Silver−copper (AgCu) bimetallic catalysts hold great potential for electrochemical carbon dioxide reduction reaction (CO 2 RR), which is a promising way to realize the goal of carbon neutrality. Although a wide variety of AgCu catalysts have been developed so far, it is relatively less explored how these AgCu catalysts evolve during CO 2 RR. The absence of insights into their stability makes the dynamic catalytic sites elusive and hampers the design of AgCu catalysts in a rational manner. Here, we synthesized intermixed and phase-separated AgCu nanoparticles on carbon paper electrodes and investigated their evolution behavior in CO 2 RR. Our time-sequential electron microscopy and elemental mapping studies show that Cu possesses high mobility in AgCu under CO 2 RR conditions, which can leach out from the catalysts by migrating to the bimetallic catalyst surface, detaching from the catalysts, and agglomerating as new particles. Besides, Ag and Cu manifest a trend to phase-separate into Cu-rich and Ag-rich grains, regardless of the starting catalyst structure. The composition of the Cu-rich and Ag-rich grains diverges during the reaction and eventually approaches thermodynamic values, i.e., Ag 0.88 Cu 0.12 and Ag 0.05 Cu 0.95 . The separation between Ag and Cu has been observed in the bulk and on the surface of the catalysts, highlighting the importance of AgCu phase boundaries for CO 2 RR. In addition, an operando high-energy-resolution X-ray absorption spectroscopy study confirms the metallic state of Cu in AgCu as the catalytically active sites during CO 2 RR. Taken together, this work provides a comprehensive understanding of the chemical and structural evolution behavior of AgCu catalysts in CO 2 RR.

The kinetic performance of methanol synthesis on a clean Ni(111) surface can be improved by doping the surface with a transition metal atom.

High-entropy alloy (HEA) nanoparticles are promising catalyst candidates for the acidic oxygen evolution reaction (OER). Herein, we report the synthesis of IrFeCoNiCu-HEA nanoparticles on a carbon paper substrate via a microwaveassisted shock synthesis method. Under OER conditions in 0.1 M HClO 4 , the HEA nanoparticles exhibit excellent activity with an overpotential of ∼302 mV measured at 10 mA cm −2 and improved stability over 12 h of operation compared to the monometallic Ir counterpart. Importantly, an active Ir-rich shell layer with nanodomain features was observed to form on the surface of IrFeCoNiCu-HEA nanoparticles immediately after undergoing electrochemical activation, mainly due to the dissolution of the constituent 3d metals. The core of the particles was able to preserve the characteristic homogeneous single-phase HEA structure without significant phase separation or elemental segregation. This work illustrates that under acidic operating conditions, the near-surface structure of HEA nanoparticles is susceptible to a certain degree of structural dynamics.

We evaluate the electrocatalytic activity of graphene-supported NiN4 active center in facilitating two-electron CO2 electrochemical reduction into CO and HCOOH, as well as the competing hydrogen evolution reaction. NiN4 center is found to be more stable in zigzag-edge and armchair-edge proximity of graphene, confirming experimental evidence. In an attempt to reduce the CO2 reduction overpotential, we construct a neighboring-site environment of NiN4 center and BN substitutional defect. B-doped structures are found to be capable of reducing the CO2 reduction energy barrier through direct (HCOOH pathway) or indirect (CO pathway) participation in facilitating CO2 reduction-related key intermediates. In most Ni sites, the presence of adjacent BN site is also discovered to change the product selectivity from CO to HCOOH. Our result predicts that B-doped NiN4 sites on the interior side (NiN4BN-G) and on the armchair-edge side of tilted orientation (t-NiN4BN-AGNR) are HCOOH-selective. Although the rest of zigzag-edge and armchair-edge sites have a tendency to selectively produce CO and HCOOH, respectively, the undesirable hydrogen evolution reaction is found to be more dominant and therefore obscuring the potential. Our result demonstrates that the hydrogen evolution reaction is most likely to occur on top of a neighboring C atom instead of on the Ni center, in contrast to the commonly understood mechanism. To ultimately suppress the activity of the hydrogen evolution reaction, we predict that an effective electrocatalyst optimization cannot be realized by only selecting the best metal center and dopant pair but also by altering the neighbor’s electronic structure.