The capping agent is the key: Structural alterations of Ag NPs during CO2 electrolysis probed in a zero-gap gas-flow configuration

• Published in: Journal of catalysis 2021-12, Vol.404, p.371-382
• Main Authors: Liu, Menglong, Kong, Ying, Hu, Huifang, Kovács, Noémi, Sun, Changzhe, Zelocualtecatl Montiel, Iván, Gálvez Vázquez, María de Jesús, Hou, Yuhui, Mirolo, Marta, Martens, Isaac, Drnec, Jakub, Vesztergom, Soma, Broekmann, Peter
• Format: Article
• Language: English
• Subjects: carbon dioxide; Carbon dioxide electroreduction; Catalyst degradation; catalysts; catalytic activity; Chemical Sciences; citrates; corrosion; crystallites; electrodes; electrolysis; ligands; nanosilver; Particle sizing; polyethylene glycol; polyethyleneimine; polyvinylpyrrolidone; Power to value; Scanning electron microscopy; shrinkage; stabilizers; Wide-angle X-ray scattering
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2021.10.016

[Display omitted] •Silver nanoparticles (Ag NPs) stabilized by four different capping agents are applied as catalysts of CO2 reduction in a zero-gap gas-flow electrolyser.•Branched polyethylenimine (BPEI), polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), and citrate are used as capping agents.•Depending on the nature of the capping agent, Ag NPs undergo different degradation pathways.•BPEI is the most effective stabilizer but also blocks CO2 reduction the most.•Particles capped by PVP tend mostly to corrode (leading to particle shrinkage) while in case of PEG- and citrate-capped particles degradation involves particle size growth.•The statistical analysis of SEM images and WAXS measurements provide an insight to the degradation pathway.•Ligand exchange and removal experiments underline the role of capping agents in catalyst degradation. We apply silver nanoparticles (Ag NPs) as catalysts of CO2 reduction in a zero-gap gas-flow electrolyser. Ag NPs stabilized by different ligands —branched polyethylenimine (BPEI), polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), and citrate— are used in the experiments. The as-prepared NPs have almost identical initial size distributions, yet their catalytic performance, in terms of achievable current and CO selectivity, is different. During electrolysis all Ag NPs exhibit unambiguous morphology changes; the degradation pathway they follow, however, markedly depends on the chemical nature of the capping agent stabilizing them. Scanning electron micrographs obtained before and after constant-charge electrolyses carried out at different potentials reveal that amongst the studied ligands, BPEI seems to be the most effective stabilizer of Ag NPs; in turn, however, BPEI also limits CO formation the most. In case of PVP, mostly corrosion (particle shrinkage) is observed at practically relevant electrolysing potentials, while the application of PEG leads more to particle coalescence. Ostwald ripening seems to appear only at high applied (H2 forming) potentials in case of the three afore-mentioned ligands while in case of citrate it becomes significant already at mild (CO forming) voltages. By studying the effects of capping agent removal and exchange we demonstrate that apart from ligands directly attached to the Ag NPs, also the excess of capping agents (adsorbed on the electrode surface) plays a decisive role in determining the extent and mode of catalyst degradation. The results of SEM-based particle sizing are also