Nitrogen-doped Graphene Sheets Research Articles

Cobalt nanoclusters Deposit on Nitrogen-Doped graphene Sheets as bifunctional electrocatalysts for high performance lithium – Oxygen batteries

Rechargeable lithium-oxygen (Li-O2) batteries are being considered as the next-generation energy storage systems due to their higher theoretical energy density. However, the practical application of Li-O2 batteries is hindered by slow kinetics and the formation of side products during the oxygen reduction and evolution reactions on the cathode. These reactions lead to high overpotentials during charging and discharging. To address these challenges, we propose a simple ultrasonic method for synthesizing cobalt nanoclusters embedded in nitrogen-doped graphene nanosheets (GrZnCo) derived from metal-organic frameworks (MOFs). The resulting material, due to the retention of metallic cobalt structure, exhibits better electronic conductivity. Additionally, the GrZnCo catalyst shows vigorous catalytic activity, which can improve reaction kinetics and suppress side reactions, thus lowering the charging overpotential. We have investigated the impact of different catalyst compositions (GrZnCox; x = 1, 3, 5) by varying the amounts of cobalt and zinc. The optimum catalyst, GrZnCo3, contains high cobalt-N active components, graphitic-N, pyridinic-N, pyrrolic-N, and abundant defect structures, which enhance the electrochemical performance. The defect-rich GrZnCo3 catalyst enables Li-O2 batteries to achieve a high discharge capacity of 13500 mAh·g−1 at 50 mA·g−1 and a remarkable long-term cycling performance of over 400 cycles at 100 mA·g−1 with a limited capacity of 500 mAh·g−1. This work demonstrates an effective approach to fabricate cost-effective electrocatalysts for various energy storage systems.

Mechanistic Study of Highly Active Bifunctional Double-Atom Electrocatalysts for Oxygen Reduction and Oxygen Evolution Reactions.

Dual-atom catalysts (DACs) can be very effective for catalyzing both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, we present theoretical evidence of a new class of highly active DACs, namely, the double-atom embedded in nitrogen-doped graphene sheet 2M-N-C (M = Mn, Fe) on the basis of density functional theory calculations. Importantly, we find that the double active sites of 2M-N-C DACs entail an unconventional catalytic reaction pathway for ORR and OER. We also show that the local coordination environment of the active sites can significantly affect the stability and oxygen catalytic activity of 2M-N-C DACs. In particular, MnFe-N-C DAC not only exhibits good stability but also possesses outstanding bifunctional ORR/OER catalytic activity with the potential difference (ΔE) between the OER and ORR as low as 0.34 V, notably lower than most bifunctional electrocatalysts reported in the literature. This finding suggests a new strategy toward the design of stable and highly active bifunctional electrocatalysts for both ORR/OER.

Plasma-Driven Tuning of Dielectric Permittivity in Graphene.

Materials with tunable negative electromagnetic performance, i.e., where dielectric permittivity becomes negative, have long been pursued in materials research due to their peculiar electromagnetic (EM) characteristics. Here, this promising feature is reported in materials on the case of plasma-synthesized nitrogen-doped graphene sheets with tunable permittivity over a wide (1-40GHz) frequency range. Selectively incorporated nitrogen atoms in a graphene scaffold tailor the electronic structure in a way that provides an ultra-low energy (0.5-2eV) 2D surface plasmon excitation, leading to subunitary and negative dielectric constant values in the Ka-band, from 30 up to 40GHz. By allowing the tailoring of structures at atomic scale, this novel plasma-based approach creates a new paradigm for designing 2D nanomaterials like nanocarbons with controllable and tunable permittivity, opening a path to the next generation of 2D metamaterials.

N-graphene synthesized in astrochemical ices

In our quest for the presence of large complex molecules containing a majority of carbon in the interstellar medium (ISM), the search for graphene plays a central role due to its nature in making other carbon structures. Although the ingredients for graphene synthesis are present in the ISM, conclusive laboratory evidence of such formation is lacking. Therefore, in our laboratory experiments simulating the cold ISM conditions, we subjected icy mantles of benzonitrile, an aromatic with a cyanide side chain that has recently been detected in the interstellar medium, to vacuum ultraviolet photon irradiation. The irradiated ice was observed to leave a residue upon warming to room temperature. The residue was removed from the substrate and placed on a Quantifoil grid for electron microscopy analysis. Transmission electron microscopy showed quantum dots (QD) and nitrogen-doped graphene (N-Graphene) sheets. Diffraction and energy-dispersive X-ray spectroscopy revealed the crystalline nature and carbon–nitrogen composition, of the observed graphene sheet. This is the first evidence of QD and N-graphene synthesis in ice irradiation at interstellar temperatures.

Oxidative Cleavage of β-O-4 Linkage in Lignin via Co Nanoparticles Embedded in 3DNG as Catalyst.

The cleavage of β-O-4 linkage in lignin is one of the key steps for oxidative conversion of lignin to low-molecular-weight aromatics. Herein, Co nanoparticles embedded in three-dimensional network of nitrogen-doped graphene (Co/NG@3DNG-X) were prepared through an immersion-pyrolysis procedure, in which X denotes the pyrolysis temperature. The detailed characterization of Co/NG@3DNG-X shows that the Co nanoparticles are coated with a few layers of nitrogen-doped graphene (NG) sheets that are further embedded in 3DNG matrix. The catalytic activities of the Co/NG@3DNG-X for the oxidative cleavage of β-O-4 linkage in lignin model compounds with O2 as oxidant are explored. It is demonstrated that catalytic activities of as-prepared Co/NG@3DNG-X can be tuned by varying the pyrolysis condition, and the Co/NG@3DNG-900 shows the highest catalytic activity, which is attributed to the enriched Co-Nx species, the strong surface basicity, the high specific surface and the mesoporous motif of 3DNG network. More pronouncedly, the Co/NG@3DNG-900 can also effectively catalyze the oxidative cleavage of organosolv lignin, generating certain monomeric aromatics. Additionally, the intrinsic magnetic property of Co nanoparticles makes the Co/NG@3DNG-X be easily recovered from the reaction mixture, and the as-coated thin NG layer can protect Co nanoparticle from oxidation condition, which putting together afford the Co/NG@3DNG-X with good reusability and stability.

Intrinsically active capsaicin non-covalently modified nitrogen doped graphene for high-performance supercapacitors

Organic molecules with multi-electron redox active centers exhibit great potential in electrochemical storage. Immobilizing them on the graphene surface through π-π interaction can effectively improve the pseudocapacitance. Nature capsaicin (Cap) molecule, with redox active sites, is good benefit for enhance the capacitance performance of the nitrogen doped graphene (NG) by non-covalent modification. In this work, the Cap-functionalized NG (Cap-NG) is successfully prepared by one-step hydrothermal method combined with vacuum freeze-drying technology. The electrochemical measurements show that the optimal Cap-NG exhibits a high capacitance of 312 F g−1 at 1 Ag−1 and an excellent durable cycling life of 102.9 % after 10,000 charging/discharging cycle times at a current density of 20 Ag−1. Furthermore, the Cap-NG-based symmetrical supercapacitor (SSC) demonstrates an energy density of 8 Wh kg−1 at 596 W kg−1. Moreover, density functional theory (DFT) calculations are used to elaborate the origin of pseudocapacitance by researching the adsorption configuration, binding energy and charge storage mechanism of Cap on NG sheet as well as to calculate the density of states (Dos). This study further enriches the application of natural capsaicin molecule on energy storage, and provides another way to build a green and environment-friendly SCs.

Fullerene Transformed into a 3-D Structure of Nitrogen-Doped Few-Layer Graphene Sheets: Growth and Field Emission Properties

3-D-structured nitrogen-doped few-layer graphene sheets (3-D NFLGs) have been prepared using a fullerene C60 precursor combined with a microwave excited nitrogen plasma process. A deep understanding of the growth mechanism and regulating of morphology that can adjust the field emission properties is crucial for its widespread application. In this work, the detailed growth process and microstructure and the field emission properties of the as-synthesized vertical aligned 3-D NFLGs were studied. The growth of the 3-D NFLGs can be divided into three steps: evaporation of the C60, opening of the C60, and formation of the 3-D NFLGs. The growth process and morphology of the materials can be neatly regulated by changing the evaporating temperature of the C60, electron temperature of the plasma, and substrate temperature through our self-designed reaction equipment. Interestingly, the vertical 3-D NFLGs grew at a limited microwave power and nitrogen pressure and could be divided into three different morphological features, reflected in their distribution uniformity, interparietal distance, number of layers, and crystallinity, which exhibited different field emission properties. Additionally, the 3-D NFLGs were all in situ doped with ∼4% nitrogen atoms from nitrogen gas during the growth process, while different compositions of the nitrogen atoms were reflected in the graphitic N increasing with increasing nitrogen pressure. Furthermore, the field emission measurements show that the as-obtained vertical 3-D NFLGs exhibited the lowest turn-on electric field (1.30 V/μm@10 μA/cm2) and threshold field (2.1 V/μm@1 mA/cm2) at the M1 morphology and the highest stability at the M3 morphology. Remarkable field emission performance was obtained for the 3-D NFLGs with M2 morphology, showing their great potential for field emission applications.

Preparation of Nitrogen-doped Holey Multilayer Graphene Using High-Energy Ball Milling of Graphite in Presence of Melamine.

Holey graphene, consisting of graphene sheets with in-plane nanopores, has recently attracted more attention as it expands graphene applications to other fields inaccessible by the pristine graphene. To ensure an effective implementation of holey graphene in the market, it is crucial to explore new preparation methods that are simple, cost effective, eco-friendly, versatile, and scalable. While ball milling of graphite in presence of exfoliating agents was found very effective in the preparation of graphene (doped and undoped) and graphene-composites, this technique remains unexplored for the preparation of holey graphene. In the present work, Nitrogen-doped multilayer holey graphene sheets were prepared by an all-solid, one-step procedure based on high-energy ball milling of graphite as the starting material in presence of melamine in a shaker-type mill for 1 hour under ambient conditions. Melamine acted simultaneously as an exfoliating agent to enhance the exfoliation of graphene layers and a diluent to protect graphite against the continuous fragmentation into amorphous carbon during the high-energy "shock" mode of ball milling. The high-energy "shock" mode of ball milling of graphite in presence of melamine induced the formation of multilayer defective graphene as an intermediate product before being converted into N-doped multilayer holey graphene after the removal of the in-plane defects during the milling process. The characterization of the final product confirmed the formation of N-doped multilayer holey graphene with a content in nitrogen as high as 12.96 at.%, making it promising for energy storage and energy conversion applications.

Nitrogen-Doped Graphene Sheets as Efficient Nanofillers at Ultra-Low Content for Reinforcing Mechanical and Wear-Resistant Properties of Acrylic Polyurethane Coatings

The enhancement of the mechanical and wear-resistant properties of polymer coatings plays a vital role for their application in hostile serving environments, and nanofiller is effective for this purpose. Herein, we systematically investigate a new nanofiller, nitrogen-doped graphene sheets (NGSs), which possess a multilayer sheet-like morphology and share a good compatibility with water. After the incorporation of NGS into a waterborne polyurethane (WPU), the mechanical and wear-resistant properties of NGS/WPU composite coatings significantly improve, and wear resistance behaves best at an ultra-low content, reaching up to 0.005 wt% (50 ppm). Furthermore, Young’s modulus is elevated by 52.67% and tensile strength is appreciably boosted by 58.87%. Simultaneously, an apparent reduction of weight loss of 78.74% is observed in the abrasion testing, and the ductility of NGS/WPU composite films is reduced by 48.38%. These make it possible that an ultra-low content of nanofiller efficiently reinforces polymer-based composites, with low cost in the wear-resistance related field.

Tuning the catalytic activity of Ag7Au6 cluster for oxygen reduction reaction via support interactions

We investigate the suitability as oxygen reduction reaction (ORR) catalysts of Ag7Au6 clusters supported by nitrogen-doped graphene (N–graphene) sheets with two different nitrogen contents (3.61% and 8.43%), as well as TiO2(101) monolayers, using post–DFT methods. We employ two energetic descriptors (namely, the O2 and OH binding energies and O–O bond length), to compare the effect of two different supports on the catalytic activity of the Ag7Au6 cluster. We find that low adsorption energies for O2 (approximately −1 eV) and OH (below the one of its reaction on Pt), and O–O bond elongation (which reaches up to 1.34 Å in our study, corresponding to the superoxide bond length) cause the high ORR activity of our materials of interest. Our results show that the supported clusters have higher catalytic performance compared to the unsupported ones due to the lower binding energies of the O2 and OH molecules. Moreover, the TiO2(101) monolayer is a better support for the Ag7Au6 cluster, due to the O–O bond distance increasing up to 1.33 Å, facilitating O2 dissociation. In addition, the low (−0.35 eV) OH adsorption energy decreases the difficulty of OH removal. Through free energy calculations, we prove the ORR mechanism in acidic conditions to display an over-potential of −1.76 V, competitive with to the ones featured by currently available catalysts.

A comparison study on single metal atoms (Fe, Co, Ni) within nitrogen-doped graphene for oxygen electrocatalysis and rechargeable Zn-air batteries

Single atom catalysts (SACs) with atomically dispersed transition metals on nitrogen-doped carbon supports have recently emerged as highly active non-noble metal electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), showing great application potential in Zn-air batteries. However, because of the complex structure-performance relationships of carbon-based SACs in the oxygen electrocatalytic reactions, the contribution of different metal atoms to the catalytic activity of SACs in Zn-air batteries still remains ambiguous. In this study, SACs with atomically dispersed transition metals on nitrogen-doped graphene sheets (M-N@Gs, M = Co, Fe and Ni), featured with similar physicochemical properties and M-N@C configurations, are obtained. By comparing the on-set potentials and the maximum current, we observed that the ORR activity is in the order of Co-N@G > Fe-N@G > Ni-N@G, while the OER activity is in the order of Co-N@G > Ni-N@G > Fe-N@G. The Zn-air batteries with Co-N@G as the air cathode catalysts outperform those with the Fe-N@G and Ni-N@G. This is due to the accelerated charge transfer between Co-N@C active sites and the oxygen-containing reactants. This study could improve our understanding of the design of more efficient bifunctional electrocatalysts for Zn-air batteries at the atomic level.

Mechanism of Catalytic Transfer Hydrogenation for Furfural Using Single Ni Atom Catalysts Anchored to Nitrogen-Doped Graphene Sheets.

Catalytic transfer hydrogenation (CTH) of α,β-unsaturated aldehydes using single metal atom catalysts supported on nitrogen-incorporated graphene sheet (M-Nx-Gr) materials has attracted increasing attention recently, yet the reaction mechanism remains to be explored. Compared to the Ni-N4-Gr model in which the dissociation of isopropanol is highly unfavorable as a result of steric hindrance and inertness of the Ni-N4 site embedded in graphene, the Ni-N3 site in Ni-N3-Gr is more active and facilitates the formation of *H with isopropanol as the H donor, where the dissociation of H from isopropanol with an energy barrier of 0.83 eV is the rate-determining step. An alternative reaction path starts from the coadsorption of isopropanol and furfural molecules at the Ni-N3 site, followed by a direct hydrogen transfer between the two molecules; however, the rate-determining step has a much higher energy barrier of 1.32 eV. Our calculations suggest that the hydrogenation of the aldehyde group is kinetically more favorable than the C═C hydrogenation, revealing the high chemoselectivity of furfural to furfuryl alcohol. Our investigations reveal that the CTH mechanism using the Ni-N3-Gr catalyst is different from that on traditional metal oxides, where the former has only one single active site, while two active sites are required for the latter. The proposed reaction mechanism of CTH for furfural in this study should be helpful to guide the design of single metal atom catalysts with appropriate N coordination for application in chemoselective hydrogenation reactions.

A powerful approach to develop nitrogen-doped graphene sheets: theoretical and experimental framework

A powerful approach to develop nitrogen-doped graphene sheets: theoretical and experimental framework

A facile one-pot synthesis of magnetic iron oxide nanoparticles embed N-doped graphene modified magnetic screen printed electrode for electrochemical sensing of chloramphenicol and diethylstilbestrol.

Trace determination of antibacterial agents is crucial to minimize risks of human intoxication and in the prevention of serious environmental impacts. Herein, a simple one-pot solvothermal synthesis approach for a magnetic iron oxide embed nitrogen-doped graphene (MIO@NG) nanohybrid was fabricated without the addition of any extra reductant and its application towards ultrasensitive chloramphenicol (CAP) and diethylstilbestrol (DES) electrochemical sensor is demonstrated to screen for antibiotic residue contamination in milk samples. The prepared nanohybrid was modified on a magnetic screen-printed electrode (MSPE) to make it portable for on-site detection. The determination of two additive drugs, CAP and DES, was achieved based on the reduction current response at MIO@NG modified MSPE (MIO@NG/MSPE) to eliminate interference as far as possible. Uniform dispersed MIO nanoparticles are grown in situ on the surface of nitrogen-doped graphene sheets. The morphology of MIO@NG was confirmed by transmission electron microscopy (TEM) analysis. The chemical structure of the prepared MIO@NG was characterized by x-ray diffraction (XRD), x-ray photoemission spectroscopy (XPS), Raman spectroscopy, and extended x-ray absorption fine structure (EXAFS). Moreover, the superparamagnism property was investigated by vibrating sample magnetometry (VSM). The electrochemical properties of MIO@NG were evaluated with cyclic voltammetry (CV) and square wave voltammetry (SWV). Sensor performance was evaluated by testing the electrochemical activity of CAP and DES in the presence of interferences. The MIO@NG modified electrode presented superior electrochemical performance, including high sensitivity, high catalytic activity, ultimate sensitivity, very fast detection, selectivity, and excellent performance. The MIO@NG modified electrode demonstrated a detection limit of 10nM for the detection of CAP and 6.5nM for DES with satisfactory recovery in real samples.

N-Graphene Sheet Stacks/Cu Electrocatalyst for CO2 Reduction to Ethylene

Renewable energy resources (wind, solar) are unpredictable, so it is wise to store the electricity they generate in an energy carrier X. Various PtX (power to useful energy-intensive raw material such as hydrogen, synthetic natural gas, fuel) applications have been proposed. At the heart of our work is widely used idea to convert residual CO2 from biogas plant into higher hydrocarbons using electricity from renewables (e.g., sun, wind, hydro). The specific goal is to produce ethylene-highly demanded hydrocarbon in plastics industry. The process itself is realised on electrocatalytic carbon/copper cathode which must be selective to reaction: 2CO2 + 12e− + 12H+→C2H4 + 4H2O. We propose a bottom-up approach to build catalyst from the smallest particles-graphene sheet stacks (GSS) coated with metallic copper nanocrystals. Composite GSS-Cu structure functions as a CO2 and proton absorber, facilitating hydrogenation and carbon–carbon coupling reactions on Cu-nanocluster/GSS for the formation of C2H4. In our design electrocatalytic electrode is made from nitrogen-doped graphene sheet stacks coated with copper nanostructures. The N-GSSitself can be drop-casted or electrophoretically incorporated onto the carbon paper and gas diffusion electrode. Electrochemical deposition method was recognized as successful and most promising to grow Cu nanocrystals on N-GSS incorporated in conducting carbon substrate. Gaseous products from CO2 electro-catalytic reformation on the cathode were investigated by mass-spectrometer but the electrode surface was analysed by SEM/EDS and XRD methods.

A Robust Bundled and Wrapped Structure Design of Ultrastable Silicon Anodes for Antiaging Lithium-Ion Batteries

Silicon with its high theoretical specific capacity for Li-ion storage has long suffered from its huge volume expansion and low intrinsic electronic properties, leading to poor rate performance and cycling stability. Recently, considerable efforts have been placed on achieving increased cycle life using nanomaterial structuring approaches. However, finding an efficient strategy to realize high capacity with a long cycle life of Si anodes is still a great challenge. In this work, a novel multileveled design of a web-like morphology is reported as a highly stable 3D interconnected Si network. This heterostructure of nano-sized Si (nSi), nitrogen-doped carbon nanotubes (N-CNTs), and graphenized polyacrylonitrile (g-PAN) is prepared via a low-cost method as an anode for LIBs. This sturdy composite integrates the individual benefits from each of its components, where nSi delivers high energy storage capacity, N-CNTs with nitrogen functionalization act as electron highways and flexible networks to connect nSi particles, and g-PAN produces nitrogen-doped graphene sheets wrapped around the entire electrode structure and buffers the volume change during lithiation. We found that only when all three components are present that significant enhancements in performance are observed. Specifically, this heterostructure exhibits excellent stability with a reversible capacity of ∼1370 mAh g–1 over 1100 cycles at a high current rate of 3000 mA g–1. Moreover, high loading cycling of up to 3 mAh cm–2 at ∼1 mgSi cm–2 was achieved at 500 mA g–1. This effective strategy introduces a promising avenue for the scalable production of high-performance next-generation LIBs.

Sensitive electrochemical detection of bisphenol A at screen-printed graphite electrode modified with nitrogen-doped graphene sheets

A novel voltammetric sensor was developed by modifying screen-printed graphite electrode (SPGE) with nitrogen doped graphene sheets (N-GSs) to detect bisphenol A. The electrochemical results exhibited that N-GSs / modified SPGE has high sensing performance towards the oxidation of bisphenol A. Excellent results were obtained for bisphenol A detection in the linear range from 0.08 to 300.0 µM with a sensitivity of 0.1626 µA µM-1 and limit of detection of 0.02 µM. Also, the fabricated N‑GSs/SPGE sensor showed good stability. The as-prepared sensor was tested towards the detection of bisphenol A in real samples. The measured results established the great sensing ability of N-GSs/SPGE for bisphenol A with high selectivity and good stability in real samples.

Core shell nanostructured of Co3O4@RuO2 assembled on nitrogen-doped graphene sheets electrode for an efficient supercapacitor application

Hybrid electrodes containing cobalt oxides (Co3O4)/ruthenium dioxide (RuO2) decorated on graphene oxide surface materials for electrochemical supercapacitor applications. The 3D porous and nanocrystalline structured Co3O4@RuO2/NGO composite was prepared by hydrothermal reaction process. The structural and morphological behaviors of the composite were examined by analytical characterization and electrode material studied via three-electrode configuration of cyclic voltammetry. The Co3O4@RuO2/NGO composite electrode accomplished of ~472 F g−1 (0.5 A/g) and showed increasing stability capable of 5000 cycles with 97.1% retention.

Fracture Analysis of Vacancy Defected Nitrogen Doped Graphene Sheets Via MD Simulations

The novel hexagonal monolayer sheet of carbon atoms, graphene, has attracted great attention due to their exceptional electrical and mechanical properties. Their phenomenally high strength and elastic strain, nevertheless, can be altered by structural defects due to stress concentration. In this paper, the fracture behaviour of graphene sheets and nitrogen doped graphene sheets with vacancies were investigated using molecular dynamics (MD) simulations at the different temperatures of 300K, 500K, and 900K. The results reveal a significant strength loss caused by both the defects and vacancies and doped nitrogen in graphene. The deformation process of graphene at various strain rate levels, with regard to the failure behaviour, is discussed. The validity of the proposed MD simulations is verified by comparing the simulation results with the available predictions from the quantized fracture mechanics.

Theoretical insights into catalytic CO2 hydrogenation over single-atom (Fe or Ni) incorporated nitrogen-doped graphene

Developing highly efficient and cheap catalysts for the CO2 hydrogenation is the key to achieve CO2 conversion into clean energy. Herein, periodic density functional theory (DFT) calculations are performed to investigate possible reaction mechanisms for the hydrogenation of CO2 to formic acid (cis- or trans-HCOOH) product over a single Fe or Ni atom incorporated nitrogen-doped graphene (Fe-N3Gr or Ni-N3Gr) sheets. Our calculations found that the CO2 hydrogenation proceeds via a coadsorption mechanism to produce cis- or trans-HCOOH over Fe-N3Gr and Ni-N3Gr surfaces, which is classified into 2 steps: (1) the CO2 hydrogenation to form a formate (HCOO*) intermediate and (2) hydrogen abstraction to produce cis- or trans-HCOOH. The formation of trans-HCOOH over both Fe-N3Gr and Ni-N3Gr surfaces exhibit the obvious superiority due to the low barrier all through the whole channel. The highest energy barriers (Ea) in the case of trans-HCOOH formation on Fe-N3Gr and Ni-N3Gr surfaces are only 0.57 and 0.37 eV, respectively, which indicated that the CO2 hydrogenation to trans-HCOOH could be realized over these catalysts at low temperatures, especially the Ni-N3Gr surface. On the other hand, our findings show that the competitive reaction that produces CO and H2O is almost impossible or extremely difficult to proceeds under ambient conditions due to the large Ea for the formation of these side products. Moreover, the microkinetic modeling of the CO2 hydrogenation on both surfaces was investigated to confirm these results. Thus, the Fe-N3Gr and Ni-N3Gr catalysts reveal excellent catalytic activity and highly selective for CO2 hydrogenation to trans-HCOOH. This theoretical investigation not only provides a promising catalyst but also gives a deeper understanding of CO2 hydrogenation reaction.