Interfacial Electronic Structure Research Articles

Strong Interactions between Au Nanoparticles and BiVO4 Photoanode Boosts Hole Extraction for Photoelectrochemical Water Splitting.

Strong metal-support interaction (SMSI) is widely proposed as a key factor in tuning catalytic performances. Herein, the classical SMSI between Au nanoparticles (NPs) and BiVO4 (BVO) supports (Au/BVO-SMSI) is discovered and used innovatively for photoelectrochemical (PEC) water splitting. Owing to the SMSI, the electrons transfer from V4+ to Au NPs, leading to the formation of electron-rich Au species (Auδ-) and strong electronic interaction (i.e., Auδ--Ov-V4+), which readily contributes to extract photogenerated holes and promote charge separation. Benefitted from the SMSI effect, the as-prepared Au/BVO-SMSI photoanode exhibits a superior photocurrent density of 6.25 mA cm-2 at 1.23 V versus the reversible hydrogen electrode after the deposition of FeOOH/NiOOH cocatalysts. This work provides a pioneering view for extending SMSI effect to bimetal oxide supports for PEC water splitting, and guides the interfacial electronic and geometric structure modulation of photoanodes consisting of metal NPs and reducible oxides for improved solar energy conversion efficiency.

Strong Interactions between Au Nanoparticles and BiVO4 Photoanode Boosts Hole Extraction for Photoelectrochemical Water Splitting

AbstractStrong metal‐support interaction (SMSI) is widely proposed as a key factor in tuning catalytic performances. Herein, the classical SMSI between Au nanoparticles (NPs) and BiVO4 (BVO) supports (Au/BVO‐SMSI) is discovered and used innovatively for photoelectrochemical (PEC) water splitting. Owing to the SMSI, the electrons transfer from V4+ to Au NPs, leading to the formation of electron‐rich Au species (Auδ−) and strong electronic interaction (i.e., Auδ−‐Ov‐V4+), which readily contributes to extract photogenerated holes and promote charge separation. Benefitted from the SMSI effect, the as‐prepared Au/BVO‐SMSI photoanode exhibits a superior photocurrent density of 6.25 mA cm−2 at 1.23 V versus the reversible hydrogen electrode after the deposition of FeOOH/NiOOH cocatalysts. This work provides a pioneering view for extending SMSI effect to bimetal oxide supports for PEC water splitting, and guides the interfacial electronic and geometric structure modulation of photoanodes consisting of metal NPs and reducible oxides for improved solar energy conversion efficiency.

Mechanical behavior of Ni/Ti bilayer-based shape memory alloys: Endorsement via atomistic simulations

To gain a structural and thermodynamic understanding along with the interpretation of atomic diffusion in a Ni/Ti bilayer, detailed first-principles simulations using density functional theory (DFT) and molecular dynamics (MD) simulations have been carried out. The interface energies and electronic structure of the Ni/Ti bilayer have been calculated using DFT. The MD simulations of interface atomic diffusion in the Ni/Ti bilayer were performed at 773 K for different annealing times to investigate the formation of Ni–Ti alloy. The simulated results indicate that Ni atoms predominantly diffuse into the Ti side. The radial distribution functions (RDFs) have been plotted to understand the nature of bonding that exists between the Ni and Ti atoms in the bilayer. The shape of the RDFs reveals information about the extent to which Ni and Ti atoms mix together. Classical MD simulations have been used to simulate the deformation behavior of the material under tension and to investigate the effects of annealing time on the mechanical properties of the materials.

Effect of multi-interface electron transportation and molecule adsorption on hydrogen evolution reaction

The widespread industrial application of water electrolysis to hydrogen production is limited by its high cost, high energy consumption and low conversion efficiency. This work demonstrates the energy-efficient hydrogen production can be attained by the rational design of electrolyser with efficient electrocatalyst. Typically, the efficient CoP3-FeOOH-Ni2P-C3N4 (CoFeNiC) electrocatalyst is prepared by calcining the mixture of both ZIF-67 and NiFe-LDH, which exhibits a good electrolysis performance in an alkaline electrolyte. At 10 mA cm−2, the oxygen evolution reaction (OER) overpotential of CoFeNiC (146 mV) is lower than the previously reported results, and the Faraday efficiency (FE) reaches 94.8 %. In addition, density functional theory (DFT) calculations demonstrate that the large work function difference between FeOOH, Ni2P and C3N4 is beneficial to form stable hetero-interface, which significantly optimize the interface electronic structure and enhances the electron transfer from FeOOH, Ni2P to C3N4; and CoP3 has a strong molecule adsorption ability. Thereby CoFeNiC shows an enhaned water-splitting efficiency. Moreover, an asymmetric electrolyzer is constructed by using CoFeNiC as cathode and NiFe-LDH as anode. At 150 mA cm−2, the cell voltage of CoFeNiC//NiFe-LDH electrolyzer decreases by 11.67 %, compared with symmetric NiFe-LDH electrolyzer. The i-t test shows that the asymmetrical electrolyzer exhibits a good stability at a high current density.

Tuning the Interfacial Electronic Structure of MoS2 by Adsorption of Cobalt Phthalocyanine Derivatives

Tuning the Interfacial Electronic Structure of MoS₂ by Adsorption of Cobalt Phthalocyanine Derivatives

Interface energy, adhesion work and electronic structure of Ti3AlC2/Ag interface calculated from first principles

In this paper, based on the first-principles calculation of density functional theory, the adhesion work, interface energy and electronic structure of Ag/Ti3AlC2 interface are systematically studied. In the calculation process, 18 interface models with different terminals and different stacking sequences are considered. After comparing the calculation results, it is found that the interface model of Al terminal is the most stable among the six interface models of Ti1(C), Al, C(Ti2), Ti2(Al), C(Ti1) and Ti2(C). After changing the stacking order of Al terminal interface atoms, it can be found that the order of interface stability of Al terminal is HCP > FCC > OT according to the interface energy, and the interface energy of HCP interface model is 2.209J/m2. After the comprehensive analysis of adhesion work, interface energy and electronic structure, it is found that the theoretical calculation results are consistent with the previous experimental results. Al atoms have a tendency to move to the Ag matrix and form Ag (Al) solid solution, and the formation of solid solution further increases the stability of the interface.

NiO surface reduction by Nd overlayers

Metal/metal oxide interfaces have significant impact on modern technologies like microelectronics, solar cells, magnetic storage, and sensors due to their distinct electronic and structural properties. Such interfaces sometimes deviate from ideal bulk-termination which influences the system's overall performance. Here, we present the study of the interfacial electronic structure formed by the deposition of Nd layers onto NiO thin films utilizing X-ray photoelectron spectroscopy (XPS) and Ultraviolet photoemission spectroscopy (UPS). Our study indicates that the interface between the rare earth metal (Nd) and NiO differs from the ideal sharp interface. The portion of NiO surface reduced to metallic Ni while the deposited Nd metal is oxidized, indicating the interfacial oxidation/reduction process. The thickness of this interfacial Ni layer increases with increase in Nd metal deposited and reaches maximum depth of 3.0 Å when effective Nd overlayer thickness reaches 7.9 Å. Such an interface reaction could be utilized in heterostructures where an intentional reduction of the oxides is desired.

An effective descriptor for identifying the electrocatalytic activity and selectivity of bilayer carbon-based heterojunction catalysts

The usage of composite carbon-based materials supported by graphene has emerged as a powerful selection for designing electrocatalytic electrodes due to their agile electronic transmission and diversiform redox active sites. Here, we constructed fresh electroactive organic catalysts for hydrogen carrier synthesis by stacking a series of organic molecules on transition metal azide doped graphene substrates, in anticipation of these bilayer heterostructures to breathe new life into electrocatalysis. As expected, several promising cathodic catalysts were speculated through first principles calculations, such as Co-PMDT for H2 generation and Co-PQ for ammonia (NH3) synthesis. However, facing such an intricate interface engineering and electronic structure regulation undoubtedly poses a challenge to the time-consuming computational screening work. To tackle this, an effective descriptor was proposed as a predictive tool for identifying the activity and selectivity toward diverse chemical reactions, which allows us to systematically fine-tune the catalysts' properties in order to enhance their electrocatalytic performance. Our work may offer feasible approaches for the rational design of advanced electrocatalysts.

Insight into the Grain Refining Mechanism of Al–Ti–C and the Interfacial Properties between the Inoculants and Aluminum

The grain refinement mechanism of Al–Ti–C grain refiners used in the casting procedure of aluminum has been studied by first‐principles calculation. Considering the controversy over Al3Ti, TiC, or Al3Ti–TiC as nucleation sites, the adsorption behavior of possible nucleation surfaces for Al atoms, including adsorption energies and adsorption sites, as well as the interfacial properties of Al/Al3Ti/TiC are calculated and compared. In the results, it is shown that the Al3Ti(112) surface has a stronger adsorption capacity for Al than TiC. By using the edge‐to‐edge matching crystallographic model and the calculation of the adsorption energy, it is found that the monolayer Al3Ti(112) can be stabilized on the TiC(100) surface, and the combination of TiC and monolayer Al3Ti can significantly improve the adsorption capacity of Al. Interfacial electronic structure analysis shows stronger chemical bonding between Al and Ti at the Al/Al3Ti/TiC interface compared to Al/Al3Ti, which explains that the monolayer Al3Ti covering the TiC surface has the strongest adsorption capacity for Al atoms. Therefore, it is speculated that TiC with a monolayer of Al3Ti covering the surface will serve as a potential nucleation site during grain refinement, which will provide a theoretical reference for future research work.

In-situ topotactic synthesis of decahedron BiVO4/2D networks Bi2S3 heterojunctions for efficient Cr(VI) reduction: Improved charge separation and imaged at the single-particle level

Epitaxial heterostructure has an optimized interfacial electronic structure compared to the traditional random heterostructures. However, accurately monitoring the interfacial charge transfer dynamics remains a grand challenge. We report here that single-particle spectroscopy techniques address this challenge by performing photoluminescence (PL) lifetime imaging and spectral fitting of interfacial micro/nano regions. A novel facet-selective BiVO4/2D nano-network Bi2S3 heterostructure is synthesized by a simple hydrothermal method. Single-particle PL spectroscopy shows that the PL emission at the oriented epitaxial heterojunction interface in BVO/S-O is weakened, and the PL lifetime increases by 213 % and 105 % compared to a single BiVO4 and random heterojunction particles, respectively, indicating that the topological heterojunction interface effectively promotes the separation of charge carriers. In addition, the possible mechanism of photocatalysis was also discussed in detail. Our work reveals the advantages of unique spatial structures and topological epitaxial interfaces in charge separation, which has great prospects for photocatalytic applications.

Generalized Substrate Screening GW for Covalently Bonded Interfaces.

An accurate description of the interfacial quasiparticle electronic structure is key to the design of heterogeneous materials. While the first-principles GW approach is state-of-the-art, the computational cost is high for large interface systems. This has led to the substrate screening GW approach for weakly coupled interfaces, which breaks down for covalently bonded interfaces. In this work, we present the generalized substrate screening GW approach, based on the following two considerations: (i) the contribution of the interfacial covalent bond to the polarizability can be efficiently calculated with a low energy cutoff; (ii) the contribution of the deprotonated adsorbate to the interface polarizability can be well approximated by that of the protonated molecule. Our approach is exemplified using interfaces formed between benzene-1,4-dithiol (BDT) and Au(111), which feature the widely used Au-S bonds in experiments. Our work provides a robust and simple scheme for accurate and efficient GW calculations of covalently bonded interfaces.

Thermopower in Underpotential Deposition-Based Molecular Junctions.

Underpotential deposition (UPD) is an intriguing means for tailoring the interfacial electronic structure of an adsorbate at a substrate. Here we investigate the impact of UPD on thermoelectricity occurring in molecular tunnel junctions based on alkyl self-assembled monolayers (SAMs). We observed noticeable enhancements in the Seebeck coefficient of alkanoic acid and alkanethiol monolayers, by up to 2- and 4-fold, respectively, upon replacement of a conventional Au electrode with an analogous bimetallic electrode, Cu UPD on Au. Quantum transport calculations indicated that the increased Seebeck coefficients are due to the UPD-induced changes in the shape or position of transmission resonances corresponding to gateway orbitals, which depend on the choice of the anchor group. Our work unveils UPD as a potent means for altering the shape of the tunneling energy barrier at the molecule-electrode contact of alkyl SAM-based junctions and hence enhancing thermoelectric performance.

Effect of Interfacial Electronic Structure on Conductivity and Space Charge Characteristics of Core-Shell Quantum Dots/Polyethylene Nanocomposite Insulation

To investigate the effect of the interface electronic structure of core-shell quantum dots on the conductivity and space charge characteristics of polyethylene insulation, nanocomposite insulations, namely CdSe@ZnS/LDPE and ZnSe@ZnS/LDPE, are synthesized. The study focuses on elucidating the evolution patterns of DC conductivity and space charge within the nanocomposite insulation, accompanied by an analysis of the impact of the interfacial electronic structure of core-shell quantum dots on the distribution of charge traps. Comparative analysis reveals that, in contrast to LDPE insulation, ZnSe@ZnS/LDPE nanocomposite insulation demonstrates a substantial reduction in DC conductivity by 47.2% and a decrease in space charge accumulation by 40.3% under conditions of elevated temperature and strong electric fields. The trap energy level experiences an increase, signifying a heightened trapping effect on carriers. Leveraging density functional theory, the band structure characteristics of core-shell quantum dots integrated with polyethylene are computationally assessed. The findings underscore that the band misalignment at the core-shell interface and the shell-insulation interface induces shifts in the conduction band bottom and valence band top, respectively. These shifts impose a confinement effect on electrons and holes, with the extent of this effect escalating with the augmented band gap difference between the core layer and the shell layer. Consequently, this phenomenon curtails carrier migration, thereby inhibiting space charge accumulation under conditions of elevated temperature and strong electric fields.

Microwave Quasi‐Solid State to Construct Strong Metal‐Support Interactions with Interfacial Electron‐Enriched Ru for Anion Exchange Membrane Electrolysis

AbstractRegulating the metal‐support interaction of the anchored metal nanoclusters is recognized as valid approach to optimize the electrocatalytic performance through tuning the interfacial electronic structure. However, developing novel support and understanding the interfacial electron accumulation on modulating the reaction kinetics are still elusive. Herein, highly‐dispersed Ruthenium (Ru) nanoclusters anchored onto phosphorous doped molybdenum boride (Ru/P‐MoB) is developed through ultrafast microwave‐plasma (60 s) approach. The synthesized Ru/P‐MoB impressively promote the hydrogen evolution with low overpotentials of 34, 45, and 40 mV to drive 10 mA cm−2 in alkaline freshwater, alkaline seawater and acid media. Specially, it presents superior turnover frequency and mass/specific activity relative to Pt/C, Ru/C, and Ru/MoB. Moreover, the anion exchange membrane (AEM) electrolyzer cell based on Ru/P‐MoB can achieve 500 and 1000 mA cm−2 with small voltages of 1.71 and 1.78 V with good durability. Experimental and density functional theoretical (DFT) analysis reveal that the strong metal‐support interactions (Ru─Mo and Ru─P bonds) with generated interfacial electron‐enriched Ru, and then favoring the water‐molecule adsorption/dissociation and optimal H intermediate adsorption free energy. This work provides novel designing avenue to exploit electrocatalysts with outstanding catalytic performance under high current density at practical high‐temperature.

Asymmetric Fe-O2-Ti structures accelerate reduced-layer-FeII “electron” conversion: Facilitating photocatalytic nitrogen fixation

As a green and sustainable method for ammonia production, solar photocatalytic nitrogen fixation (PNRR) provides a new approach to slowing down the consumption of non-renewable energy resources. Given the extremely huge energy required to activate inert nitrogen, a rational design of efficient nitrogen fixation catalytic materials is essential. This study constructs defective Ti3+-Ti3C2Ox to regulate the NH2-MIL-101(Fe) reduced layer-FeII 'electron' transition; meanwhile, the heterojunction interface electronic structure formed by coupling promotes catalytic charges' transfer/separation, while the interface-asymmetric Fe-O2-Ti structure accelerates the response with nitrogen. It is shown that the heterojunction NM-101(FeII/FeIII)-1.5 exhibits a 75.1 % FeII enrichment (FeII:FeIII), which successfully impedes the fouling relationship between the two (FeII/FeIII). Mössbauer spectroscopy analysis demonstrates that the presence of D1-high spin state FeIII and D2-low/medium spin state FeII structures in the heterojunction boosts the PNRR activity. Furthermore, it is found that the defective state Ti3+-Ti3C2Ox modulation enhances the reduced nitrogen fixation capacity of the heterojunction (CB = -0.84 eV) and decreases the interfacial charge transfer resistance, yielding 450 umol·g−1·h−1 ammonia. Furthermore, this study modulates the charge ration of the catalyst reduction layer by constructing a charge-asymmetric structure with Ti3+-deficient carriers; this method provides a potential opportunity for enhancing photocatalytic nitrogen fixation in the future.

Design of Hierarchical Nickel-Cobalt Phosphide/Nickel Oxide with Tunable Electronic Structure and Strong Chemical Interface for Advanced Supercapacitors

The design of a reasonable heterostructure electrode to achieve enhanced areal performance for supercapacitors remains a great challenge. Here, we constructed hierarchical porous NiCoP/NiO nanocomposites anchored on Ni foam with tunable electronic and structural properties, as well as robust interfacial interaction. In NiCoP/NiO, the interconnected NiO nanosheets serve as a carrier with enriched anchoring sites to confine the NiCoP and improve its stability. Meanwhile, the ultrathin NiCoP nanosheets with bimetallic centers are connected with porous NiO nanosheets to form a reliable heterojunction, enhancing the electrochemical reaction kinetics. Taking advantage of the synergistic contribution of bimetallic centers, phosphides and unique structure, the NiCoP/NiO delivers a high areal specific capacitance (1860 mF cm−2 at 5 mA cm−2), good rate performance of 78.5% at six times the increased current density, and remarkable durability (11.0% decrease after 10,000 cycles). Furthermore, the assembled hybrid supercapacitor NiCoP/NiO//porous-activated carbon (PAC) delivers a high areal energy density of 173.7 μWh cm−2 (116.4 μWh cm−2) at 1.6 mW cm−2 (32 mW cm−2). The results indicate that the design of the heterostructure interface with strong chemical interface and tunable electronic structure is an effective and promising approach to boost the electrochemical performance for advanced supercapacitors.

Sulfur Vacancy-Engineered Co3S4/MoS2-Interfaced Nanosheet Array for Enhanced Alkaline Overall Water Splitting.

Electrochemical water splitting, a crucial reaction for renewable energy storage, demands highly efficient and stable catalysts. Defect and interface engineering has been widely acknowledged to play a pivotal role in improving electrocatalytic performance. Herein, we demonstrate a facile strategy to construct sulfur vacancy (Sv)-engineered Co3S4/MoS2-interfaced nanosheet arrays to modulate the interface electronic structure in situ reduction with NaBH4. The abundant sulfur vacancies and well-arranged nanosheet arrays in Sv-Co3S4/MoS2 lead to pronounced electrocatalytic properties for hydrogen and oxygen evolution reactions (HER/OER) in an alkaline medium, with observed overpotentials of 156 and 209 mV at 10 mA cm-2, respectively. Additionally, as a bifunctional electrocatalyst, Sv-Co3S4/MoS2 requires a cell voltage of 1.67 V at 10 mA cm-2 for overall water splitting and exhibits long-term stability with activity sustained for more than 20 h. This study provides a novel approach to producing transition metal compound-interfaced electrocatalysts with rich vacancies under mild conditions, showcasing their potential for efficient water splitting applications.

First-principles study on the interfacial electronic structure and analysis of the bonding properties of NbC/Fe composites

This paper investigated the bonding mode and atoms’ surface energy in the α-Fe and NbC bulk phases in NbC/Fe composites using the first-principles calculation of density functional theory. Different interface models were established to evaluate the interface bonding strength and stability considering the total interface energy and work of adhesion. After structural optimization, four interface models were established, α-Fe(100)/NbC(100) at the C-terminus, α-Fe(100)/NbC(100) at the Nb-terminus, α-Fe(100)/NbC(111) at the C-terminus, and α-Fe(100)/NbC(111) at the Nb-terminus, defined as interfaces I, II, III, and IV, respectively. The results show that the interface adhesion of the C-terminal interface is higher than the Nb-terminal interface. The minimum total energy of interface I and the maximum adhesion work are − 1.80 × 104 eV and 5.31 J/m2, respectively, indicating the most stable interfacial bonding method. The effects of different terminal atoms on the electronic structure and bonding characteristics of the α-Fe(100)/NbC(100) interface were analyzed. The bonding characteristics of the atomic interfaces I and II of the two interface models demonstrated covalent binding of different intensities. Interface I depends on the covalent-ionic bond formed by Fe and C atoms, while interface II relies on metal bonds formed by Fe and Nb atoms and weaker Fe-C bonds. Mulliken's analysis revealed that the bond population of Fe-Nb at interfaces I and II were negative, indicating an intense anti-bonding state between Fe and Nb atoms and a severe anti-bonding effect of Fe-Nb at interface II, resulting in its structural instability. Moreover, because of the covalent bonding (Fe-C) at interface I, the binding strength of the interface was higher with a stable interface.

Significant Strain Dissipation via Stiff-Tough Solid Electrolyte Interphase Design for Highly Stable Alloying Anodes.

The pulverization of alloying anodes significantly restricts their use in lithium-ion batteries (LIBs). This study presents a dual-phase solid electrolyte interphase (SEI) design that incorporates finely dispersed Al nanoparticles within the LiPON matrix. This distinctive dual-phase structure imparts high stiffness and toughness to the integrated SEI film. In comparison to single-phase LiPON film, the optimized Al/LiPON dual-phase SEI film demonstrates a remarkable increase in fracture toughness by 317.8%, while maintaining stiffness, achieved through the substantial dissipation of strain energy. Application of the dual-phase SEI film on an Al anode leads to a 450% enhancement in cycling stability for lithium storage in dual-ion batteries. A similar enhancement in cycling stability for silicon anodes, which face severe volume expansion issues, is also observed, demonstrating the broad applicability of the dual-phase SEI design. Specifically, homogeneous Li-Al alloying has been observed in conventional LIBs, even when paired with a high mass loading LiNi0.5Co0.3Mn0.2O2 cathode (7 mg cm-2). The dual-phase SEI film design can also accelerate the diffusion kinetics of Li-ions through interface electronic structure regulation. This dual-phase design can integrate stiffness and toughness into a single SEI film, providing a pathway to enhance both the structural stability and rate capability of alloying anodes.

Significant Strain Dissipation via Stiff‐Tough Solid Electrolyte Interphase Design for Highly Stable Alloying Anodes

AbstractThe pulverization of alloying anodes significantly restricts their use in lithium‐ion batteries (LIBs). This study presents a dual‐phase solid electrolyte interphase (SEI) design that incorporates finely dispersed Al nanoparticles within the LiPON matrix. This distinctive dual‐phase structure imparts high stiffness and toughness to the integrated SEI film. In comparison to single‐phase LiPON film, the optimized Al/LiPON dual‐phase SEI film demonstrates a remarkable increase in fracture toughness by 317.8 %, while maintaining stiffness, achieved through the substantial dissipation of strain energy. Application of the dual‐phase SEI film on an Al anode leads to a 450 % enhancement in cycling stability for lithium storage in dual‐ion batteries. A similar enhancement in cycling stability for silicon anodes, which face severe volume expansion issues, is also observed, demonstrating the broad applicability of the dual‐phase SEI design. Specifically, homogeneous Li−Al alloying has been observed in conventional LIBs, even when paired with a high mass loading LiNi0.5Co0.3Mn0.2O2 cathode (7 mg cm−2). The dual‐phase SEI film design can also accelerate the diffusion kinetics of Li‐ions through interface electronic structure regulation. This dual‐phase design can integrate stiffness and toughness into a single SEI film, providing a pathway to enhance both the structural stability and rate capability of alloying anodes.