface enhances the adsorption strength of *COOH, a key reaction intermediate for CO production, while destabilizes the adsorption of *H, an intermediate for H 2 evolution. We believe that these findings will provide guidance on the rational design of high-performance bimetallic catalysts for CO 2 electroreduction by creating the metal−metal interface structure.

Synergistic effects at metal/metal oxide interfaces often give rise to highly active and selective catalytic motifs. So far, such interactions have been rarely explored to enhance the selectivity in the electrochemical CO 2 reduction reaction (CO 2 RR). Herein, Cu/CeO 2-x heterodimers (HDs) are synthesized and presented as one of the prime examples where such effects promote CO 2 RR. A colloidal seeded-growth synthesis is developed to connect the two highly mismatched domains (Cu and CeO 2-x) through an interface. The Cu/CeO 2-x HDs exhibit state-of-the-art selectivity towards CO 2 RR (up to ~80%) against the competitive hydrogen evolution reaction (HER) and high faradaic efficiency for methane (up to ~54%) at-1.2 V RHE , which is 5 times higher than that obtained when the Cu and CeO 2-x nanocrystals are physically mixed. Operando X-Ray absorption spectroscopy along with other ex-situ spectroscopies evidences the partial reduction from Ce 4+ to Ce 3+ in the HDs during CO 2 RR. A Density Functional Theory (DFT) study of the active site motif in reducing condition reveals synergistic effects in the electronic structure at the interface. The proposed lowest free energy pathway utilizes O-vacancy site with intermediates binding to both Cu and Ce atoms, a configuration which allows to break the CHO*/CO* scaling relation. The suppression of HER is attributed to the spontaneous formation of CO* at this interfacial motif and subsequent blockage of the Cu-sites.

Octahedral Cu nanocrystals in the size range of 75–310 nm are synthesized and investigated for electrochemical CO2 reduction.