Decoupling the Size and Loading Effects in Silver Nanoparticles for Efficient Paired Carbon Dioxide and Formaldehyde Electrolysis

ABSTRACT Successful integration of silver nanoparticles (Ag NPs) towards highly selective electrochemical CO 2 reduction to carbon monoxide (CO) is often hindered by size‐dependent selectivity trade‐offs in Ag NPs and by inefficient full‐cell operation. Here, we systematically investigate ligand‐mediated colloidal synthesis of (quasi) monodisperse Ag NPs (6–15 nm) and evaluate them in a gas‐diffusion‐electrode‐based flow‐cell architecture, revealing a pronounced size‐dependent activity volcano. By incorporating a non‐catalytic carbon support, we demonstrate that an optimized Ag‐to‐carbon (Ag/C) loading, specifically 20% with 10 nm Ag NPs, achieves nearly 100% Faradaic Efficiency (FE) for CO at −100 mA·cm −2 , significantly outperforming other particle sizes and a commercial Ag catalyst at similar loadings. In situ Raman spectroscopy reveals a substantial role of Ag/C interactions in enhancing the affinity toward the * COOH intermediates, thereby promoting high CO 2 ‐to‐CO selectivity. Post‐electrolysis, X‐ray photoelectron spectroscopy (XPS) further indicates the electronic and chemical structural stability of the optimized Ag/C, which retains the metallic Ag 0 state. Finally, we demonstrate the bifunctional nature of Ag/C electrodes by pairing CO 2 and formaldehyde electrolysis, enabling simultaneous CO generation at the cathode and formate (HCOO − ) with hydrogen (H 2 ) at the anode at reduced cell potentials. This work highlights an energy‐efficient paired electrosynthesis strategy supporting the progress toward a circular carbon economy.