Sub-Nanoscale Electrocatalyst Design for Enhanced CO2 Conversion

Abstract

The majority of today's research in electrochemical catalysis is centered in designing catalyst materials and processes that can surpass the current benchmarks of the classical catalysis. However, developments of the performance parameters of the important electrochemical reaction such as CO2 reduction reaction has been sluggish due to the intrinsic limitations such as adsorption energy scaling relations of the intermediate species.1 Recently, theoretical and experimental studies have revealed that the electrochemical reactions confined within a very small space with a wall separation under 1 nanometer outperforms the reactions without confinement.2-4 Theoretical models suggested that the enhancement from the nanoscopic confinement arises from the electronic interaction of the adsorbed species with multiple surfaces, which breaks the adsorption energy scaling relations of the important intermediate species.2

As a proof-of-concept, we synthesized novel copper oxide (CuOx) nanoparticles (NP) and tin oxide (SnOx) NP with highly controlled sub-nanoscale interplanar gaps of widths <1 nm via the lithium electrochemical tuning method. Transmission electron microscopy (TEM) and 3D tomo-scanning TEM (STEM) analysis confirm the presence of a distinct segmentation pattern and the newly engineered interparticle confined space in the designed catalysts. Atomic-gap controlled to 5-6 Å CuOx allows a current density exceeding that of unmodified CuOx nanoparticles by about 12 folds and a Faradaic efficiency of ≈80% to C2+.3 Separately, lithiated SnOx exhibits a significant increase in CO2RR vs. hydrogen evolution selectivity by a factor of ~5 with 20% higher formate selectivity relative to pristine SnO2 NPs at −1.2 VRHE.4 Density functional theory calculations indicate that the enhanced performance is attributable to a gap-stabilization of the rate-limiting *COOH and/or *OCHO intermediates. These results highlight the potential of controlled atomic spaces in directing electrochemical reaction selectivity and the design of highly optimized catalytic materials.