The electronic structure effect in heterogeneous catalysis

Engineering the electronic structure of high performance FeCo bimetallic cathode catalysts for microbial fuel cell application in treating wastewater

The development of high-performance, strong-durability and low-cost cathode catalysts toward oxygen reduction reaction (ORR) is of great significance for microbial fuel cells (MFCs). In this study, a series of bimetallic catalysts were synthesized by pyrolyzing a mixture of g-C₃N₄ and Fe, Co-tannic complex with various Fe/Co atomic ratios. The initial Fe/Co atomic ratio (3.5:0.5, 3:1, 2:2, 1:3) could regulate the electronic state, which effectively promoted the intrinsic electrocatalytic ORR activity. The alloy metal particles and metal-N_x sites presented on the catalyst surface. In addition, N-doped carbon interconnected network consisting of graphene-like and bamboo-like carbon nanotube structure derived from g-C₃N₄ provided more accessible active sites. The resultant Fe₃Co₁ catalyst calcined at 700 °C (Fe₃Co₁-700) exhibited high catalytic performance in neutral electrolyte with a half-wave potential of 0.661 V, exceeding that of the commercial Pt/C (0.6 V). As expected, the single chamber microbial fuel cell (SCMFC) with 1 mg/cm² loading of Fe₃Co₁-700 catalyst as the cathode catalyst afforded a maximum power density of 1425 mW/m², which was 10.5% higher than commercial Pt/C catalyst with the same loading (1290 mW/m²) and comparable to the Pt/C catalyst with 2.5 times higher loading ( 1430 mW/m²). Additionally, the Fe₃Co₁-700 also displayed better long-term stability over 1100 h than the Pt/C. This work provides an effective strategy for regulating the surface electronic state in the bimetallic electro-catalyst.

Atom-Specific Probing of Electron Dynamics in an Atomic Adsorbate by Time-Resolved X-Ray Spectroscopy

The electronic excitation occurring on adsorbates at ultrafast timescales from optical lasers that initiate surface chemical reactions is still an open question. Here, we report the ultrafast temporal evolution of x-ray absorption spectroscopy (XAS) and x-ray emission spectroscopy (XES) of a simple well-known adsorbate prototype system, namely carbon (C) atoms adsorbed on a nickel [Ni(100)] surface, following intense laser optical pumping at 400 nm. We observe ultrafast (∼100  fs) changes in both XAS and XES showing clear signatures of the formation of a hot electron-hole pair distribution on the adsorbate. This is followed by slower changes on a few picoseconds timescale, shown to be consistent with thermalization of the complete C/Ni system. Density functional theory spectrum simulations support this interpretation.

Intelligent route to design efficient CO2 reduction electrocatalysts using ANFIS optimized by GA and PSO

Recently, electrochemical reduction of CO₂ into value-added fuels has been noticed as a promising process to decrease CO₂ emissions. The development of such technology is strongly depended upon tuning the surface properties of the applied electrocatalysts. Considering the high cost and time-consuming experimental investigations, computational methods, particularly machine learning algorithms, can be the appropriate approach for efficiently screening the metal alloys as the electrocatalysts. In doing so, to represent the surface properties of the electrocatalysts numerically, d-band theory-based electronic features and intrinsic properties obtained from density functional theory (DFT) calculations were used as descriptors. Accordingly, a dataset containg 258 data points was extracted from the DFT method to use in machine learning method. The primary purpose of this study is to establish a new model through machine learning methods; namely, adaptive neuro-fuzzy inference system (ANFIS) combined with particle swarm optimization (PSO) and genetic algorithm (GA) for the prediction of *CO (the key intermediate) adsorption energy as the efficiency metric. The developed ANFIS-PSO and ANFIS-GA showed excellent performance with RMSE of 0.0411 and 0.0383, respectively, the minimum errors reported so far in this field. Additionally, the sensitivity analysis showed that the center and the filling of the d-band are the most determining parameters for the electrocatalyst surface reactivity. The present study conveniently indicates the potential and value of machine learning in directing the experimental efforts in alloy system electrocatalysts for CO₂ reduction.

Hydrogen Adsorption on Pd–In Intermetallic Surfaces

It has recently been shown that $$\hbox {CO}_2$$ CO 2 hydrogenation to methanol over PdIn and $$\hbox {In}_2\hbox {O}_3$$ In 2 O 3 depends critically on the adsorption energy of hydrogen. Here we use density functional theory calculations to investigate hydrogen adsorption over Pd–In intermetallic compound surfaces with different Pd:In ratios. The electronic structure and properties of hydrogen adsorption are investigated for a range of surface facets and compared to the corresponding results for the pure parent metals and Cu. Increased In content is found to shift the Pd(d) density of states away from the Fermi level, making the intermetallic Pd–In compounds to appear “Cu-like”. We find a linear correlation between the hydrogen binding energy and the d-band center of surface Pd atoms. Understanding of how the hydrogen adsorption energy depends on composition and structure provides a possibility to enhance the performance of $$\hbox {CO}_2$$ CO 2 hydrogenation catalysts to methanol.

Atomic Hydrogen in Electrocatalytic Systems: Generation, Identification, and Environmental Applications

Electrochemical reduction has emerged as a viable technology for the removal of a variety of organic contaminants from water. Atomic hydrogen (H*) is the primary species generated in electrochemical reduction processes. In this work, identification and quantification for H* are reviewed with a focus on methods used to generate H* at different positions. Additionally, we present recently developed proposals for the surface chemistry mechanisms of H* on the most commonly used cathodes as well as the use of H* in standard electrochemical reactors. The proposed reaction pathways in different H* systems for environmental applications are also discussed in detail. As shown in this review, the key hurdles facing H* reduction technologies are related to i) the establishment of systematic and practical synthetic methods; ii) the development of effective identification approaches with high specificity; and, iii) an in-depth exploration of the H* reaction mechanism to better understand the reaction process of H*.

Subnanometric Ru clusters with upshifted D band center improve performance for alkaline hydrogen evolution reaction

Subnanometric metal clusters usually have unique electronic structures and may display electrocatalytic performance distinctive from single atoms (SAs) and larger nanoparticles (NPs). However, the electrocatalytic performance of clusters, especially the size-activity relationship at the sub-nanoscale, is largely unexplored. Here, we synthesize a series of Ru nanocrystals from single atoms, subnanometric clusters to larger nanoparticles, aiming at investigating the size-dependent activity of hydrogen evolution in alkaline media. It is found that the d band center of Ru downshifts in a nearly linear relationship with the increase of diameter, and the subnanometric Ru clusters with d band center closer to Femi level display a stronger water dissociation ability and thus superior hydrogen evolution activity than SAs and larger nanoparticles. Benefiting from the high metal utilization and strong water dissociation ability, the Ru clusters manifest an ultrahigh turnover frequency of 43.3 s^-1 at the overpotential of 100 mV, 36.1-fold larger than the commercial Pt/C.

Strain Engineering: A Boosting Strategy for Photocatalysis

Whilst the photocatalytic technique is considered to be one of the most significant routes to address the energy crisis and global environmental challenges, the solar-to-chemical conversion efficiency is still far from satisfying practical industrial requirements, which can be traced to the suboptimal bandgap and electronic structure of photocatalysts. Strain engineering is a universal scheme that can finely tailor the bandgap and electronic structure of materials, hence supplying a novel avenue to boost their photocatalytic performance. Accordingly, to explore promising directions for certain breakthroughs in strained photocatalysts, an overview on the recent advances of strain engineering from the basics of strain effect, creations of strained materials, as well as characterizations and simulations of strain level is provided. Besides, the potential applications of strain engineering in photocatalysis are summarized, and a vision for the future controllable-electronic-structure photocatalysts by strain engineering is also given. Finally, perspectives on the challenges for future strain-promoted photocatalysis are discussed, placing emphasis on the creation and decoupling of strain effect, and the modification of theoretical frameworks.

Orbital Dependence in Single-Atom Electrocatalytic Reactions

Transition metal single-atom catalysts supported on N-doped graphene (TM-N-C) could serve as an ideal model for studying orbital dependence in electrocatalytic reactions because the atom on the catalytic active site has discrete single-atom-like orbitals. In this work, the catalytic efficiency of Fe-N-C for the oxygen evolution reaction (OER) under a small structural perturbation has been comprehensively investigated with density functional theory calculations. The results suggest that the subtle local environment of a single atom can significantly modulate the catalytic reactivity. Further analysis demonstrates that the energy level of the TM d_z² orbital center, rather than the d-band center, is responsible for the OER catalytic efficiency as the d_z² orbital participates mainly in the reactions. Essentially, the d-band theory can be extended to the sub-d orbital level, and a small perturbation of the crystal field, induced by lattice strain or z-direction displacement of the TM atom, can prominently change the sub-d orbital associated with the reaction and in turn affect the catalytic activity.

Rational Design of Better Hydrogen Evolution Electrocatalysts for Water Splitting: A Review

The excessive dependence on fossil fuels contributes to the majority of CO2 emissions, influencing on the climate change. One promising alternative to fossil fuels is green hydrogen, which can be produced through water electrolysis from renewable electricity. However, the variety and complexity of hydrogen evolution electrocatalysts currently studied increases the difficulty in the integration of catalytic theory, catalyst design and preparation, and characterization methods. Herein, this review first highlights design principles for hydrogen evolution reaction (HER) electrocatalysts, presenting the thermodynamics, kinetics, and related electronic and structural descriptors for HER. Second, the reasonable design, preparation, mechanistic understanding, and performance enhancement of electrocatalysts are deeply discussed based on intrinsic and extrinsic effects. Third, recent advancements in the electrocatalytic water splitting technology are further discussed briefly. Finally, the challenges and perspectives of the development of highly efficient hydrogen evolution electrocatalysts for water splitting are proposed.

Fermi–Löwdin orbital self-interaction correction of adsorption energies on transition metal ions

Density functional theory (DFT)-based descriptions of the adsorption of small molecules on transition metal ions are prone to self-interaction errors. Here, we show that such errors lead to a large over-estimation of adsorption energies of small molecules on Cu+, Zn+, Zn2+, and Mn+ in local spin density approximation (LSDA) and Perdew, Burke, Ernzerhof (PBE) generalized gradient approximation calculations compared to reference values computed using the coupled-cluster with single, doubles, and perturbative triple excitations method. These errors are significantly reduced by removing self-interaction using the Perdew–Zunger self-interaction correction (PZ-SIC) in the Fermi–Löwdin Orbital (FLO) SIC framework. In the case of FLO-PBE, typical errors are reduced to less than 0.1 eV. Analysis of the results using DFT energies evaluated on self-interaction-corrected densities [DFT(@FLO)] indicates that the density-driven contributions to the FLO-DFT adsorption energy corrections are roughly the same size in DFT = LSDA and PBE, but the total corrections due to removing self-interaction are larger in LSDA.

Dynamic Pt-OH-·H2O-Ag species mediate coupled electron and proton transfer for catalytic hydride reduction of 4-nitrophenol at the confined nanoscale interface

Generally, the catalytic transformation of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) at heterogeneous metal surfaces follows a Langmuir-Hinshelwood (L-H) mechanism when sodium borohydride (NaBH₄) is used as the sacrificial reductant. Herein, with Pt-Ag bimetallic nanoparticles confined in dendritic mesoporous silica nanospheres (DMSNs) as a model catalyst, we demonstrated that the conversion of 4-NP did not pass through the direct hydrogen transfer route with the hydride equivalents being supplied by borohydride via the bimolecular L-H mechanism, since Fourier transform infrared (FTIR) spectroscopy with the use of isotopically labeled reactants (NaBD₄ and D₂O) showed that the final product of 4-AP was composed of protons (or deuterons) that originated from the solvent water (or heavy water). Combined characterization by X-ray photoelectron spectroscopy (XPS), ¹H nuclear magnetic resonance (NMR) and the optical excitation and photoluminescence spectrum evidenced that the surface hydrous hydroxide complex bound to the metal surface (also called structural water molecules, SWs), due to the space overlap of p orbitals of two O atoms in SWs, could form an ensemble of dynamic interface transient states, which provided the alternative electron and proton transfer channels for selective transformation of 4-NP. The cationic Pt species in the Ag-Pt bimetallic catalyst mainly acts as a dynamic adsorption center to temporally anchor SWs and related reactants, and not as the active site for hydrogen activation.

Real-Time Modulation of Hydrogen Evolution Activity of Graphene Electrodes Using Mechanical Strain

This paper reports the effect of mechanically applied elastic strain on the hydrogen evolution reaction (HER) activity of graphene under acidic conditions. An applied tensile strain of 0.2% on a graphene electrode is shown to lead to a 1-3% increase in the HER current. The tensile strain increases HER activity, whereas compressive strain decreases it. Density functional theory (DFT) calculations using a periodic graphene slab model predict an increase in the adsorption energy of the H atom with growing tensile strain, consistent with an enhancement of the current density in HER, similar to that observed experimentally.

Construction of stable MoxSy/CeO2 heterostructures for the electrocatalytic hydrogen evolution reaction

The unique structures of polynuclear Mo_xS_y clusters make it possible to maximize the number of their active sites and for them to be good candidates for HER catalysts. An appropriate support is highly necessary not only to avoid the desorption of Mo_xS_y clusters in a working environment, but also to improve their HER activity. Our work here shows that the CeO₂ support could provide strong support for interaction with various Mo_xS_y clusters and the formed Mo_xS_y/CeO₂ hetero-structures also have modest ΔG_H* for the HER. The electronic features of Mo_xS_y clusters are regulated by the CeO₂ support, which leads to charge redistribution on edge atoms and plays a key role in H adsorption. Our studies provide instructive predictions on efficient candidates of molybdenum-sulfur based catalysts for the HER.

Tuning Catalytic Activity in Ultrathin Bimetallic Nanowires via Surface Segregation: Some Insights

The efficiency of heterogeneous catalysts critically depends on the nature of the surface. We present results on controlling the composition in ultrathin bimetallic AuPd. AuPd wires were grown using Au nanowire templates; the surface composition could be tuned by increasing the amount of Pd. Further, segregation of Pd to the surface could be induced in alloyed nanowires by annealing under a controlled CO atmosphere. Electrocatalytic activity of these bimetallic systems is assessed for the methanol oxidation reaction (MOR). While the MOR potential shows a monotonic increase with Pd content, the specific activity displays a typical volcano-type behavior. The CO-annealed nanowires show a lowering of potential owing to a higher Pd content on the surface while still maintaining the specific activity. These findings provide clear strategies to independently control the reaction potential and the activities of nanocatalysts. The experimental findings are well supported by the theoretical investigations using density functional theory (DFT) calculations.

Unravelling the metal–support interactions in χ-Fe5C2/MgO catalysts for olefin synthesis directly from syngas

The structural and electronic modifications of χ-Fe5C2 by MgO contribute to the high selectivity towards lower olefins and the high catalyst stability.

Effects of alloying for steam or dry reforming of methane: a review of recent studies

A survey on the catalytic nature of Ni-based alloy catalysts in recent years provides a direction for future catalyst development.

Design principles of noble metal-free electrocatalysts for hydrogen production in alkaline media: combining theory and experiment

Water electrolysis is a promising solution to convert renewable energy sources to hydrogen as a high-energy-density energy carrier. Although alkaline conditions extend the scope of electrocatalysts beyond precious metal-based materials to earth-abundant materials, the sluggish kinetics of cathodic and anodic reactions (hydrogen and oxygen evolution reactions, respectively) impede the development of practical electrocatalysts that do not use precious metals. This review discusses the rational design of efficient electrocatalysts by exploiting the understanding of alkaline hydrogen evolution reaction and oxygen evolution reaction mechanisms and of the electron structure-activity relationship, as achieved by combining experimental and computational approaches. The enhancement of water splitting not only deals with intrinsic catalytic activity but also includes the aspect of electrical conductivity and stability. Future perspectives to increase the synergy between theory and experiment are also proposed.

Strain in a platinum plate induced by an ultrahigh energy laser boosts the hydrogen evolution reaction

The ligand and the strain near the active sites in catalysts jointly affect the electrocatalytic activity for the catalytic industry. In many cases, there is no effective strategy for the independent study of the strain effect without the ligand effect on the electrocatalytic activity for the hydrogen evolution reaction (HER). Laser shock peening (LSP) with a GW cm-2 level power density and a 10-30 ns short pulse is employed to form compressive strain on the surface and in the depth direction of a platinum (Pt) plate, which changes the inherent interatomic distance and modifies the energy level of the bonded electrons, thereby greatly optimizing the energy barrier for the HER. The crystal lattice near the surface of the LSP Pt plate is distorted by the strain, and the interplanar spacing decreases from 0.225 nm in the undeformed region to 0.211 nm in the deformed region. The specific activity of the LSP Pt has an increase of 2.9 and 6.4 times in comparison with that of the pristine Pt in alkaline and acidic environments, respectively. This investigation provides a novel strategy for the independent study of the strain effect on the electrocatalytic activity and the improvement of electrocatalysts with high performance in extensive energy conversion.

Achievements in Pt nanoalloy oxygen reduction reaction catalysts: strain engineering, stability and atom utilization efficiency

The Pt nanoalloy surfaces often show unique electronic and physicochemical properties that are distinct from those of their parent metals, which provide significant room for manipulating their oxygen reduction reaction (ORR) behaviour. In this Feature Article, we present the progress of our recent research and that of other groups in Pt nanoalloy catalysts for ORR from three aspects, namely, strain engineering, stability and atom utilization efficiency. Some new insights into Pt surface strain engineering will be firstly introduced, with a focus on discussing the effect of compressive and tensile strain on the chemisorption properties. Secondly, the design concepts and synthetic methodologies to intensify the inherent stability of Pt nanoalloys will be summarized. Then, the exciting research push in developing nanostructured alloys with high atom utilization efficiency of Pt will be presented. Finally, a brief illumination of challenges and future developing perspectives of Pt nanoalloy catalysts will be provided.

Rationalization of Nonlinear Adsorption Energy-Strain Relations and Brønsted-Evans-Polanyi and Transition State Scaling Relationships under Strain

Scaling relations play a vital role in high-throughput screening of catalytic materials, and more and more attention is being paid to strain-based regulation of catalytic performance. Here we investigated the variation of several energetics, including adsorption energies in the initial state, transition state, and final state, reaction energies, and energy barriers with strain, by studying CO, BH, NH, CH, and NO adsorption and dissociation on M(111) (M = Cu, Ag, Ni, Pd, or Pt) surfaces. We show that energy barriers, reaction energies, and adsorption energies can vary either linearly or nonlinearly (quadratically) with strain. Systems with stronger adsorbate-substrate interaction and weaker atom-atom interaction in substrates are more likely to exhibit nonlinear relations. The well-known Brønsted-Evans-Polanyi relationships and transition state scaling relationships under strain were also examined, and both of them can be nonlinear under strain, in principle. The observed nonlinear relationships were satisfactorily rationalized with the equations derived from Mechanics of Solids.

Local Environment Determined Reactant Adsorption Configuration for Enhanced Electrocatalytic Acetone Hydrogenation to Propane

We demonstrate a widely applicable method to alter the adsorption configuration of multi-carbon containing reactants by no catalyst engineering but simply adjusting the local reaction environment of the catalyst surface. Using electrocatalytic acetone to propane hydrogenation (APH) as a model reaction and common commercial Pt/Pt-based materials as catalysts, we found local H⁺ concentration can significantly influence the adsorption mode of acetone reactant, for example, in vertical or flat mode, and target product selectivity. Electrocatalytic measurement combined with in situ spectroscopic characterizations reveals that the vertically adsorbed acetone is favorable for propane production while the flatly adsorbed mode suppresses the reaction. DFT calculations indicate that the H coverage on catalyst surface plays a decisive role in the adsorption configuration of acetone. The increased local acidity can facilitate the adsorption configuration of acetone from flat to vertical mode and suppress the competing hydrogen evaluation reaction, which consequently enhances the APH selectivity.

What Is the Real State of Single-Atom Catalysts under Electrochemical Conditions—From Adsorption to Surface Pourbaix Plots?

The interest in single-atom catalysts (SACs) is increasing, as these materials have the ultimate level of catalyst utilization, while novel reactions where SACs are used are constantly being discovered. However, to properly understand SACs and to further improve these materials, it is necessary to consider the nature of active sites under operating conditions. This is particularly important when SACs are used as electrocatalysts due to harsh experimental conditions, including extreme pH values or high anodic and cathodic potential. In this contribution, density functional theory-based thermodynamic modelling is used to address the nature of metal centers in SACs formed by embedding single metal atoms (Ru, Rh, Ir, Ni, Pd, Pt, Cu, Ag, and Au) into graphene monovacancy. Our results suggest that none of these SAC metal centers are clean at any potential or pH in the water thermodynamic stability region. Instead, metal centers are covered with Hads, OHads, or Oads, and in some cases, we observed the restructuring of the metal sites due to oxygen incorporation. Based on these findings, it is suggested that setting up theoretical models for SAC modelling and the interpretation of ex situ characterization results using ultra-high vacuum (UHV) techniques requires special care, as the nature of SAC active sites under operating conditions can significantly diverge from the basic models or the pictures set by the UHV measurements.

Main Descriptors To Correlate Structures with the Performances of Electrocatalysts

Traditional trial and error approaches to search for hydrogen/oxygen redox catalysts with high activity and stability are typically tedious and inefficient. There is an urgent need to identify the most important parameters that determine the catalytic performance and so enable the development of design strategies for catalysts. In the past decades, several descriptors have been developed to unravel structure-performance relationships. This Minireview summarizes reactivity descriptors in electrocatalysis including adsorption energy descriptors involving reaction intermediates, electronic descriptors represented by a d-band center, structural descriptors, and universal descriptors, and discusses their merits/limitations. Understanding the trends in electrocatalytic performance and predicting promising catalytic materials using reactivity descriptors should enable the rational construction of catalysts. Artificial intelligence and machine learning have also been adopted to discover new and advanced descriptors. Finally, linear scaling relationships are analyzed and several strategies proposed to circumvent the established scaling relationships and overcome the constraints imposed on the catalytic performance.

Unveiling the Mechanisms Ruling the Efficient Hydrogen Evolution Reaction with Mitrofanovite Pt3Te4

By means of electrocatalytic tests, surface-science techniques and density functional theory, we unveil the physicochemical mechanisms ruling the electrocatalytic activity of recently discovered mitrofanovite (Pt₃Te₄) mineral. Mitrofanovite represents a very promising electrocatalyst candidate for energy-related applications, with a reduction of costs by 47% compared to pure Pt and superior robustness to CO poisoning. We show that Pt₃Te₄ is a weak topological metal with the Z2 invariant, exhibiting electrical conductivity (∼4 × 10⁶ S/m) comparable with pure Pt. In hydrogen evolution reaction (HER), the electrode based on bulk Pt₃Te₄ shows a very small overpotential of 46 mV at 10 mA cm^-2 and a Tafel slope of 36-49 mV dec^-1 associated with the Volmer-Heyrovsky mechanism. The outstanding ambient stability of Pt₃Te₄ also provides durability of the electrode and long-term stability of its efficient catalytic performances.

Electrochemically active site-rich nanocomposites of two-dimensional materials as anode catalysts for direct oxidation fuel cells: new age beyond graphene

Direct oxidation fuel cell (DOFC) has been opted as a green alternative to fossil fuels and intermittent energy resources as it is economically viable, possesses good conversion efficiency, as well as exhibits high power density and superfast charging. The anode catalyst is a vital component of DOFC, which improves the oxidation of fuels; however, the development of an efficient anode catalyst is still a challenge. In this regard, 2D materials have attracted attention as DOFC anode catalysts due to their fascinating electrochemical properties such as excellent mechanical properties, large surface area, superior electron transfer, presence of active sites, and tunable electronic states. This timely review encapsulates in detail different types of fuel cells, their mechanisms, and contemporary challenges; focuses on the anode catalyst/support based on new generation 2D materials, namely, 2D transition metal carbide/nitride or carbonitride (MXene), graphitic carbon nitride, transition metal dichalcogenides, and transition metal oxides; as well as their properties and role in DOFC along with the mechanisms involved.

Atomically Precise Gold Nanoclusters as Model Catalysts for Identifying Active Sites for Electroreduction of CO2

Accurate identification of active sites is critical for elucidating catalytic reaction mechanisms and developing highly efficient and selective electrocatalysts. Herein, we report the atomic-level identification of active sites using atomically well-defined gold nanoclusters (Au NCs) Au₂₅ , Au₃₈ , and Au₁₄₄ as model catalysts in the electrochemical CO₂ reduction reaction (CO₂ RR). The studied Au NCs exhibited remarkably high CO₂ RR activity, which increased with increasing NC size. Electrochemical and X-ray photoelectron spectroscopy analyses revealed that the Au NCs were activated by removing one thiolate group from each staple motif at the beginning of CO₂ RR. In addition, density functional theory calculations revealed higher charge densities and upshifts of d-states for dethiolated Au sites. The structure-activity properties of the studied Au NCs confirmed that dethiolated Au sites were the active sites and that CO₂ RR activity was determined by the number of active sites on the cluster surface.

Transition Metal Chalcogenides as a Versatile and Tunable Platform for Catalytic CO2 and N2 Electroreduction

Group VI transition metal chalcogenides are the subject of increasing research interest for various electrochemical applications such as low-temperature water electrolysis, batteries, and supercapacitors due to their high activity, chemical stability, and the strong correlation between structure and electrochemical properties. Particularly appealing is their utilization as electrocatalysts for the synthesis of energy vectors and value-added chemicals such as C-based chemicals from the CO₂ reduction reaction (CO₂R) or ammonia from the nitrogen fixation reaction (NRR). This review discusses the role of structural and electronic properties of transition metal chalcogenides in enhancing selectivity and activity toward these two key reduction reactions. First, we discuss the morphological and electronic structure of these compounds, outlining design strategies to control and fine-tune them. Then, we discuss the role of the active sites and the strategies developed to enhance the activity of transition metal chalcogenide-based catalysts in the framework of CO₂R and NRR against the parasitic hydrogen evolution reaction (HER); leveraging on the design rules applied for HER applications, we discuss their future perspective for the applications in CO₂R and NRR. For these two reactions, we comprehensively review recent progress in unveiling reaction mechanisms at different sites and the most effective strategies for fabricating catalysts that, by exploiting the structural and electronic peculiarities of transition metal chalcogenides, can outperform many metallic compounds. Transition metal chalcogenides outperform state-of-the-art catalysts for CO₂ to CO reduction in ionic liquids due to the favorable CO₂ adsorption on the metal edge sites, whereas the basal sites, due to their conformation, represent an appealing design space for reduction of CO₂ to complex carbon products. For the NRR instead, the resemblance of transition metal chalcogenides to the active centers of nitrogenase enzymes represents a powerful nature-mimicking approach for the design of catalysts with enhanced performance, although strategies to hinder the HER must be integrated in the catalytic architecture.

What Atomic Positions Determines Reactivity of a Surface? Long-Range, Directional Ligand Effects in Metallic Alloys

Ligand and strain effects can tune the adsorption energy of key reaction intermediates on a catalyst surface to speed up rate-limiting steps of the reaction. As novel fields like high-entropy alloys emerge, understanding these effects on the atomic structure level is paramount: What atoms near the binding site determine the reactivity of the alloy surface? By statistical analysis of 2000 density functional theory calculations and subsequent host/guest calculations, it is shown that three atomic positions in the third layer of an fcc(111) metallic structure fourth-nearest to the adsorption site display significantly increased influence on reactivity over any second or third nearest atomic positions. Subsequently observed in multiple facets and host metals, the effect cannot be explained simply through the d-band model or a valence configuration model but rather by favorable directions of interaction determined by lattice geometry and the valence difference between host and guest elements. These results advance the general understanding of how the electronic interaction of different elements affect adsorbate-surface interactions and will contribute to design principles for rational catalyst discovery of better, more stable and energy efficient catalysts to be employed in energy conversion, fuel cell technologies, and industrial processes.

Bandgap-Coupled Template Autocatalysis toward the Growth of High-Purity sp2 Nanocarbons

Extraordinary properties and great application potentials of carbon nanotubes (CNT) and graphene fundamentally rely on their large-scale perfect sp2 structure. Particularly for high-end applications, ultralow defect density and ultrahigh selectivity are prerequisites, for which metal-catalyzed chemical vapor deposition (CVD) is the most promising approach. Due to their structure and peculiarity, CNTs and graphene can themselves provide growth templates and nonlocal dual conductance, serving as template autocatalysts with tunable bandgap during the CVD. However, current growth kinetics models all focus on the external factors and edges. Here, the growth kinetics of sp2 nanocarbons is elaborated from the perspective of template autocatalysis and holistic electronic structure. After reviewing current growth kinetics, various representative works involving CVD growth of different sp2 nanocarbons are analyzed, to reveal their bandgap-coupled kinetics and resulting selective synthesis. Recent progress is then reviewed, which has demonstrated the interlocking between the atomic assembly rate and bandgap of CNTs, with an explicit volcano dependence whose peak would be determined by the environment. In addition, the topological protection for perfect sp2 structure and the defect-induced perturbation for the interlocking are discussed. Finally, the prospects for the kinetic selective growth of perfect nanocarbons are proposed.

Elucidating the Influence of the d-Band Center on the Synthesis of Isobutanol

As the search for carbon-efficient synthesis pathways for green alternatives to fossil fuels continues, an expanding class of catalysts have been developed for the upgrading of lower alcohols. Understanding of the acid base functionalities has greatly influenced the search for new materials, but the influence of the metal used in catalysts cannot be explained in a broader sense. We address this herein and correlate our findings with the most fundamental understanding of chemistry to date by applying it to d-band theory as part of an experimental investigation. The commercial catalysts of Pt, Rh, Ru, Cu, Pd, and Ir on carbon as a support have been characterized by means of SEM, EDX-mapping, STEM, XRD, N2-physisorption, and H2-chemisorption. Their catalytic activity has been established by means of c-methylation of ethanol with methanol. For all catalysts, the TOF with respect to i-butanol was examined. The Pt/C reached the highest TOF with a selectivity towards i-butanol of 89%. The trend for the TOFs could be well correlated with the d-band centers of the metal, which formed a volcano curve. Therefore, this study is another step towards the rationalization of catalyst design for the upgrading of alcohols into carbon-neutral fuels or chemical feedstock.