Identification of Single-Atom Ni Site Active toward Electrochemical CO₂ Conversion to CO

Abstract

Electrocatalytic conversion of CO2 into value-added products offers a new paradigm for a sustainable carbon economy. For active CO2 electrolysis, the single-atom Ni catalyst has been proposed as promising from experiments, but an idealized Ni–N4 site shows an unfavorable energetics from theory, leading to many debates on the chemical nature responsible for high activity. To resolve this conundrum, here we investigated CO2 electrolysis of Ni sites with well-defined coordination, tetraphenylporphyrin (N4–TPP) and 21-oxatetraphenylporphyrin (N3O–TPP). Advanced spectroscopic and computational studies revealed that the broken ligand-field symmetry is the key for active CO2 electrolysis, which subordinates an increase in the Ni redox potential yielding NiI. Along with their importance in activity, ligand-field symmetry and strength are directly related to the stability of the Ni center. This suggests the next quest for an activity–stability map in the domain of ligand-field strength, toward a rational ligand-field engineering of single-atom Ni catalysts for efficient CO2 electrolysis.

Scalable two-step annealing method for preparing ultra-high-density single-atom catalyst libraries

“…As a proof of concept, we chose to evaluate the catalytic performance of the UHD-SACs in the electrochemical CO 2 reduction to carbon monoxide, an application where nickel single atoms demonstrate promising technical potential 35,36 . For the Ni 1 /NC catalyst, the only products detected are gas-phase CO and H 2 and no liquids in the voltage range from 0 to -1.15 V versus RHE.…”

The atomic-level regulation of single-atom site catalysts for the electrochemical CO2 reduction reaction

“…In addition to metal phthalocyanines, some other molecular complexes, such as metal porphyrins, also have a defined M–N 4 structure. Kim et al reported carbon substrate supported Ni molecular complexes with two different porphyrins ligands, tetraphenylporphyrin (N 4 –TPP) and 21-oxatetraphenylporphyrin (N 3 O-TPP) 88 Spectroscopic and computational studies of Ni–N 4 -TPP and Ni(–Cl)–N 3 O-TPP revealed that the destruction of the ligand field symmetry could increase the redox potential from 0 to +1, leading to a better performance in the CO 2 RR. The additional ligand for the central atoms could also be a modification strategy to regulate the interfacial electronic structure from the axial direction.…”

Integrating Single Atoms with Different Microenvironments into One Porous Organic Polymer for Efficient Photocatalytic CO2 Reduction

“…[ 4 ] The recent implementation of SACs into CO 2 reduction has proven that the microenvironments and electronic properties of single‐atom active centers are essential for catalytic activity. [ 5 ] Up to now, pioneering work have reported several strategies to modulate the local structure of single‐atom active sites and compare their catalytic performance on CO 2 conversion, such as designing molecular catalysts, [ 6 ] carbonization of functionalized precursors, [ 7 ] or tuning coordination number of metal centers supported on metal organic layers. [ 8 ] Despite of these developments, these methods either suffered from tedious synthetic process or indirectly controlled SACs configuration at atomic level.…”