Synthesis of a Nickel Single-Atom Catalyst Based on Ni–N_4–xC_x Active Sites for Highly Efficient CO₂ Reduction Utilizing a Gas Diffusion Electrode

Abstract

A Ni single-atom catalyst with Ni–N4–x C x active sites is prepared in a single pyrolysis step in which the Ni single atom is incorporated in the carbon framework through nitrogen and carbon coordination utilizing the ionothermal synthesis method. In comparison to the complicated synthesis procedures of single-atom catalysts, this method provides a general and facile method to obtain single-atom catalysts with an opportunity to synthesize catalysts at a large scale. The precursors used in this method such as adenine, fructose, and glucose are derived from the biomass which is the essential requirement for a green process. The synthetic procedure developed here enables tunable properties of the catalysts, such as the density of active sites and characteristics of the carbon framework. In this study, the catalytic properties of our materials are investigated for an electrochemical CO2 reduction reaction. The overall catalytic activity of the catalyst depends on the density of active sites, but the properties of the carbon framework also affect the intrinsic activity of the catalyst. From the commercial prospect, a Ni single-atom catalyst with a high density of Ni–N4–x C x active sites can achieve a current density of −300 mA cm–2 with a CO faradaic efficiency of 99.4% at an overpotential of 235 mV in a gas diffusion electrode cell system.

From CO2 to Value-Added Products: A Review about Carbon-Based Materials for Electro-Chemical CO2 Conversion

“…It also reports a much lower over potential equal to 50 mV. At the same time, Abbas and co-workers [141] used as a carbon and nitrogen precursor a molecule derived from biomass such as lignin and cellulose called adenine, which contains equal molar ratios of C and N. The adenine was taken together with the Ni precursor to a pyrolysis process varying the temperature among 800, 900 and 1000 • C to optimize the amount of nickel and nitrogen in the electrochemical performance. However, the sample synthesized at a temperature of 800 • C proved to be the optimal one with respect to its physicochemical and electrochemical properties, since it presented a high density of Ni-N 4-x -C x type active sites located in the carbon support frameworks, which allowed obtaining a superior electrochemical performance with a high current density −300 mA/cm 2 , an FE (CO) = 99.4% at a low over potential of 235 mV.…”

“…Recent research [139][140][141] highlights two important points to consider when designing single atoms catalysts, as they have been overlooked so far: (1) The first point is that in addition to taking into consideration the formation of catalytic sites, it is crucial to also study the structural geometry of the carbon matrix because it also plays a key role in the catalytic activity since the structure can influence the coordination environment of the single atoms [118,142,143]. Hollow N-doped carbon spheres are a type of support in which individual atoms can be immobilized and their synthesis process allows good control in the design of the catalyst structure.…”

Race on High‐loading Metal Single Atoms and Successful Preparation Strategies

“…[8] (Figure 5e is reproduced with permission from Ref. [8] Copyright 2021 Elsevier) nanoparticles usually occur, [179] and several steps of acid treatment are still needed. On the other hand, slight modification of the general procedures can further increase the metal loading.…”

Electrocatalytic Reduction of Low Concentrations of CO2 Gas in a Membrane Electrode Assembly Electrolyzer

“…Electrochemical CO 2 reduction (CO 2 R) producing valuable chemicals is a promising technology for mitigating the global climate crisis and developing new processes for chemical production. − The recent development of an electrolyzer gave a remarkable advancement of CO 2 R performance in production rate and selectivity. − In particular, a zero-gap membrane electrode assembly electrolyzer (MEA) whose electrodes and membrane are assembled without a catholyte has been studied as a promising configuration for stackable applications. − Most research has been conducted using a pure CO 2 stream (>99%) as the feedstock, but flue gases generally contain 5–40% of CO 2 primarily diluted by N 2 . Furthermore, the production of pure CO 2 requires a cost-intensive process, including energy-intensive CO 2 capture. ,− The direct conversion of flue gas has economic advantages, but technological issues must be overcome, including competitive oxygen reduction reactions, poisoning by toxic impurities, and poor CO 2 R performance limited by low concentrations of the CO 2 feedstock. ,,− …”

“…As an alternative CO production catalyst, a Ni single-atom catalyst (Ni-N/C) has recently attracted attention because of its competitively superior CO selectivity associated with a preferable intermediate interaction for the CO 2 R over the hydrogen evolution reaction (HER) in comparison to other metal-incorporated single-atom catalysts. ,,− Ni-N/C demonstrated its outstanding performance, giving an FE CO value of ∼80% with a j CO value of −2.9 mA cm –2 at 15% CO 2 concentration in a H-cell system . However, further systematic studies are required to understand the dependence of the behavior on the CO 2 concentration and the controlling fundamentals in the MEA system, the most promising system for practical applications.…”