Reversible metal cluster formation on Nitrogen-doped carbon controlling electrocatalyst particle size with subnanometer accuracy

Copper and nitrogen co-doped carbon catalysts exhibit a remarkable behavior during the electrocatalytic CO2 reduction (CO2RR), namely, the formation of metal nanoparticles from Cu single atoms, and their subsequent reversible redispersion. Here we show that the switchable nature of these species holds the key for the on-demand control over the distribution of CO2RR products, a lack of which has thus far hindered the wide-spread practical adoption of CO2RR. By intermitting pulses of a working cathodic potential with pulses of anodic potential, we were able to achieve a controlled fragmentation of the Cu particles and partial regeneration of single atom sites. By tuning the pulse durations, and by tracking the catalyst's evolution using operando quick X-ray absorption spectroscopy, the speciation of the catalyst can be steered toward single atom sites, ultrasmall metal clusters or large metal nanoparticles, each exhibiting unique CO2RR functionalities. Copper-based materials can convert CO2 into hydrocarbons and other chemicals via CO2RR, but controlling selectivity is challenging. Cu and nitrogen co-doped carbon (Cu-N-C) catalysts host singly dispersed cationic Cu species that are unstable under CO2RR, forming metallic particles; this process is reversible upon lifting reducing conditions and is general for a broad range of Cu-N-C catalysts. Here, using a pulsed CO2RR protocol alternating between a cathodic potential and an anodic potential, we control the average size of Cu particles with subnanometer accuracy in situ and reversibly switch between catalytic functionalities. Singly dispersed cationic Cu species favor hydrogen production, ultrasmall Cu clusters yield methane, while larger Cu nanoparticles - CO and multicarbon products.

Janis Timoshenko, Clara Rettenmaier, Dorottya Hursán, Martina Rüscher, Eduardo Ortega, Antonia Herzog, Timon Wagner, Arno Bergmann, Uta Hejral, Aram Yoon, Andrea Martini, Eric Liberra, Mariana Cecilio de Oliveira Monteiro, Beatriz Roldan Cuenya