Interfacial Electronic Structure Research Articles

Heterogeneous bimetallic FeP4/NiP2 nanosheets as efficient electrocatalyst for alkaline oxygen evolution reaction

Constructing high-efficient transition metal phosphides (TMPs) toward the oxygen evolution reaction (OER) is critical but challenging for the development of alkaline water splitting. Particularly, the electrocatalytic OER activity can be enhanced by designing a reasonable heterojunction and fine-tuning the interface electronic structure. Hence, in this work, simple and low-cost two-step strategy is proposed to prepare the heterostructured FeP4/NiP2 nanosheets composed of tremendous interconnected nanoparticles on carbon cloth (denoted as FeNiP NSs/CC). This study indicates that the rationally interface engineering in FeNiP/CC can effectively modulate the electroactive sites and accelerate the charge transfer between catalysts and substrate, leading to a dramatic boost in catalytic activity for the OER. Consequently, the optimized FeNiP/CC OER electrocatalyst possesses an outstanding overpotential of only 233 mV @ 10 mA cm−2, relatively low Tafel slope of 45.2 mV dec−1, and prominent long-term durability in alkaline electrolyte.

Interfacial Electronic and Photovoltaic Performance of a Novel Lead‐Free Z‐Scheme CsSnBr3/MoSe2 Perovskite Heterostructure: A Theoretical and Experimental Study

Sn‐based perovskite materials with nontoxic, low cost, and unique structure have attracted much attention. However, their efficiency only reaches 14.09% due to the higher carrier recombination rate and short carrier lifetime in photovoltaic applications. Herein, the interfacial electronic structure, optical absorption, interfacial charge transfer mechanism, and photovoltaic performance of the CsSnBr3/MoSe2 perovskite heterostructure are systematically investigated by theoretical calculation and experimental observation. The results indicate that the strong coupling and hybridization of interfacial electronic states can lead to a narrowing bandgap, which induces an excellent optical absorption of the CsSnBr3/MoSe2 perovskite heterostructure in the visible spectrum. Excitingly, the charge transfer at the interface forms a built‐in electric field, which can effectively promote the interfacial charge transfer between CsSnBr3 (001) and MoSe2 monolayer, complying with a Z‐scheme mechanism. Moreover, the photovoltaic performance of the CsSnBr3/MoSe2 heterostructure significantly enhances due to excellent light absorption and Z‐scheme system for extending carrier lifetime. An effective strategy for designing highly efficient Sn‐based perovskite solar cells is reported.

In-plane graphene incorporated borocarbonitride: Directional utilization of disorder charge via micro π-conjugated heterointerface for photocatalytic CO2 reduction

Despite the potential of hexagonal boron carbon nitride (h-BCN) with a unique graphite-like structure in the field of photocatalysis, the serious photocarrier recombination caused by disordered charge transfer has limited its practical application. In this work, we propose a conceptual design of in-plane heterostructures consisting of graphene sheet and non-phase-separated borocarbonitride (Gsheet–BCN) with micro π-conjugated heterointerface for directional utilization of disorder charge. The obtained G150–BCN exhibits 10 times longer carrier decay lifetime (16.82 ns) and 3.7 times higher CO yield (51.14 μmol g−1 h−1) than pristine BCN. It was confirmed by systematical characterizations and theoretical calculations that the micro π-conjugated heterointerface enables the directional transport of photo-induced electrons from BCN to graphene domains, resulting in enhanced carrier separation and CO2 reduction efficiency. This work developed a unique synthetic route to the design and construction of heterojunction with proper interface and rational electronic structure for efficient separation of photoexcited charges.

Interfacial charge transfer and electronic structure of diamond/c-BN heterointerface

In this work, the interfacial structures and electronic properties of diamond and cubic boron nitride heterostructures are investigated using first principles calculation. It is found that the n-type (p-type) surface doping appears at the heterostructures with interface CN (C—B) bonds, which is attributed to the interface charge transfer. The doping feature of heterostructures is determined by the interface bonds, and it is not related to the surface functionalization and crystal orientation. The areal electron (hole) density values are 6.57 × 1013 — 1.57 × 1014 cm−2 (2.24 × 1014 — 3.72 × 1014 cm−2). This work is helpful for promoting diamond applied in electronic and opto-electronic devices.

Atomically thin interlayer phase from first principles enables defect-free incommensurate SnO2/CdTe interface

Advancing optoelectronic and emerging technologies increasingly requires control and design of interfaces between dissimilar materials. However, incommensurate interfaces are notoriously defective and rarely benefit from first-principles predictions, because no explicit atomic-structure models exist. Here, we adopt a bulk crystal structure prediction method to the interface geometry and apply it to SnO2/CdTe heterojunctions without and with the addition of CdCl2, a ubiquitous and beneficial, but abstruse processing step in CdTe photovoltaics. Whereas the direct SnO2/CdTe interface is highly defective, we discover a unique two-dimensional CdCl2 interphase, unrelated to the respective bulk structure. It facilitates a seamless transition from the rutile to zincblende lattices and removes defect-states from the interface bandgap. Implementing the predicted interface electronic structure in device simulations, we demonstrate the theoretical feasibility of bufferless oxide-CdTe heterojunction solar cells approaching the Shockley–Queisser limit. Our results highlight the broader potential of designing atomically thin interlayers to enable defect-free incommensurate interfaces.

Metal sulfide heterojunction with tunable interfacial electronic structure as an efficient catalyst for lithium-oxygen batteries

The design and preparation of catalysts with excellent stability and high activity are critical to improving the performance of lithium-oxygen (Li-O2) batteries. Heterostructural catalysts have attracted wide attention due to their tunable structure and effectiveness in promoting oxygen reduction reaction and oxygen evolution reaction kinetics. In this study, CuCo2S4/CoS1.097 polymetallic sulfides were proposed as effective electrocatalysts toward oxygen electrode reactions in Li-O2 batteries. Density functional theory calculations demonstrated that the electronic structure of CuCo2S4/CoS1.097 was regulated at the heterogeneous interface, which was beneficial for optimizing the adsorption of intermediates during the reaction, eventually accelerating the sluggish kinetics of oxygen electrode reactions. The CuCo2S4/CoS1.097-based Li-O2 batteries exhibited a high specific capacity of 26,727.8 mAh g−1 and an outstanding durability of over 267 cycles at 100 mA g−1. This study provides a new perspective on the design and application of excellent cathode materials in Li-O2 batteries.

Realizing the synergy of interface engineering and surface reconstruction in Ni(OH)2 for superior water oxidation

Exploring cost-effective and stable electrocatalysts for the oxygen evolution reaction (OER) is of great importance to converting renewable electricity into fuels. Herein, we demonstrate the preparation of phytic acid-iron complex (PAFe) decorated Co3O4/Ni(OH)2 core-shell heterojunction using a hydrothermal-solvothermal combined with the typical coordination chemistry technique. The Co3O4 nanowires increase the electrical conductivity and inhibit the agglomeration of Ni(OH)2 nanosheets. The core-shell structure with a tightly contacted interface can regulate the interfacial electronic structure and enhance electron transfer ability. More importantly, the leach of PA under OER operation benefits the dissolution and re-adsorption of Fe species on the surface of the catalyst. The formed amorphous and active multi-metallic oxyhydroxides accelerate the catalytic reaction kinetics. As a result, the Co3O4/Ni(OH)2 @PAFe exhibits excellent OER performance with a low overpotential of 230 mV at 10 mA cm−2 (reduced by 84 mV compared with that of the original Ni(OH)2), a small Tafel slope of 43 mV dec−1, and prominent long-term durability. This research offers a new sight to enhance the catalytic performance of hydroxides and makes for future energy storage and conversion systems.

NiAl-layered double hydroxides stabilized Pt clusters with enhanced metal-support interaction: Boosting hydrogen isotope separation

Metal-support interaction plays a key role and remains a challenge in exploring highly efficient heterogeneous catalysts, especially for hydrophobic catalysts in Liquid Phase Catalytic Exchange (LPCE) process for water detritiation. In this work, supported Pt catalysts using layered double hydroxides (LDHs) as supports are featured by highly dispersed Pt nanoparticles, water resisting property, and strong interaction of Pt with LDHs, exhibiting excellent anti-aggregation of Pt nanoparticles and catalytic performance over traditional Pt/C at high temperature and humidity conditions. Density Functional Theory calculations show that there is strong interaction between Pt nanoclusters and hydrogen defective LDHs surface, together with significant interfacial charge transfer and metal electronic structure modification, which can restrain the aggregation of Pt on LDHs and enhance catalytic activity. These findings are helpful to deepen understandings of the effects of metal-support interactions in LPCE process, which shed valuable insights for the design and preparation of highly-efficient hydrophobic catalysts on LDHs with prospective applications in water detritiation.

The effects of solutes like ruthenium on precipitation of σ phase and σ/γ interface stability in Ni-based superalloys

σ and μ phases are two of the most common topological close-packed (TCP) phases in nickel-based single crystal superalloys, which are detrimental to the comprehensive properties of superalloys. It is universally acknowledged that Ru plays an important role in the precipitation of TCP, and its inhibiting effects on the nucleation and precipitation of μ phases have already been confirmed, but its effects on σ phases remain vague. In this work, the types and area fractions of the TCP phases precipitated from 4 alloys with different compositions have been characterized. It is found that Ru has different effects on the precipitation of different types of TCP. With the help of density functional theory (DFT), the interface structures between σ and matrix γ are further studied, and on this basis, the effects of different solutes such as Ru on interface stability and electronic structure are discussed in detail. Ru, Re, W, Cr and Ta are able to enhance the interface stability, boosting the nucleation of σ phase. Co is different, for it can reduce the interface stability and elevate the nucleation difficulty of σ. Additionally, the distribution behaviors of solutes between σ and γ phases have been calculated, from which it can be found that the energies of solutes like Cr and Ru distributing in σ are more stable than distributing inside γ, and these solutes have the tendency to diffuse from γ to σ. These results reveal the effects of solutes like Ru on the precipitation of σ phase in terms of interfacial stability and atomic diffusion, which provide a new understanding of Ru effects.

Transient Spin Injection Efficiencies at Ferromagnet–Metal Interfaces

AbstractSpin injection across interfaces driven by ultrashort optical pulses on femtosecond timescales constitutes a new way to design spintronics applications. Targeted utilization of this phenomenon requires knowledge of the efficiency of non‐equilibrium spin injection. From a quantitative comparison of ab initio time‐dependent density functional theory and interface‐sensitive, time‐resolved non‐linear optical experiment, the spin injection efficiency (SIE) at the Co/Cu(001) interface is determined, and its microscopic origin, i.e., the influence of spin‐orbit coupling and the interface electronic structure, is discussed. Moreover, we theoretically predict that the SIE at ferromagnetic–metal interfaces can be optimized through laser pulse and materials parameters, namely the fluence, pulse duration, and substrate material.

Tuning the Carrier Transfer Behavior of Coaxial ZnO/ZnS/ZnIn2 S4 Nanorods with a Coherent Lattice Heterojunction Structure for Photoelectrochemical Water Oxidation.

Serious degradation and the short photogenerated carrier lifetime for the wide-bandgap semiconductor ZnO have become prominent issues that negatively affect photoelectrochemical (PEC) water splitting. Herein, a novel electron transport pathway was constructed by simple but effective coaxial growth of ZnO/ZnS/ZnIn2 S4 heterostructure nanoarrays to increase the carrier separation efficiency. This new photoanode fulfilled the requirements of both favorable band alignment and stability, achieving a stable photocurrent density of 1.146 mA cm-2 at 1.2 VRHE , which was approximately twice that of pristine ZnO. Detailed experimental studies revealed that the improved PEC activity was due to the lattice-matching interface coherency that activated the carrier transport pathway, giving rise to an optimized interfacial electronic structure for promoted charge separation by the built-in electric field and strengthened water oxidation activity. This design may provide a new approach to fabricating various efficient lattice-matching coherent interface photoanodes for PEC water splitting.

Heterostructured V-Doped Ni2 P/Ni12 P5 Electrocatalysts for Hydrogen Evolution in Anion Exchange Membrane Water Electrolyzers.

Regulating the electronic structure and intrinsic activity of catalysts' active sites with optimal hydrogen intermediates adsorption is crucial to enhancing the hydrogen evolution reaction (HER) in alkaline media. Herein, a heterostructured V-doped Ni2 P/Ni12 P5 (V-Ni2 P/Ni12 P5 ) electrocatalyst is fabricated through a hydrothermal treatment and controllable phosphidation process. In comparison with pure-phase V-Ni2 P, in/ex situ characterizations and theoretical calculations reveal a redistribution of electrons and active sites in V-Ni2 P/Ni12 P5 due to the V doping and heterointerfaces effect. The strong coupling between Ni2 P and Ni12 P5 at the interface leads to an increased electron density at interfacial Ni sites while depleting at P sites, with V-doping further promoting the electron accumulation at Ni sites. This is accompanied by the change of active sites from the anionic P sites to the interfacial Ni-V bridge sites in V-Ni2 P/Ni12 P5 . Benefiting from the interface electronic structure, increased number of active sites, and optimized H-adsorption energy, the V-Ni2 P/Ni12 P5 exhibits an overpotential of 62mV to deliver 10mA cm-2 and excellent long-term stability for HER. The V-Ni2 P/Ni12 P5 catalyst is applied for anion exchange membrane water electrolysis to deliver superior performance with a current density of 500mA cm-2 at a cell voltage of 1.79V and excellent durability.

Momentum-selective orbital hybridisation

When a molecule interacts chemically with a metal surface, the orbitals of the molecule hybridise with metal states to form the new eigenstates of the coupled system. Spatial overlap and energy matching are determining parameters of the hybridisation. However, since every molecular orbital does not only have a characteristic spatial shape, but also a specific momentum distribution, one may additionally expect a momentum matching condition; after all, each hybridising wave function of the metal has a defined wave vector, too. Here, we report photoemission orbital tomography measurements of hybrid orbitals that emerge from molecular orbitals at a molecule-on-metal interface. We find that in the hybrid orbitals only those partial waves of the original orbital survive which match the metal band structure. Moreover, we find that the conversion of the metal’s surface state into a hybrid interface state is also governed by momentum matching constraints. Our experiments demonstrate the possibility to measure hybridisation momentum-selectively, thereby enabling deep insights into the complicated interplay of bulk states, surface states, and molecular orbitals in the formation of the electronic interface structure at molecule-on-metal hybrid interfaces.

Boron-doped CN supported metallic Co catalysts with interfacial electron transfer for enhanced photothermal CO hydrogenation

Solar-driven Fischer-Tropsch synthesis (FTS) is a promising route to produce solar fuels of value-added hydrocarbons. Herein, an approach of boron doping in CN support to modulate the interfacial electronic structure of Co–BCN catalysts is developed to promote the yield of hydrocarbon products in photothermal FTS. Under light irradiation, the optimized Co–BCN catalyst delivers a hydrocarbon selectivity of 96.9 % at a CO conversion over 40 %, which is 4.3 and 10.2 times that of Co–CN and Co–C catalysts, respectively. Detailed characterizations demonstrate that the electron transfer between Co nano-metal and BCN support, where electronic structure at interface is modulated. The formation of electron-rich interface in Co–BCN could promote CO activation with assistance of H* and thus enhance the conversion of CO. This work not only paves the way for the modulation of interface electrons to enhance photothermocatalytic activity but also offers a promising strategy toward the rational design and preparation of highly efficient catalysts.

Understanding interfacial energy structures in organic solar cells using photoelectron spectroscopy: A review

Organic solar cells (OSCs) have received considerable attention as a promising clean energy-generating technology because of their low cost and great potential for large-scale commercial manufacturing. With significant advances in new charge-transport material design, interfacial engineering, and their operating conditions, power conversion efficiencies of OSCs have continued to increase. However, a fundamental understanding of charge carrier transport and especially how ionic moieties affect carrier transport is still lacking in OSCs. In this regard, photoelectron spectroscopy has provided valuable information about interfacial electronic structures. The interfacial electronic structure of OSC interlayers greatly impacts charge extraction and recombination, controls energy level alignment, guides active layer morphology, improves material’s compatibility, and plays a critical role in the resulting power conversion efficiency of OSCs. Interfacial engineering incorporating inorganic, organic, and hybrid materials can effectively enhance the performance of organic photovoltaic devices by reducing energy barriers for charge transport and injection while improving compatibility between metal oxides and donor–acceptor based active layers or transparent conducting electrodes. This article provides a review of recent developments in interfacial engineering underlying organic photovoltaic devices of donor–acceptor interfaces.

Engineering multiphasic heterostructure NiCoP@Co0.5Ni0.5Se2 with optimized electronic structure enabling robust hydrogen evolution

Multiphasic engineering is powerful to improve the performance of hydrogen evolution. Here, NiCoP@Co0.5Ni0.5Se2 heterostructure with a fish-gill-like morphology has been initially prepared via an epitaxial controlled growth strategy. When used as catalyst in the hydrogen evolution, this heterostructure gives low overpotential of 235 mV and long-term durability of 100 h at high current density of 500 mA cm−2 in 1.0 M KOH, showing a superior activity and excellent stability. Such superior performances are achieved by its 3D multiphasic heterostructure and optimized interface electronic structure because extremely porous superhydrophilic and superaerophobic surface of hierarchical morphology enhance kinetic of hydrogen evolution. The findings reported in this work open new occasion for creating novel technologies based on nature-inspired strategy and multiphasic engineering, as evidenced by a superior overall water splitting performance of an assembled NiCoP@Co0.5Ni0.5Se2/NF‖NiFe-LDH/NF cell under industrial condition (30 % KOH, 25 and 60 °C).

Multiple carbon interface engineering to boost oxygen evolution of NiFe nanocomposite electrocatalyst

Interface engineering has been widely investigated to regulate the structure and performance of electrodes and photoelectrodes, but the investigation of multiple carbon interface modifications on the electrocatalytic oxygen evolution reaction (OER) is still shortage. Herein, we report remarkable promotion of OER performance on the NiFe-based nanocomposite electrocatalyst via the synergy of multiple carbon-based interface engineering. Specifically, carbon nanotubes were in situ grown on carbon fiber paper to improve the interface between CFP and NiFeOxHy, and graphite carbon nanoparticles were in situ loaded and partly doped into the NiFeOxHy to modify the intergranular interface charge transfer and electronic structure of NiFeOxHy. Consequently, the as-obtained NiFeOxHy-C/CNTs/CFP catalyst exhibited significantly enhanced electrocatalytic OER activity with an overpotential of 202 mV at 10 mA cm−2 in 1 mol L−1 KOH. Our work not only extends application of carbon materials but also provides an alternative strategy to develop highly efficient electrocatalysts.

Simulation and experiments on the performance of Co and Mo doped AgNi contact materials

In response to the inadequacy of experimental methods to explore the effect of doping modification on the performance of AgNi contact materials, the Ag/Ni interface simulation model was established based on the first-principles density functional theory to study the interfacial stability and electronic structure of Ag/Ni with Co-doped and Mo-doped. The stability at the interface can directly affect the anti-melt welding performance of AgNi contact materials. The doping can enhance the interfacial bonding stability of Ag/Ni, the hybridization of Ag and Ni orbitals and the bonding strength of Ag-Ni metal bonds, among which the Mo-doped Ag/Ni has the best stability. The contact materials were prepared by powder metallurgy method. Wettability test and electrical contact performance test were conducted on AgNi contacts before and after doping. It was found that Co and Mo doping improved the anti-melt welding performance and anti-arc erosion performance of the intrinsic contact materials, which verified the simulation conclusions. The doping of Mo in AgNi contacts resulted in a substantial reduction of melt welding force and a significant reduction of material loss, which had the most obvious improvement effect on the contact materials.

Tuning lower dimensional superconductivity with hybridization at a superconducting-semiconducting interface

The influence of interface electronic structure is vital to control lower dimensional superconductivity and its applications to gated superconducting electronics, and superconducting layered heterostructures. Lower dimensional superconductors are typically synthesized on insulating substrates to reduce interfacial driven effects that destroy superconductivity and delocalize the confined wavefunction. Here, we demonstrate that the hybrid electronic structure formed at the interface between a lead film and a semiconducting and highly anisotropic black phosphorus substrate significantly renormalizes the superconductivity in the lead film. Using ultra-low temperature scanning tunneling microscopy and spectroscopy, we characterize the renormalization of lead’s quantum well states, its superconducting gap, and its vortex structure which show strong anisotropic characteristics. Density functional theory calculations confirm that the renormalization of superconductivity is driven by hybridization at the interface which modifies the confinement potential and imprints the anisotropic characteristics of the semiconductor substrate on selected regions of the Fermi surface of lead. Using an analytical model, we link the modulated superconductivity to an anisotropy that selectively tunes the superconducting order parameter in reciprocal space. These results illustrate that interfacial hybridization can be used to tune superconductivity in quantum technologies based on lower dimensional superconducting electronics.

The N3/TiO2 interfacial structure is dependent on the pH conditions during sensitization.

The electronic structure of the N3/TiO2 interface can directly influence the performance of a dye sensitized solar cell (DSSC). Therefore, it is crucial to understand the parameters that control the dye's orientation on the semiconductor's surface. A typical step in DSSC fabrication is to submerge the nanoparticulate semiconductor film in a solution containing the dye, the sensitizing solution. The pH of the N3 sensitizing solution determines the distribution of the N3 protonation states that exist in solution. Altering the pH of the sensitizing solution changes the N3 protonation states that exist in solution and, subsequently, the N3 protonation states that anchor to the TiO2 substrate. We utilize the surface specific technique of heterodyne detected vibrational sum frequency generation spectroscopy to determine the binding geometry of N3 on a TiO2 surface as a function of the sensitizing solution pH conditions. It is determined that significant reorientation of the dye occurs in pH ≤2.0 conditions due to the lack of N3-dye carboxylate anchoring groups participating in adsorption to the TiO2 substrate. Consequently, the change in molecular geometry is met with a change in the interfacial electronic structure that can hinder electron transfer in DSSC architectures.