Confining Chainmail-Bearing Ni Nanoparticles in N-doped Carbon Nanotubes for Robust and Efficient Electroreduction of CO2

Doping and defect engineering in carbon-based electrocatalysts for enhanced electrochemical CO2 reduction: From 0D to 3D materials

The increasing atmospheric CO2 levels and the urgent need for sustainable energy solutions have driven research into electrochemical CO2 reduction. Carbon-based materials have received significant attention for their potential as electrocatalysts, yet their inert nature often limits their performance. Defect engineering and heteroatom doping have emerged as transformative approaches to overcome these limitations, enhancing both catalytic activity and Faradaic efficiency. This review systematically examines the role of these strategies across diverse carbon materials, including graphene, carbon nanotubes, carbon dots, and boron-doped diamond. Special attention is given to the incorporation of heteroatoms, such as nitrogen and boron, and the modulation of defect structures to optimize CO2 reduction pathways. By exploring the interplay between dopant type, defect density, and material dimensionality, we provide a comprehensive understanding of how tailored carbon-based electrocatalysts can drive advancements in sustainable electrochemical CO2 conversion. This work underscores the potential of defect-engineered and doped carbon materials to revolutionize the field of electrocatalysis, paving the way for innovative solutions to environmental and energy challenges.

Guanine-derived carbon nanosheet encapsulated Ni nanoparticles for efficient CO2 electroreduction

Developing novel electrocatalysts for achieving high selectivity and faradaic efficiency in the carbon dioxide reduction reaction (CO2RR) poses a major challenge. In this study, a catalyst featuring a nitrogen-doped carbon shell-coated Ni nanoparticle structure is designed for efficient carbon dioxide (CO2) electroreduction to carbon monoxide (CO). The optimal Ni@NC-1000 catalyst exhibits remarkable CO faradaic efficiency (FECO) values exceeding 90% across a broad potential range of -0.55 to -0.9 V (vs. RHE), and attains the maximum FECO of 95.6% at -0.75 V (vs. RHE) in 0.5 M NaHCO3. This catalyst exhibits sustained carbon dioxide electroreduction activity with negligible decay after continuous electrolysis for 20 h. More encouragingly, a substantial current density of 200.3 mA cm-2 is achieved in a flow cell at -0.9 V (vs. RHE), reaching an industrial-level current density. In situ Fourier transform infrared spectroscopy and theoretical calculations demonstrate that its excellent catalytic performance is attributed to highly active pyrrolic nitrogen sites, promoting CO2 activation and significantly reducing the energy barrier for generating *COOH. To a considerable extent, this work presents an effective strategy for developing high-efficiency catalysts for electrochemical CO2 reduction across a wide potential window.

Cooperative adsorption of interfacial Ga-N dual-site in GaOOH@N-doped carbon nanotubes for enhanced electrocatalytic reduction of carbon dioxide

To reduce activation energy barrier and promote the kinetics of electrocatalytic CO2 reduction reaction (eCO2RR), the performance of CO2 adsorption and activation on electrocatalysts should be optimized. Here, GaOOH is successfully coupled with N-doped carbon nanotubes (NC) via a facile self-assembly-calcination process. The obtained GaOOH@N-doped carbon nanotubes (Ga-NC) display the best CO faradaic efficiency of 96.1 % at -0.6 V (vs. reversible hydrogen electrode). Control-experiment and characterization results suggest Ga-N dual-site in interface between GaOOH and NC shows cooperative adsorption of CO2. C atom in CO2 is adsorbed on N site while O atom in CO2 is adsorbed on Ga site. This cooperative adsorption efficiently promotes the CO2 adsorption and activation performance, as well as the breaking of CO bond due to opposite attraction from Ga-N dual-site. Moreover, in-situ Fourier transform infrared spectroscopy confirms decreased reaction barrier for formation of *CO2- and *COOH intermediates. This work inspires us to construct interfacial dual-site structure with cooperative adsorption property for promoting eCO2RR activity.

Elucidating the origin of catalytic activity of nitrogen-doped carbon coated nickel toward electrochemical reduction of CO2

Converting CO2 into valuable chemicals and fuels through clean and renewable energy electricity provides a way to achieve sustainable development for human societies. In this study, carbon coated nickel catalysts (Ni@NCT) were prepared by solvothermal and high-temperature pyrolysis methods. A series of Ni@NC-X catalysts were obtained by pickling with different kinds of acids for electrochemical CO2 reduction reaction (ECRR). The results show that Ni@NC-N treated with nitric acid has the highest selectivity but lower activity, Ni@NC-S treated with sulfuric acid has the lowest selectivity, and Ni@NC-Cl treated with hydrochloric acid shows the best activity and good selectivity. At -1.16 V, Ni@NC-Cl has a considerable CO yield of 472.9 μmol h-1 cm-2, which is significantly superior to Ni@NC-N (327.5), Ni@NC-S (295.6) and Ni@NC (270.8). The controlled experiments show that there is a synergistic effect between Ni and N. The chlorine adsorbed on the surface can promote the performance of ECRR. The poisoning experiments indicate that the contribution of surface Ni atoms to the ECRR is very small, and the increase of activity is mainly due to the nitrogen doped carbon coated Ni particles. The relationship between activity and selectivity of ECRR on different acid-washed catalysts was correlated by theoretical calculations for the first time, which is also in good agreement with the experimental results.

Ultrathin Nitrogen-Doped Carbon Encapsulated Ni Nanoparticles for Highly Efficient Electrochemical CO2 Reduction and Aqueous Zn-CO2 Batteries

Electrochemical CO₂ reduction reaction (CO₂ RR), powered by renewable electricity, has attracted great attention for producing high value-added fuels and chemicals, as well as feasibly mitigating CO₂ emission problem. Here, this work reports a facile hard template strategy to prepare the Ni@N-C catalyst with core-shell structure, where nickel nanoparticles (Ni NPs) are encapsulated by thin nitrogen-doped carbon shells (N-C shells). The Ni@N-C catalyst has demonstrated a promising industrial current density of 236.7 mA cm^-2 with the superb FE_CO of 97% at -1.1 V versus RHE. Moreover, Ni@N-C can drive the reversible Zn-CO₂ battery with the largest power density of 1.64 mW cm^-2 , and endure a tough cycling durability. These excellent performances are ascribed to the synergistic effect of Ni@N-C that Ni NPs can regulate the electronic microenvironment of N-doped carbon shells, which favor to enhance the CO₂ adsorption capacity and the electron transfer capacity. Density functional theory calculations prove that the binding configuration of N-C located on the top of Ni slabs (Top-Ni@N-C) is the most thermodynamically stable and possess a lowest thermodynamic barrier for the formation of COOH^* and the desorption of CO. This work may pioneer a new method on seeking high-efficiency and worthwhile electrocatalysts for CO₂ RR and Zn-CO₂ battery.

Recent Advances of the Confinement Effects Boosting Electrochemical CO2 Reduction

Powered by clean and renewable energy, electrocatalytic CO₂ reduction reaction (CO₂ RR) to chemical feedstocks is an effective way to mitigate the greenhouse effect and artificially close the carbon cycle. However, the performance of electrocatalytic CO₂ RR was impeded by the strong thermodynamic stability of CO₂ molecules and the high susceptibility to hydrogen evolution reaction (HER) in aqueous phase systems. Moreover, the numerous reaction intermediates formed at very near potentials lead to poor selectivity of reaction products, further preventing the industrialization of CO₂ RR. Catalysis in confined space can enrich the reaction intermediates to improve their coverage at the active site, increase local pH to inhibit HER, and accelerate the mass transfer rate of reactants/products and subsequently facilitate CO₂ RR performance. Therefore, we summarize the research progress on the application of the confinement effects in the direction of CO₂ RR in theoretical and experimental directions. We first analyzed the mechanism of the confinement effect. Subsequently, the confinement effect was discussed in various forms, which can be characterized as an abnormal catalytic phenomenon due to the relative limitation of the reaction region. In specific, based on the physical structure of the catalyst, the confinement effect was divided in four categories: pore structure confinement, cavity structure confinement, active center confinement, and other confinement methods. Based on these discussions, we also have summarized the prospects and challenges in this field. This review aims to stimulate greater interests for the development of more efficient confined strategy for CO₂ RR in the future.