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Ag nanoparticles (NPs) are efficient electrocatalysts for electrochemical CO2‐to‐CO conversion. However, NPs are thermodynamically unstable and can undergo structural alterations under electrolysis operating conditions. These structural changes may play a crucial role in the deterioration of CO2 reduction reaction (CO2RR) performance on the long‐term electrolysis time scale. Here, we studied the effect of NP size on NP degradation during CO2RR. Polyvinylpyrrolidone‐capped 10, 40, and 100 nm Ag NPs deposited on a gas diffusion electrode were used as testbed catalysts in a gas‐fed zero‐gap electrolyzer. Inductively coupled plasma mass spectrometry indicated insignificant catalyst‐material detachment after galvanostatic CO2 electrolysis. Scanning electron microscopy analysis showed that smaller NPs tended to agglomerate during CO2 electrolysis. 100 nm NPs formed agglomerates consisting of only two‐three NPs and underwent pronounced fragmentation with the formation of particles several nanometers in size. The fragmentation was associated with cathodic corrosion of Ag NPs under conditions of intensive CO2RR and hydrogen evolution. [ABSTRACT FROM AUTHOR]

The reduction of CO2 to CO from a bicarbonate feedstock offers an opportunity to directly use aqueous carbon capture solutions, while bypassing ex‐situ energy‐intensive gaseous CO2 regeneration. In this study, we resolved how the electrolyte cation identity (Li+, Na+, K+, Cs+) affects the two reactions that make bicarbonate electrolysis possible: (i) the production of in‐situ CO2 formed through reaction of HCO3− (from the catholyte) with H+ (sourced from the membrane); and (ii) the electroreduction of CO2 into CO. Our results show that cation identity does not change the rate of in‐situ CO2 formation, but it does enhance the rate of the CO2 reduction reaction (CO2RR). Electrolysis experiments performed with a constant [HCO3−] showed that CO selectivities progressively increased for the series Li+, Na+, K+, and Cs+, respectively. Optimization of the electrolyte composition yielded a CO selectivity of ∼80 % during electrolysis of 1.5 M CsHCO3 solutions at 100 mA cm−2, while saturated LiHCO3 solutions (0.84 M) yielded CO selectivities values of merely 30 % at the same current density. This study demonstrates a quantitative relationship between CO product selectivity and the cation radius, which provides a pathway to integrate bicarbonate electrolysis to carbon capture. [ABSTRACT FROM AUTHOR]

Electroreduction of CO2 (eCO2RR) is a potentially sustainable approach for carbon‐based chemical production. Despite significant progress, performing eCO2RR economically at scale is challenging. Here we report meeting key technoeconomic benchmarks simultaneously through electrolyte engineering and process optimization. A systematic flow electrolysis study ‐ performing eCO2RR to CO on Ag nanoparticles as a function of electrolyte composition (cations, anions), electrolyte concentration, electrolyte flow rate, cathode catalyst loading, and CO2 flow rate ‐ resulted in partial current densities of 417 and 866 mA/cm2 with faradaic efficiencies of 100 and 98 % at cell potentials of −2.5 and −3.0 V with full cell energy efficiencies of 53 and 43 %, and a conversion per pass of 17 and 36 %, respectively, when using a CsOH‐based electrolyte. The cumulative insights of this study led to the formulation of system design rules for high rate, highly selective, and highly energy efficient eCO2RR to CO. [ABSTRACT FROM AUTHOR]