The electronic structure effect in heterogeneous catalysis

Toward Durable CO2 Electroreduction with Cu-Based Catalysts via Understanding Their Deactivation Modes

The technology of CO2 electrochemical reduction (CO2ER) provides a means to convert CO2, a waste greenhouse gas, into value-added chemicals. Copper is the most studied element that is capable of catalyzing CO2ER to obtain multicarbon products, such as ethylene, ethanol, acetate, etc., at an appreciable rate. Under the operating condition of CO2ER, the catalytic performance of Cu decays because of several factors that alters the surface properties of Cu. In this review, these factors that cause the degradation of Cu-based CO2ER catalysts are categorized into generalized deactivation modes, that are applicable to all electrocatalytic systems. The fundamental principles of each deactivation mode and the associated effects of each on Cu-based catalysts are discussed in detail. Structure- and composition-activity relationship developed from recent in situ/operando characterization studies are presented as evidence of related deactivation modes in operation. With the aim to address these deactivation modes, catalyst design and reaction environment engineering rationales are suggested. Finally, perspectives and remarks built upon the recent advances in CO2ER are provided in attempts to improve the durability of CO2ER catalysts.

Enhancing Electrocatalytic CO2-to-CO Conversion by Weakening CO Binding through Nitrogen Integration in the Metallic Fe Catalyst

Metallic iron (Fe) typically demonstrates the unfavorable catalytic activity for the CO2 reduction reaction (CO2RR), mainly attributed to the excessively strong binding of CO products on Fe sites. Toward this end, we employed an effective approach involving electronic structure modulation through nitrogen (N) integration to enhance the performance of the CO2RR. Here, an efficient catalyst has been developed, composed of N-doped metallic iron (Fe) nanoparticles encapsulated in a porous N-doped carbon framework. Notably, this N-integrated Fe catalyst displays significantly enhanced performance in the electrocatalytic reduction of CO2, yielding the highest CO Faradaic efficiency of 97.5% with a current density of 6.68 mA cm-2 at -0.7 V versus the reversible hydrogen electrode. The theoretical calculations, combined with the in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy study, reveal that N integration modulates the electron density around Fe, resulting in the weakening of the binding strength between the Fe active sites and *CO intermediates, consequently promoting the desorption of CO and the overall CO2RR process.

Defect Engineering in Composition and Valence Band Center of Y2(YxRu1-x)2O7-δ Pyrochlore Electrocatalysts for Oxygen Evolution Reaction

Oxygen evolution reaction (OER) takes place in various types of electrochemical devices that are pivotal for the conversion and storage of renewable energy. This paper describes a strategy in the design of solid-state structures of OER electrocatalysts through controlling the cation substitution on the active metal site and consequently valence band center position of site-mixed Y2(YxRu1-x)2O7-δ pyrochlore to achieve high catalytic activity. We found that partially replacing the B-site Ru4+ cation with A-site Y3+ in pyrochlore-structured Y2Ru2O7-δ modifies the oxidation state of B-site Ru from 4+ to 5+, as observed by electron paramagnetic resonance (EPR) spectroscopy but does not continuously increase the oxygen vacancy concentration in these oxygen substoichiometric compositions, as quantified by thermogravimetric analysis (TGA) decomposition studies. We found the increased Ru oxidation state leads to a downshift in valence band center. X-ray photoelectron spectroscopy (XPS) analysis was performed to quantitatively determine the optimal band center to be ∼1.27 eV below the Fermi energy level based on the analysis of the valence band edge of these Ru-based Y2(YxRu1-x)2O7-δ OER electrocatalysts. This work highlights that defect engineering can be a practical, effective approach to the optimization of oxidation state and electronic band center for high OER catalytic performance in a quantitative manner.

First synthesis of RuSn solid-solution alloy nanoparticles and their enhanced hydrogen evolution reaction activity

Solid-solution alloys based on platinum group metals and p-block metals have attracted much attention due to their promising potential as materials with a continuously fine-tunable electronic structure. Here, we report on the first synthesis of novel solid-solution RuSn alloy nanoparticles (NPs) by electrochemical cyclic voltammetry sweeping of RuSn@SnOx NPs. High-angle annular dark-field scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy maps confirmed the random and homogeneous distribution of Ru and Sn elements in the alloy NPs. Compared with monometallic Ru NPs, the RuSn alloy NPs showed improved hydrogen evolution reaction (HER) performance. The overpotentials of Ru0.94Sn0.06 NPs/C and Ru0.87Sn0.13 NPs/C to achieve a current density of 10 mA cm-2 were 43.41 and 33.19 mV, respectively, which are lower than those of monometallic Ru NPs/C (53.53 mV) and commercial Pt NPs/C (55.77 mV). The valence-band structures of the NPs investigated by hard X-ray photoelectron spectroscopy demonstrated that the d-band centre of RuSn NPs shifted downward compared with that of Ru NPs. X-ray photoelectron spectroscopy and X-ray absorption near-edge structure analyses indicated that in the RuSn alloy NPs, charge transfer occurs from Sn to Ru, which was considered to result in a downward shift of the d-band centre in RuSn NPs and to regulate the adsorption energy of intermediate Hads effectively, and thus enable the RuSn solid-solution alloy NPs to exhibit excellent HER catalytic properties.

Self-Consistent Convolutional Density Functional Approximations: Application to Adsorption at Metal Surfaces

The exchange-correlation (XC) functional in density functional theory is used to approximate multi-electron interactions. A plethora of different functionals are available, but nearly all are based on the hierarchy of inputs commonly referred to as "Jacob's ladder." This paper introduces an approach to construct XC functionals with inputs from convolutions of arbitrary kernels with the electron density, providing a route to move beyond Jacob's ladder. We derive the variational derivative of these functionals, showing consistency with the generalized gradient approximation (GGA), and provide equations for variational derivatives based on multipole features from convolutional kernels. A proof-of-concept functional, PBEq, which generalizes the PBE α ${\alpha }$ framework with α ${\alpha }$ being a spatially-resolved function of the monopole of the electron density, is presented and implemented. It allows a single functional to use different GGAs at different spatial points in a system, while obeying PBE constraints. Analysis of the results underlines the importance of error cancellation and the XC potential in data-driven functional design. After testing on small molecules, bulk metals, and surface catalysts, the results indicate that this approach is a promising route to simultaneously optimize multiple properties of interest.

An approach for patterned molecular adsorption on ferromagnets, achieved via Moiré superstructures

We have used a scanning tunneling microscope operated under ultrahigh vacuum conditions to investigate an oxo-vanadium-salen complex V(O)salen, that has potential applications as qubits in future quantum-based technologies. The adsorption and self-assembly of V(O)salen on a range of single crystal metal surfaces and nanoislands and the influence of substrate morphology and reactivity has been measured. On the close-packed flat Ag(111) and Cu(111) surfaces, the molecules adsorb isolated or form small clusters arranged randomly on the surface, whereas structured adsorption occurs on two types of Co nanoislands; Co grown on Ag(111) and Ag capped Co islands grown on Cu(111), both forming a Moiré pattern at the surface. The adsorption configuration can by scanning tunneling spectroscopy be linked to the geometric and electronic properties of the substrates and traced back to a Co d-related surface state, illustrating how the modulated reactivity can be used to engineer a pattern of adsorbed molecules on the nanoscale.

Phase control of solid-solution RuIn nanoparticles and their catalytic properties

The properties of solids could be largely affected by their crystal structures. We achieved, for the first time, the phase control of solid-solution RuIn nanoparticles (NPs) from face-centred cubic (fcc) to hexagonal close-packed (hcp) crystal structures by hydrogen heat treatment. The effect of the crystal structure of RuIn alloy NPs on the catalytic performance in the hydrogen evolution reaction (HER) was also investigated. In the hcp RuIn NPs, enhanced HER catalytic performance was observed compared to the fcc RuIn NPs and monometallic Ru NPs. The intrinsic electronic structures of the NPs were investigated by valence-band X-ray photoelectron spectroscopy (VB-XPS). The d-band centre of hcp RuIn NPs obtained from VB-XPS was deeper than that of fcc RuIn NPs and monometallic Ru NPs, which is considered to enable the hcp RuIn NPs to exhibit enhanced HER catalytic performance.

Sub-10-nm-sized Au@AuxIr1-x metal-core/alloy-shell nanoparticles as highly durable catalysts for acidic water splitting

The absence of efficient and durable catalysts for oxygen evolution reaction (OER) is the main obstacle to hydrogen production through water splitting in an acidic electrolyte. Here, we report a controllable synthesis method of surface IrOx with changing Au/Ir compositions by constructing a range of sub-10-nm-sized core-shell nanocatalysts composed of an Au core and AuxIr1-x alloy shell. In particular, Au@Au0.43Ir0.57 exhibits 4.5 times higher intrinsic OER activity than that of the commercial Ir/C. Synchrotron X-ray-based spectroscopies, electron microscopy and density functional theory calculations revealed a balanced binding of reaction intermediates with enhanced activity. The water-splitting cell using a load of 0.02 mgIr/cm2 of Au@Au0.43Ir0.57 as both anode and cathode can reach 10 mA/cm2 at 1.52 V and maintain activity for at least 194 h, which is better than the cell using the commercial couple Ir/C‖Pt/C (1.63 V, 0.2 h).

Structured Catalysts and Catalytic Processes: Transport and Reaction Perspectives

The structure of catalysts determines the performance of catalytic processes. Intrinsically, the electronic and geometric structures influence the interaction between active species and the surface of the catalyst, which subsequently regulates the adsorption, reaction, and desorption behaviors. In recent decades, the development of catalysts with complex structures, including bulk, interfacial, encapsulated, and atomically dispersed structures, can potentially affect the electronic and geometric structures of catalysts and lead to further control of the transport and reaction of molecules. This review describes comprehensive understandings on the influence of electronic and geometric properties and complex catalyst structures on the performance of relevant heterogeneous catalytic processes, especially for the transport and reaction over structured catalysts for the conversions of light alkanes and small molecules. The recent research progress of the electronic and geometric properties over the active sites, specifically for theoretical descriptors developed in the recent decades, is discussed at the atomic level. The designs and properties of catalysts with specific structures are summarized. The transport phenomena and reactions over structured catalysts for the conversions of light alkanes and small molecules are analyzed. At the end of this review, we present our perspectives on the challenges for the further development of structured catalysts and heterogeneous catalytic processes.

Computational chemistry for water-splitting electrocatalysis

Electrocatalytic water splitting driven by renewable electricity has attracted great interest in recent years for producing hydrogen with high-purity. However, the practical applications of this technology are limited by the development of electrocatalysts with high activity, low cost, and long durability. In the search for new electrocatalysts, computational chemistry has made outstanding contributions by providing fundamental laws that govern the electron behavior and enabling predictions of electrocatalyst performance. This review delves into theoretical studies on electrochemical water-splitting processes. Firstly, we introduce the fundamentals of electrochemical water electrolysis and subsequently discuss the current advancements in computational methods and models for electrocatalytic water splitting. Additionally, a comprehensive overview of benchmark descriptors is provided to aid in understanding intrinsic catalytic performance for water-splitting electrocatalysts. Finally, we critically evaluate the remaining challenges within this field.

Feeble Single-Atom Pd Catalysts for H2 Production from Formic Acid

Single-atom catalysts are thought to be the pinnacle of catalysis. However, for many reactions, their suitability has yet to be unequivocally proven. Here, we demonstrate why single Pd atoms (PdSA) are not catalytically ideal for generating H2 from formic acid as a H2 carrier. We loaded PdSA on three silica substrates, mesoporous silicas functionalized with thiol, amine, and dithiocarbamate functional groups. The Pd catalytic activity on amino-functionalized silica (SiO2-NH2/PdSA) was far higher than that of the thiol-based catalysts (SiO2-S-PdSA and SiO2-NHCS2-PdSA), while the single-atom stability of SiO2-NH2/PdSA against aggregation after the first catalytic cycle was the weakest. In this case, Pd aggregation boosted the reaction yield. Our experiments and calculations demonstrate that PdSA in SiO2-NH2/PdSA loosely binds with amine groups. This leads to a limited charge transfer from Pd to the amine groups and causes high aggregability and catalytic activity. According to the density functional calculations, the loose binding between Pd and N causes most of Pd's 4d electrons in amino-functionalized SiO2 to remain close to the Fermi level and labile for catalysis. However, PdSA chemically binds to the thiol group, resulting in strong hybridization between Pd and S, pulling Pd's 4d states deeper into the conduction band and away from the Fermi level. Consequently, fewer 4d electrons were available for catalysis.

Photodriven Methane Conversion on Transition Metal Oxide Catalyst: Recent Progress and Prospects

Methane as the main component in natural gas is a promising chemical raw material for synthesizing value-added chemicals, but its harsh chemical conversion process often causes severe energy and environment concerns. Photocatalysis provides an attractive path to active and convert methane into various products under mild conditions with clean and sustainable solar energy, although many challenges remain at present. In this review, recent advances in photocatalytic methane conversion are systematically summarized. As the basis of methane conversion, the activation of methane is first elucidated from the structural basis and activation path of methane molecules. The study is committed to categorizing and elucidating the research progress and the laws of the intricate methane conversion reactions according to the target products, including photocatalytic methane partial oxidation, reforming, coupling, combustion, and functionalization. Advanced photocatalytic reactor designs are also designed to enrich the options and reliability of photocatalytic methane conversion performance evaluation. The challenges and prospects of photocatalytic methane conversion are also discussed, which in turn offers guidelines for methane-conversion-related photocatalyst exploration, reaction mechanism investigation, and advanced photoreactor design.

Latent Variable Machine Learning Framework for Catalysis: General Models, Transfer Learning, and Interpretability

Machine learning has been successfully applied in recent years to screen materials for a variety of applications. However, despite recent advances, most screening-based machine learning approaches are limited in generality and transferability, requiring new models to be created from scratch for each new application. This is particularly apparent in catalysis, where there are many possible intermediates and transition states of interest in addition to a large number of potential catalytic materials. In this work, we developed a new machine learning framework that is built on chemical principles and allows the creation of general, interpretable, reusable models. Our new architecture uses latent variables to create a set of submodels that each take on a relatively simple learning task, leading to higher data efficiency and promoting transfer learning. This architecture infuses fundamental chemical principles, such as the existence of elements as discrete entities. We show that this architecture allows for the creation of models that can be reused for many different applications, providing significant improvements in efficiency and convenience. For example, our architecture allows simultaneous prediction of adsorption energies for many adsorbates on a broad array of alloy surfaces with mean absolute errors (MAEs) around 0.20-0.25 eV. The integration of latent variables provides physical interpretability, as predictions can be explained in terms of the learned chemical environment as represented by the latent space. Further, these latent variables also serve as new feature representations, allowing efficient transfer learning. For example, new models with useful levels of accuracy can be created with less than 10 data points, including transfer learning to an experimental data set with an MAE less than 0.15 eV. Lastly, we show that our new machine learning architecture is general and robust enough to handle heterogeneous and multifidelity data sets, allowing researchers to leverage existing data sets to speed up screening using their own computational setup.

Defective Biphenylene as High-Efficiency Hydrogen Evolution Catalysts

Electrocatalysts play a pivotal role in advancing the application of water splitting for hydrogen production. This research unveils the potential of defective biphenylenes as high-efficiency catalysts for the hydrogen evolution reaction. Using first-principles simulations, we systematically investigated the structure, stability, and catalytic performance of defective biphenylenes. Our findings unveil that defect engineering significantly enhances the electrocatalytic activity for hydrogen evolution. Specifically, biphenylene with a double-vacancy defect exhibits an outstanding Gibbs free energy of -0.08 eV, surpassing that of Pt, accompanied by a remarkable exchange current density of -3.08 A cm-2, also surpassing that of Pt. Furthermore, we find the preference for the Volmer-Heyrovsky mechanism in the hydrogen evolution reaction, with a low energy barrier of 0.80 eV. This research provides a promising avenue for developing novel metal-free electrocatalysts for water splitting with earth-abundant carbon elements, making a significant step toward sustainable hydrogen production.

Preventing Alloy Electrocatalyst Segregation in Air Using Sacrificial Passivating Overlayers

Many alloy electrocatalysts, including intermetallics, are exceptionally sensitive to segregation in air due to the electronic dissimilarity of the constituent metals. We demonstrate that even alloys with strong cohesive energies rapidly segregate upon air exposure, completely burying the less reactive constituent metal beneath the surface. To circumvent this issue, we develop and validate a new experimental approach for bridging the pressure gap between electronic structure characterization performed under ultrahigh vacuum and electrocatalytic activity testing performed under ambient conditions. This method is based on encapsulation of the alloy surface with a sacrificial passivating overlayer of aluminum oxide. These passivating overlayers protect the underlying material from segregation in the air and can be completely and rapidly removed in an alkaline electrochemical environment under potential control. We demonstrate that alloy surfaces prepared, protected, and introduced into the electrolyte in this manner exhibit near-surface compositions consistent with those of the bulk material despite prior air exposure. We also demonstrate that this protection scheme does not alter the electrocatalytic activity of benchmark electrocatalysts. Implementation of this approach will enable reliable correlations between the electrocatalytic activity measured under ambient conditions and the near-surface electronic structure measured under ultrahigh vacuum.

Correlating Single-Atomic Ruthenium Interdistance with Long-Range Interaction Boosts Hydrogen Evolution Reaction Kinetics

Correlated single-atom catalysts (c-SACs) with tailored intersite metal-metal interactions are superior to conventional catalysts with isolated metal sites. However, precise quantification of the single-atomic interdistance (SAD) in c-SACs is not yet achieved, which is essential for a crucial understanding and remarkable improvement of the correlated metal-site-governed catalytic reaction kinetics. Here, three Ru c-SACs are fabricated with precise SAD using a planar organometallic molecular design and π-π molecule-carbon nanotube confinement. This strategy results in graded SAD from 2.4 to 9.3 Å in the Ru c-SACs, wherein tailoring the Ru SAD into 7.0 Å generates an exceptionally high turnover frequency of 17.92 H2 s-1 and a remarkable mass activity of 100.4 A mg-1 under 50 and 100 mV overpotentials, respectively, which is superior to all the Ru-based catalysts reported previously. Furthermore, density functional theory calculations confirm that Ru SAD has a negative correlation with its d-band center owing to the long-range interactions induced by distinct local atomic geometries, resulting in an appropriate electrostatic potential and the highest catalytic activity on c-SACs with 7.0 Å Ru SAD. The present study promises an attractive methodology for experimentally quantifying the metal SAD to provide valuable insights into the catalytic mechanism of c-SACs.

Nano-Scale Engineering of Heterojunction for Alkaline Water Electrolysis

Alkaline water electrolysis is promising for low-cost and scalable hydrogen production. Renewable energy-driven alkaline water electrolysis requires highly effective electrocatalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). However, the most active electrocatalysts show orders of magnitude lower performance in alkaline electrolytes than that in acidic ones. To improve such catalysts, heterojunction engineering has been exploited as the most efficient strategy to overcome the activity limitations of the single component in the catalyst. In this review, the basic knowledge of alkaline water electrolysis and the catalytic mechanisms of heterojunctions are introduced. In the HER mechanisms, the ensemble effect emphasizes the multi-sites of different components to accelerate the various intermedium reactions, while the electronic effect refers to the d-band center theory associated with the adsorption and desorption energies of the intermediate products and catalyst. For the OER with multi-electron transfer, a scaling relation was established: the free energy difference between HOO* and HO* is 3.2 eV, which can be overcome by electrocatalysts with heterojunctions. The development of electrocatalysts with heterojunctions are summarized. Typically, Ni(OH)2/Pt, Ni/NiN3 and MoP/MoS2 are HER electrocatalysts, while Ir/Co(OH)2, NiFe(OH)x/FeS and Co9S8/Ni3S2 are OER ones. Last but not the least, the trend of future research is discussed, from an industry perspective, in terms of decreasing the number of noble metals, achieving more stable heterojunctions for longer service, adopting new craft technologies such as 3D printing and exploring revolutionary alternate alkaline water electrolysis.

Molecular Orbital Insights into Plasmon-Induced Methane Photolysis

As a promising way to reduce the temperature for conventional thermolysis, plasmon-induced photocatalysis has been utilized for the dehydrogenation of methane. Here we probe the microscopic dynamic mechanism for plasmon-induced methane dissociation over a tetrahedral Ag20 nanoparticle with molecular orbital insights using time-dependent density functional theory. We ingeniously built the relationship between the chemical bonds and molecular orbitals via Hellmann-Feynman forces. The time- and energy-resolved photocarrier analysis shows that the indirect hot hole transfer from the Ag nanoparticle to methane dominates the photoreaction at low laser intensity, due to the strong hybridization of the Ag nanoparticle and CH4 orbitals, while indirect and direct charge transfer coexist to facilitate methane dissociation in intense laser fields. Our findings can be used to design novel methane photocatalysts and highlight the broad prospects of the molecular orbital approach for adsorbate-substrate systems.

Role of Transition Metals in Pt Alloy Catalysts for the Oxygen Reduction Reaction

In pursuit of higher activity and stability of electrocatalysts toward the oxygen reduction reaction, it has become standard practice to alloy platinum in various structural configurations. Transition metals have been extensively studied for their ability to tune catalyst functionality through strain, ligand, and ensemble effects. The origin of these effects and potential for synergistic application in practical materials have been the subject of many theoretical and experimental analyses in recent years. Here, a comprehensive overview of these phenomena is provided regarding the impact on reaction mechanisms and kinetics through combined experimental and theoretical approaches. Experimental approaches to electrocatalysis are discussed.

Computational Design of Ni6@Pt1M31 Clusters for Multifunctional Electrocatalysts

High-efficiency and low-cost multifunctional electrocatalysts for hydrogen evolution reaction (HERs), oxygen evolution reaction (OERs) and oxygen reduction reaction (ORRs) are important for the practical applications of regenerative fuel cells. The activity trends of core-shell Ni6@M32 and Ni6@Pt1M31 (M = Pt, Pd, Cu, Ag, Au) were investigated using the density functional theory (DFT). Rate constant calculations indicated that Ni6@Pt1Ag31 was an efficient HER catalyst. The Volmer-Tafel process was the kinetically favorable reaction pathway for Ni6@Pt1M31. The Volmer-Heyrovsky reaction mechanism was preferred for Ni6@M32. The Pt active site reduced the energy barrier and changed the reaction mechanism. The ORR and OER overpotentials of Ni6@Pt1Ag31 were calculated to be 0.12 and 0.33 V, indicating that Ni6@Pt1Ag31 could be a promising multifunctional electrocatalyst. Ni6@Pt1M31 core-shell clusters present abundant active sites with a moderate adsorption strength for *H, *O, *OH and *OOH. The present study shows that embedding a single Pt atom onto a Ni@M core-shell cluster is a rational strategy for designing an effective multifunctional electrocatalyst.

DFT-assisted low-dimensional carbon-based electrocatalysts design and mechanism study: a review

Low-dimensional carbon-based (LDC) materials have attracted extensive research attention in electrocatalysis because of their unique advantages such as structural diversity, low cost, and chemical tolerance. They have been widely used in a broad range of electrochemical reactions to relieve environmental pollution and energy crisis. Typical examples include hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), carbon dioxide reduction reaction (CO2RR), and nitrogen reduction reaction (NRR). Traditional "trial and error" strategies greatly slowed down the rational design of electrocatalysts for these important applications. Recent studies show that the combination of density functional theory (DFT) calculations and experimental research is capable of accurately predicting the structures of electrocatalysts, thus revealing the catalytic mechanisms. Herein, current well-recognized collaboration methods of theory and practice are reviewed. The commonly used calculation methods and the basic functionals are briefly summarized. Special attention is paid to descriptors that are widely accepted as a bridge linking the structure and activity and the breakthroughs for high-volume accurate prediction of electrocatalysts. Importantly, correlated multiple descriptors are used to systematically describe the complicated interfacial electrocatalytic processes of LDC catalysts. Furthermore, machine learning and high-throughput simulations are crucial in assisting the discovery of new multiple descriptors and reaction mechanisms. This review will guide the further development of LDC electrocatalysts for extended applications from the aspect of DFT computations.

Tuning Surface Reactivity and Electric Field Strength via Intermetallic Alloying

Many electrosynthesis reactions, such as CO2 reduction to multicarbon products, involve the formation of dipolar and polarizable transition states during the rate-determining step. Systematic and independent control over surface reactivity and electric field strength would accelerate the discovery of highly active electrocatalysts for these reactions by providing a means of reducing the transition state energy through field stabilization. Herein, we demonstrate that intermetallic alloying enables independent and systematic control over d-band energetics and work function through the variation of alloy composition and oxophilic constituent identity, respectively. We identify several intermetallic phases exhibiting properties that should collectively yield higher intrinsic activity for CO reduction compared to conventional Cu-based electrocatalysts. However, we also highlight the propensity of these alloys to segregate in air as a significant roadblock to investigating their electrocatalytic activity.

Structurally-Distorted RuIr-Based Nanoframes for Long-Duration Oxygen Evolution Catalysis

Oxygen evolution reaction (OER) plays a key role in proton exchange membrane water electrolysis (PEMWE), yet the electrocatalysts still suffer from the disadvantages of low activity and poor stability in acidic conditions. Here, a new class of CdRu2 IrOx nanoframes with distorted structure for acidic OER is successfully fabricated. Impressively, CdRu2 IrOx displays an ultralow overpotential of 189 mV and an ultralong stability of 1500 h at 10 mA cm⁻2 toward OER in 0.5 M H2 SO4 . Moreover, a PEMWE using the distorted CdRu2 IrOx can be steadily operated at 0.1 A cm⁻2 for 90 h. Microstructural analyses and X-ray absorption spectroscopy (XAS) demonstrate that the synergy between Ru and Ir in CdRu2 IrOx induces the distortion of Ru-O, Ir-O, and Ru-M (M = Ru, Ir) bonds. In situ XAS indicates that the applied potential leads to the deformation octahedral structure of RuOx /IrOx and the formation of stable Ru5+ species for OER. Theoretical calculations also reveal that the distorted structures can reduce the energy barrier of rate-limiting step during OER. This work provides an efficient strategy for constructing structural distortion to achieve significant enhancement on the activity and stability of OER catalysts.

Lattice strain controlled Ni@NiCu efficient anode catalysts for direct borohydride fuel cells

We successfully fabricated a novel tensile lattice strained Ni@NiCu catalyst with a popcorn-like morphology, which is composed of a crystalline Ni core and a NiCu alloy shell. It exhibits outstanding catalytic activity, selectivity, and stability towards borohydride electrooxidation. Moreover, a direct borohydride fuel cell (DBFC) with a Ni@NiCu anode can deliver a power density of 433 mW cm-2 and an open circuit voltage of 1.94 V, much better than the performances of DBFCs employing other anode catalysts reported in the literature. This could be attributed to the fact that the tensile lattice strain generated by the introduction of Cu leads to a rise in the d-band center of the Ni metal and promotes the final B-H decoupling, which is the rate-determining step in the borohydride oxidation reaction, thus improving remarkably the catalytic performances of Ni@NiCu.

Non-precious metal-based heterostructure catalysts for hydrogen evolution reaction: mechanisms, design principles, and future prospects

As a highly promising clean energy source to replace fossil fuels in the 21st century, hydrogen energy has garnered considerable attention, with water electrolysis emerging as a key hydrogen production technology. The development of highly active and stable non-precious metal-based catalysts for the hydrogen evolution reaction (HER) is crucial for achieving efficient and low-cost hydrogen production through electrolysis. Recently, heterostructure composite catalysts comprising two or more non-precious metals have demonstrated outstanding catalytic performance. First, we introduced the basic mechanism of the HER and, based on the reported HER theory, discussed the essence of constructing heterostructures to improve the catalytic activity of non-noble metal-based catalysts, that is, the coupling effect between components effectively regulates the electronic structure and the position of d-band centers. Then three catalytic effects of non-precious metal-based heterogeneous catalysts are described: synergistic effect, electron transfer effect and support effect. Lastly, we emphasized the potential of non-precious metal-based heterogeneous catalysts to replace precious metal-based catalysts, and summarized the future prospects and challenges.

Crystal Facet Structure Dependence and Promising Pd-Pt Catalytic Materials for Perhydroacenaphthene Dehydrogenation

Designing an effective Pd-Pt catalytic material with excellent catalytic performance for perhydroacenaphthene (PHAN) dehydrogenation is a great challenge. In this work, in order to explore the crystal facet structure over the bimetallic Pd-Pt catalyst on the dehydrogenation performance of PHAN, the surface compositions of two kinds of Pd (Pt) atoms with different coverage on Pd modulated Pt (PdPt) and Pt modulated Pd (PtPd) catalysts were designed and studied by means of density functional theory (DFT). Through the investigation of the reaction path of PHAN dehydrogenation on PdMLPt(111) and PtMLPd(111) surfaces, it was found that PdMLPt(111) was advantageous to PHAN dehydrogenation (Ea = 2.317 eV). This was attributed to a lower energy barrier, more stable dehydrogenation products, and the fact that Pd doping brought Pt(111) close to the Fermi level. Apparently, Pd modulated Pt catalyst has a broad application prospect in the dehydrogenation of PHAN. In the process of optimizing the PdPt morphology, a method for selecting the minimum active unit of PdPt catalysts with different ratios was proposed, that is, the most stable active unit: rhombus structure was determined according to the surface formation energy. Moreover, we correlated the relationship among the number of H atoms removed, adsorption energy, surface charge, activation energy, reaction energy, and surface coverage, and obtained the important parameters to predict the performance of PdPt catalyst in PHAN dehydrogenation system: surface charge and d-band center. Finally, the essential correlativity among Pd-Pt surface characteristics, catalytic PHAN activity, and adsorption energy was constructed; that is, the relationship model among d-band center, H atom, and product C12H8 adsorption energy was established. This work opens a new simultaneous path to improve the catalytic performance of Pd-Pt-based catalytic materials for PHAN dehydrogenation, which can be achieved by regulating the rhombic active units of Pt modulated by Pd.

Strain and Surface Engineering of Multicomponent Metallic Nanomaterials with Unconventional Phases

Multicomponent metallic nanomaterials with unconventional phases show great prospects in electrochemical energy storage and conversion, owing to unique crystal structures and abundant structural effects. In this review, we emphasize the progress in the strain and surface engineering of these novel nanomaterials. We start with a brief introduction of the structural configurations of these materials, based on the interaction types between the components. Next, the fundamentals of strain, strain effect in relevant metallic nanomaterials with unconventional phases, and their formation mechanisms are discussed. Then the progress in surface engineering of these multicomponent metallic nanomaterials is demonstrated from the aspects of morphology control, crystallinity control, surface modification, and surface reconstruction. Moreover, the applications of the strain- and surface-engineered unconventional nanomaterials mainly in electrocatalysis are also introduced, where in addition to the catalytic performance, the structure-performance correlations are highlighted. Finally, the challenges and opportunities in this promising field are prospected.

Axial Oxygen Ligands Regulating Electronic and Geometric Structure of Zn-N-C Sites to Boost Oxygen Reduction Reaction

Zn-N-C possesses the intrinsic inertia for Fenton-like reaction and can retain robust durability in harsh circumstance, but it is often neglected in oxygen reduction reaction (ORR) because of its poor catalytic activity. Zn is of fully filled 3d10 4s2 configuration and is prone to evaporation, making it difficult to regulate the electronic and geometric structure of Zn center. Here, guided by theoretical calculations, five-fold coordinated single-atom Zn sites with four in-plane N ligands is constructed and one axial O ligand (Zn-N4 -O) by ionic liquid-assisted molten salt template method. Additional axial O not only triggers a geometry transformation from the planar structure of Zn-N4 to the non-planar structure of Zn-N4 -O, but also induces the electron transfer from Zn center to neighboring atoms and lower the d-band center of Zn atom, which weakens the adsorption strength of *OH and decreases the energy barrier of rate determining step of ORR. Consequently, the Zn-N4 -O sites exhibit improved ORR activity and excellent methanol tolerance with long-term durability. The Zn-air battery assembled by Zn-N4 -O presents a maximum power density of 182 mW cm-2 and can operate continuously for over 160 h. This work provides new insights into the design of Zn-based single atom catalysts through axial coordination engineering.

Tracking C-H bond activation for propane dehydrogenation over transition metal catalysts: work function shines

The activation of the C-H bond in heterogeneous catalysis plays a privileged role in converting light alkanes into commodity chemicals with a higher value. In contrast to traditional trial-and-error approaches, developing predictive descriptors via theoretical calculations can accelerate the process of catalyst design. Using density functional theory (DFT) calculations, this work describes tracking C-H bond activation of propane over transition metal catalysts, which is highly dependent on the electronic environment of catalytic sites. Furthermore, we reveal that the occupancy of the antibonding state for metal-adsorbate interaction is the key factor in determining the ability to activate the C-H bond. Among 10 frequently used electronic features, the work function (W) exhibits a strong negative correlation with C-H activation energies. We demonstrate that e^-W can effectively quantify the ability of C-H bond activation, surpassing the predictive capacity of the d-band center. The C-H activation temperatures of the synthesized catalysts also confirm the effectiveness of this descriptor. Apart from propane, e^-W applies to other reactants like methane.

Alloying with Mn Enhances the Activity and Durability of the CoPt Catalyst toward the Methanol Oxidation Reaction

To improve the catalytic performance and durability of Pt catalysts used for the methanol oxidation reaction (MOR) in direct methanol fuel cells (DMFCs), alloying of Pt with other transition metals such as Ru, Co, Ni, and Fe is considered an effective approach. Despite the significant progress made in the preparation of bimetallic alloys and their utilization for MOR, improving the activity and durability of the catalysts to make them commercially viable remains a stiff challenge. In this work, trimetallic Pt_100-x(MnCo)_x (16 < x < 41) catalysts were successfully synthesized via borohydride reduction followed by hydrothermal treatment at 150 °C. The electrocatalytic performance of the synthesized trimetallic Pt_100-x(MnCo)_x (16 < x < 41) catalysts toward MOR was studied using cyclic voltammetry and chronoamperometry. The results affirm that all Pt_100-x(MnCo)_x (16 < x < 41) alloys have superior MOR activity and durability as compared to bimetallic PtCo alloys and commercially available Pt/C (comm. Pt/C) catalysts. Among all the compositions studied, the Pt₆₀Mn_1.7Co_38.3/C catalyst exhibited superior mass activity (1.3 and 1.9 times higher than those of Pt₈₁Co₁₉/C and comm. Pt/C, respectively) toward MOR. Furthermore, all the newly synthesized Pt_100-x(MnCo)_x/C (16 < x < 41) catalysts showed better CO tolerance when compared with comm. Pt/C. This improved performance of the Pt_100-x(MnCo)_x/C (16 < x < 41) catalyst can be attributed to the synergistic effect of Co and Mn on the Pt lattice.

Probing the binding and activation of small molecules by gas-phase transition metal clusters via IR spectroscopy

Isolated transition metal clusters have been established as useful models for extended metal surfaces or deposited metal particles, to improve the understanding of their surface chemistry and of catalytic reactions. For this objective, an important milestone has been the development of experimental methods for the size-specific structural characterization of clusters and cluster complexes in the gas phase. This review focusses on the characterization of molecular ligands, their binding and activation by small transition metal clusters, using cluster-size specific infrared action spectroscopy. A comprehensive overview and a critical discussion of the experimental data available to date is provided, reaching from the initial results obtained using line-tuneable CO₂ lasers to present-day studies applying infrared free electron lasers as well as other intense and broadly tuneable IR laser sources.

Progress in electrocatalytic hydrogen evolution of transition metal alloys: synthesis, structure, and mechanism analysis

At present, the problems of high energy consumption and low efficiency in electrocatalytic hydrogen production have limited the large-scale industrial application of this technology. Constructing effective catalysts has become the way to solve these problems. Transition metal alloys have been proved to be very promising materials in hydrogen evaluation reaction (HER). In this study, the related theories and characterization methods of electrocatalysis are summarized, and the latest progress in the application of binary, ternary, and high entropy alloys to HER in recent years is analyzed and studied. The synthesis methods and optimization strategies of transition metal alloys, including composition regulation, hybrid engineering, phase engineering, and morphological engineering were emphatically discussed, and the principles and performance mechanism analysis of these strategies were discussed in detail. Although great progress has been made in alloy catalysts, there is still considerable room for applications. Finally, the challenges, prospects, and research directions of transition metal alloys in the future were predicted.

Dopant triggered atomic configuration activates water splitting to hydrogen

Finding highly efficient hydrogen evolution reaction (HER) catalysts is pertinent to the ultimate goal of transformation into a net-zero carbon emission society. The design principles for such HER catalysts lie in the well-known structure-property relationship, which guides the synthesis procedure that creates catalyst with target properties such as catalytic activity. Here we report a general strategy to synthesize 10 kinds of single-atom-doped CoSe₂-DETA (DETA = diethylenetriamine) nanobelts. By systematically analyzing these products, we demonstrate a volcano-shape correlation between HER activity and Co atomic configuration (ratio of Co-N bonds to Co-Se bonds). Specifically, Pb-CoSe₂-DETA catalyst reaches current density of 10 mA cm^-2 at 74 mV in acidic electrolyte (0.5 M H₂SO₄, pH ~0.35). This striking catalytic performance can be attributed to its optimized Co atomic configuration induced by single-atom doping.

Electronic Modulation of Metal-Organic Frameworks Caused by Atomically Dispersed Ru for Efficient Hydrogen Evolution

Designing excellent electrocatalysts for the hydrogen evolution reaction (HER) is extremely significant in producing clean and sustainable hydrogen fuel. Herein, a rational strategy is developed to fabricate a promising electrocatalyst by introducing atomically dispersed Ru into a cobalt-based metal-organic framework (MOF), Co-BPDC (Co(bpdc)(H₂ O)₂ , BPDC: 4,4'-Biphenyldicarboxylic acid). The obtained CoRu-BPDC nanosheet arrays exhibit remarkable HER performance with an overpotential of 37 mV at a current density of 10 mA cm^-2 in alkaline media, which is superior to most of the MOF-based electrocatalysts and comparable to the commercial Pt/C. Synchrotron radiation-based X-ray absorption fine structure (XAFS) spectroscopy studies verify that the isolated Ru atoms are dispersed in Co-BPDC nanosheets with the formation of five-coordinated Ru-O₅ species. XAFS spectroscopy combined with density functional theory (DFT) calculations unravels that atomically dispersed Ru can modulate the electronic structure of the as-obtained Co-BPDC, contributing to the optimization of binding strength for H* and the enhancement of HER performance. This work opens a new avenue to rationally design highly-active single-atom modified MOF-based HER electrocatalysts via modulating electronic structures of MOF.

Insights into the Origin of High Activity of Ni5P4(0001) for Hydrogen Evolution Reaction

Hydrogen evolution reaction (HER) is directly relevant to green hydrogen production from water splitting. Recently, a low-cost Ni₅P₄ material has been demonstrated experimentally and theoretically to exhibit excellent electrocatalytic activity toward HER. However, a fundamental understanding of the origin of Ni₅P₄(0001) activity is still lacking. In this work, density functional theory (DFT) calculations were employed for a comprehensive investigation. The calculation results indicate that the Ni₅P₄(0001) surface exposing Ni₃P₄ termination gains the highest stability, on which a nearly thermoneutral hydrogen adsorption was found at the P₃-hollow sites, providing a high activity for HER. The activity was also observed to be maintained over a wide H-coverage. HER occurs via the Volmer-Heyrovsky mechanism as evidenced from the optimal hydrogen adsorption free energy, but unlikely through the Tafel reaction due to its large energy barrier. Furthermore, the P₃-hollow sites also exhibit a low kinetic barrier for water dissociation, promoting HER in alkaline media. A series of electronic structure analyses were performed in gaining insights into the origin of the HER activity. First, the density of states (DOS) and crystal orbital Hamilton population (COHP) analyses revealed a favorable interaction of electronic states between P and H atoms, leading to stable H adsorption at P₃-hollow sites. In addition, the Bader charge analysis demonstrates that the strength of H adsorption at P₃-hollow sites linearly increases with the electrons carried by the latter. The optimal net charge on the P₃-hollow sites leads to a desired ΔG _H that is close-to-zero. Finally, a highly efficient electron transfer was observed between the P₃-hollow sites and their neighboring atoms, facilitating the HER.

Challenges and Opportunities in Engineering the Electronic Structure of Single-Atom Catalysts

Controlling the electronic structure of transition-metal single-atom heterogeneous catalysts (SACs) is crucial to unlocking their full potential. The ability to do this with increasing precision offers a rational strategy to optimize processes associated with the adsorption and activation of reactive intermediates, charge transfer dynamics, and light absorption. While several methods have been proposed to alter the electronic characteristics of SACs, such as the oxidation state, band structure, orbital occupancy, and associated spin, the lack of a systematic approach to their application makes it difficult to control their effects. In this Perspective, we examine how the electronic configuration of SACs can be engineered for thermochemical, electrochemical, and photochemical applications, exploring the relationship with their activity, selectivity, and stability. We discuss synthetic and analytical challenges in controlling and discriminating the electronic structure of SACs and possible directions toward closing the gap between computational and experimental efforts. By bringing this topic to the center, we hope to stimulate research to understand, control, and exploit electronic effects in SACs and ultimately spur technological developments.

Tubular palladium-based catalysts enhancing direct ethanol electrooxidation

Direct ethanol fuel cell (DEFC) has the advantages of high power density, high energy conversion efficiency and environmental friendliness, but its commercialization is restricted by factors such as insufficient activity and low anti-poisoning ability of anode catalyst for incomplete oxidation of ethanol. It is of great significance to design and prepare anode catalyst with high activity and high anti-poisoning ability that can be recycled. In this work, tubular palladium-based (Pd-based) catalysts with abundant lattice defect sites were prepared by simple and reproducible electro-displacement reactions using Cu nanowires as sacrificial template. Pd is the main catalytic element which provides adsorption sites for ethanol oxidation. Ag and Cu introduced facilitates the formation of hydroxyl groups to oxidize toxicity intermediates, and changes the d-band center position of Pd, so as to adjust the adsorption and desorption of ethanol and its intermediates on the Pd surface. At the same time, Au introduced with high potential maintains the stability of the catalyst structure. The tubular structure exposes more active sites, improves the atomic utilization rate and enhances the ability of the catalyst resisting dissolution and aggregation. The series of PdAuAgCu tubular catalysts with outer layer dendrites were prepared by electro-displacement reactions using the mixture (ethylene glycol : ultra-pure water = 3 : 1) as the reaction solvent and fivefold twinned Cu nanowires as sacrificial template. The performance evaluation of ethanol electrocatalytic oxidation showed that the Pd₁₇Au₄₀Ag₁₁Cu₃₂ tubular catalysts were prepared at 120 °C and 10 mM CTAB had excellent overall performance, with a peak mass activity of 6335 mA mg_Pd^-1, which was 9.6 times of Pd/C (JM). The residual current density after the stability test of 3000 s was 249 mA mg_Pd^-1, which was 3.3 times of Pd/C (JM).

The Influence of Active Phase Content on Properties and Activity of Nd2O3-Supported Cobalt Catalysts for Ammonia Synthesis

A series of neodymium oxide-supported cobalt catalysts with cobalt content ranging from 10 to 50 wt.% was obtained through the recurrent deposition-precipitation method. The effect of active phase, i.e., metallic cobalt, content on structural parameters, morphology, crystal structure, surface state, composition and activity of the catalysts was determined after detailed physicochemical measurements were performed using ICP-AES, N2 physisorption, XRPD, TEM, HRTEM, STEM-EDX, H2-TPD and XPS methods. The results indicate that the catalyst activity strongly depends on the active phase content due to the changes in average cobalt particle size. With the increase of the cobalt content, the productivity per catalyst mass increases, while TOF maintains a constant value. The TOF is below average only for the catalyst with the lowest cobalt content, i.e., when the average Co particle size is below 20 nm. This is due to the predominance of strong hydrogen binding sites on the surface, leading to hydrogen poisoning which prevents nitrogen adsorption, thus inhibiting the rate-determining step of the process.

Carbon-Conjugated Co Complexes as Model Electrocatalysts for Oxygen Reduction Reaction

Single-atom catalysts are a family of heterogeneous electrocatalysts widely used in energy storage and conversion. The determination of the local structure of the active metal sites is challenging, which limits the establishment of the reliable structure-property relationship of single-atom catalysts. A carbon black-conjugated complex can be used as the model catalyst to probe the intrinsic activity of metal sites with certain local structures. In this work, we prepared carbon black-conjugated [Co(phenanthroline)Cl2], [Co(o-phenylenediamine)Cl2] and [Co(salophen)]. In these catalysts, the Co complexes with well-defined structures are anchored on the edge of carbon black by pyrazine moieties. The number of electrochemical accessible Co sites can be measured from the area of the redox peaks of pyrazine linkers in the cyclic voltammetry curve. Then, the intrinsic electrocatalytic activity of one Co site can be obtained. The catalytic performances of the three catalysts towards oxygen reduction reaction in alkaline conditions were measured. Carbon black-conjugated [Co(salophen)] showed the highest intrinsic activity with the turnover frequency of 0.72 s−1 at 0.75 V vs. the reversible hydrogen electrode. The strategy developed in this work can be used to explore and verify the possible local structure of active sites proposed for single-atom catalysts.

Dilute Alloying to Implant Activation Centers in Nitride Electrocatalysts for Lithium-Sulfur Batteries

Dilute alloying is an effective strategy to tune properties of solid catalysts but is rarely leveraged in complex reactions beyond small molecule conversion. In this work, dilute dopants are demonstrated to serve as activating centers to construct multiatom catalytic domains in metal nitride electrocatalysts for lithium-sulfur (Li-S) batteries, of which the sulfur cathode suffers from sluggish and complex conversion reactions. With titanium nitride (TiN) as a model system, the dilute cobalt alloying is shown to greatly improve the reaction kinetics while inducing negligible catalyst reconstruction. Compared to the pristine TiN, the dilute nitride alloy catalyst enables onefold increase in the high rate (2.0 C) capacities of Li-S batteries, as well as an impressively low cyclic decay rate of 0.17% at a sulfur loading of 4.0 mg_S cm^-2 . This work opens up new opportunities toward the rational design of Li-S electrocatalysts by dilute alloying and also enlightens the understandings of complex domain-catalyzed reactions in energy applications.

Unraveling Polysulfide's Adsorption and Electrocatalytic Conversion on Metal Oxides for Li-S Batteries

Lithium sulfur (LiS) batteries possess high theoretical capacity and energy density, holding great promise for next generation electronics and electrical vehicles. However, the LiS batteries development is hindered by the shuttle effect and sluggish conversion kinetics of lithium polysulfides (LiPSs). Designing highly polar materials such as metal oxides (MOs) with moderate adsorption and effective catalytic activity is essential to overcome the above issues. To design efficient MOs catalysts, it is critical and necessary to understand the adsorption mechanism and associated catalytic processes of LiPSs. However, most reviews still lack a comprehensive investigation of the basic mechanism and always ignore their in-depth relationship. In this review, a systematic analysis toward understanding the underlying adsorption and catalytic mechanism in LiS chemistry as well as discussion of the typical works concerning MOs electrocatalysts are provided. Moreover, to improve the sluggish "adsorption-diffusion-conversion" process caused by the low conductive nature of MOs, oxygen vacancies and heterostructure engineering are elucidated as the two most effective strategies. The challenges and prospects of MOs electrocatalysts are also provided in the last section. The authors hope this review will provide instructive guidance to design effective catalyst materials and explore practical possibilities for the commercialization of LiS batteries.

Transplanting Gold Active Sites into Non-Precious-Metal Nanoclusters for Efficient CO2-to-CO Electroreduction

Electrocatalytic CO₂ reduction reaction (CO₂RR) is greatly facilitated by Au surfaces. However, large fractions of underlying Au atoms are generally unused during the catalytic reaction, which limits mass activity. Herein, we report a strategy for preparing efficient electrocatalysts with high mass activities by the atomic-level transplantation of Au active sites into a Ni₄ nanocluster (NC). While the Ni₄ NC exclusively produces H₂, the Au-transplanted NC selectively produces CO over H₂. The origin of the contrasting selectivity observed for this NC is investigated by combining operando and theoretical studies, which reveal that while the Ni sites are almost completely blocked by the CO intermediate in both NCs, the Au sites act as active sites for CO₂-to-CO electroreduction. The Au-transplanted NC exhibits a remarkable turnover frequency and mass activity for CO production (206 mol_CO/mol_NC/s and 25,228 A/g_Au, respectively, at an overpotential of 0.32 V) and high durability toward the CO₂RR over 25 h.

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.