Boron-doped graphene as active electrocatalyst for oxygen reduction reaction at a fuel-cell cathode

B-N Co-Doped Graphene: Stability and Catalytic Activity in Oxygen Reduction Reaction - A Theoretical Insight

We systematically investigated the stable configurations and catalytic activity in the Oxygen Reduction Reaction (ORR) of graphene co-doped with boron and nitrogen (B-N) using first-principles methods. Compared to single B/N doping, co-doping with BN is energetically favored. We found that intermediate species of ORR process adsorb on boron atoms, which act as catalytic sites. The presence of neighboring nitrogen atoms around boron plays a crucial role in modulating the catalytic activity of boron. For the same adsorption configuration, the adsorption energy of the adsorbate increases with the number of neighboring nitrogen atoms around boron and generally correlates positively with the number of electrons gained by the adsorbate. Regarding the catalytic activity of ORR, excessively strong adsorption of adsorbates impedes their hydrogenation. The best substrates for ORR catalytic activity are B-N-graphene and N-B2-graphene, with the rate-determining step being the hydrogenation of *OO and overpotentials of 0.49 V and 0.54 V, respectively.

Exploration of metal-free 2D electrocatalysts toward the oxygen electroreduction

The advancement of economical and readily available electrocatalysts for the oxygen reduction reaction (ORR) holds paramount importance in the advancement of fuel cells and metal-air batteries. Recently, 2D non-metallic materials have obtained substantial attention as viable alternatives for ORR catalysts due to their manifold advantages, encompassing low cost, ample availability, substantial surface-to-volume ratio, high conductivity, exceptional durability, and competitive activity. The augmented ORR performances observed in metal-free 2D materials typically arise from heteroatom doping, defects, or the formation of heterostructures. Here, the authors delve into the realm of electrocatalysts for the ORR, pivoting around metal-free 2D materials. Initially, the merits of metal-free 2D materials are explored and the reaction mechanism of the ORR is dissected. Subsequently, a comprehensive survey of diverse metal-free 2D materials is presented, tracing their evolutionary journey from fundamental concepts to pragmatic applications in the context of ORR. Substantial importance is given on the exploration of various strategies for enhancing metal-free 2D materials and assessing their impact on inherent material performance, including electronic properties. Finally, the challenges and future prospects that lie ahead for metal-free 2D materials are underscored, as they aspire to serve as efficient ORR electrocatalysts.

Progress of Nonmetallic Electrocatalysts for Oxygen Reduction Reactions

As a key role in hindering the large-scale application of fuel cells, oxygen reduction reaction has always been a hot issue and nodus. Aiming to explore state-of-art electrocatalysts, this paper reviews the latest development of nonmetallic catalysts in oxygen reduction reactions, including single atoms doped with carbon materials such as N, B, P or S and multi-doped carbon materials. Afterward, the remaining challenges and research directions of carbon-based nonmetallic catalysts are prospected.

Atomistic Understanding of Two-dimensional Electrocatalysts from First Principles

Two-dimensional electrocatalysts have attracted great interest in recent years for renewable energy applications. However, the atomistic mechanisms are still under debate. Here we review the first-principles studies of the atomistic mechanisms of common 2D electrocatalysts. We first introduce the first-principles models for studying heterogeneous electrocatalysis then discuss the common 2D electrocatalysts with a focus on N doped graphene, single metal atoms in graphene, and transition metal dichalcogenides. The reactions include hydrogen evolution, oxygen evolution, oxygen reduction, and carbon dioxide reduction. Finally, we discuss the challenges and the future directions to improve the fundamental understanding of the 2D electrocatalyst at atomic level.

Site dependent catalytic water dissociation on an anisotropic buckled black phosphorus surface

Black phosphorus (BP) is unique among 2D materials due to its anisotropic puckered structure. It has been used as a multifunctional catalyst for various purposes. In this study, we performed first principles molecular dynamics simulations to understand the water-splitting reaction on a bi-layer BP surface. We focused on the site-specific aqueous reactivity of the buckled surface. A difference in the axis-dependent reactivity is observed owing to edge defects and exposed sites. Thus, we believe that BP edges, which significantly affect the interfacial water or organic solvent molecules, must exhibit very different edge-dependent reactivity. Experiments suggested the increasing catalytic efficiency of undisturbed BP in the order bulk, few-layered BP, and BP quantum dots. We choose three active sites to investigate the mechanistic details of the OER: the zigzag (ZZ), armchair (AC), and bulk sites. This study will provide insight into the enhanced catalytic activity when more edges are exposed as the active surface. We hope to clarify the reactive pathway in an aqueous solution supported by bi-layer BP by exploring the two different mechanisms for forming the OOH* complex. We explore and report two mechanisms: a simple push-pull reaction for oxygen-oxygen bond formation, the nucleophilic attack by formed OH^- and an attack by a water molecule. The free energy barriers procured for mechanism 1 taking place at the zigzag, armchair, and bulk sites are 7.59 ± 0.33, 9.04 ± 0.01, and 12.80 ± 0.09 kcal mol^-1, respectively. For mechanism 2 the free energy barriers are 7.62 ± 0.11, 9.15 ± 0.16, and 11.63 ± 0.11 kcal mol^-1 for the ZZ, AC, and bulk sites. The interlink between both the mechanisms is established concerning the reported free energy barriers for OOH* formation. The ZZ site is found to lower the activation barrier for the rate-determining step, followed by the AC and bulk.

Conversion of rice husk biomass into electrocatalyst for oxygen reduction reaction in Zn-air battery: Effect of self-doped Si on performance

An outstanding oxygen reduction reaction (ORR) electrocatalyst is firstly developed deriving from sustainable rice husk (RH) biomass. Benefiting from self-doped Si in RH, the higher proportion of pyridine N, graphite N and expecially Fe-N_x as well as thiophene S contents were produced in Si-Fe/S/N-RH₃ in comparison with those of Si-free Fe/S/N-RH_3. Consequently, the half-wave potential of 0.89 V and the onset potential of 0.96 V are achieved for Si-Fe/S/N-RH₃, outperforming the benchmark electrocatalyst Pt/C and other Fe-based electrocatalysts reported in alkaline media. Furthermore, it is found that the exisentence of self-doped Si can improve the graphitization degree of the catalyst, leading to the long-term stability (larger than 85% retention after 40000 s) and prominent methanol tolerance for Si-Fe/S/N-RH₃. In addition, Si-Fe/S/N-RH₃ shows a power density of 86.2 mW cm^-2 and excellent durability in Zn-air battery. The work highlights the potential to develop sustainable and cost-effective ORR electrocatalysts from waste biomass as the substitute for precious metal catalysts.

Activity origin of boron doped carbon cluster for thermal catalytic oxidation: Coupling effects of dopants and edges

Catalytic oxidation plays important roles in energy conversion and environment protection. Boron-doped crystalline carbocatalyst has been demonstrated effective; however, the application potential of boron-doped amorphous carbocatalyst remains to be explored. For amorphous carbon material, finite-sized carbon clusters are the basic structural units, which exhibit unique activity due to edge and size effect. Herein, using sulfur dioxide (SO₂) and carbon monoxide (CO) oxidation as probe thermal-catalysis reactions, we found the distribution and reactivity of active sites in boron-doped carbon clusters are simultaneously determined by dopants and edges. According to comparisons of oxygen (O₂) chemisorption energy at different sites of symmetric and non-symmetric carbon cluster, the most active site is found to be the edge carbon atom with high electron donation ability, which can be accurately identified by electrophilic Fukui function. More importantly, the reactivity of boron-doped cluster is simultaneously influenced by doping configuration and the type of edge, based on which -O-B-O- configuration embedded into K-region edge (isolated carbon-carbon double bonds that do not belong to Clar sextet) is predicted to exhibit the highest reactivity among various boron doping configurations. This work clarifies unique activity origin of heteroatom-doped amorphous carbon materials, providing new insights into designing high-performance carbocatalysts.

Precisely controlled synthesis of Co/N species containing porous carbon for oxygen reduction reaction via anion exchange and CO2 activation

The synthesis strategy of highly dispersed Co/N-doped porous carbon materials using anion exchange resin and ionic liquids.

Boron-Doped Edges as Active Sites for Water Adsorption in Activated Carbons

Investigating the surface properties of heteroatom-doped carbon materials is essential because these versatile materials have found use in a variety of energy and environmental applications; an understanding of these properties would also lead to an improved appreciation of the direct interaction between the reactant and the functionalized surface. Herein, we explore the effect of boron (B) doping on the surface properties of activated carbon (AC) materials based on their water adsorption behavior and oxygen reduction reaction. In the high-temperature B doping process, B-doped AC materials at 1400 °C exhibit an open pore structure with B-O bonds, whereas at a temperature of 1600 °C, a nonporous structure containing a large amount of B-C bonds prevails. The B-O species act as active sites for water adsorption on the carbon surface. On the basis of the isothermal adsorption heat, we suggest that B atoms are present at the pore openings and on the surfaces. The B-O moieties at the open edges improve the electrocatalytic activity, whereas the B-C bonds at the closed edges decrease the electrocatalytic activity because of the stable structure of these bonds. Our findings provide new evidence for the electrocatalytic properties associated with the structure of B-doped edges.

Comparative first principles-based molecular dynamics study of catalytic mechanism and reaction energetics of water oxidation reaction on 2D-surface

The study of the water-splitting process, which can proceed in 2e^- as well as 4e^- pathway, reveals that the process is entirely an uphill process, and the third step, that is, the oxooxo bond formation is the rate-determining step. The kinetic barrier of the oxygen evolution reaction (OER) on the 2D material catalysts in the presence of explicit solvents is scarcely studied. Here, we investigate the dynamics of the OER on the undoped graphene and the activation energy barrier of each step using first principles molecular dynamics simulations. Here we provide a detailed analysis of the kinetics of all the 4e^- transfer steps of OER on the graphene surface. We also compare the accuracy of one of the density functional theory (DFT) functionals and density functional based tight binding (DFTB) method in explaining the OER steps. The comparative study reveals that DFTB can be used for performing metadynamics simulations quipped with much less computational cost than DFT functionals. By both Perdew-Burke-Ernzerhof and DFTB methods, the third step is revealed to be the rate-determining step with an energy barrier of 21.19 ± 0.51 and 20.23 ± 0.20 kcal mol^-1 , respectively. DFTB gives an impression of being successful in predicting the energy barriers of OER in 4e- transfer pathway and comparable to the DFT method, and we would like to extend the use of DFTB for further studies with a sizable and complex system.

Effects of Doped N, B, P, and S Atoms on Graphene toward Oxygen Evolution Reactions

Molecular oxygen and hydrogen can be obtained from the water-splitting process through the electrolysis technique. However, harnessing energy is very challenging in this way due to the involvement of the 4e- reaction pathway, which is associated with a substantial amount of reaction barrier. After the report of the first N-doped graphene acting as an oxygen reduction reaction catalyst, the scientific community set out on exploring more reliable doping materials, better material engineering techniques, and developing computational models to explain the interfacial reactions. In this study, we modeled the graphene surface with four different nonmetal doping atoms N, B, P, and S individually by replacing a carbon atom from one of the graphitic positions. We report the mechanism of the complete catalytic cycle for each of the doped surfaces by the doping atom. The energy barriers for individual steps were explored using the biased first-principles molecular dynamics simulations to overcome the high reaction barrier. We explain the active sites and provide a comparison between the activation energy obtained by the application of two computational methods. Observing the rate-determining step, that is, oxo-oxo bond formation, S-doped graphene is the most effective. In contrast, N-doped graphene seems to be the least useful for oxygen evolution catalysis compared to the undoped graphene surface. B-doped graphene and P-doped graphene have an equivalent impact on the catalytic cycle.

Catalytic role of graphitic nitrogen atoms in the CO oxidation reaction over N-containing graphene: a first-principles mechanistic evaluation

The catalytic role of graphitic nitrogen atoms of a series of nitrogen-doped graphene surfaces is explored for low-temperature oxidation of CO using periodic DFT calculations.

Novel joint catalytic properties of Fe and N co-doped graphene for CO oxidation

Using density functional theory, we have performed detailed calculations of the joint catalytic activity of graphene co-doped with Fe and N atoms. The Fe atom can be located on single vacancy graphene and acts as the active site. Due to the strong attraction of the Fe ion, the O-O bond length of the O2 molecule is elongated, which decreases the bonding energy between the O atoms. The energy barrier of CO oxidization is 0.84 eV. When N atoms are doped into the graphene, the interactions between the Fe ions and O2 molecules are stronger, and the O-O bond lengths are elongated further, which makes the desorption of the quasi-CO2 molecule easier. The energy barriers are reduced to 0.62 eV, 0.49 eV, and 0.33 eV for graphene doped with one, two and three N atoms, respectively. The O atom remaining on the Fe ion can form a CO2 molecule with an additional CO molecule. The produced CO2 molecule can be released with a small or even zero energy barrier by adsorbing an O2 molecule. The adsorbed O2 molecule is then involved in the next reaction process, and the material can be used as a recycled catalyst.

Revealing the role of nitrogen dopants in tuning the electronic and optical properties of graphene quantum dots via a TD-DFT study

Graphene quantum dots (GQDs) have been suggested to have a wide range of applications due to their unique electronic and optical properties. Moreover, heteroatom doping has become a viable way to fine-tune the properties of GQDs. However, the working principle of the doping strategy is still not conclusive. In this study, the effects of size, configuration of the nitrogen dopant, and N/C ratio on the electronic and optical properties of GQDs have been carefully examined. First, the variation of the adsorption wavelength of pristine GQDs was evaluated for which a linear relation is established against different diameters. Moreover, it is found that both the configuration and content of nitrogen dopants have a significant impact on the adsorption wavelength and band gap of GQDs. In particular, different nitrogen species could have exactly opposite effects on the adsorption behavior. The origin of the nitrogen doping effect is calibrated from orbital localization, charge analysis, natural transition orbitals, and atomic contribution towards excitation. It is noted that nitrogen doping can simultaneously reduce both light adsorption energy and emission energy compared with the pristine one. This study provides an insightful explanation for the electronic and optical properties of GQDs and consolidates the theory base of the doping strategy.

Oxygen Reduction Reaction Catalyzed by Pt3M (M = 3d Transition Metals) Supported on O-doped Graphene

Pt3M (M = 3d transition metals) supported on oxygen-doped graphene as an electrocatalyst for oxygen reduction was investigated using the periodic density functional theory-based computational method. The results show that oxygen prefers to adsorb on supported Pt3M in a bridging di-oxygen configuration. Upon reduction, the O–O bond breaks spontaneously and the oxygen adatom next to the metal–graphene interface is hydrogenated, resulting in co-adsorbed O* and OH* species. Water formation was found to be the potential-limiting step on all catalysts. The activity for the oxygen reduction reaction was evaluated against the difference of the oxygen adsorption energy on the Pt site and the M site of Pt3M and the results indicate that the oxygen adsorption energy difference offers an improved prediction of the oxygen reduction activity on these catalysts. Based on the analysis, Pt3Ni supported on oxygen-doped graphene exhibits an enhanced catalytic performance for oxygen reduction over Pt4.

Synergistic effect on BCN nanomaterials for the oxygen reduction reaction – a kinetic and mechanistic analysis to explore the active sites

The rGO doped with boron and nitrogen reduce the oxygen via the dissociative four-electron pathway whereas the two-electron oxygen reduction reaction is more predominant on the rGO doped with either of the two individual heteroatoms.

Recent advances in two-dimensional materials and their nanocomposites in sustainable energy conversion applications

Two-dimensional (2D) materials have a wide platform in research and expanding nano- and atomic-level applications. This study is motivated by the well-established 2D catalysts, which demonstrate high efficiency, selectivity and sustainability exceeding that of classical noble metal catalysts for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and/or hydrogen evolution reaction (HER). Nowadays, the hydrogen evolution reaction (HER) in water electrolysis is crucial for the cost-efficient production of a pure hydrogen fuel. We will also discuss another important point related to electrochemical carbon dioxide and nitrogen reduction (ECR and N2RR) in detail. In this review, we mainly focused on the recent progress in the fuel cell technology based on 2D materials, including graphene, transition metal dichalcogenides, black phosphorus, MXenes, metal-organic frameworks, and metal oxide nanosheets. First, the basic attributes of the 2D materials were described, and their fuel cell mechanisms were also summarized. Finally, some effective methods for enhancing the performance of the fuel cells based on 2D materials were also discussed, and the opportunities and challenges of 2D material-based fuel cells at the commercial level were also provided. This review can provide new avenues for 2D materials with properties suitable for fuel cell technology development and related fields.

Electronic properties and oxygen reduction reaction catalytic activity of h-BeN2 and MgN2 by first-principles calculations

Currently, identifying suitable oxygen reduction reaction (ORR) catalysts in novel two-dimensional (2D) materials has attracted more and more research attention. Here, we have studied the catalytic activities of 2D h-BeN₂ and MgN₂ monolayers for ORR by using first-principles calculations. The calculated results reveal that the direct quasiparticle bandgap of BeN₂ monolayer is 3.32 eV, and the indirect bandgap of MgN₂ is 3.42 eV. 2D h-BeN₂ and MgN₂ exhibit high exciton binding energies of 1.07 and 0.83 eV respectively, and their optical properties are determined by bound exciton transitions due to the strong quantum confinement effects. Importantly, h-BeN₂ and MgN₂ monolayers with positive-charged (+1.6 e) metal atom (Be/Mg) on the surface exhibit excellent adsorption ability for O₂ and ORR intermediates, and show better CO tolerance than Pt(111). The calculated free energy plots are always downhill for ORR catalyzed by BeN₂ in both acid and alkaline environments, and by MgN₂ in alkaline environments. The detailed reaction mechanism analyses show that high-efficient four-electron pathway is the optimal pathway for ORR catalyzed by BeN₂ in acid environments. Surprisingly, there is a low overpotential of 0.45 eV for ORR catalyzed by BeN₂ in the acid solution and no overpotential in the alkaline solution. Our studies found for the first time that 2D h-BeN₂ shows huge potential as a non-precious metal ORR catalyst in acid and alkaline environments.

Size, Composition, and Support-Doping Effects on Oxygen Reduction Activity of Platinum-Alloy and on Non-platinum Metal-Decorated-Graphene Nanocatalysts

Recent investigations reported in the open literature concerning the functionalization of graphene as a support material for transition metal nanoparticle catalysts have examined isolated systems for their potential Oxygen Reduction Reaction (ORR) activity. In this work we present results which characterize the ability to use functionalized graphene (via dopants B, N) to upshift and downshift the adsorption energy of mono-atomic oxygen, O* (the ORR activity descriptor on ORR Volcano Plots), for various compositions of 4-atom, 7-atom, and 19-atom sub-nanometer binary alloy/intermetallic transition metal nanoparticle catalysts on graphene (TMNP-MDG). Our results show several important and interesting features: (1) that the combination of geometric and electronic effects makes development of simple linear mixing rules for size/composition difficult; (2) that the transition from 4- to 7- to 19-atom TMNP on MDG has pronounced effects on ORR activity for all compositions; (3) that the use of B and N as dopants to modulate the graphene-TMNP electronic structure interaction can cause shifts in the oxygen adsorption energy of 0.5 eV or more; (4) that it might be possible to make specific doped-graphene-Ni_xCu_y TMNP systems which fall close to the Volcano Peak for ORR. Our results point to systems which should be investigated experimentally and may improve the viability of future fuel cell or other ORR applications, and provide new paths for future investigations of more detail for TMNP-MDG screening.

Theoretical investigation of the ORR on boron-silicon nanotubes (B-SiNTs) as acceptable catalysts in fuel cells

Here, the potential of boron doped silicon nanotubes (7, 0) as ORR catalysts is examined. Acceptable paths for the ORR on studied catalysts are examined through DFT. The optimum mechanism of the ORR on the surface of B2-SiNT (7, 0) is shown. The ORR on the surface of B2-SiNTs (7, 0) can continue through LH and ER mechanisms. The calculated beginning voltage for the ORR on B2-SiNTs (7, 0) is 0.37 V and it is smaller than the beginning voltage (0.45 V) for platinum-based catalysts. In the acidic solution the beginning voltage for the oxygen reduction process can be evaluated to be 0.97 V, which corresponds to 0.37 V as a minimum overvoltage for the ORR. The B2-SiNTs (7, 0) are suggested as an ORR catalyst in acidic environments.

Activating Graphyne Nanosheet via sp-Hybridized Boron Modulation for Electrochemical Nitrogen Fixation

Exploring new metal-free catalysts with high activity for nitrogen reduction reaction (NRR) is highly desirable but remains a big challenge. Graphyne (GY) is a typical two-dimensional carbon material with many excellent properties. However, the NRR has rarely been envisaged on a GY-based metal-free catalyst up to now. Density functional theory calculations reveal that although pristine GY is inactive for N₂ reduction, boron modulation can endow it with efficient activity toward NRR. Natural bond orbitals analysis, spin/charge density distributions, and free energy change diagrams are performed and discussed. Three boron doping formats including sp²-substituted, sp-substituted, and adsorbed configuration are considered. The obtained data show sp-substitution will induce local moderate spin and charge densities at the boron site on the GY surface, which is convenient for N₂ adsorption and activation, and conductive to N-related intermediates formation and transformation. Moreover, the incorporated sp-hybridized boron can provide one empty p orbital and one occupied p orbital around itself, which plays a key role as an electron reservoir to accept electrons from and donate electrons to the adsorbed N-related species, and thus facilitate N₂ reduction and ammonia synthesis. Henceforth, it provides more opportunities for preparing GY and other carbon materials as efficient catalysts toward renewable energy conversion and storage.

Investigation of performance of aluminum doped carbon nanotube (8, 0) as adequate catalyst to oxygen reduction reaction

The discovery of novel nano-catalysts to oxygen reduction reaction with high performance due to various application of fuel cells is very important. In present study the potential of aluminum doped carbon nanotube (8, 0) to oxygen reduction reaction in acidic condition was examined through theoretical models. The possible paths to oxygen reduction reaction on Al₂-CNT (8, 0) surfaces were investigated and optimal path was identified from thermodynamic standpoint. Results indicated that the Al₂-CNT (8, 0) catalyzed the oxygen reduction reaction through the Eley-Rideal and Langmuir-Hinshelwood mechanisms. The Al₂-CNT (8, 0) catalyst has much better methanol and CO tolerance than platinum-based catalysts. In this study, the overpotential value of oxygen reduction reaction on aluminum doped carbon nanotube (8, 0) surface (ca 0.38 V) is lower than corresponding values on platinum-based catalysts (ca 0.45 V). Finally, results demonstrated that the Al₂-CNT (8, 0) can be proposed as efficiency catalyst to oxygen reduction reaction.

Origin of the catalytic activity of phosphorus doped MoS2 for oxygen reduction reaction (ORR) in alkaline solution: a theoretical study

Phosphorus doped MoS₂ nanosheets (P-doped MoS₂) have been reported as excellent oxygen reduction reaction (ORR) catalysts with four-electron selectivity in alkaline solution. By performing density functional theory (DFT) calculations, we revealed the detailed reaction mechanism and the key reaction sites on surface of P-doped MoS₂ for ORR catalysis. The double P-doped MoS₂ (2P-MoS₂) is calculated to be more stable than the single P-doped MoS₂ (P-MoS₂), and the configuration with two P atoms in neighboring sites exhibits the highest stability. The surface of P-doped MoS₂ is found highly active for dissociation of O₂. Comparative calculations reveal that P-MoS₂ is unsuitable as ORR catalyst due to the high dissociation barrier of H₂O (1.19 and 2.06 eV for the first and second adsorbed H₂O), while the 2P-MoS₂ shows good ORR catalytic activity with much lower dissociation barrier of H₂O (0.62 eV). Furthermore, we elucidated that the ORR catalytic activity in 2P-MoS₂ originates from the activated S2 atom, which provides an extra adsorption site for the first H₂O and the following OH group benefited from the enhanced hydrogen bond interaction. Our results illustrate the mechanisms of doped MoS₂ based catalysts and provide rational way for designing ORR catalysts with high activity.

Computational study of the NO, SO2, and NH3 adsorptions on fragments of 3N-graphene and Al/3N graphene

The adsorption properties of common gas molecules (NO, NH₃, and SO₂) on the surface of 3N-graphene and Al/3N graphene fragments are investigated using density functional theory. The adsorption energies have been calculated for the most stable configurations of the molecules on the surface of 3N-graphene and Al/3N graphene fragments. The adsorption energies of Al/3N graphene-gas systems are -220.5 kJ mol^-1 for Al/3NG-NO, -111.9 kJ mol^-1 for Al/3NG-NH₃, and -347.7 kJ mol^-1 for Al/3NG-SO₂, respectively. Compared with the 3N-graphene fragment, the Al/3N graphene fragment has significant adsorption energy. Furthermore, the molecular orbital, density of states, and electron densities distribution were used to explore the interaction between these molecules and the surface. We found that orbital hybridization exists between these molecules and the Al/3N graphene surface, which indicates that doping Al significantly increases the interaction between the gas molecules and Al/3N graphene. In addition, compared with Li, Al can more powerfully enhance adsorption of the 3N-graphene fragment. The results indicate that Al/3N graphene can be viewed as a new nanomaterial adsorbent for NO, NH₃, and SO₂.

Modulating the oxygen reduction activity of heteroatom-doped carbon catalysts via the triple effect: charge, spin density and ligand effect

For metal-doped-G and dual-heteroatom-doped-G, the triple effect can activate double carbon sites, and lead to the ORR following the dissociative mechanism, which breaks through the activity limitation of the association mechanism, and further enhances the catalytic activity for the ORR.

To enhance the intrinsic activity of and increase the number of active sites in heteroatom-doped graphene (doped-G), it is necessary to recognize the origin of its catalytic activity, and to search for a universal definition and description of the different active sites. Herein, we report an evaluation of a series of heteroatom-doped graphene materials as oxygen reduction reaction (ORR) catalysts with the aid of density functional theory (DFT) calculations. The results of the DFT calculations indicate that the intrinsic catalytic activity and the ORR mechanism depend on the triple effect, that is, the charge, the spin density and the coordinate state (ligand effect) of the carbon sites. The contribution of the above effects towards increasing the binding energies of *OOH or *OH has the following order: negative charge effect < positive charge effect < low spin effect < ligand effect < high spin effect. For nonmetallic single-heteroatom-doped-G, the triple effect separately activates the carbon sites around the doped atom. On each single carbon active site, only the end-on adsorption of *OOH is preferred, leading to the ORR following the associative mechanism, which has an intrinsic limitation in its overpotential of 0.44 V. However, for metal-doped-G and dual-heteroatom-doped-G, the triple effect can activate double carbon sites, and lead to the ORR following the dissociative mechanism, which breaks through the activity limitation of the associative mechanism, and further enhances the catalytic activity for the ORR. With comprehensive theoretical calculation, we conclude that it is possible for the heteroatom-doped-G, if well-modulated via the triple effect, to exceed Pt-based materials in catalysis of the ORR.

Well-Defined Cobalt Catalyst with N-Doped Carbon Layers Enwrapping: The Correlation between Surface Atomic Structure and Electrocatalytic Property

Admittedly, the surface atomic structure of heterogenous catalysts toward the electrochemical oxygen reduction reaction (ORR) are accepted as the important features that can tune catalytic activity and even catalytic pathway. Herein, a surface engineering strategy to controllably synthesize a carbon-layer-wrapped cobalt-catalyst from 2D cobalt-based metal-organic frameworks is elaborately demonstrated. Combined with synchrotron radiation X-ray photoelectron spectroscopy, the soft X-ray absorption near-edge structure results confirmed that rich covalent interfacial CoNC bonds are efficiently formed between cobalt nanoparticles and wrapped carbon-layers during the polydopamine-assisted pyrolysis process. The X-ray absorption fine structure and corresponding extended X-ray absorption fine structure spectra further reveal that the wrapped cobalt with Co-N coordinations shows distinct surface distortion and atomic environmental change of Co-based active sites. In contrast to the control sample without coating layers, the 800 °C-annealed cobalt catalyst with N-doped carbon layers enwrapping achieves significantly enhanced ORR activity with onset and half-wave potentials of 0.923 and 0.816 V (vs reversible hydrogen electrode), highlighting the important correlation between surface atomic structure and catalytic property.

Theoretical study of the CO, NO, and N2 adsorptions on Li-decorated graphene and boron-doped graphene

The adsorption properties of common gas molecules (CO, NO, and N2) on the surface of Li-decorated pristine graphene and Li-decorated boron doped graphene are investigated using density functional theory. The adsorption energy, charge transfer, and density of states of gas molecules on three surfaces have been calculated and discussed, respectively. The results show that Li-decorated pristine graphene has strong interaction with CO and N2. Compared with Li-decorated pristine graphene, Li-decorated boron doped graphene exhibit a comparable adsorption ability of CO and N2. Moreover, Li-decorated boron doped graphene have a more significant adsorption energy to NO than that of Li-decorated pristine graphene because of the chemical interaction of the NO gas molecule. The strong interaction between the NO molecule and substrate (Li-decorated boron doped graphene) induces dramatic changes to the electrical conductivity of Li-decorated boron doped graphene. The results indicate that Li-decorated boron doped graphene would be an excellent candidate for sensing NO gas.

Boron-doped graphene as a promising electrocatalyst for NO electrochemical reduction: a computational study

The B-doped graphene is a quite promising metal free electrocatalyst for NO reduction to N₂O and NH₃.

Methanol decomposition reactions over a boron-doped graphene supported Ru–Pt catalyst

In-depth investigations of adsorption and decomposition of methanol over boron-doped graphene supported Ru–Pt catalyst are presented using periodic density functional theory calculations. Methanol decomposition on such catalyst proceeds through formation of methoxide (CH₃O) and via stepwise dehydrogenation of formaldehyde (CH₂O), formyl (CHO), and carbon monoxide (CO).