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.

Understanding the structural and compositional sensitivities of the electrochemical CO2 reduction reaction (CO2RR) is fundamentally important for developing highly efficient and selective electrocatalysts. Here, we use Ag/Cu nanocrystals to uncover the key role played by the Ag/Cu interface in promoting CO2RR. Nanodimers including the two constituent metals as segregated domains sharing a tunable interface are obtained by developing a seeded growth synthesis, wherein preformed Ag nanoparticles are used as nucleation seeds for the Cu domain. We find that the type of metal precursor and the strength of the reducing agent play a key role in achieving the desired chemical and structural control. We show that tandem catalysis and electronic effects, both enabled by the addition of Ag to Cu in the form of segregated nanodomain within the same catalyst, synergistically account for an enhancement in the Faradaic efficiency for C2H4 by 3.4-fold and in the partial current density for CO2 reduction by 2-fold compared with the pure Cu counterpart. The insights gained from this work may be beneficial for designing efficient multicomponent catalysts for electrochemical CO2 reduction.

Surface-enhanced Raman scattering (SERS) is a highly sensitive probe for molecular detection. The aim of this study was to develop an efficient platform for investigating the kinetics of catalytic reactions with SERS. To achieve this, we synthesized a novel Au-Pd bimetallic nanostructure (HIF-AuNR@AuPd) through site-specific epitaxial growth of Au-Pd alloy horns as catalytic sites at the ends of Au nanorods. Using high-resolution electron microscopy and tomography, we successfully reconstructed the complex three-dimensional morphology of HIF-AuNR@AuPd and identified that the horns are bound with high-index {11l} (0.25 < l < 0.43) facets. With an electron beam probe, we visualized the distribution of surface plasmon over the HIF-AuNR@AuPd nanorods, finding that strong longitudinal surface plasmon resonance concentrated at the rod ends. This unique crystal morphology led to the coupling of high catalytic activity with a strong SERS effect at the rod ends, making HIF-AuNR@AuPd an excellent bifunctional platform for in situ monitoring of surface catalytic reactions. Using the hydrogenation of 4-nitrothiophenol as a model reaction, we demonstrated that its first-order reaction kinetics could be accurately determined from this platform. Moreover, we clearly identified the superior catalytic activity of the rod ends relative to that of the rod bodies, owing to the different SERS activities at the two positions. In comparison with other reported Au-Pd bimetallic nanostructures, HIF-AuNR@AuPd offered both higher catalytic activity and greater detection sensitivity.

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.

Pd-Ag bimetallic dendrites have been synthesized via a galvanic replacement reaction of Ag dendrites in a Na 2 PdCl 4 solution. Scanning and transmission electron microscopy (SEM and TEM), energy dispersive X-ray spectrometry (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analysis reveal that the resulting product is composed of partially depleted Ag dendrites covered with a rough surface with many Pd granules protruding by up to about 20 nm. High-solution TEM combined with EDX and selected area electron diffraction (SAED) confirms the formation of bimetallic interfaces between Pd and Ag. These Pd-Ag dendrites show up to four times higher catalytic activity toward the reduction of 4-nitrophenol (4-NP) by sodium borohydride (NaBH 4 ) than the best recently reported catalysts. This further enhancement over the already strong performance of similarly synthesized Au-Ag dendrites is explained by the presence of Pd, adding a hydrogen relay mechanism on top of the very effective electron relay capability of bimetallic dendrites.