93% single-atom utilization in base-resistant metal–organic framework quantum dots for ampere-level CO2 electroreduction

Abstract

Single atoms confined in crystalline porous materials such as metal–organic frameworks (MOFs) feature unparallel multidimensional interactions with the molecular wall of nano-cavities, showcasing a synergistic catalytic effect. Nevertheless, the insulating nature and long yet narrow diffusion channels of MOFs render most single-atom mass/electrons inaccessible, resulting in an exceedingly low single-atom utilization efficiency. Herein, we propose downsizing MOF particles into quantum dots (QDs) to shorten the mass transfer route and amplify interfacial electron transfer. As a proof of concept, base-resistant MOF QDs with isolated Co atoms (PCN-QDs, ∼1.5 nm) were constructed for CO₂ electroreduction. A reduction in diffusion time by five orders of magnitude was realized compared to pristine MOF particles. A strong MOF QD-support electronic interaction was confirmed, which not only expedited interfacial electron transfer but also introduced electronic regulation in the Co atoms. Theoretical calculations showed greater electron accumulation on the Co atom and an up-shifted d-band center, resulting in a moderate adsorption strength for *COOH and *CO. Eventually, the PCN-QD delivered a record high single-atom utilization efficiency of 93.0% and manifested an FE_CO higher than 90.0% within the range of −0.13 to −1.05 V, even under an ampere-level current density (−0.95 A cm⁻²).