Colloidal Cu–Ag nanocrystals measuring less than 10 nm across are promising candidates for integration in hybrid CO2 reduction reaction (CO2RR) interfaces, especially in the context of tandem catalysis and selective multicarbon (C2–C3) product formation. In this work, we vary the synthetic-ligand/copper molar ratio from 0.1 to 1.0 and the silver/copper atomic ratio from 0 to 0.7 and study the variations in the nanocrystals’ size distribution, morphology and reactivity at rates of ≥100 mA cm–2 in a gas-fed recycle electrolyzer operating under neutral to mildly basic conditions (0.1–1.0 M KHCO3). High-resolution electron microscopy and spectroscopy are used in order to characterize the morphology of sub-10 nm Cu–Ag nanodimers and core–shells and to elucidate trends in Ag coverage and surface composition. It is shown that Cu–Ag nanocrystals can be densely dispersed onto a carbon black support without the need for immediate ligand removal or binder addition, which considerably facilitates their application. Although CO2RR product distribution remains an intricate function of time, (kinetic) overpotential and processing conditions, we nevertheless conclude that the ratio of oxygenates to hydrocarbons (which depends primarily on the initial dispersion of the nanocrystals and their composition) rises 3-fold at moderate Ag atom % relative to Cu NCs-based electrodes. Finally, the merits of this particular Cu–Ag/C system and the recycling reactor employed are utilized to obtain maximum C2–C3 partial current densities of 92–140 mA cm–2 at −1.15 VRHE and liquid product concentrations in excess of 0.05 wt % in 1 M KHCO3 after short electrolysis periods.

Bimetallic nanoparticles with tailored size and specific composition have shown promise as stable and selective catalysts for electrochemical reduction of CO 2 (CO 2 R) in batch systems. Yet, limited effort was devoted to understand the effect of ligand coverage and postsynthesis treatments on CO 2 reduction, especially under industrially applicable conditions, such as at high currents (>100 mA/cm 2 ) using gas diffusion electrodes (GDE) and flow reactors. In this work, Cu−Ag core−shell nanoparticles (11 ± 2 nm) were prepared with three different surface modes: (i) capped with oleylamine, (ii) capped with monoisopropylamine, and (iii) surfactant-free with a reducing borohydride agent; Cu− Ag (OAm), Cu−Ag (MIPA), and Cu−Ag (NaBH 4 ), respectively. The ligand exchange and removal was evidenced by infrared spectroscopy (ATR-FTIR) analysis, whereas high-resolution scanning transmission electron microscopy (HAADF-STEM) showed their effect on the interparticle distance and nanoparticle rearrangement. Later on, we developed a process-on-substrate method to track these effects on CO 2 R. Cu−Ag (OAm) gave a lower on-set potential for hydrocarbon production, whereas Cu−Ag (MIPA) and Cu−Ag (NaBH 4 ) promoted syngas production. The electrochemical impedance and surface area analysis on the well-controlled electrodes showed gradual increases in the electrical conductivity and active surface area after each surface treatment. We found that the increasing amount of the triple phase boundaries (the meeting point for the electron−electrolyte−CO 2 reactant) affect the required electrode potential and eventually the C +2e ̅ /C 2e ̅ product ratio. This study highlights the importance of the electron transfer to those active sites affected by the capping agents particularly on larger substrates that are crucial for their industrial application.

No abstract

Bifunctionality is a key feature of many industrial catalysts, supported metal clusters and particles in particular, and the development of such catalysts for the CO 2 reduction reaction (CO 2 RR) to hydrocarbons and alcohols is gaining traction in light of recent advancements in the field. Carbonsupported Cu nanoparticles are suitable candidates for integration in the state-ofthe-art reaction interfaces, and here, we propose, synthesize, and evaluate a bifunctional Ni−N-doped-C-supported Cu electrocatalyst, in which the support possesses active sites for selective CO 2 conversion to CO and Cu nanoparticles catalyze either the direct CO 2 or CO reduction to hydrocarbons. In this work, we introduce the scientific rationale behind the concept, its applicability, and the challenges with regard to the catalyst. From the practical aspect, the deposition of Cu nanoparticles onto carbon black and Ni−N−C supports via an ammonia-driven deposition precipitation method is reported and explored in more detail using X-ray diffraction, thermogravimetric analysis, and hydrogen temperature-programmed reduction. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and energy-dispersive X-ray spectroscopy (EDXS) give further evidence of the presence of Cu-containing nanoparticles on the Ni−N−C supports while revealing an additional relationship between the nanoparticle's composition and the electrode's electrocatalytic performance. Compared to the benchmark carbon black-supported Cu catalysts, Ni−N−C-supported Cu delivers up to a 2-fold increase in the partial C 2 H 4 current density at −1.05 V RHE (C 1 /C 2 = 0.67) and a concomitant 10-fold increase of the CO partial current density. The enhanced ethylene production metrics, obtained by virtue of the higher intrinsic activity of the Ni−N−C support, point out toward a synergistic action between the two catalytic functionalities.

Nickel-containing N-doped carbons were synthesized and analyzed for the electrochemical reduction of CO2 to CO under industrially relevant conditions.