Free Energy Diagram Research Articles

Theoretical Advances in MBenes for Hydrogen Evolution Electrocatalysis

Two-dimensional transition metal borides (MBenes) have emerged as promising electrocatalysts for hydrogen evolution reactions (HERs), attracting significant research interest due to theoretical computations that enhance the understanding and optimization of their performance. This review begins with a comprehensive summary of HER mechanisms, followed by an in-depth examination of the geometric and electronic properties of MBenes. Subsequently, this review explores MBene-based electrocatalysts for HERs, employing free-energy diagrams and an electronic structure analysis to assess both the intrinsic catalytic activity of MBenes and the theoretical performance of single-atom modified MBenes. Finally, the prospects and challenges associated with MBenes are discussed, providing valuable insights to guide future research in this area. Overall, this topic holds significant relevance for researchers in the HER field, and this review aims to deliver theoretical insights for the optimal design of advanced MBene electrocatalysts.

Hydrazone Based pH‐Responsive Configurational Molecular Rotary Switches Containing a New Conjugated π‐Electronic Framework

AbstractA pyrido‐pyrimidinone heterocycle derived pH‐activated, hydrazone based molecular switch and its switching mechanism are reported here. The introduction of a new conjugated π electronic framework (enone part in the molecule) allowed the system to undergo hydrazone‐azo tautomerization, followed by E‐Z isomerization through rotation around the partial C−N single bond. Under acidic pH, protonation took place selectively on pyrimidinone nitrogen, and that turned the molecule to the corresponding ZH+ configuration. On the other hand, addition of triethylamine in the same solution reverted the molecule back to its original E‐configuration. Extensive proton‐NMR, and detailed X‐ray crystallography coupled with UV‐vis spectroscopy were carried out to establish the switching phenomena. Theoretical DFT calculations leading to free energy diagrams, transition states, and intermediates shed light on the mechanism behind the switching phenomenon.

Valence-engineered catalysis-selectivity regulation of molybdenum oxide nanozyme for acute kidney injury therapy and post-cure assessment.

The optimization of the enzyme-like catalytic selectivity of nanozymes for specific reactive oxygen species (ROS)-related applications is significant, and meanwhile the real-time monitoring of ROS is really crucial for tracking the therapeutic process. Herein, we present a mild oxidation valence-engineering strategy to modulate the valence states of Mo in Pluronic F127-coated MoO3-x nanozymes (denoted as MF-x, x: oxidation time) in a controlled manner aiming to improve their specificity of H2O2-associated catalytic reactions for specific therapy and monitoring of ROS-related diseases. Experimentally, MF-0 (Mo average valence 4.64) and MF-10 (Mo average valence 5.68) exhibit exclusively optimal catalase (CAT)- or peroxidase (POD)-like activity, respectively. Density functional theory (DFT) calculations verify the most favorable reaction path for both MF-0- and MF-10-catalyzed reaction processes based on free energy diagram and electronic structure analysis, disclosing the mechanism of the H2O2 activation pathway on the Mo-based nanozymes. Furthermore, MF-0 poses a strong potential in acute kidney injury (AKI) treatment, achieving excellent therapeutic outcomes in vitro and in vivo. Notably, the ROS-responsive photoacoustic imaging (PAI) signal of MF-0 during treatment guarantees real-time monitoring of the therapeutic effect and post-cure assessment in vivo, providing a highly desirable non-invasive diagnostic approach for ROS-related diseases.

Ligand engineering regulates the electronic structure of Ni-N-C sites to promote electrocatalytic acetylene semi-hydrogenation

Compared with traditional thermal catalytic hydrogenation technology, electrocatalytic acetylene semi-hydrogenation (EASH) is a green and environmentally friendly method. EASH utilizes renewable electricity under normal temperature and pressure conditions, and uses water as a hydrogen source to electrocatalytically semi-hydrogenate acetylene to ethylene. Ni-based single-atom catalysts (SACs) have shown good application prospects in EASH, but there is still much room for optimization. The axial coordination regulation of the active center is a potential means to improve its activity. In this work, the activity and selectivity of NiN4 SACs with 14 axial ligands (X) for EASH were systematically studied via density functional theory (DFT). First, the binding energy and ab initio molecular dynamics simulation results show that all the NiN4-X can exist stably. Second, the Gibbs free energy diagram shows that the activation and adsorption of C2H2 is the rate-determining step of the reaction. The introduction of the –ONO ligand enhances the activation and adsorption of C2H2 by NiN4, which is beneficial to the occurrence of EASH and inhibits the side reactions of hydrogen evolution. The two parameters ΔG∗CHCH and ΔG∗CH2CH3 can be used as characteristic descriptors to predict the activity and selectivity of EASH. Finally, the catalytic activity mechanism was explained from the perspective of electrons and orbitals, and it was found that the dz2 orbital played a leading role in the axial ligand regulation of C2H2 catalytic activity. This work provides a new method for the development of efficient EASH catalysts.

Adjusting the Catalytic Performance of MIL-88B(Fe/Co) through Structural Transitions

Metal-organic frameworks (MOFs) are a family of highly porous materials, which are composed of metal-based nodes and organic ligands. Thanks to the large surface areas and tunable chemical functionalities, MOFs are emerging as excellent catalysts for the sector of renewable energy. Of particular interest, the structures of certain MOFs are highly flexible, allowing for reversible structural transitions upon the stimuli from various external sources. Such stimuli-responsive behaviors of MOFs create new opportunities to design functional materials for switchable catalysis. Nevertheless, the exploration of the flexible MOF-based catalysts is still at a nascent stage. Herein, to advance the fundamental understanding of how the dynamic behaviors of flexible MOFs could affect the catalytic performance, first-principles calculations were carried out using the density functional theory, where a bimetallic MOF, MIL-88B(Fe/Co), was selected as a model structure. Results showed that the lattice contraction can result in twisted ligands as well as the rotary metal nodes, which subsequently lead to variations of the free energy diagrams for the oxygen evolution reaction, demonstrating the critical role of structural flexibility in determining the energy barriers during the elementary steps. Further analysis using the pair distribution function and electron localization function confirmed the rigid short-range order of MOFs during the structural transitions, as well as the tunable guest-host interactions upon lattice contraction/expansion, which could be responsible for the observed differences in the energy barriers during catalysis. Overall, the findings from this work offer new insights into the catalyst design for the modulated production of renewable fuels.Reference: CrystEngComm, 2023, 25, 6441 - 6448

High throughput MN4-G screening electrocatalyst for highly selective acetylene semi-hydrogenation

The large-scale production of polyethylene in the petrochemical industry requires the effective removal of trace amounts of acetylene impurities. Currently, acetylene is selectively reduced to ethylene via catalytic hydrogenation under high-temperature and high-pressure conditions. However, owing to the harsh reaction conditions of this thermocatalytic method, it requires significant energy and lacks selectivity. Electrocatalytic acetylene semi-hydrogenation (EASH) has emerged as a promising alternative to traditional thermal catalytic hydrogenation. In this study, the density functional theory (DFT) calculations were used to systematically investigate the electrocatalytic activity and selectivity of 25 nitrogen-doped graphene composites containing 3d, 4d, and 5d transition metals (MN4-G) toward EASH, aiming to identify efficient single-atom catalysts (SACs) for EASH reactions. Firstly, the binding, cohesive, and formation energy calculations reveal that all single metal atoms except Mo, Ru, Ag, W Re and Os can be stably immobilized on nitrogen-doped graphene. Secondly, the Gibbs free energy diagram exhibits that Cu and Ni SACs promote EASH and inhibit the hydrogen evolution side reaction. Moreover, the d-band center of the metal site and the acetylene adsorption energy can be used as characteristic descriptors to predict the EASH selectivity of the catalyst. Finally, the mechanism of catalytic activity is described from the perspective of electrons and orbitals, revealing the coupling between dz2 and C2H4-πz∗ orbitals plays a vital role in ethylene desorption. This study provides an in-depth understanding of the mechanism of high-efficiency EASH catalysts at the electronic orbital level.

Error Awareness in the Volcano Plots of Oxygen Electroreduction to Hydrogen Peroxide.

Electrocatalysis holds the key to the decentralized production of hydrogen peroxide via the two-electron oxygen reduction reaction (ORR, O2g+2H++e-→H2O2aq). However, cost-effective, active, and selective catalysts are still sought after. While density functional theory (DFT) has already led to the discovery of various enhanced catalysts, it has a severe yet often unnoticed drawback: the ill description of O2 and H2O2. Here, we analyze the impact of the errors in those two species on the most widespread activity plots in the literature, namely free-energy diagrams and Sabatier-type volcano plots. Uncorrected or partially corrected gas-phase energies lead to appreciably different activity plots that may provide inaccurate predictions. Indeed, we show for a variety of electrocatalysts that only when the errors in O2 and H2O2 are corrected can DFT mimic the experiments. In sum, this work provides concrete guidelines to avoid a common pitfall of computational models for electrocatalytic hydrogen peroxide production.

The Effect of Surface Oxygen Coverage on the Oxygen Evolution Reaction over a CoFeNiCr High-Entropy Alloy.

Developing cost-effective and highly active electrocatalysts for the oxygen evolution reaction (OER) is crucial for advancing sustainable energy applications. High-entropy alloys (HEAs) made from earth-abundant transition metals, thanks to their remarkable stability and electrocatalytic performance, provide a promising alternative to expensive electrocatalysts typically derived from noble metals. While pristine HEA surfaces have been theoretically investigated, and the effect of oxygen coverage on conventional metal electrocatalysts has been examined, the impact of surface oxygen coverage on the electrocatalytic performance of HEAs remains poorly understood. To bridge this gap, we employ density functional theory (DFT) calculations to reconstruct the free energy diagram of OER intermediates on CoFeNiCr HEA surfaces with varying oxygen coverages, evaluating their impact on the rate-limiting step and theoretical overpotential. Our findings reveal that increased oxygen coverage weakens the adsorption of HO* and O*, but not HOO*. As a result, the theoretical overpotential for the OER decreases with higher oxygen coverage, and the rate-limiting step shifts from the third oxidation step (HOO* formation) at low coverage to the first oxidation step (HO* formation) at higher coverage.

Optimization of Electrochemical Reduction of Biomass Derived 5-Hydroxymethylfurfural (HMF): A Volcano Plot and Bimetallic Catalysts.

2,5-bis(hydroxymethyl)furan (BHMF) derived from 5-Hydroxymethylfurfural (HMF) through a hydrogenation process has extensive applications in the production of resins, polymers, and artificial fibers. However, screening out the candidate and then modulating the active site to optimize the catalyst for high yield of BHMF are currently insufficient. In this study, Gibbs free energy diagrams of the reduction of HMF on 13 metals were presented, along with the identification of the rate-determining step (RDS) with the highest reaction barrier for each metal. We attempted to construct a volcano plot for HMFRR reaction. Additionally, a strategy was proposed to adjust the reaction barriers of RDS by combining two appropriate metals. Further experiments confirmed that Pb with the lowest energy barrier exhibited the highest HMF conversion (BHMF selectivity) among single metals. The modified catalyst by doping Ag on Pb, further boosted the HMF conversion (BHMF selectivity) from 42.1% (59.4%) to 80.8% (80.9%), respectively. These results provide an approach to rationally design and construct the catalyst system for efficient conversion of HMF.

Active Sites of Mixed-Metal Core-Shell Oxygen Evolution Reaction Catalysts: FeO4 Sites on Ni Cores or NiN4 Sites in C Shells?

Water electrolysis for clean hydrogen production requires high-activity, high-stability, and low-cost catalysts for its particularly sluggish half-reaction, the oxygen evolution reaction (OER). Currently, the most promising of such catalysts working in alkaline conditions is a core-shell nanostructure, NiFe@NC, whose Fe-doped Ni (NiFe) nanoparticles are encapsulated and interconnected by N-doped graphitic carbon (NC) layers, but the exact OER mechanism of these catalysts is still unclear, and even the location of the OER active site, either on the core side or on the shell side, is still debated. Therefore, we herein derive a plausible active-site model for each side based on various experimental evidence and density functional theory calculations and then build OER free-energy diagrams on both sides to determine the active-site location. The core-side model is an FeO4-type (rather than NiO4-type) active site where an Fe atom sits on Ni oxide layers grown on top of the core surface during catalyst activation, whose facile dissolution provides an explanation for the activity loss of such catalysts directly exposed to the electrolyte. The shell-side model is a NiN4-type (rather than FeN4-type) active site where a Ni atom is intercalated into the porphyrin-like N4C site of the NC shell during catalyst synthesis. Their OER free-energy diagrams indicate that both sites require similar amounts of overpotentials, despite a complete shift in their potential-determining steps, i.e., the final O2 evolution from the oxophilic Fe on the core and the initial OH adsorption to the hydrophobic shell. We conclude that the major active sites are located on the core, but the NC shell not only protects the vulnerable FeO4 active sites on the core from the electrolyte but also provides independent active sites, owing to the N doping.

Nitrogen reduction reaction enhanced by single-atom transition metal catalysts on functionalized graphene: A first-principles study

Ammonia production seeks alternatives to the conventional Haber-Bosch process, with nitrogen reduction reaction (NRR) emerging promising. Addressing the challenge of efficient catalysts, the functionalized graphene-based single atom catalysts (SACs) stand out. While prior studies have favored heteroatom-doped catalysts, the coordination of metal centers with nitrogen atoms remains underexplored. This work investigates transition metal (TM) SACs on nitrogen-doped graphene (N3G) using density functional theory (DFT) for electro-catalytic NRR. Results highlight the stability of V@N3G, Mo@N3G, W@N3G, with binding energies of −7.77, −5.43, and −3.89 eV, respectively. Insights into work function, d-band center, N–N bond, and IR stretching's role in N2 activation are gained through this study. Bader charge analysis reveals electron redistribution between the support and adsorbed N2. Employing Computational Hydrogen Electrode (CHE) method, comparative free energy diagrams for TM@N3G (V, Mo, W) via., enzymatic, consecutive, alternating, and distal pathways outline potential rate determining step (PDS) with and without the Implicit solvation method. Remarkably, W@N3G catalyst exhibits the lowest PDS in the presence of solvation energy, surpassing other catalysts. The multi-adsorption of N2 on W@N3G enhances NRR process, stabilizing intermediates for efficient ammonia production. This computational study sheds light on metal center SACs on functionalized graphene support as a potential electro-catalyst for efficient and stable NRR.

Electrochemical Nitrogen Reduction to Ammonia at Ambient Condition on the (111) Facets of Transition Metal Carbonitrides.

We conducted Density Functional Theory calculations to investigate a class of materials with the goal of enabling nitrogen activation and electrochemical ammonia production under ambient conditions. The source of protons at the anode could originate from either water splitting or H2, but our specific focus was on the cathode reaction, where nitrogen is reduced into ammonia. We examined the conventional associative mechanism, dissociative mechanism, and Mars-van Krevelen mechanism on the (111) facets of the NaCl-type structure found in early transition metal carbonitrides, including Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Sc, Y, and W. We explored the catalytic activity by calculating the free energy of all intermediates along the reaction pathway and constructing free energy diagrams to identify the steps that determine the reaction's feasibility. Additionally, we closely examined the potential for catalyst poisoning within the electrochemical environment, considering the bias required to drive the reaction. Furthermore, we assessed the likelihood of catalyst decomposition and the potential for catalyst regeneration among the most intriguing carbonitrides. Our findings revealed that the only carbonitride catalyst considered here exhibiting both activity and stability, capable of self-regeneration and nitrogen-to-ammonia activation, is NbCN with a low potential-determining step energy of 0.58 eV. This material can facilitate ammonia formation via a mixed associative-MvK mechanism. In contrast, other carbonitrides of this crystallographic orientation are likely to undergo decomposition, reverting to their parent metals under operational conditions.

Semimetallic state transition in Two-Dimensional carbon nitride covalent networks and enhanced electrocatalytic activity for nitrate to ammonia conversion

Single-atom catalysts (SACs), due to their maximum atomic utilization rate, show tremendous potential for application in the electrocatalytic synthesis of ammonia from nitrate. Yet, the development of superior supports that preserve the high selectivity, activity, and stability of SACs remains an imperative challenge. In this work, based on first-principles calculations and tight-binding (TB) model analysis, a new two-dimensional (2D) carbon nitride monolayer, C7N6, is proposed. The C7N6 structure exhibits a strong covalent network, with dynamical, thermal, and mechanical stability. Surprisingly, the structural transition from C9N4 to C7N6 corresponds to a semimetallic state transition. Further symmetry analysis unveils that the Dirac states in C7N6 are protected by space–time inversion symmetry, and the physical origin of the Dirac cone was confirmed using the TB model. Additionally, a non-zero Z2 invariant and significant topological edge states demonstrate its topologically nontrivial nature. Considering the excellent structural and topological properties of C7N6, a three-step screening strategy is designed to identify eligible SACs for electrochemical nitrate reduction reaction (NO3RR), and Ti@C7N6 is identified as possessing the best activity, with the last proton-electron coupling step *NH2→*NH3 being the potential-determining step (PDS), for which the limiting potential is 0.48 V. Moreover, a free energy diagram shows that the *NOH reaction pathway is energetically preferred on Ti@C7N6, and ab initio molecular dynamics (AIMD) calculations at 500 K confirm its good thermal stability. Our study not only provides excellent CN-based support material but also offers theoretical guidance for constructing highly active and selective SACs for nitrate reduction.

Rational Design of Cost-Effective Metal-Doped ZrO2 for Oxygen Evolution Reaction

HighlightsSurface energy and surface Pourbaix diagram reveal that ZrO2 (1¯11\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\overline{1 }11$$\\end{document}) is the most thermodynamically stable facet and is preferentially occupied by HO* at the equilibrium potential of oxygen evolution reaction (OER).Microkinetic modeling analyzed the OER activity of 40 single-metal doped ZrO2 and identified 16 metals exhibit improved catalytic activity, with Rh and Fe dopants showing the remarkable improvement.Thermodynamic free energy diagrams, density of states analysis, and ab initio molecular dynamics simulations further confirm that Fe–ZrO2 and Rh–ZrO2 are highly promising catalysts for OER, showcasing low ΔG for the rate-determining step, high conductivity, and exceptional stability.

Constructing built-in electric field via CuO/NiO heterojunction for electrocatalytic reduction of nitrate at low concentrations to ammonia

Electrocatalytic reduction of nitrate (NO3−) at low concentrations to ammonia (NH4+) still faces challenges of low NO3− conversion and NH4+ selectivity due to the sluggish mass transfer and insufficient atomic hydrogen (H*) supply. Herein, we propose CuO/NiO heterojunction with the assistance of a built-in electric field to enhance mass transfer and H* provision. The built-in electric field in CuO/NiO is successfully formed as demonstrated by X-ray photoelectron spectroscopy and ultraviolet photoemission spectroscopy. The results reveal that CuO/NiO achieves high NO3− reduction activity (100 %) and NH4+ selectivity (100 %) under low NO3− concentration conditions (100 mg/L NO3−, ca. 22.6 mg/L NO3−-N), which is superior to that of many recently reported electrocatalysts. Density functional theory calculations further clarify that the built-in electric field triggers the enhanced adsorption of reactants on CuO/NiO heterojunction interface and strong d-p orbital hybridization between reactants and CuO/NiO. Besides, the free energy diagram of hydrogen evolution reaction of CuO/NiO confirms the realization of enhanced H* provision. Moreover, coupling experiments and consecutive cycle tests demonstrate the potential of CuO/NiO in practical applications. This work may open up a new path and guide the development of efficient electrocatalysts for electrocatalytic reduction of NO3− at low concentrations to NH4+.

First-principles study on MoSSe/ GaTe van der Waals heterostructures: A promising water-splitting photocatalyst

Photocatalytic water splitting using semiconductor electrocatalysts in photoelectrochemical cells is an appealing approach to converting sunlight and water into clean and renewable hydrogen fuel. MoSSe/GaTe der Waals heterojunctions has recently been suggested as a promising photocatalyst for water splitting. Depending on the stacking mode, the two type MoSSe/GaTe heterojunctions have moderate band gaps of 1.081 eV and 1.307 eV, significant visible absorption coefficients, and band-edge positions spanning the redox potential of water. Bader charge and differential charge density analyses show that the GaTe layer loses electrons and the MoSSe monolayer gains electrons, resulting in a built-in electric field pointing from the GaTe layer to the MoSSe layer. Moreover, the Gibbs free energy diagram indicates that solar energy can effectively drive water splitting on MoSSe/GaTe junction. The influence of the bi-axial strain and pH value of water are discussed. Therefore, the MoSSe/GaTe heterostructures are promising for applications in photocatalytic water decomposition.

Oiling-Out: Insights from Gibbsian Surface Thermodynamics by Stability Analysis.

The crystallization process is a significant stage in the pharmaceutical industry. During the process of crystallization with cooling, it is possible for a secondary liquid phase to appear before the formation of crystals. This phenomenon is called "oiling out" or liquid-liquid phase separation (LLPS). In this article, we explore the oiling-out phenomenon in a binary system of water and vanillin using stability analysis based on Gibbsian surface thermodynamics. To obtain the full picture of oiling out, we investigated three cases: droplet-solute-lean liquid equilibrium (DLE), crystal-solute-rich liquid equilibrium (CL'E), and crystal-solute-lean liquid equilibrium (CLE). The phase diagram of the system is plotted using the NRTL model for activity coefficients, along with considering the effect of the interfacial curvature on the phase diagram. From the phase boundaries and free-energy diagram of each case, we showed that the occurrence of the oiling-out phenomenon is justified based on the lower energy barrier of the droplet formation compared to that of the crystal formation. However, the energy level of a stable crystal is significantly lower and hence more stable than that of a stable droplet. Finally, we have determined different regions for droplet and crystal formation in the metastable phase diagram based on their supersaturation and provide insight for the oiling-out phenomenon.

Thermal Decomposition Mechanism of Ammonium Nitrate on the Main Crystal Surface of Ferric Oxide: Experimental and Theoretical Studies.

Understanding the decomposition process of ammonium nitrate (AN) on catalyst surfaces is crucial for the development of practical and efficient catalysts in AN-based propellants. In this study, two types of nano-Fe2O3 catalysts were synthesized: spherical particles with high-exposure (104) facets and flaky particles with high-exposure (110) facets. Through thermal analysis and particle size analysis, it was found that the nanosheet-Fe2O3 catalyst achieved more complete AN decomposition despite having a larger average particle size compared to nanosphere-Fe2O3. Subsequently, the effects of AN pyrolysis on the (110) and (104) facets were investigated by theoretical simulations. Through studying the interaction between AN and crystal facets, it was determined that the electron transfer efficiency on the (110) facet is stronger compared to that on the (104) facet. Additionally, the free-energy step diagrams for the reaction of the AN molecule on the two facets were calculated with the DFT + U method. Comparative analysis led us to conclude that the (110) facet of α-Fe2O3 is more favorable for AN pyrolysis compared to the (104) facet. Our study seeks to deepen the understanding of the mechanism underlying AN pyrolysis and present new ideas for the development of effective catalysts in AN pyrolysis.

A theoretical investigation on the OER and ORR activity of graphene-based TM-N3 and TM-N2X (X = B, C, O, P) single atom catalysts by density functional theory calculations.

Single-atom catalysts (SACs) have shown promising activity in electrocatalysis, such as CO2 reduction (CO2RR), the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR). Transition-metal-embedded N-doped graphene (M-N-C) with TM-N4 active sites (where TM represents a transition metal) is a representative SAC family that has attracted the most attention in both experimental and theoretical studies. However, TM-N3 type M-N-C has received less attention than TM-N4, although some experimental studies have reported its excellent activity in OER and CO2RR. To fully explore the electrocatalytic activity of TM-N3 type M-N-C, in this work we systematically investigate the OER and ORR activity of TM-N3 (TM = Ti, V, Cr, Mn, Fe, Co, Ni, Cu) and TM-N2X (X = B, C, O, P) using density functional theory (DFT) calculation. We examine the formation energies, OER/ORR free energy diagrams, overpotentials, charge density, d-band center and electronic structure of each candidate. Our computational screening shows that CuN3 is a promising bifunctional electrocatalyst for both OER and ORR with low overpotentials of 0.31 V (OER) and 0.44 V (ORR), while CrN3 and CuN2B are predicted to be promising OER catalysts, with overpotentials of 0.26 V and 0.50 V, respectively. A volcano plot derived from the scaling relationships suggests that substituting one nitrogen atom with a hetero atom significantly affects the potential-limiting step in OER/ORR, leading to worse activity in most cases. Density of states and d-band center analyses indicate that the change in OER/ORR activity is strongly correlated with the binding strength of *OH, which is dominated by the location of the d-band center. Our simulation results introduce a comprehensive insight into the activity of the TM-N3 site in TM-N-C, which could benefit the further development of graphene-based SACs for fuel cells and renewable energy applications.

A p-d block synergistic effect enables robust electrocatalytic oxygen evolution

Oxygen evolution reaction (OER), occurring at the anode of electrochemical water splitting requires a comprehensive understanding of oxygen electrocatalysis mechanism to optimize its efficiency. Atomically dispersed transition metal supported by nitrogen-doped carbon is featured with excellent catalytic performance. Herein, we report a Mg/Co bimetal site which utilizes Mg 3p electrons with strong binding of *OH (the first key reaction intermediates in the free energy diagram) to trigger the OER reaction and Co 3d itinerant character to regulate the binding strength of *O. Benefiting from the fine-tuned adsorption/desorption possesses, the optimized catalyst delivers superior OER activity with low overpotential, i.e., 310 mV at a current density of 10 mA/cm2 and 455 mV at 100 mA/cm2. Moreover, the current density is able to be maintained at 10 mA/cm2 for 10 h, consistent with the theoretical simulations for oxidization process, which demonstrates stable configurations after multiple *OH modification, revealing robust applicability in alkaline medium.