Real‐Time Mimicking the Electronic Structure of N‐Coordinated Ni Single Atoms: NiS‐Enabled Electrochemical Reduction of CO₂ to CO

Abstract

as a side reaction, thereby diminishing the selectivity of the CO 2 RR. To increase the selectivity and catalytic activity of the CO 2 RR, several materials, such as Ag, Cu, Au, Sn, N-coordinated Ni single atoms (NiNC), FeNC, and so on have been reported as electrochemical catalysts. [4][5][6][7][8][9][10][11][12] These catalysts possess high H* chemisorption energies and moderate *COOH chemisorption energies, suppressing the HER and accelerating formation of carbonaceous products. In contrast, other materials such as bulk Ni and Pt have low H* chemisorption energies, exhibiting small kinetic barrier and high selectivity for the HER. [2,13,14] Single-atom catalysts have attracted significant attention from researchers because their properties significantly differ from those of bulk materials. Many previous studies focused on determining efficient designs of single-atom catalysts to maximize their activity. [4,15,16] Generally, a NiNC catalyst has a structure in which a support N atoms surrounds the center of a single Ni atom, exhibiting outstanding catalytic activity, unlike bulk N-coordinated Ni single atom (Ni-NC) is one of the best catalysts for the CO 2 reduction reaction (CO 2 RR) to produce CO. However, no bulk Ni materials have exhibited high catalytic activity for CO 2 RR. Herein, it is shown that NiS nanoparticles mimicking the electronic structure of Ni-NC in real-time enhance the CO 2 RR activity in a zero-gap electrolyzer. In situ/Operando X-ray absorption spectroscopy suggests that under a cathodic potential, the electronic structure of NiS changes similarly to that of Ni-NC and modulated O x-z S y ligands with similar properties to Ni ligands, resulting in a mimicked electronic structure. However, NiS exhibits low stability owing to the loss of S species, key to mimicking N ligands. The future challenges in finding a stable mimicked electronic structure are discussed. Moreover, this work provides new insights into the development of catalysts from materials that have not generally been considered previously.

Integrating Electrochemical CO2 Reduction on α-NiS with the Water or Organic Oxidations by Its Electro-Oxidized NiO(OH) Counterpart to an Artificial Photosynthetic Scheme

“…Recent studies on CO 2 R with Cu 2 Se have shown that the presence of Se 2– with Cu­(I) resulted in ligand (Se)-to-metal (Cu) back-bonding, which increases the electron density on Cu to have better CO adsorption . In the NiS or CuS nanoparticle studied as the cathode for CO 2 R, the metal center acted as the active species for reduction, while they initially reduced to Ni 0 /Cu 0 . A partial loss of sulfide from the NiS structure may also be associated with the reduction …”

“…In the NiS or CuS nanoparticle studied as the cathode for CO 2 R, the metal center acted as the active species for reduction, while they initially reduced to Ni 0 /Cu 0 . A partial loss of sulfide from the NiS structure may also be associated with the reduction …”

Operandocharacterization of continuous flow CO2electrolyzers: current status and future prospects

“…X-ray absorption spectroscopy is currently the most widely applied operando spectroscopy to study the evolution of catalyst structure during CO 2 RR under high current density conditions. 18,113,115,118–123 Because of its great compatibility with flow cell designs, the operando measurement requires only minor cell modifications (Fig. 5).…”

“…12 Ni–N–C materials were found to be excellent catalysts for CO production, but their long-term stability is a major issue, particularly at high current densities. 18,68,121 This might be overcome by understanding the evolution of the active metal sites during operation. A catalyst containing dinuclear Ni 2 sites anchored on a N–C matrix exhibited 94.3% FE towards CO at 150 mA cm −2 current density in a microfluidic flow cell.…”

“…16 As it became clear that the CO 2 RR has relevance for industrialization, electrolyzer development had also become a focus of research. Researchers concentrating on catalyst development tend to benchmark their catalysts in flow electrolyzers too 17,18 to demonstrate the potential for practical application, already at the early stage of catalyst development. Several cell designs exist for low temperature CO 2 electrolysis, 16 which differ in the presence/absence of electrolytes and ion transport characteristics among others.…”