Transition Metal Surfaces Research Articles

Novel P2-Type Na0.66Fe0.5-2xMn0.5TixVxO2 Cathode for High-Capacity

Necessity of energy storage and battery production is soaring up day by day due to the growth of portable electronic devices and surging evolution of electric vehicles (EVs), plug-in-hybrid electric vehicles (PHEVs) and renewables. Lithium-ion battery (LIB) technology has been the primary choice for such applications due to its high-energy-density, high-stability, and longer cycle life. Albeit with all merits of LIB, the prime concern has been the scarcity of lithium in earth’s crust and depletion of lithium reserve due to its wide usage in batteries, resulting in a higher production cost. This has prompted battery researchers to search for new alternatives to LIB for energy storage applications. Sodium, in this respect, can be a viable solution as it is the sixth most abundant element and shares the same group with lithium in the periodic table. Sodium has similar structural and electrochemical working mechanisms of lithium. The pivotal factors hindering the deployment of the laboratory-based sodium-ion battery (SIB) technologies into the commercial energy storage market are low energy density compared to that of LIB, lower stability, lower ion-transport mechanism, and lower operating voltage. Improvement of overall electrochemical performance of cathode materials can be a game-changer as it affects the energy density, lifespan, and tolerance of batteries. In this research, a cobalt-free novel P2-type transition metal cathode Na0.66Fe0.5-2xMn0.5TixVxO2 was synthesized by doping NaFeMnO2 with vanadium and titanium for SIB battery applications. The cathode was synthesized based on a sol-gel reaction where citric acid was used as a chelating agent. A set of physicochemical analysis, including Field-Effect Scanning Electron Microscopy (FESEM) and Energy Dispersive X-ray Spectroscopy (EDAX) analysis, as well as electrochemical analysis like Cyclic Voltammetry and Galvanometric Charge/ Discharge were performed to understand the correspondence between layered transition metal oxide chemistry, surface morphology and electrochemical competence of the new material. The crystal structures of the pristine material and cathodes containing different percentages of doped vanadium and titanium were examined and lattice parameters were refined through X-ray Diffraction (XRD) and Rietveld analysis. These exhaustive structural and morphological comparisons were performed between the pristine and modified NaFeMnO2 (NFM) cathode structures, which provided insights on the effects of vanadium and titanium doping on stabilizing surface structures, reducing Jahn-Teller distortion, enhancing stability and capacity retention and promoting Na+ carrier transport mechanism.

(Invited) Understanding Electrocatalytic Pathways in Complex Organic and Inorganic Composites in Aqueous and Non Aqueous Environments

There are very few techniques that lend themselves to rigorous requirements, where the individual role of different transition metal components of nano-phasic materials can be investigated in both amorphous and crystalline forms. We have been at the forefront of various analytical techniques along with theoretical calculations, which enables the amount and specific adsorption site of species such as H, OH, O, CO, other C1 moieties and even anions such as bisulfate to be determined in situ on a metal surfaces using synchrotron XANES data. This technique, commonly called the ‘Delta Mu (∆μ) Technique’ can be taken in situ in both electrochemical cells and operating fuel cells, and can be obtained from a wide variety of transition metal surfaces and alloys, including non-Pt based metal electrocatalysts with element specificity. EXAFS data taken concurrently provide information on the changes in short range atomic order around the absorber atom thereby providing structural information such as bond distances and coordination numbers (thereby information on average cluster size, homogeneity and surface segregation etc.).In this presentation among other things we will show in-situ XAS study of group of (Metal-Nitrogen-Carbon) MNC catalysts from perspective of metal center. We will demonstrate the presence of ORR active bio-mimetic porphyrin-like FeNx functionalities (Fig.1), as well as other forms of the metal which indicate no catalytic activity. The XAS in-situ studies will be combined with electroanalytical evaluations using cyclic voltammetry (CV) and square wave voltammetry (SWV). Further the factors governing the ORR activity at MNC centers, such as the Lewis basicity of the carbon support and the accompanying changes in the redox potential of the metal center will be discussed. This part of the presentation will bring together electrochemistry and XAS spectroscopy (including ∆μ) on effect of pH (inner and outer sphere charge transfer) and aqueous vs. non aqueous electrolyte (concerted vs. non concerted charge transfer).

Fe-Phthalocyanine on Cu(111) and Ag(111): A DFT+vdWs investigation

Starting from dyes in the industrial domain, Metal-Phthalocyanine (MPc), a macrocyclic planar organo-metallic molecule, can nowadays be used in various applications at low cost in several areas such as oncology, sensors, catalysts, spintronic devices, to name a few. Some applications require the deposition of these molecules on metallic surfaces, whereas sometimes the bulk molecular system is used. In this work, we study both the bulk system of iron-Phthalocyanine (FePc) and its adsorption on Cu(111) and Ag(111). We investigate the structural, electronic, and magnetic properties of these materials using Density Functional Theory (DFT) taking into consideration van der Waals effects to further reflect the importance of the involved interactions on the properties. We found that the FePc bulk system displays a magnetic state resulting from the metallic central Fe atom. However, the adsorbed FePc partially loses its magnetization when it is deposited on a transition metal surface of Cu(111) or Ag(111). Additionally, both C4 symmetry and C2 symmetry were observed with STM images for FePc/Ag(111) and FePc/Cu(111), respectively. The adsorption is found to be of a strong chemisorption type with relatively large binding energy (∼x223C 5 eV/molecule) and charge transfer (∼x223C 0.7e−) from the metal surface to the molecule.

Nonaqueous Solvent Adsorption on Transition Metal Surfaces with Density Functional Theory: Interaction of N,N-Dimethylformamide (DMF), Tetrahydrofuran (THF), and Dimethyl Sulfoxide (DMSO) with Ag, Cu, Pt, Rh, and Re Surfaces

Interfaces between solvents and transition metals play a critical role in many catalytic and electrochemical systems. In this work, we use density functional theory (DFT) to study the interactions between several common nonaqueous solvents and a number of transition metal surfaces. We investigate trends in binding energies among the metals, and the influence of specific surface sites and facets. We examine the electrostatic field dependence of the most stable binding configurations, and shed light on experimentally observed field-dependent or potential-dependent adsorption structures. We demonstrate that the reorientation of DMSO on noble metal surfaces can occur with only a relatively small change in the surface dipole moment; this result is simultaneously consistent with experimental evidence for field-dependent reorientation and measurements of surprisingly low differential capacitance of DMSO on noble metals. These results contribute to understanding competitive adsorption effects in catalysis, and also have implications for fundamental surface properties such as the surface structure, solvated work function, and potential of zero charge.

Infusing theory into deep learning for interpretable reactivity prediction

Despite recent advances of data acquisition and algorithms development, machine learning (ML) faces tremendous challenges to being adopted in practical catalyst design, largely due to its limited generalizability and poor explainability. Herein, we develop a theory-infused neural network (TinNet) approach that integrates deep learning algorithms with the well-established d-band theory of chemisorption for reactivity prediction of transition-metal surfaces. With simple adsorbates (e.g., *OH, *O, and *N) at active site ensembles as representative descriptor species, we demonstrate that the TinNet is on par with purely data-driven ML methods in prediction performance while being inherently interpretable. Incorporation of scientific knowledge of physical interactions into learning from data sheds further light on the nature of chemical bonding and opens up new avenues for ML discovery of novel motifs with desired catalytic properties.

Prediction of Transition-State Scaling Relationships and Universal Transition-State Vibrational and Entropic Correlations for Dehydrogenations

Linear scaling relationships (LSRs) and Brønsted–Evans–Polanyi (BEP) or transition-state scaling (TSS) relations aid with the prediction of electronic energies. However, temperature effects and pre-exponentials are often taken as constants across metal surfaces or a homologous series. Vibrational scaling relationships (VSRs) offer a way to determine such parameters. Transition-state VSRs (TSVSRs) between local minima and transition states of AHX (A = C, N, O) surface diffusions correlate with BEP relations and broaden to thermochemical property scaling. Using density functional theory, we extend TSVSRs to AHX dehydrogenation reactions on transition-metal surfaces, relating vibrational modes of local minima to transition states. We first predict the slopes of the TSS relations by incorporating bond angles using the Slater–Koster structure factors and hybridization through crystal orbital overlap population analysis and energy overlap integrals between adsorbates and metal surfaces. Additionally, we uncover universal thermochemical property scaling, enabling the estimation of entropies and temperature corrections to enthalpies across a homologous series. We demonstrate both significant vibrational corrections in reactions with low intrinsic electronic barriers and considerable variation in the pre-exponential of a simple dehydrogenation reaction across metals and AHX adsorbates.

Identifying Outstanding Transition-Metal-Alloy Heterogeneous Catalysts for the Oxygen Reduction and Evolution Reactions via Subgroup Discovery

In order to estimate the reactivity of a large number of potentially complex heterogeneous catalysts while searching for novel and more efficient materials, physical as well as data-centric models have been developed for a faster evaluation of adsorption energies compared to first-principles calculations. However, global models designed to describe as many materials as possible might overlook the very few compounds that have the appropriate adsorption properties to be suitable for a given catalytic process. Here, the subgroup-discovery (SGD) local artificial-intelligence approach is used to identify the key descriptive parameters and constrains on their values, the so-called SG rules, which particularly describe transition-metal surfaces with outstanding adsorption properties for the oxygen-reduction and -evolution reactions. We start from a data set of 95 oxygen adsorption-energy values evaluated by density-functional-theory calculations for several monometallic surfaces along with 16 atomic, bulk and surface properties as candidate descriptive parameters. From this data set, SGD identifies constraints on the most relevant parameters describing materials and adsorption sites that (i) result in O adsorption energies within the Sabatier-optimal range required for the oxygen-reduction reaction and (ii) present the largest deviations from the linear-scaling relations between O and OH adsorption energies, which limit the catalyst performance in the oxygen-evolution reaction. The SG rules not only reflect the local underlying physicochemical phenomena that result in the desired adsorption properties, but also guide the challenging design of alloy catalysts.

De-hybridization effect of transition metal catalysts on AlH4-based hydrogen storage materials

Understanding the microscopic impact of catalysis on the de-hydrogenation process of hydrides is crucial for the development of hydrogen storage materials. In this paper, density functional theory calculations are employed to study the adsorption and dissociation of the AlH4 cluster, which is the building block of many complex hydrides, on a series of transition metal surfaces. We find that the hybrid bonding of the AlH4 cluster is weakened when adsorption on metal surfaces and the Al–H bonds are stretched accordingly. This de-hybridization effect enhances from Sc to Ni in correlation with the work function. Based on the results, we predict Ni to be the most effective transition metal in lowering the de-hydrogenation barrier of AlH4-based hydrides. Detail electronic structure analysis show that the de-hybridization effect mainly resulted from the charge transfer between metals surface and AlH4 clusters. Our results provide deep insight into improving the properties of hydrogen storage materials.

Activating Basal Surface of Palladium by Electronic Modulation via Atomically Dispersed Nitrogen Doping for High-Efficiency Hydrogen Evolution Reaction.

Surface doping by atomically dispersed heteroatoms has become one of the most promising strategies for facilitating the catalytic activity of non-noble transition metals to replace platinum-based catalysts in the hydrogen evolution reaction (HER). However, the underlying mechanism for the atomically dispersed heteroatoms to modulate the electronic structure and the HER activity of a metal surface is still ambiguous. Moreover, the active catalytic region is limited by the small fraction of doped atoms, and the remaining basal surface is inactivated. Here, we demonstrate that the nitrogen doping is atomically dispersed on the palladium surface, which can achieve the near-thermoneutral hydrogen adsorption and promote the HER activity of the basal surface. The theoretical modeling reveals that the dispersed nitrogen atoms attract electrons from palladium and downdrift the d-band center for accelerating the hydrogen desorption. Our work offers understandings of atomically dispersed nitrogen doping on the surface of transition metals and paves the way for a further optimization of nonprecious-metal HER electrocatalysts.

Comparative study of adsorptions, reactions and electronic properties of U atoms on Cu(111), Ag(111), Au(111) and Ru(0001) surfaces

The mysterious properties of individual U atoms on transition metal surfaces play indispensable parts in supplementing our understanding of uranium-transition metal systems, which are important subjects for both nuclear energy applications and fundamental scientific studies. By using scanning tunneling microscopy and density functional theory calculations, the adsorptions, reactions and electronic properties of individual U atoms on Cu(111), Ag(111), Au(111) and Ru(0001) surfaces were comparatively studied for the first time in this work. Upon the deposition of a small amount of U onto Cu(111) or Ag(111) at 8 K, individual U atoms show relatively high activity and can either be adsorbed on intact substrate surfaces or induce various surface vacancies surrounded by clusters of substrate atoms. By contrast, the majority of U atoms tend to dispersedly adsorb on intact surfaces of Au(111) and Ru(0001) rather than producing surface vacancies at the same temperature. In all cases, Kondo resonance manifested as asymmetric dip feature around Fermi energy is only observed in the differential tunneling conductance spectra of single U adatoms on Ag(111).

Sensitivity to crystal stacking in low-energy electron microscopy

In this work we demonstrate the general characteristics of hcp and fcc stacking in low-energy electron reflectivity for transition metal surfaces, by following the restacking during homoepitaxial growth in real-time. For this purpose, the stacking of a model system, single-crystalline Ag islands during layer-by-layer growth at high temperature on O/W(110), is chosen. Multiple scattering calculations are used to model the relation between electron reflectivity and the crystal geometry. The changes in the electron reflectivity are shown to derive from the changes in the stacking sequence of the topmost surface layers. The results allow to distinguish between the hcp and fcc crystalline arrangements at a surface based on typical differences in the reflectivity curves, making the Ag results relevant for a variety of materials with hexagonal surface geometry. In particular, the multiplet structure within the first Bragg peak in the very low electron energy regime is identified with the fcc structure and thus it can be utilized as a fingerprint to determine the stacking sequence.

Tensile strain induced surface reactions for co-adsorption of H2O and OH− on vacancy Al (111) surface

The strain and stress are important factors for influencing the performances of transition metal surface. The co-adsorption H2O and OH− on vacancy Al (111) surface under tensile strain conditions was investigated based on the density functional theory. We found that OH− can induce dissociation of H2O molecules, the dissociation phenomenon only occurs on three special configurations. The lattice distortion of vacancy Al surface is more sensitive to strain than the perfect surface, and the description of vacancy formation energy and surface energy is limited by the strain of each time. Although the strain cannot change the reaction path of H2O on the dissociated surfaces, it can reduce the energy barrier of the dissociation reaction and induce more stable adsorption of the reactants on the vacancy Al surface, promoting erosion of Al surface.

Factors that influence hydrogen binding at metal-atop sites.

The d-band model has proven to be effective for understanding trends in the chemisorption of various adsorbates on transition metal surfaces. However, hydrogen adsorption at the atop site of transition metals and their bimetallic alloy surfaces do not always correlate well with the d-band center of the adsorption site. Additionally, the d-band model cannot explain the disappearance of the local minima for H adsorption at the hollow site on the potential energy surface of 5d single-atom element doped Au and Ag(111) surfaces. Here, we use a simple model with factors, including the d-band center, filling of the d-band, renormalized adsorbate states, coupling matrix elements, and surface-adsorbate bond lengths, to correlate with the density functional theory calculated H binding energies on both mono- and bimetallic (111) surfaces. Our results suggest that H adsorption at metal-atop sites is determined by all these factors, not only by the d-band center. The strong adsorption of H at the atop sites of 5d metal surfaces can be explained by their lower repulsive contribution.

Formation of diethylamine thermal ionization mass spectrum on NaAux intermetallide.

The mass spectra of amine thermal ionization on intermetallic NaAux emitters differ significantly from those of the same compounds on the surfaces of transition metals and their oxides. The factors underlying these differences are determined through studying the processes taking place on intermetallic surfaces, which give rise to the corresponding mass spectra. The dependence of mass spectral composition and individual line intensity of diethylamine thermal ionization on intermetallic NaAux surface on diethylamine pressure, oxygen, sodium atom current and emitter temperature was studied using a magnet sector mass spectrometer. Diethylamine mass spectral composition is determined by the reaction between the molecules adsorbed on the NaAux surface. Oxygen and sodium concentration on the surface does not affect the mass spectral composition. Mass line intensity depends on diethylamine pressure and emitter temperature affecting the reaction efficiency on the surface. Intermetallic NaAux is an ionic semiconductor that can provide sufficient lifetime for adsorbed molecules to efficiently interact with each other and with their decomposition products. This creates unique conditions for the formation of various compounds on the surface with their mass exceeding by 2.5 times that of diethylamine.

Tuning the electronic band structure of metal surfaces for enhancing high-order harmonic generation

High-harmonic generation (HHG) from the condensed matter phase holds promise to promote future cutting-edge research in the emerging field of attosecond nanoscopy. The key for the progress of the field relies on the capability of the existing schemes to enhance the harmonic yield and to push the photon energy cutoff to the extreme-ultraviolet (XUV, 10-100eV) regime and beyond toward the spectral "water window" region (282-533eV). Here, we demonstrate a coherent control scheme of HHG, which we show to give rise to quantum modulations in the XUV region. These modulations are shown to be caused by quantum-path interferences and are found to exhibit a strong sensitivity to the delocalized character of bulk states of the material. The control scheme is based on exploring surface states in transition-metal surfaces and, specifically, tuning the electronic structure of the metal surface itself together with the use of optimal chirped pulses. Moreover, we show that the use of such pulses having moderate intensities permits us to push the harmonic cutoff further to the spectral water window region and that the extension is found to be robust against the change in the intrinsic properties of the material. The scenario is numerically implemented using a minimal model by solving the time-dependent Schrödinger equation for the metal surface Cu(111) initially prepared in the surface state. Our findings elucidate the importance of metal surfaces for generating coherent isolated attosecond XUV and soft-x-ray pulses and for designing compact solid-state HHG devices.

Emergence of Subsurface Oxygen on Rh(111).

Oxygen atoms on transition metal surfaces are highly mobile under the demanding pressures and temperatures typically employed for heterogeneously catalyzed oxidation reactions. This mobility allows for rapid surface diffusion of oxygen atoms, as well as absorption into the subsurface and reemergence to the surface, resulting in variable reactivity. Subsurface oxygen atoms play a unique role in the chemistry of oxidized metal catalysts, yet little is known about how subsurface oxygen is formed or returns to the surface. Furthermore, if oxygen diffusion between the surface and subsurface is mediated by defects, there will be localized changes in the surface chemistry due to the elevated oxygen concentration near the emergence sites. We observed that oxygen atoms emerge preferentially along the boundary between surface phases and that subsurface oxygen is depleted before the surface oxide decomposes.

(Invited) Exploring the Roles of Interfacial Water for the HER/HOR of Pt-Surfaces in Aqueous Solutions

Previous studies focus mainly on the inherent properties of the catalysts such as the metal-hydrogen binding energy (EM-H) to rationalize their catalytic activities toward the hydrogen evolution and oxidation reactions (HER/HOR) in aqueous solutions. While this strategy proves effective in rationalizing and predicting the HER/HOR activity trend across a wide range of elements in dilute acidic solutions as per the Sabatier Principle, it cannot fully account for the sluggish HER/HOR kinetics of many transition metals in alkaline solutions. Recent works suggest that interfacial water plays critical roles in affecting the HER/HOR kinetics of Pt-based surfaces in alkaline solutions.1-5 However, the specific roles of interfacial water for the HER/HOR kinetics remain elusive, partly because of the lack of methods to explore the surface-electrolyte interface.Herein, we probe the Pt electrode/electrolyte interface by depositing a variety of transition metals (TMs) onto Pt surfaces and monitoring their redox-controlled interactions with the HOR/HER intermediates and interfacial water via in situ x-ray absorption spectroscopy. Carbon monoxide stripping experiments with varied alkaline metal cations (AM+) concentrations are conducted to facilitate correlating the redox-controlled interactions to the TM-induced changes of the HOR/HER kinetics of Pt. We found that the TM-induced changes of the HOR/HER kinetics of Pt in alkaline are governed by the TM0/TM(OH)x redox potential or the metal-oxygen binding energy (ETM-O). The TMs with too strong ETM-O or too low redox potentials such as Mn or Co are dominated by TM(OH)x within the HOR potential region and can only improve the HER kinetics of Pt but not the HOR. The TMs with moderate ETM-O or redox potentials located within the HOR kinetic potential region of Pt (0-0.25 V) such as Ni and Ru can simultaneously improve the HOR/HER of Pt in alkaline, but the HOR improvement vanishes as the TM0 transforms to TM(OH)x with increasing potentials. The TMs with too high redox potentials or weak ETM-O(s) such as Cu improve neither. According to these results, we propose that the TM in either the form of TM0 or TM(OH)x can improve the HER of Pt in alkaline by hosting the OHad generated from water dissociation that is subsequently removed by the interfacial water coordinated to AM+ via the HSAB interaction: TM0/TM(OH)x-OHad-[AM(H2O)x]+ + e- ↔ TM0/TM(OH)x + OH--[AM(H2O)x]+;1 whereas only the form of TM0 can improve the HOR by hosting the water molecule with the oxygen facing-down orientation (H2O↓ad) that removes Had from the Pt atoms nearby via the L-H mechanism: Pt-Had + TM0-H2O↓ad ↔ Pt + TM0 + H3O+ + e-. By this new notion, the surface TM promotes the HOR/HER kinetics of Pt by facilitating interfacial water shuffling reaction intermediates against the electric field, rather than by weakening the electric field by negatively shifting the potential of zero free charge (pzfc)2, or by weakening the (apparent) EPt-H,6 or by facilitating the chemical dissociation and formation of water molecules via bifunctional mechanism.7 The participation of interfacial water in the HOR/HER of Pt is further supported by the experiments that adding some organic compounds into the alkaline solutions improves the HER/HOR kinetics of Pt by interacting with interfacial water rather than Pt surfaces. Acknowledgements.This work was supported by the Office of Naval Research under award number N00014-18-1-2155. The authors declare no competing financial interests. This research used beamline 7-BM and 8-ID (ISS) of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704. References (1) Liu, E.; Li, J.; Jiao, L.; Doan, H. T. T.; Liu, Z.; Zhao, Z.; Huang, Y.; Abraham, K. M.; Mukerjee, S.; Jia, Q. J. Am. Chem. Soc. 2019, 141, 3232.(2) Ledezma-Yanez, I.; Wallace, W. D. Z.; Sebastián-Pascual, P.; Climent, V.; Feliu, J. M.; Koper, M. T. M. Nat. Energy 2017, 2, 17031.(3) Herranz, J.; Durst, J.; Fabbri, E.; Patru, A.; Cheng, X.; Permyakova, A. A.; Schmidt, T. J. Nano Energy 2016, 29, 4.(4) Rebollar, L.; Intikhab, S.; Snyder, J. D.; Tang, M. H. J. Phys. Chem. Lett. 2020, 11, 2308.(5) Liu, E.; Jiao, L.; Li, J.; Stracensky, T.; Sun, Q.; Mukerjee, S.; Jia, Q. Energ Environ Sci 2020, 13, 3064.(6) Schwämmlein, J. N.; Stühmeier, B. M.; Wagenbauer, K.; Dietz, H.; Tileli, V.; Gasteiger, H. A.; El-Sayed, H. A. J. Electrochem. Soc. 2018, 165, H229.(7) Li, J.; Ghoshal, S.; Bates, M. K.; Miller, T. E.; Davies, V.; Stavitski, E.; Attenkofer, K.; Mukerjee, S.; Ma, Z.-F.; Jia, Q. Angew. Chem. Int. Ed. 2017, 56, 15594.

MXenes as Superexcellent Support for Confining Single Atom: Properties, Synthesis, and Electrocatalytic Applications.

Single atom catalysts (SACs) have shown their noticeable potential and gradually become a new favorite in catalytic field due to the particular selectivity, high catalytic performance, and strong durability. The most important factor in the synthesis of SACs is the selection of appropriate support and formation of metal-support interaction. Among a large number of nanomaterials, MXenes can be utilized as benign supports for fixing SACs because of their expansive specific surface area, regulable bandgap, superior electronic conductivity, and strong mechanical stability. The structure and property of MXenes can be manipulated by changing transition metal elements and surface termination. Here, the uniqueness and superiority of MXenes as superexcellent supports for confining SACs are analyzed from structure and property. The synthetic strategy of MXene-supported SACs is also summarized, especially emphasizing the immobilization of isolated atom against aggregation by utilizing the formidable metal-support covalent coordination interaction. In addition, the applications of MXene-supported SACs in electrocatalytic field are highlighted, including hydrogen evolution reaction, oxygen evolution reaction, overall water splitting, oxygen reduction reaction, and nitrogen reduction reaction. Finally, the challenges and prospects are pointed out for the further understanding and practical application of MXene-supported SACs in electrocatalysis.

Generalizable Trends in Electrochemical Protonation Barriers.

Predicting activation energies for reaction steps is essential for modeling catalytic processes, but accurate barrier simulations often require considerable computational expense, especially for electrochemical reactions. Given the challenges of barrier computations and the growing promise of electrochemical routes for various processes, generalizable energetic trends in electrochemistry can significantly aid in analyzing reaction networks and building microkinetic models. Herein, we employ density functional theory and machine learning nudged elastic band models to simulate electrochemical protonation of *C, *N, and *O monatomic adsorbates from hydronium on a series of transition metal surfaces. We observe a consistent trend of decreasing protonation reaction energies yet increasing activation barriers from *O to *N to *C. Analysis of bond orders and reaction pathways provides insight into the origin of the observed trends in protonation energetics. We hypothesize that these results are relevant for polyatomic adsorbates, which can simplify analysis of reaction mechanisms and inform catalyst design.

Oxidation Reaction Kinetics on Transition Metal Surfaces Observed by Real-time Photoelectron Spectroscopy

Oxidation Reaction Kinetics on Transition Metal Surfaces Observed by Real-time Photoelectron Spectroscopy