Tris(2‐benzimidazolylmethyl)amine‐Directed Synthesis of Single‐Atom Nickel Catalysts for Electrochemical CO Production from CO₂

Abstract

The electrochemical reduction of carbon dioxide (CO ) to value-added products is a promising approach to reducing excess CO in the atmosphere. However, the development of electrocatalysts for highly selective and efficient electrochemical CO reduction has been challenging because protons are usually easier to reduce than CO in an aqueous electrolyte. Recently, single-atom catalysts (SACs) have been suggested as candidate CO reduction catalysts due to their unique catalytic properties. To prepare single-atom metal active sites, the stabilization of metal atoms over conductive supports such as graphene sheets to prevent metal aggregation is crucial. To address this issue, a facile method was developed to prepare single-atom nickel active sites on reduced graphene oxide (RGO) sheets for the selective production of carbon monoxide (CO) from CO . The tris(2-benzimidazolylmethyl)amine (NTB) ligand was introduced as a linker that can homogeneously disperse nickel atoms on the graphene oxide (GO) sheets. Because the NTB ligands form strong interactions with the GO sheets by π-π interactions and with nickel ions by ligation, they can effectively stabilize nickel ions on GO sheets by forming Ni(NTB)-GO complexes. High-temperature annealing of Ni(NTB)-GO under inert atmosphere produces nickel- and nitrogen-doped reduced graphene oxide sheets (Ni-N-RGO) with single-atom Ni-N active sites. Ni-N-RGO shows high CO reduction selectivity in the reduction of CO to CO with 97 % faradaic efficiency at -0.8 V vs. RHE (reversible hydrogen electrode).

Transition metal-based catalysts for the electrochemical CO2reduction: from atoms and molecules to nanostructured materials

“…For instance, the annealing of a Ni complex with a flexible tripodal nitrogen ligand led to a SAC containing distorted square-planar Ni II -N 4 species uniformly dispersed over GO sheets, which displayed superior CO 2 RR performance than the molecular derivative. 316 The presence of GO in the synthetic process was found to play an essential role in preventing the formation of metallic bulk NPs which reduce the catalytic activity.…”

“…In contrast to the superior CO 2 RR performances displayed by the heterogenized molecular Co phthalocyanine complexes in comparison with derivatives containing other metals, 204 Co-N-C SACs (especially Co-N 4 sites) are typically intrinsically less selective for CO 2 RR than their Ni and Fe analogs, resulting in lower faradaic yields for CO production. 297,337 This behavior is generally due to the predominant competitive HER process on Co-N-C catalysts, 316,358 related to unfavorable *H adsorption energies and higher energetic barriers for *CO desorption as compared to the Fe and Ni analogues. 306,314,318 Notably, the lower selectivity displayed by atomically dispersed Co-N 4 sites versus the Ni counterparts reflects the different reactivity of molecular Ni and Co systems based on tetraazamacrocyclic ligands.…”

Reduced graphene oxide‐based materials for electrochemical energy conversion reactions

“…In this situation, rGO can be a promising candidate substrate to achieve electroactive single atom catalysts . Nam group reported a new strategy to synthesize single‐atom nickel sites over N‐doped rGO sheets using tris(2‐benzimidazolylmethyl)amine (NTB) ligand for stabilization . First, NTB ligands were adsorbed onto the GO sheets, resulting in self‐assembly of the GO sheets.…”

Recent Progress in Self‐Supported Catalysts for CO2 Electrochemical Reduction

“…In recent years, carbon‐based materials have been used as promising CO 2 RR electrocatalysts with remarkable efficiency, high selectivity, and long‐time stability. Carbon‐based materials have unique properties, e.g., massive resources, high specific surface area, tailorable porous structures, excellent stability, and ideal nonpollution 91–107. Benefiting from these outstanding advantages, carbon‐based materials are considered to be one of most promising self‐supported CO 2 RR electrocatalysts.…”