Doping monolayer graphene with single atom substitutions

Fabricating polyoxometalates-stabilized single-atom site catalysts in confined space with enhanced activity for alkynes diboration

Effecting the synergistic function of single metal atom sites and their supports is of great importance to achieve high-performance catalysts. Herein, we successfully fabricate polyoxometalates (POMs)-stabilized atomically dispersed platinum sites by employing three-dimensional metal-organic frameworks (MOFs) as the finite spatial skeleton to govern the accessible quantity, spatial dispersion, and mobility of metal precursors around each POM unit. The isolated single platinum atoms (Pt₁) are steadily anchored in the square-planar sites on the surface of monodispersed Keggin-type phosphomolybdic acid (PMo) in the cavities of various MOFs, including MIL-101, HKUST-1, and ZIF-67. In contrast, either the absence of POMs or MOFs yielded only platinum nanoparticles. Pt₁-PMo@MIL-101 are seven times more active than the corresponding nanoparticles in the diboration of phenylacetylene, which can be attributed to the synergistic effect of the preconcentration of organic reaction substrates by porous MOFs skeleton and the decreased desorption energy of products on isolated Pt atom sites.

It is of great significance to exert the synergistic effect between single atom and support. Here, the authors prepare polyoxometalates-stabilized single-atom site catalysts in confined space with enhanced activity for alkynes diboration.

Antiferromagnetic spin ordering in two-dimensional honeycomb lattice of SiP3

Magnetism in low-dimensional materials has been of sustained interest due to its intriguing quantum mechanical origin and promising device applications. Here, we propose a buckled honeycomb lattice of stoichiometry SiP₃, a two-dimensional binary group-IV and V material that exhibits an antiferromagnetic ground state with itinerant electrons. Here we perform elemental Si substitution in pristine blue phosphorene to downshift the Fermi energy and induce the Fermi instability that results in a spin polarized ground state. Within first-principles calculations, we observe antiferromagnetic spin alignment between adjacent ferromagnetic triangular domains where each Si atom is coupled with three neighboring P atoms with a ferromagnetic interaction. Such unique spin structure and resulting magnetic ground state are unprecedented in defect-free two-dimensional materials made of only p-block elements. This metal-free magnetism can be exploited for advanced spintronic and memory storage applications.

CO oxidation over defective and nonmetal doped MoS2monolayers

Defective (missing S atoms) and nonmetal (C- and N-) doped MoS₂monolayers in the 2H and 1T' phases have been evaluated for catalyzing CO oxidation based on first-principles calculations. For the reaction 2CO + O₂→ 2CO₂, the oxidization of the first CO molecule is fairly easy and sometimes is even spontaneous, as the O₂ molecule is highly activated or dissociates upon adsorption. However, for the defective (2H-), C-doped (1T'-), and N-doped (2H- and 1T'-) MoS₂monolayers, the remaining O^*adatom often refuses to react with other CO molecules and is hard to be removed (barrier > 1.20 eV). Only when over the C-doped 2H- and defective 1T'-MoS₂monolayers, the removal of the second O^*adatom requires to overcome moderate barriers (0.74 and 0.88 eV, respectively) by reacting with another CO molecule via the Eley-Rideal mechanism and the catalysts are recovered. The barriers can be further reduced by applying either tensile or compressive strain to the MoS₂nanosheet. In contrast, the Langmuir-Hinshelwood mechanism is followed over the metal-containing MoS₂nanosheets, as the bigger size of metal dopants allow the co-adsorption of CO and O₂. Therefore, the C-doped 2H- and defective 1T'-MoS₂monolayers are promising nonmetal-doped catalysts for CO oxidation.

Electronic excitation in graphene under single-particle irradiation

Single-particle irradiation is a typical condition in space applications, which could be detrimental for electronic devices through processes such as single-event upset or latch-up. For functional devices made of few-atom-thick monolayers that are entirely exposed to the environment, the irradiation effects could be manifested through localized or delocalized electronic excitation, in addition to lattice defect creation. In this work, we explore the single-H irradiation effects on bare or coated graphene monolayers. Real-time time-dependent density functional theory-based first-principles calculation results elucidate the evolution of charge densities in the composite system, showing notable charge excitation but negligible charge deposition. A hexagonal boron nitride coating layer does not protect graphene from these processes. Principal component analysis demonstrates the dominance of localized excitation accompanied by nuclear motion, bond distortion and vibration, as well as a minor contribution from delocalized plasmonic excitation. The significance of coupled electron-ion dynamics in modulating the irradiation processes is identified from comparative studies on the spatial and temporal patterns of excitation for unconstrained and constrained lattices. The stopping power or energy deposition is also calculated, quantifying the dissipative nature of charge density excitation. This study offers fundamental understandings of the single-particle irradiation effects on optoelectronic devices constructed from low-dimensional materials, and inspires unconventional techniques to excite the electrons and ions in a controllable way.

Doping Graphene with Substitutional Mn

We report the incorporation of substitutional Mn atoms in high-quality, epitaxial graphene on Cu(111), using ultralow-energy ion implantation. We characterize in detail the atomic structure of substitutional Mn in a single carbon vacancy and quantify its concentration. In particular, we are able to determine the position of substitutional Mn atoms with respect to the Moiré superstructure (i.e., local graphene-Cu stacking symmetry) and to the carbon sublattice; in the out-of-plane direction, substitutional Mn atoms are found to be slightly displaced toward the Cu surface, that is, effectively underneath the graphene layer. Regarding electronic properties, we show that graphene doped with substitutional Mn to a concentration of the order of 0.04%, with negligible structural disorder (other than the Mn substitution), retains the Dirac-like band structure of pristine graphene on Cu(111), making it an ideal system in which to study the interplay between local magnetic moments and Dirac electrons. Our work also establishes that ultralow-energy ion implantation is suited for substitutional magnetic doping of graphene. Given the flexibility, reproducibility, and scalability inherent to ion implantation, our work creates numerous opportunities for research on magnetic functionalization of graphene and other two-dimensional materials.

Robust Magnetoelectric Effect in the Decorated Graphene/In2Se3 Heterostructure

The magnetoelectric effect is a fundamental physical phenomenon that synergizes electric and magnetic degrees of freedom to generate distinct material responses like electrically tuned magnetism, which serves as a key foundation of the emerging field of spintronics. Here, we show by first-principles studies that ferroelectric (FE) polarization of an In₂Se₃ monolayer can modulate the magnetism of an adjacent transition-metal (TM)-decorated graphene layer via a ferroelectrically induced electronic transition. The TM nonbonding d-orbital shifts downward and hybridizes with carbon-p states near the Fermi level, suppressing the magnetic moment, under one FE polarization, but on reversed FE polarization this TM d-orbital moves upward, restoring the original magnetic moment. This finding of robust magnetoelectric effect in the TM-decorated graphene/In₂Se₃ heterostructure offers powerful insights and a promising avenue for experimental exploration of ferroelectrically controlled magnetism in two-dimensional (2D) materials.

Single-atom catalysis in advanced oxidation processes for environmental remediation

This review presents the recent advances in synthetic strategies, characterisation, and computations of carbon-based single-atom catalysts, as well as their innovative applications and mechanisms in advanced oxidation technologies.

Radical-Assisted Formation of Pd Single Atoms or Nanoclusters on Biochar

Supported single atom or nanocluster catalysts have been widely studied due to their excellent catalytic properties. Many methods to prepare such catalysts start with constructing defects on supports, and the main focus is to improve dispersion and stability of the active sites. This paper for the first time reports a radical-assisted method to prepare single atom or nanocluster Pd on a biochar. The char was prepared by pyrolyzing walnut shell at 600°C under N₂, and Pd was loaded on the char by impregnating with palladium acetate in toluene under an oxygen-free atmosphere. It is found that there are three types of radicals in the fresh char (F-Char-600), two of them may adsorb/bond with O₂ or Pd²⁺ resulting in decreases in the char's radical concentration. The Pd on F-Char-600 for 24 h impregnation are single atoms (0.1-0.3 nm, 2%) and nanoclusters (0.3-1.2 nm, 98%), which grow larger (0.3-4 nm, 100%) for 84 h impregnation. The Pd on N₂ purged O₂-adsorbed-char (N-O-Char-600) is much larger in size. The bond between Pd and char is probably C-Pd in F-Char-600 or C-O-Pd in N-O-Char-600.

Vacancies in graphene: an application of adiabatic quantum optimization

Quantum annealers have grown in complexity to the point that quantum computations involving a few thousand qubits are now possible. In this paper, with the intentions to show the feasibility of quantum annealing to tackle problems of physical relevance, we used a simple model, compatible with the capability of current quantum annealers, to study the relative stability of graphene vacancy defects. By mapping the crucial interactions that dominate carbon-vacancy interchange onto a quadratic unconstrained binary optimization problem, our approach exploits the ground state as well as the excited states found by the quantum annealer to extract all the possible arrangements of multiple defects on the graphene sheet together with their relative formation energies. This approach reproduces known results and provides a stepping stone towards applications of quantum annealing to problems of physical-chemical interest.

Theoretical Understandings of Graphene-based Metal Single-Atom Catalysts: Stability and Catalytic Performance

Research on heterogeneous single-atom catalysts (SACs) has become an emerging frontier in catalysis science because of their advantages in high utilization of noble metals, precisely identified active sites, high selectivity, and tunable activity. Graphene, as a one-atom-thick two-dimensional carbon material with unique structural and electronic properties, has been reported to be a superb support for SACs. Herein, we provide an overview of recent progress in investigations of graphene-based SACs. Among the large number of publications, we will selectively focus on the stability of metal single-atoms (SAs) anchored on different sites of graphene support and the catalytic performances of graphene-based SACs for different chemical reactions, including thermocatalysis and electrocatalysis. We will summarize the fundamental understandings on the electronic structures and their intrinsic connection with catalytic properties of graphene-based SACs, and also provide a brief perspective on the future design of efficient SACs with graphene and graphene-like materials.

Unusual features of nitrogen substitutions in silicene

The quasiparticle properties resulting from charge and spin are clearly identified in nitrogen-substituted silicenes, for which a theoretical framework is successfully developed from first-principles calculations. Such systems create extremely non-uniform chemical and physical environments through the distribution of the guest atoms. They present unusual geometric, electronic, and magnetic properties, which can be identified from the optimal honeycomb lattices, the atom- and spin-dominated energy spectra, the spatial charge density distributions, and the atom-, orbital- and spin-projected van Hove singularities [the net magnetic moments]. The complicated relations between the highly hybridized sp2-N-Si bonds and the ferromagnetic/non-magnetic configurations are responsible for the p-type or semiconducting behavior, the significant modifications to the Dirac cone structures, the difficulty in identifying the π and σ bands, and the vanishing or finite magnetic moments. The theoretical predictions could be verified by high-resolution experimental measurements.

Magneto-electronics, transport properties, and tuning effects of arsenene armchair nanotubes doped with transition metal atoms

Recently, the arsenic monolayer has been successfully fabricated by micromechanical stripping. However, it is a non-magnetic semiconductor, including its derivatives. Here, we theoretically explore how to induce magnetism for arsenene armchair nanotubes (AsANTs) with a low-concentration TM (TM = Co, Y, Rh, Ni, Mo, Ru) atom doping, especially focusing on their structural stability, magneto-electronic property, carrier mobility, and strain effects. The high stability of these doped tubes are confirmed by the calculated binding energy and formation energy, as well as Forcite annealing molecular dynamics simulations. The AsANT can act as bandgap narrowed non-magnetic semiconductors or highly spin-polarized magnetic semiconductors (half-semiconductor or bipolar magnetic semiconductor) depending on TM types, suggesting different promising applications such as developing infrared photodetectors with broadband detectionin or spintronic devices. The magnetic thermal stability beyond room temperature is predicted for doped tubes. Furthermore, the carrier mobility of AsANTs can be tuned into a wide region by TM doping, but it is enhanced in most cases. The carrier and spin polarity of mobility can also be clearly observed. Particularly, the applied strain can induce a rich magnetic phase transition among a half-semiconductor, half-metal, bipolar magnetic semiconductor and nonmagnetic state. Furthermore, the presented stepwise change of total magnetic moment between high magnetized and nonmagnetic states is highly desirable for engineering a mechanical switch which can reversibly work between magnetism and demagnetism to control spin-polarized transport by applying strain.

Density functional study on the CO oxidation reaction mechanism on MnN2-doped graphene

The CO oxidation mechanisms over three different MnN2-doped graphene (MnN2C2: MnN2C2-hex, MnN2C2-opp, MnN2C2-pen) structures were investigated through first-principles calculations. The vacancy in graphene can strongly stabilize Mn atoms and make them positively charged, which promotes O2 activation and weakens CO adsorption. Hence, CO oxidation activity is enhanced and the catalyst is prevented from being poisoned. CO oxidation reaction (COOR) on MnN2C2 along the Eley-Rideal (ER) mechanism and the Langmuir-Hinshelwood (LH) mechanism will leave one O atom on the Mn atom, which is difficult to react with isolated CO. COOR on MnN2C2-opp along the ER mechanism and termolecular Eley-Rideal (TER) mechanism need overcome low energy barriers in the rate limiting step (RLS), which are 0.544 and 0.342 eV, respectively. The oxidation of CO along TER mechanism on MnN2C2-opp is the best reaction pathway with smallest energy barrier. Therefore, the MnN2C2-opp is an efficient catalysis and this study has a guiding role in designing effective catalyst for CO oxidation.

Effect of Structural Disorders on the Li Storage Capacity of Graphene Nanomaterials: A First-Principles Study

We employed first-principles calculations to investigate the effect of structural disorders on the Li storage capacity of graphene nanomaterials. Our calculations first revealed that the Li storage capacity of a graphene monolayer does not necessarily increase with the size of a C vacancy created but is largely determined by the local geometry of the defect sites. Our electronic structure analysis further revealed that the enhanced Li storage capacity by the C vacancy defect is mainly attributed to the increased number of the unoccupied electronic density of states lying near the Fermi level, which can be substantially increased by raising the number of bond rotations within the vacancy sites. Furthermore, it was also found that the Li storage capacity of graphene can be effectively enhanced by increasing the degree of local ring disorders without the presence of any vacancy defect. The amorphous graphene structure was shown to possess a relatively higher Li storage capacity compared to pristine graphene, primarily owing to the presence of many nonhexagonal rings randomly distributed in the graphene lattice. These nonhexagonal rings can create many electron-deficient regions on the graphene surface to effectively accommodate more electrons from Li, thereby substantially enhancing the Li storage capacity of graphene nanomaterials.

Chemical Synthesis of Single Atomic Site Catalysts

Manipulating metal atoms in a controllable way for the synthesis of materials with the desired structure and properties is the holy grail of chemical synthesis. The recent emergence of single atomic site catalysts (SASC) demonstrates that we are moving toward this goal. Owing to the maximum efficiency of atom-utilization and unique structures and properties, SASC have attracted extensive research attention and interest. The prerequisite for the scientific research and practical applications of SASC is to fabricate highly reactive and stable metal single atoms on appropriate supports. In this review, various synthetic strategies for the synthesis of SASC are summarized with concrete examples highlighting the key issues of the synthesis methods to stabilize single metal atoms on supports and to suppress their migration and agglomeration. Next, we discuss how synthesis conditions affect the structure and catalytic properties of SASC before ending this review by highlighting the prospects and challenges for the synthesis as well as further scientific researches and practical applications of SASC.

First-Principles Study of 3d Transition-Metal-Atom Adsorption onto Graphene Embedded with the Extended Line Defect

A type of line defect (LD) composed of alternate squares and octagons (4-8) as the basic unit is currently an experimentally available topological defect in the graphene lattice, which brings some interesting modifications to the magnetic and electronic properties of graphene. The transitional-metal (TM) atoms adsorb on graphene with a line defect (4-8), and they show interesting and attractive structural, magnetic, and electronic properties. For different TMs such as Fe, Co, Mn, Ni, and V, the complex systems show different magnetic and electronic properties. The TM atoms can spontaneously adsorb at quadrangular sites, forming a metallic atomic chain along LD on graphene. The most stable configuration is the hollow site of a regular tangle. The TMs (TM = Co, Fe, Mn, Ni, V) tend to form extended metal lines, showing a ferromagnetic (FM) ground state. For the Co, Fe, and V atoms, the system is half-metal. The spin-α electron is insulating, while the spin-β electron is conductive. For the Mn and Ni atoms, Mn-LD and Ni-LD present a spin-polarized metal; for the Fe atom, Fe-LD shows a semimetal with Dirac cones. For Fe and V atoms, both Fe-LD and V-LD show spin-polarized half-metallic properties. And its spin-α electron is conducting, while the spin-β electron is insulating. Different TMs adsorbing on a graphene nanoribbon forming the same stable configurations of metal lines show different electronic properties. The adsorption of TMs induces magnetism and spin polarization. These metal lines have potential applications in spintronic devices and work as a quasi-one-dimensional metallic wire, which may form building blocks for atomic-scale electrons with well-controlled contacts at the atomic level.

Graphyne-anchored single Fe atoms as efficient CO oxidation catalysts as predicted by DFT calculations

By performing first-principles calculations, CO oxidation catalyzed by Fe-embedded defective α-graphyne was systematically investigated. It was found that Fe atoms were strongly anchored at the sp-C vacancy site of α-graphyne with a large binding energy of -5.28 eV and effectively adsorbed and activated O2 molecules. Then, we systematically compared CO oxidation by activated O2via Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms. The calculated potential energy surfaces show that the Fe-doped α-graphyne can efficiently oxidize CO via the ER mechanism, in which the threshold of the rate determining step is 0.77 eV. Furthermore, Fe doping shows little effect on the diffusivities of CO, O2, and CO2, which can further enhance its catalytic performance.

Nanocarbon Catalysts: Recent Understanding Regarding the Active Sites

Although carbon itself acts as a catalyst in various reactions, the classical carbon materials (e.g., activated carbons, carbon aerogels, carbon black, carbon fiber, etc.) usually show low activity, stability, and oxidation resistance. With the recent availability of nanocarbon catalysts, the application of carbon materials in catalysis has gained a renewed momentum. The research is concentrated on tailoring the surface chemistry of nanocarbon materials, since the pristine carbons in general are not active for heterogeneous catalysis. Surface functionalization, doping with heteroatoms, and creating defects are the most used strategies to make efficient catalysts. However, the nature of the catalytic active sites and their role in determining the activity and selectivity is still not well understood. Herein, the types of active sites reported for several mainstream nanocarbons, including carbon nanotubes, graphene-based materials, and 3D porous nanocarbons, are summarized. Knowledge about the active sites will be beneficial for the design and synthesis of nanocarbon catalysts with improved activity, selectivity, and stability.

Theoretical investigation on graphene-supported single-atom catalysts for electrochemical CO2 reduction

TM atoms supported on the graphene sheet (TM@Gr_s) as promising CO₂ catalysts were investigated by first-principles calculations. Cr-, Co- and Rh@Gr_s show remarkable performance with the low limiting potentials for CO₂RR.

Single-atom metal-modified graphenylene as a high-activity catalyst for CO and NO oxidation

Herein, the adsorption behaviors and interactions of different gas species on single-metal atom-anchored graphenylene (M–graphenylene, M = Mn, Co, Ni, and Cu) sheets were investigated by first-principles calculations.

Graphene-Based Heterogeneous Catalysis: Role of Graphene

Graphene, the reincarnation of a surface, offers new opportunities in catalytic applications, not only because of its peculiar electronic structure, but also because of the ease of modulating it. A vast number of proposals have been made to support this point, but there has been a lack of a systematic understanding of the different roles of graphene, as many other reviews published have focused on the synthesis and characterization of the various graphene-based catalysts. In this review, we surveyed the vast literature related to various theoretical proposals and experimental realizations of graphene-based catalysts to first classify and then elucidate the different roles played by graphene in solid-state heterogeneous catalysis. Owing to its one-atom thickness and zero bandgap with low density of states around Fermi level, graphene has great potential in catalysis applications. In general, graphene can function as a support for catalysts, a cover to protect catalysts, or the catalytic center itself. Understanding these functions is important in the design of catalysts in terms of how to optimize the electronic structure of the active sites for particular applications, a few case studies of which will be presented for each role.

Metallic single-atoms confined in carbon nanomaterials for the electrocatalysis of oxygen reduction, oxygen evolution, and hydrogen evolution reactions

Recent advances of single-atom-based carbon nanomaterials for the ORR, OER, HER, and bifunctional electrocatalysis are covered in this review article.

Catalytic oxidation mechanisms of carbon monoxide over single- and double-vacancy Mn-embedded graphene

CO oxidation on MnC₃ and MnC₄ has fast kinetics and a low energy barrier.

Proton irradiation of graphene: insights from atomistic modeling

Various types of topological defects are produced during proton irradiation, which are crucial in functionalizing graphene, but the mechanisms of the defect generation process and the structure change are still elusive. Herein, we investigated the graphene defect generation probabilities and defect structures under proton irradiation using both ab initio and classical molecular dynamics simulations. As the proton energy increases from 0.1 keV to 100 keV, defect structures transition from single vacancy and Frenkel pairs to a rich variety of topological defects with the possibility of ejecting multiple atoms. We show that, relatively good agreement on defect generation probabilities can be reached between the two simulation approaches at a proton energy of 1 and 10 keV. However, at 0.1 keV, the single vacancy generation probability differs significantly in two methods due to the difference in the energy required to form single vacancy. Using the classical molecular dynamics simulation, we also studied the evolution of different types of defects and the dependence of their probabilities of occurrence on the proton energy and incident angle. The correlation between the impact positions and defect types allows for the convoluted relationship between the defect probabilities, geometric parameters, and proton energy to be elucidated. We show that the proton energy and incident angle can be used to effectively tune the generation probabilities of different types of defects. Our results provide insights into the controlled defect engineering through ion irradiation, which will be useful for the development of functionalized graphene and graphene electronics.

Controlled Electrodeposition of Gold on Graphene: Maximization of the Defect-Enhanced Raman Scattering Response

A reliable method to prepare a surface-enhanced Raman scattering (SERS) active substrate is developed herein, by electrodeposition of gold nanoparticles (Au NPs) on defect-engineered, large area chemical vapour deposition graphene (GR). A plasma treatment strategy is used in order to engineer the structural defects on the basal plane of large area single-layer graphene. This defect-engineered Au functionalized GR, offers reproducible SERS signals over the large area GR surface. The Raman data, along with X-ray photoelectron spectroscopy and analysis of the water contact angle are used to rationalize the functionalization of the graphene layer. It is found that Au NPs functionalization of the "defect-engineered" graphene substrates permits detection of concentrations as low as 10^-16 m for the probe molecule Rhodamine B, which offers an outstanding molecular sensing ability. Interestingly, a Raman signal enhancement of up to ≈10⁸ is achieved. Moreover, it is observed that GR effectively quenches the fluorescence background from the Au NPs and molecules due to the strong resonance energy transfer between Au NPs and GR. The results presented offer significant direction for the design and fabrication of ultra-sensitive SERS platforms, and also open up possibilities for novel applications of defect engineered graphene in biosensors, catalysis, and optoelectronic devices.

Doping of epitaxial graphene by direct incorporation of nickel adatoms

Direct incorporation of Ni adatoms during graphene growth on Ni(111) is evidenced by scanning tunneling microscopy. The structure and energetics of the observed defects is thoroughly characterized at the atomic level on the basis of density functional theory calculations. Our results show the feasibility of a simple scalable method, which could be potentially used for the realization of macroscopic practical devices, to dope graphene with a transition metal. The method exploits the kinetics of the growth process for the incorporation of Ni adatoms in the graphene network.

Enhanced Valley Splitting of Transition-Metal Dichalcogenide by Vacancies in Robust Ferromagnetic Insulating Chromium Trihalides

Recently, single-layer CrI₃, a member of the chromium trihalides CrX₃ (where X = Cl, Br, or I), has been exfoliated and experimentally demonstrated as an atomically thin material suitable for two-dimensional spintronics. Valley splitting due to the magnetic proximity effect has been demonstrated in a WSe₂/CrI₃ van der Waals heterojunction. However, the understanding of the mechanisms behind the favorable performance of CrI₃ is still limited. Here, we systematically study the carrier mobility and the intrinsic point defects in CrX₃ and assess their influence on valley splitting in WSe₂/CrI₃ by first-principles calculations. The flat-band nature induces extremely large carrier mass and ultralow carrier mobility. In addition, intrinsic point defects-localized states in the middle of the band gap-show deep transition energy levels and act as carrier recombination centers, further lowering the carrier mobility. Moreover, vacancies in CrI₃ can enhance ferromagnetism and valley splitting in a WSe₂/CrI₃ heterojunction, proving that chromium trihalides are excellent ferromagnetic insulators for spintronic and valleytronic applications.

Defective Graphene on the Transition-Metal Surface: Formation of Efficient Bifunctional Catalysts for Oxygen Evolution/Reduction Reactions in Alkaline Media

Supported single-atom catalysts (SACs) have attracted enormous attention because of their high selectivity, activity, and efficiency, compared to conventional nanoparticles and metal bulk catalysts. However, all of these unique merits rely on the stability of the SAC, as reported by many investigators. To avoid aggregation of single-metal atoms and maintain the high performance of the SAC, various substrates have been tried to support them, particularly on graphene nanosheets. A spontaneous interface phenomenon between graphene and the Co (and Ni) substrate discovered in this work is that the holes in the graphene layer can stimulate metal atoms to pop up from a metal substrate and fill the double vacancy in graphene (DV-G) and stabilize on the graphene surface. The unique structure of the lifted metal atom is expected to be useful for the bifunctional SAC for electrocatalytic oxygen evolution reactions (OERs) and oxygen reduction reactions (ORRs). Our first-principles calculations indicate that the DV-G on the Co(0001) surface can serve as an excellent bifunctional OER/ORR catalyst in alkaline media with extremely low overpotentials of 0.39 V for OER and only 0.36 V for ORR processes, which are even lower than those for previously reported bifunctional catalysts. We believe that the catalytic activity stems from the interface coupling effect between the DV-G and metal substrate, as well as the charge redistribution in the graphitic sheet.

The atomic origin of nickel-doping-induced catalytic enhancement in MoS2 for electrochemical hydrogen production

Transition metal (TM) doping has been demonstrated to be an efficacious way to boost the catalytic activity of molybdenum disulfide (MoS2) for energy storage and conversion, especially for the hydrogen evolution reaction (HER). Real-space visualization of the atomic structure of Ni doped MoS2 is crucial to understand the role of heteroatoms in enhancing electrocatalysis. By utilizing aberration corrected scanning transmission electron microscopy (STEM), we found that Ni dopants occupy Mo sites in MoS2 synthesized by a one-pot hydrothermal method. Such selective occupation of the single-atom Ni dopants leads to significant lattice distortion and electronic structure modification of the catalytically inert basal planes of MoS2, which are responsible for the enhanced HER catalysis of MoS2 in both acidic and alkaline solutions.

Engineering the magnetic properties of PtSe2 monolayer through transition metal doping

Using first-principles calculations, we have studied the energetic feasibility and magnetic properties of transition metal (TM) doped PtSe₂ monolayers. Our study shows that TM doped PtSe₂ layers with 6.25% doping exhibit versatile spintronic behaviour depending on the nature of the dopant TM atoms. Groups IVB and VIII10 TM doped PtSe₂ layers are non magnetic semiconductors, while groups IIIB, VB, VIII8, VIII9, IB TM doped PtSe₂ layers are half-metals and finally, groups VIB, VIIB and IIB TM doped PtSe₂ layers are spin polarized semiconductors. The presence of half-metallic and magnetic semiconducting characteristics suggest that TM doped PtSe₂ layers can be considered as a new kind of dilute magnetic semiconductor and thus have the promise to be used in spintronics. By studying the magnetic interactions between two TM dopants in PtSe₂ monolayers for dopant concentration of 12.5% and dopant distance of 12.85 [Formula: see text], we have found that in particular, Fe and Ru doped PtSe₂ systems are ferromagnetic half-metal having above-room-temperature Curie point of 422 and 379.9 K, respectively. By varying the dopant distance and concentration we have shown that the magnetic interaction is strongly dependent on dopant distance and concentration. Interestingly, the Curie temperature of TM doped PtSe₂ layers is affected by the correlation effects on the TM d states and also spin-orbit coupling. We have also studied the magnetic properties of defect complex composed of one TM dopant and one Pt vacancy (TM_Pt  +  V_Pt) which shows novel magnetism.