Layered Confinement Reaction: Atomic-level Dispersed Iron-Nitrogen Co-Doped Ultrathin Carbon Nanosheets for CO2 Electroreduction

Modulating the Structure and Composition of Single-Atom Electrocatalysts for CO2 reduction

Electrochemical CO2 reduction reaction (eCO2 RR) is a promising strategy to achieve carbon cycling by converting CO2 into value-added products under mild reaction conditions. Recently, single-atom catalysts (SACs) have shown enormous potential in eCO2 RR due to their high utilization of metal atoms and flexible coordination structures. In this work, the recent progress in SACs for eCO2 RR is outlined, with detailed discussions on the interaction between active sites and CO2 , especially the adsorption/activation behavior of CO2 and the effects of the electronic structure of SACs on eCO2 RR. Three perspectives form the starting point: 1) Important factors of SACs for eCO2 RR; 2) Typical SACs for eCO2 RR; 3) eCO2 RR toward valuable products. First, how different modification strategies can change the electronic structure of SACs to improve catalytic performance is discussed; Second, SACs with diverse supports and how supports assist active sites to undergo catalytic reaction are introduced; Finally, according to various valuable products from eCO2 RR, the reaction mechanism and measures which can be taken to improve the selectivity of eCO2 RR are discussed. Hopefully, this work can provide a comprehensive understanding of SACs for eCO2 RR and spark innovative design and modification ideas to develop highly efficient SACs for CO2 conversion to various valuable fuels/chemicals.

Enhanced Electrocatalytic CO2 Reduction Reactivity of S- and N-Doped Fe-Embedded Graphene

In this work, we studied the reaction mechanisms for CO2 reduction reaction (CRR) on the iron-doped graphene and its coordinating sulfur (S) and nitrogen (N) variants, FeNn S4-n (n=1-4), using density functional theory calculations. Our results revealed that the electronic property and catalytic reactivity of the surfaces can be tuned by varying the N and S atoms ratio. The CRR activities of the mixed surfaces, FeN3 S1 , FeN2 S2 , and FeN1 S3 , were better than FeN4 and FeS4 , where the absolute value of the limiting potential of the mixed surface decreased by 0.3 V. Considering the stability, we suggest FeN3 S surface to be favorable for CRR. For the bare surfaces, we found a positive linear correlation between the magnetic moment and the charge of Fe metal. For these surfaces, the reduction of CO (*CO+(H+ +e- )→*CHO) was important in deciding the limiting potential. We found that the adsorption energy of CO displayed a volcano relationship with the magnetic moment of the Fe atom. The study showed that the change of local coordinating structure around the Fe atom could modify the electronic and magnetic properties of the active Fe center and improve the CRR activity performance.

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

The global warming and the dangerous climate change arising from the massive emission of CO2 from the burning of fossil fuels have motivated the search for alternative clean and sustainable energy sources. However, the industrial development and population necessities make the decoupling of economic growth from fossil fuels unimaginable and, consequently, the capture and conversion of CO2 to fuels seems to be, nowadays, one of the most promising and attractive solutions in a world with high energy demand. In this respect, the electrochemical CO2 conversion using renewable electricity provides a promising solution. However, faradaic efficiency of common electro-catalysts is low, and therefore, the design of highly selective, energy-efficient, and cost-effective electrocatalysts is critical. Carbon-based materials present some advantages such as relatively low cost and renewability, excellent electrical conductivity, and tunable textural and chemical surface, which show them as competitive materials for the electro-reduction of CO2. In this review, an overview of the recent progress of carbon-based electro-catalysts in the conversion of CO2 to valuable products is presented, focusing on the role of the different carbon properties, which provides a useful understanding for the materials design progress in this field. Development opportunities and challenges in the field are also summarized.

Engineering Atomically Dispersed FeN4 Active Sites for CO2 Electroreduction

Atomically dispersed FeN₄ active sites have exhibited exceptional catalytic activity and selectivity for the electrochemical CO₂ reduction reaction (CO2RR) to CO. However, the understanding behind the intrinsic and morphological factors contributing to the catalytic properties of FeN₄ sites is still lacking. By using a Fe-N-C model catalyst derived from the ZIF-8, we deconvoluted three key morphological and structural elements of FeN₄ sites, including particle sizes of catalysts, Fe content, and Fe-N bond structures. Their respective impacts on the CO2RR were comprehensively elucidated. Engineering the particle size and Fe doping is critical to control extrinsic morphological factors of FeN₄ sites for optimal porosity, electrochemically active surface areas, and the graphitization of the carbon support. In contrast, the intrinsic activity of FeN₄ sites was only tunable by varying thermal activation temperatures during the formation of FeN₄ sites, which impacted the length of the Fe-N bonds and the local strains. The structural evolution of Fe-N bonds was examined at the atomic level. First-principles calculations further elucidated the origin of intrinsic activity improvement associated with the optimal local strain of the Fe-N bond.

Transition metal-based catalysts for the electrochemical CO2 reduction: from atoms and molecules to nanostructured materials

An overview of the main strategies for the rational design of transition metal-based catalysts for the electrochemical conversion of CO₂, ranging from molecular systems to single-atom and nanostructured catalysts.

A redox interaction-engaged strategy for multicomponent nanomaterials

The review article focuses on the redox interaction-engaged strategy that offers a powerful way to construct multicomponent nanomaterials with precisely-controlled size, shape, composition and hybridization of nanostructures.

Electrochemical CO2 Reduction to C1 Products on Single Nickel/Cobalt/Iron-Doped Graphitic Carbon Nitride: A DFT Study

Electrocatalytic CO₂ reduction reaction (CRR) is one of the most promising strategies to convert greenhouse gases to energy sources. Herein, the CRR was applied towards making C₁ products (CO, HCOOH, CH₃ OH, and CH₄ ) on g-C₃ N₄ frameworks with single Ni, Co, and Fe introduction; this process was investigated by density functional theory. The structures of the electrocatalysts, CO₂ adsorption configurations, and CO₂ reduction mechanisms were systematically studied. Results showed that the single Ni, Co, and Fe located from the corner of the g-C₃ N₄ cavity to the center. Analyses of the adsorption configurations and electronic structures suggested that CO₂ could be chemically adsorbed on Co-C₃ N₄ and Fe-C₃ N₄ , but physically adsorbed on Ni-C₃ N₄ . The H₂ evolution reaction (HER), as a suppression of CRR, was investigated, and results showed that Ni-C₃ N₄ , Co-C₃ N₄ , and Fe-C₃ N₄ exhibited more CRR selectivity than HER. CRR proceeded via COOH and OCHO as initial protonation intermediates on Ni-C₃ N₄ and Co/Fe-C₃ N₄ , respectively, which resulted in different C₁ products along quite different reaction pathways. Compared with Ni-C₃ N₄ and Fe-C₃ N₄ , Co-C₃ N₄ had more favorable CRR activity and selectivity for CH₃ OH production with unique rate-limiting steps and lower limiting potential.