Promising Single-atom Catalysts Research Articles

Theoretical study of transition metal-doped β12 borophene as a new single-atom catalyst for carbon dioxide electroreduction.

The electrocatalytic carbon dioxide reduction reaction (CO2RR) presents a viable and cost-effective approach for the elimination of CO2 by transforming it into valuable products. Nevertheless, this process is impeded by the absence of exceptionally active and stable catalysts. Herein, a new type of electrocatalyst of transition metal (TM)-doped β12-borophene (TM@β12-BM) is investigated via density functional theory (DFT) calculations. Through comprehensive screening, two promising single-atom catalysts (SACs), Sc@β12-BM and Y@β12-BM, are successfully identified, exhibiting high stability, catalytic activity and selectivity for the CO2RR. The C1 products methane (CH4) and methanol (CH3OH) are synthesized with limiting potentials (UL) of -0.78 V and -0.56 V on Sc@β12-BM and Y@β12-BM, respectively. Meanwhile, CO2 is more favourable for reduction into the C2 product ethanol (CH3CH2OH) compared to ethylene (C2H4) via C-C coupling on these two SACs. More importantly, the dynamic barriers of the key C-C coupling step are 0.53 eV and 0.73 eV for the "slow-growth" sampling approach in the explicit water molecule model. Furthermore, Sc@β12-BM and Y@β12-BM exhibit higher selectivity for producing C1 compounds (CH4 and CH3OH) than C2 (CH3CH2OH) in the CO2RR. Compared with Sc@β12-BM, Y@β12-BM demonstrates superior inhibition of the competitive hydrogen evolution reaction (HER) in the liquid phase. These results not only demonstrate the great potential of SACs for direct reduction of CO2 to C1 and C2, but also help in rationally designing high-performance SACs.

From Porphyrin-Like Rings to High-Density Single-Atom Catalytic Sites: Unveiling the Superiority of p-C2N for Bifunctional Oxygen Electrocatalysis.

With effective utilization of the catalytic site, single-atom catalysts (SACs) supported by nitrogen atoms surrounding built-in pores of two-dimensional (2D) materials, such as porphyrin/phthalocyanine-based covalent organic frameworks, have been highly promising electrocatalysts in the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) processes for the air electrode of the metal-air battery. However, the number of stable single-atom anchoring sites, i.e., accessible single-atom metal sites, has been concerning as a result of the appearance of heterogeneous or large and even supersized pores in substrate materials. 2D porous graphitic carbon nitride (PGCN) with a stronger stability and smaller component is regarded as a more potential alternative owing to similar controllability and designability. In this work, inspired by the robust coordinated TM-N4 environment of porphyrin/phthalocyanine molecules, novel p-C2N with a high density of porphyrin-like organic units is rationally designed. In well-designed p-C2N, a higher homogeneity and uniformity of coordination sites can enhance the electrocatalytic activity in the whole catalytic material and better prevent SACs from sintering and agglomerating into thermodynamically stable nanoclusters. Utilizing density functional theory (DFT), the stability of the p-C2N monolayer, TM@p-C2N, and OER/ORR catalytic activities of TM@p-C2N (TM including Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au) are systematically evaluated. Among them, Ir@p-C2N (0.31 V of the OER and 0.36 V of the ORR), Co@p-C2N (0.47 and 0.22 V), and Rh@p-C2N (0.55 and 0.27 V) are screened as promising SACs for the bifunctional ORR and OER. The proposal of p-C2N guides a new direction for the development of TM-N-C-based SAC bifunctional electrocatalysts.

Nb2S2C Monolayers with Transition Metal Atoms Embedded at the S Vacancy Are Promising Single-Atom Catalysts for CO Oxidation.

Single atoms anchored on stable and robust two-dimensional (2D) materials are attractive catalysts for carbon monoxide (CO) oxidation. Here, 3d (Fe-Zn), 4d (Ru-Cd), and 5d (Os-Hg) transition metal-decorated Nb2S2C monolayers were systematically studied as potential single-atom catalysts for low-temperature CO oxidation reactions by performing first-principles calculations. Sulfur vacancies are essential for stabilizing the transition metals anchored on the surface of defective Nb2S2C. After estimating the structure stability, the aggregation trend of the embedded metal atoms, and adsorption strength of reactants and products, Zn-decorated defective Nb2S2C is predicted to be a promising catalyst to facilitate CO oxidation through the Langmuir-Hinshelwood (LH) mechanism with an energy barrier of only 0.25 eV. Our investigation indicates that defective carbosulfides can be promising substrates to generate efficient and low-cost single-atom catalysts for low-temperature CO oxidation.

Mechanistic understanding on effect of doping nitrogen with graphene supported single-atom Fe toward electrochemical CO2 reduction: A computational consideration

In this study, we constructed single-atom Fe materials (Fe-Nx-Cyv) as the electrocatalysts for CO2 electrochemical reduction reaction (CO2ERR) and examined the reduction mechanisms on the basis of periodic density functional theory computations. The adsorption strength of HCOO* and COOH* species is found to play an important role for CO2ERR. The formation of HCOO* on the Fe-C1v, Fe-N3-C1v, and Fe-C2v catalysts is much preferred than the COOH* formation resulting in the production of CH4 with limiting potentials of −0.41 V for the potential-determining step (PDS) of HCOOH* → H2COOH* on the Fe-C1v, −0.63 V for the PDS of HCO* → H2CO* on the Fe-N3-C1v, and −0.68 V for the PDS of H3CO* → O* + CH4(g) on the Fe-C2v. While the COOH* formation on the Fe-N4-C2v catalyst becomes more favorable leading to the production of CO with a limiting potential of −0.20 V for the PDS of CO2 → COOH*. In addition, nitrogen doping effect on the adsorption of important intermediates are also investigated. It is found that the adsorption of CO* and COOH* is enhanced that facilitates CO generation of CO2ERR on the Fe-N4-C2v. Therefore, Fe-N4-C2v materials is a promising single-atom catalyst for CO2 electro-reduction to CO.

P‐d Orbital Hybridization Engineered Single‐Atom Catalyst for Electrocatalytic Ammonia Synthesis

The rational design of metal single‐atom catalysts (SACs) for electrochemical nitrogen reduction reaction (NRR) is challenging. Two‐dimensional metal–organic frameworks (2DMOFs) is a unique class of promising SACs. Up to now, the roles of individual metals, coordination atoms, and their synergy effect on the electroanalytic performance remain unclear. Therefore, in this work, a series of 2DMOFs with different metals and coordinating atoms are systematically investigated as electrocatalysts for ammonia synthesis using density functional theory calculations. For a specific metal, a proper metal‐intermediate atoms p‐d orbital hybridization interaction strength is found to be a key indicator for their NRR catalytic activities. The hybridization interaction strength can be quantitatively described with the p−/d‐ band center energy difference (∆d‐p), which is found to be a sufficient descriptor for both the p‐d hybridization strength and the NRR performance. The maximum free energy change (ΔGmax) and ∆d‐p have a volcanic relationship with OsC4(Se)4 located at the apex of the volcanic curve, showing the best NRR performance. The asymmetrical coordination environment could regulate the band structure subtly in terms of band overlap and positions. This work may shed new light on the application of orbital engineering in electrocatalytic NRR activity and especially promotes the rational design for SACs.

One-dimensional 3d-TM–solophene polymers as high-activity single‐atom catalysts for CO oxidation

Inspired by the successful synthesized one-dimensional (1D) 3d-transition metal solophene polymer (TM-SP), we systematically investigate CO oxidation reactions on TM-SP as single atom catalysts (SACs) by density functional theory (DFT). The stabilities, adsorptive profiles of reactants and chemical kinetics as three descriptors are taken into account to efficiently select promising SACs among nine candidates (TM-SP, TM = Sc-Cu). Our calculations reveal that Sc-SP shows the highest catalytic activity for CO oxidation. After considering the Langmuir Hinshelwood (LH), Eley Rideal (ER) and tri-molecular Eley-Rideal (TER) mechanisms, we found the rate-determining step of CO oxidation on Sc-SP prefers to follow the LH mechanism whose energy barrier is 0.58 eV. The second CO2 generated fast via either LH or ER mechanisms with no activation barrier. Moreover, our results verify that the catalytic behavior of transition metals is intrinsic, because the kinetic characteristic is independent by changes in the different macrocyclic ligands (N2O2, N3O and N4) of the active sites in the kinetically-controlled CO oxidation reaction. The high catalytic performance of Sc-SP may be attributed to the proper strengths of adsorbates, high stabities and fast kinetics. These results provide atomic-level insights into CO oxidation which opens up a novel strategy for rational design of efficient SACs.

Computational Study on the Catalytic Performance of Single-Atom Catalysts Anchored on g-CN for Electrochemical Oxidation of Formic Acid

The electrochemical formic acid oxidation reaction (FAOR) has attracted great attention due to its high volumetric energy density and high theoretical efficiency for future portable electronic applications, for which the development of highly efficient and low-cost electrocatalysts is of great significance. In this work, taking single-atom catalysts (SACs) supported on graphitic carbon nitrides (g-CN) as potential catalysts, their catalytic performance for the FAOR was systemically explored by means of density functional theory computations. Our results revealed that the strong hybridization with the unpaired lone electrons of N atoms in the g-CN substrate ensured the high stability of these anchored SACs and endowed them with excellent electrical conductivity. Based on the computed free energy changes of all possible elementary steps, we predicted that a highly efficient FAOR could be achieved on Ru/g-CN with a low limiting potential of −0.15 V along a direct pathway of HCOOH(aq) → HCOOH* → HCOO* → CO2* → CO2(g), in which the formation of HCOO* was identified as the potential-determining step, while the rate-determining step was located at the CO2* formation, with a moderate kinetic barrier of 0.89 eV. Remarkably, the moderate d-band center and polarized charge of the Ru active site caused the Ru/g-CN catalyst to exhibit an optimal binding strength with various reaction intermediates, explaining well its superior FAOR catalytic performance. Hence, the single Ru atom anchored on g-CN could be utilized as a promising SAC for the FAOR, which opens a new avenue to further develop novel catalysts for a sustainable FAOR in formic-acid-based fuel cells.

Theoretical investigations of electrochemical nitrogen reduction on single transition metal atom catalysts supported by 1T-MoSe2

The search for stable and efficient single-atom catalysts (SACs) for the electrocatalytic nitrogen reduction reaction (eNRR) has garnered significant theoretical interest. In this study, we evaluate the eNRR performance of eighteen two-dimensional 1T-MoSe2-supported transition metal single-atom catalysts (TM@1T-MoSe2, TM=V, Cr, Mn, Fe, Co, Ni, Nb, Mo, Tc, Ru, Rh, Pd, Ta, W, Re, Os, Ir, and Pt) using density functional theory calculations. We assess the stability of each TM@1T-MoSe2, as well as the limiting potential of eNRR and the ammonia selectivity on each stable TM@1T-MoSe2. Our results show that W@1T-MoSe2 is the most promising single-atom catalyst for eNRR, with a limiting potential of -0.23 V via the distal pathway starting from three co-adsorbed nitrogen molecules. Furthermore, the multi-adsorption of N2 on W@1T-MoSe2 effectively suppress the hydrogen evolution reaction, thus enhancing the selectivity of the eNRR. This research provides a promising avenue for the development of a new class of 1T-MoSe2-based single-atom catalysts for electrocatalytic ammonia synthesis.

CO2 electroreduction performance of PtS2 supported single transition metal atoms: a theoretical study.

Electrocatalytic CO2 reduction is a sustainable strategy to convert CO2 into valuable carbon products. Atomically dispersed single-atom catalysts (SACs) have great potential as effective electrocatalysts for the CO2 reduction reaction (CO2RR). Transition metal dichalcogenides (TMDs) are considered to be a kind of promising SAC supports. In this work, ten different 3d TM single atoms (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) embedded in PtS2 with single S-vacancy (TM-PtS2) were designed by density functional theory (DFT) as candidate electrocatalysts for the CO2RR. Possible reaction pathways of CO2 reduction to different C1 products were systematically investigated. The results show that for all these TM-PtS2 SACs, higher selectivity was achieved for CO2 reduction to C1 products than for the competing hydrogen evolution. HCOOH is the most favorable reduction product on PtS2-Sv supported Sc, Ti, V, Cr, Mn, Fe and Cu SACs, while multiple C1 products are generated on Co-, Ni- and Zn-PtS2. In particular, it is found that Sc-, V-, Fe-, Co- and Cu-PtS2 exhibit higher electrocatalytic performance for the CO2RR than Cu(211). Therefore, these five SACs are promising CO2RR electrocatalysts.

Insights into the mechanistic CO2 conversion to methanol on single Ru atom anchored on MoS2 monolayer

Single atom catalysts (SACs) have received great attention due to their promising catalytic activity and sustainability. In this regard, the catalytic activity toward CO2 conversion reaction can be efficiently improved by the addition of single transition metal anchored on the 2D MoS2 monolayer. In this work, we explore the potential utilization of Ru@MoS2 as a promising SAC for the CO2 reduction reaction (CO2RR) by using first-principles simulations. The stability of the so-formed SAC was evaluated in terms of binding energy, and the reaction paths leading to the production of CO and methanol was investigated. Our results show the great potential of Ru@MoS2 as SAC for the CO2 conversion to methanol as the main product, and contribute to shed light on the complex reaction mechanism aiming at the development of more efficient catalytic systems.

Enhancing Oxygen Reduction Reaction Activity Using Single Atom Catalyst Supported on Tantalum Pentoxide

AbstractTransition metal oxides have emerged as promising cost‐effective alternatives to Pt catalysts for oxygen reduction reaction (ORR) in fuel cell applications. However, their low stability under harsh electrochemical conditions hinders their widespread applications. Tantalum pentoxide (Ta2O5) has proven to be a stable material under ORR conditions, but its activity is limited. In this work, we incorporate single atom catalysts (SACs) in Ta2O5 to resolve the limited ORR activity of this material by altering the electronic structures of surface Ta atoms. We use density functional theory (DFT) calculations to identify the most promising SACs with enhanced ORR activity. Pt, Rh, and Ir, are found to be the most promising SACs with improved ORR activity and high stability. This work suggests that SACs are effective in enhancing Ta2O5 catalytic activities for ORR.

Transition metal anchored on C9N4 as a single-atom catalyst for CO2 hydrogenation: A first-principles study

To alleviate the greenhouse effect and maintain the sustainable development, it is of great significance to find an efficient and low-cost catalyst to reduce carbon dioxide (CO2) and generate formic acid (FA). In this work, based on the first-principles calculation, the catalytic performance of a single transition metal (TM) (TM = Cr, Mn, Fe, Co, Ni, Cu, Zn, Ru, Rh, Pd, Ag, Cd, Ir, Pt, Au, or Hg) atom anchored on C9N4 monolayer (TM@C9N4) for the hydrogenation of CO2 to FA is calculated. The results show that single TM atom doping in C9N4 can form a stable TM@C9N4 structure, and Cu@C9N4 and Co@C9N4 show better catalytic performance in the process of CO2 hydrogenation to FA (the corresponding maximum energy barriers are 0.41 eV and 0.43 eV, respectively). The partial density of states (PDOS), projected crystal orbital Hamilton population (pCOHP), difference charge density analysis and Bader charge analysis demonstrate that the TM atom plays an important role in the reaction. The strong interaction between the 3d orbitals of the TM atom and the non-bonding orbitals (1π g) of CO2 allows the reaction to proceed under mild conditions. In general, our results show that Cu@C9N4 and Co@C9N4 are a promising single-atom catalyst and can be used as the non-precious metals electrocatalyst for CO2 hydrogenation to formic acid.

Termination-Accelerated Electrochemical Nitrogen Fixation on Single-Atom Catalysts Supported by MXenes.

The synthesis of ammonia (NH3) from nitrogen (N2) under ambient conditions is of great significance but hindered by the lack of highly efficient catalysts. By performing first-principles calculations, we have investigated the feasibility for employing a transition metal (TM) atom, supported on Ti3C2T2 MXene with O/OH terminations, as a single-atom catalyst (SAC) for electrochemical nitrogen reduction. The potential catalytic performance of TM single atoms is evaluated by their adsorption behavior on the MXene, together with their ability to bind N2 and to desorb NH3 molecules. Of importance, the OH terminations on Ti3C2T2 MXene can effectively enhance the N2 adsorption and decrease the NH3 adsorption for single atoms. Based on proposed criteria for promising SACs, our calculations further demonstrate that the Ni/Ti3C2O0.19(OH)1.81 exhibits reasonable thermodynamics and kinetics toward electrochemical nitrogen reduction.

A mechanistic study of selective propane dehydrogenations on MoS2 supported single Fe atoms

On-purpose propane dehydrogenation (PDH) has emerged as a profitable alternative to the traditional cracking of oil products for propylene production. By means of density functional theory (DFT) calculations, the present work demonstrates that Fe atoms may atomically disperse on MoS2 (Fe1/MoS2) and serve as a promising single-atom catalyst (SAC) for PDH. The catalytic activity of Fe1/MoS2 is attributed to the highly exposed d orbitals of single Fe atoms, while the propylene selectivity is originated from the kinetic inhibition of propylene dehydrogenation resulting from fast propenyl hydrogenation. The unique catalytic selectivity of Fe1/MoS2 may inspire further investigations of on-purpose dehydrogenations of propane on SACs.

Theoretical Investigation on the Hydrogen Evolution, Oxygen Evolution, and Oxygen Reduction Reactions Performances of Two-Dimensional Metal-Organic Frameworks Fe3(C2X)12 (X = NH, O, S)

Two-dimensional metal-organic frameworks (2D MOFs) inherently consisting of metal entities and ligands are promising single-atom catalysts (SACs) for electrocatalytic chemical reactions. Three 2D Fe-MOFs with NH, O, and S ligands were designed using density functional theory calculations, and their feasibility as SACs for hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) was investigated. The NH, O, and S ligands can be used to control electronic structures and catalysis performance in 2D Fe-MOF monolayers by tuning charge redistribution. The results confirm the Sabatier principle, which states that an ideal catalyst should provide reasonable adsorption energies for all reaction species. The 2D Fe-MOF nanomaterials may render highly-efficient HER, OER, and ORR by tuning the ligands. Therefore, we believe that this study will serve as a guide for developing of 2D MOF-based SACs for water splitting, fuel cells, and metal-air batteries.

In-Situ Silica Xerogel Assisted Facile Synthesis of Fe-N-C Catalysts with Dense Fe-Nx Active Sites for Efficient Oxygen Reduction.

In the past decade, atomically dispersed Fe active sites (coordinated with nitrogen) on carbon materials (FeNC) have emerged rapidly as promising single-atom catalysts (SACs) for the oxygen reduction reaction (ORR) to substitute precious group metal (PGM) catalysts, owing to their earth abundance and low cost. Nonetheless, the production of highly active FeNC SACs is largely restricted by material cost, low product yield and difficulty of microstructure design. Herein, the authors demonstrate a facile in-situ xerogel (ISG) assisted synthetic strategy, using cheap materials, to construct FeNC SACs (ISG FeNC). The porous silica xerogel, formed in-situ with the FeNC precursors, encourages the emergence of enormous micropores/mesopores and homogeneous confinement/protection to the precursors during pyrolysis, benefiting to the formation of abundant accessible active sites (27.6 × 1019 sites g-1 ). Correspondingly, the ISG FeNC exhibits excellent ORR activity with a half-wave potential (E1/2 = 0.91V) in alkaline medium. The Zn-air battery assembled using the ISG FeNC SACs as the bifunctional catalyst of air cathode, demonstrates commendable performance with high peak power density of 249.1mW cm-2 and superior long-term stability (660 cycles with 220 h). This work offers an economic and efficient way to fabricate PGM-free SACs for diverse applications.

Coronene-Based 2D Metal–Organic Frameworks: A New Family of Promising Single-Atom Catalysts for Nitrogen Reduction Reaction

Electrochemical nitrogen reduction reaction (NRR) is becoming increasingly important for ammonia (NH3) synthesis, but the development of effective electrocatalysts remains a great challenge. Here, by means of extensive first-principles calculations, we systematically study the potential of coronene-based two-dimensional (2D) metal–organic frameworks (TM–PTC, TM = Fe, Sc, Ti, V, Cr, Mn, Co, Ni, Cu) as single-atom catalysts for dinitrogen (N2) fixation. Our results show that the gas phase N2 can be readily reduced to NH3 on V/Fe–PTC through the enzymatic/distal mechanism with a quite low overpotential of 0.60/0.53 V. The underlying physics for the excellent NRR performance is discussed in detail. Moreover, the competing reaction of hydrogen evaluation reaction (HER) is dramatically suppressed in Fe–PTC, endowing them with high selectivity and thus rendering them ideal for NH3 synthesis. This work not only provides efficient electrocatalysts for NRR under mild reaction conditions but also helps guide the future development of single-atom electrocatalysts.

A comparative study of CO catalytic oxidation on the single vacancy and di-vacancy graphene supported single-atom iridium catalysts: A DFT analysis

Engineering of high-performance catalysts is of great importance for reducing the greenhouse gas emission by the electrocatalytic oxidation of CO. Single-atom-catalysts (SACs) have gained substantial attention thanks to their superior catalytic activity for CO oxidation, and graphene has been considered as one most promising supporting material owing to its peculiar physicochemical properties. In this work, the mechanism of CO oxidation over iridium (Ir) embedded on both single vacancy graphene (Ir-GNSV) and di-vacancy graphene (Ir-GNDV) has been investigated with the aid of density functional theory (DFT). The structural properties of Ir-GNSV and Ir-GNDV were analyzed by Bader charge analysis and electron density difference map. The calculated adsorption energy values of CO and O2 molecules on both the Ir-GNSV and Ir-GNDV have validated that both molecules can be molecularly adsorbed on the surface of each catalyst at room temperature. The results put forth that the reaction mechanism of CO + O2 → OOCO → CO2 + O* prefers to Langmuir − Hinshelwood (LH) mechanism. The activation energy for the transition-state for Ir-GNSV has been calculated to be 0.31 eV, whereas the first transition state (TS1) and the second transition state (TS2) of Ir-GNDV have been determined as 0.30 eV and 0.26 eV, respectively. Moreover, the results have confirmed that Ir-GNSV and Ir-GNDV surfaces have high catalytic activity and selectivity towards CO oxidation. On the basis of these findings, the proposed Ir-GNSV and Ir-GNDV catalysts are considered to be promising SAC for CO oxidation at low-temperature. It can be speculated that this work paves the way for the engineering of boosted-performance Ir-based heterogeneous catalysts by providing deeper mechanistic insights.

CO oxidation on atomic nickel/phosphorene nanosheet: An efficient single-atom catalyst

• Single Ni atom doped into phosphorene has better stability than other metals supported or doped conditions. • Ni-phosphorene single-atom catalyst can improve the adsorption capacity of O 2 and CO, better catalyzing CO oxidation. • The LH mechanism is more reasonable with low energy barrier of 0.59 eV. • Results demonstrate that Ni-phosphorene can serve as a potential single-atom catalyst for CO oxidation. Various metals decorated phosphorene nanosheet as single-atom catalyst (SAC) for CO oxidation have been investigated systematically by employing spin-polarized density functional theory. Ni-phosphorene is found to be the promising SAC for CO oxidation after comparing with other noble and non-noble metal candidates, such as Fe, Co, Cu, Al, Ag, Au, and Pt. Moreover, the structure of Ni-phosphorene remains stable at the end of 5 ps under 300 K using first-principles molecular dynamics simulations. Additionally, O 2 and CO are difficult to dissociate on Ni-phosphorene at room temperature because their dissociation energies are greater than 1 eV in possible paths. Three feasible reaction mechanisms (Langmuir-Hinshelwool (LH), Eley-Rideal, and Termolecular Eley-Rideal) are taken into account to seek the path with the lowest energy barrier. The LH mechanism is the most favorable one with the lowest energy barrier (0.59 eV) in the rate-determining step, which is facile to occur under ambient temperature. Our results provide theoretical guidance to design highly active heterogeneous catalysts based on phosphorene substrate for CO oxidation at low temperature. A single atom catalyst Ni-phosphorene can catalyze CO oxidation with low activation energy of 0.59 eV for rate-determining step.

Single Mn Atom Anchored on Nitrogen-Doped Graphene as a Highly Efficient Electrocatalyst for Oxygen Reduction Reaction.

Single Mn atom on nitrogen-doped graphene (MnN4 -G) has exhibited good structural stability and high activity for the adsorption and dissociation of an O2 molecule, becoming a promising single-atom catalyst (SAC) candidate for oxygen reduction reaction (ORR). However, the catalytic activity of MnN4 -G for the ORR and the optimal reaction pathway remain obscure. In this work, density-functional theory calculations were employed to comprehensively investigate all the possible pathways and intermediate reactions of the ORR on MnN4 -G. The feasible active sites and the most stable adsorption configurations of the intermediates and transition states during the ORR were identified. Screened from all the possibilities, three optimal four-electron O2 hydrogenation pathways with an ultralow energy barrier of 0.13 eV were discovered that are energetically more favorable than direct O2 dissociation pathways. Analysis of the free energy diagram further verified the thermodynamical feasibility of the three pathways. Thus, MnN4 -G possesses superior ORR activity. This study provides a fundamental understanding of the design of highly efficient SACs for the ORR.