Work Function Difference Research Articles

Strong interface coupling of H-substituted graphdiyne-based promotes photocatalytic hydrogen production

As an advanced material, graphdiyne (GDY) is expected to be an ideal platform for photocatalytic reactions due to its large π-conjugated structure on the surface, rich sp-C triple-bond skeleton with catalytic activity, and high carrier mobility. However, the electronic configuration of graphdiyne makes it difficult to achieve efficient interfacial contact and photocatalysis. In this study, a new method based on ball milling technology was developed to efficiently produce GDY and hydrogen substituted graphdiyne (H-GDY), and it was proved that H-GDY can achieve efficient interface contact and promote the separation of interface charges to improve photocatalytic hydrogen evolution. The experimental and theoretical calculation results show that the high work function of H-GDY can enlarge the larger work function difference (ΔΦ) between NiSe2, which drives the effective transfer of charges at the interface, and then forms a stronger built-in electric field, thus significantly improving the separation efficiency of photogenerated electrons and holes.

Co-CoSe heterogeneous fibers with strong interfacial built-in electric field as bifunctional electrocatalyst for high-performance Zn-air battery

The explorations of efficient electrocatalysts to accelerate oxygen reactions in a wide temperature range is a crucial issue to the development of zinc-air batteries (ZAB) for all-climate applications. Herein, the Co-CoSe heterogeneous furry fibers (Co-CoSe@NHF) are developed as a bifunctional oxygen electrocatalyst for ZAB towards wide-temperature range applications. The Co-CoSe heterostructure with large work function difference (ΔWF) endows interfacial electron redistribution, which builds strong interfacial built-in electric field (BIEF) and improves the oxygen reactions. Meanwhile, the Co-CoSe heterostructure is encapsulated by in-situ grown carbon nanotubes, and forms the hollow fiber (NHF) with furry surface and beads-on-string configuration. The highly porous and conductive NHF configuration facilitates the fast kinetics and favors to accommodates volume change during cycling. As a result, the Co-CoSe@NHF achieves the superior bifunctional properties and good reliability for oxygen reactions. Integrated with the Co-CoSe@NHF fiber, the ZAB cell delivers the superior power density (301 mW cm−2) and long-term cycling stability over 280 h at 25 °C, and maintains the power densities of 126 mW cm−2 even the temperature decreases to −25 °C. Moreover, the solid-state ZAB exhibits significant flexibility and superior properties in a wide temperature range. Therefore, this work not only proposes a new strategy to design the high-performance bifunctional electrocatalysts, but also propels the development of flexible power sources for all-climate applications.

Accelerating ion diffusion kinetics with an intensified interfacial electric field for efficient hybrid capacitive deionization

The interfacial electric field (IEF) represents a cutting-edge strategy for enhancing ion diffusion kinetics, pivotal in various technological applications. Despite its extensive use, the mechanisms and strategies for regulating IEF remain underexplored. In this study, we enhanced the IEF in a MnO2-x/g-C3N4 (CN) heterostructure by engineering oxygen vacancies in MnO2, which increased the work function difference between MnO2 and CN. The increased work function difference effectively lowers the energy barrier for electron transfer at the heterostructure interface, thereby intensifying the IEF. The enhanced IEF subsequently provides a more potent driving force, facilitating ion movement within the electrode materials during the desalination process. The modified MnO2-x/CN heterostructure demonstrates a notable salt removal capacity of 45.5 mg g−1 and an impressive salt removal rate of 4 mg g−1 min−1, under an operational voltage of 1.2 V in a 500 mg/L NaCl solution. This research not only deepens our understanding of IEF modulation in materials but also sets the stage for the development of high-performance electrodes for hybrid capacitive deionization systems.

Efficient Charge Transfer in Graphene/CrOCl Heterostructures by van der Waals Interfacial Coupling.

Due to the large volume of exposed atoms and electrons at the surface of two-dimensional materials, interfacial charge coupling has been proven as an efficient strategy to engineer the electronic structures of two-dimensional materials assembled in van der Waals heterostructures. Recently, heterostructures formed by graphene stacked with CrOCl have demonstrated intriguing quantum states, including a distorted quantum Hall phase in the monolayer graphene and the unconventional correlated insulator in the bilayer graphene. Yet, the understanding of the interlayer charge coupling in the heterostructure remains challenging. Here, we demonstrate clear evidences of efficient hole doping in the interfacial-coupled graphene/CrOCl heterostructure by detailed Raman spectroscopy and electrical transport measurements. The observation of significant blue shifts and stiffness of graphene Raman modes quantitatively determines the concentration of hole injection of about 1.2 × 1013 cm-2 from CrOCl to graphene, which is highly consistent with the enhanced conductivity of graphene. First-principles calculations based on density functional theory reveal that due to the large work function difference and the electronegativity of Cl atoms in CrOCl, the electrons are efficiently transferred from graphene to CrOCl, leading to hole doping in graphene. Our findings provide clues for understanding the exotic physical properties of graphene/CrOCl heterostructures, paving the way for further engineering of quantum electronic states by efficient interfacial charge coupling in van der Waals heterostructures.

Carbon‐Based Textile‐Structured Triboelectric Nanogenerators for Smart Wearables

Recent advances in wearable electronics have been propelled by the rapid growth of microelectronics and Internet of Things. The proliferation of electronic devices and sensors relies heavily on power sources, predominantly batteries, with significant implications for the environment. To address this concern and to reduce carbon emissions, there is a growing emphasis on renewable energy harvesting technologies, among which textile‐based triboelectric nanogenerators (T‐TENGs) stand out as an innovative and sustainable solution due to having the interesting characteristics like large contact area, lightweight design, flexibility, comfort, scalability, and breathability. T‐TENGs can harness mechanical energy from human movement and convert it into electric energy. However, one of the challenges is low electric power output, which can be addressed by meticulous selection of material pairs with significant differences in work function and optimizing contact areas. The incorporation of carbon‐based nanomaterials, such as carbon nanotubes and graphene, emerges as a key strategy to enhance output. This review delineates recent progress in T‐TENGs incorporating carbonaceous nanofillers, comprehensively addressing fundamental classification, operational mode, structural design, working performance, and potential challenges that are hindering commercialization. By doing this, this review aims to stimulate future investigations into sustainable, high‐performance smart wearables integrated with T‐TENGs.

Strong electronic coupling between Ni-based MOF and Ni2P enables high-efficiency oxygen evolution reaction for various application scenarios

The high overpotential and sluggish kinetics of oxygen evolution reaction (OER) severely hinder the widespread application of electrochemical water splitting, especially at industrial-level current densities. Herein, we report a novel heterostructural Ni-based metal organic framework (MOF)-Ni2P in-situ grown on iron foam (NiMOF-Ni2P/IF), which shows remarkable OER activity and stability. We demonstrate that the work function difference between NiMOF and Ni2P leads to the strong electron coupling effect by promoting electron transfer at the interface and results in a discernible upward shift of the d-band center of Ni sites for favorable OH− adsorption. The as-fabricated NiMOF-Ni2P/IF exhibits an ultralow overpotential of 330 mV and a small cell voltage of 1.796 V to drive NiMOF-Ni2P/IF‖Pt/C system at 1000 mA cm−2 in 1 M KOH, outperforming the majority of state-of-the-art non-noble-metal-based electrocatalysts. Furthermore, the catalyst shows remarkable performance even under harsh industrial conditions of 40, 60, and 80 °C in 6 M KOH. In addition, NiMOF-Ni2P/IF holds great promise with remarkable stability of 200 h and 600 cycles in simulated seawater and secondary zinc-air batteries (ZABs), respectively. This work offers a rational design strategy for low cost, high activity, and long durability OER electrocatalyst based on in-depth comprehension of the electronic coupling effect.

Contact engineering for two-dimensional metal/qHP C60 van der Waals heterostructure

The fabrication of two-dimensional (2D) quasi-hexagonal phase (qHP) C60 semiconductor material offers a promising candidate for high-performance electronic devices. Selecting appropriate metals is crucial for achieving Ohmic contact (OhC) to enhance carrier injection efficiency. In this Letter, we used first-principles calculations to study the contact properties of seven 2D metal/qHP C60 van der Waals heterostructures. Metals with suitable work functions can form p-type Schottky contacts (p-ShCs), n-type Schottky contacts (n-ShCs), and OhCs. Differences in work function affect interface charge transfer, creating interface dipoles and causing band alignment deviations from the ideal Schottky–Mott limit. The calculated Fermi level pinning factors for n-type and p-type 2D metal/qHP C60 vdWh are 0.528 and 0.521, respectively. By regulating Φn and Φp based on electrostatic potential difference ΔV, we have achieved the ideal Schottky–Mott limit. We also studied the Schottky barrier height of the germanene/qHP C60 vdWh, finding that using electric field is an effective way to convert n-ShC to OhC or p-ShC. These findings provide theoretical guidance for constructing efficient 2D qHP C60 electronic devices.

Enhancing the dipole ring of hexagonal boron nitride nanomesh by surface alloying

Surface templating by electrostatic surface potentials is the least invasive way to design large-scale artificial nanostructures. However, generating sufficiently large potential gradients remains challenging. Here, we lay the groundwork for significantly enhancing local electrostatic fields by chemical modification of the surface. We consider the hexagonal boron nitride (h-BN) nanomesh on Rh(111), which already exhibits small surface potential gradients between its pore and wire regions. Using photoemission spectroscopy, we show that adding Au atoms to the Rh(111) surface layer leads to a local migration of Au atoms below the wire regions of the nanomesh. This significantly increases the local work function difference between the pore and wire regions that can be quantified experimentally by the changes in the h-BN valence band structure. Using density functional theory, we identify an electron transfer from Rh to Au as the microscopic origin for the local enhancement of potential gradients within the h-BN nanomesh.

2D MXene/MBene Superlattice with Narrow Bandgap as Superior Electrocatalyst for High-Performance Lithium-Oxygen Battery.

Lithium-oxygen (Li-O2) battery with large theoretical energy density (≈3500Whkg-1) is one of the most promising energy storage and conversion systems. However, the slow kinetics of oxygen electrode reactions inhibit the practical application of Li-O2 battery. Thus, designing efficient electrocatalysts is crucial to improve battery performance. Here, Ti3C2 MXene/Mo4/3B2-x MBene superlattice is fabricated its electrocatalytic activity toward oxygen redox reactions in Li-O2 battery is studied. It is found that the built-in electric field formed by a large work function difference between Ti3C2 and Mo4/3B2-x will power the charge transfer at the interface from titanium (Ti)site in Ti3C2 to molybdenum (Mo) site in Mo4/3B2-x. This charge transfer increases the electron density in 4d orbital of Mo site and decreases the d-band center of Mo site, thus optimizing the adsorption of intermediate product LiO2 at Mo site and accelerating the kinetics of oxygen electrode reactions. Meanwhile, the formed film-like discharge products (Li2O2) improve the contact with electrode and facilitate the decomposition of Li2O2. Based on the above advantages, the Ti3C2 MXene/Mo4/3B2-x MBene superlattice-based Li-O2 battery exhibits large discharge specific capacity (17167 mAhg-1), low overpotential (1.16V), and superior cycling performance (475 cycles).

Flash Joule Heating: A Promising Method for Preparing Heterostructure Catalysts to Inhibit Polysulfide Shuttling in Li-S Batteries.

The "shuttle effect" issue severely hinders the practical application of lithium-sulfur (Li-S) batteries, which is primarily caused by the significant accumulation of lithium polysulfides in the electrolyte. Designing effective catalysts is highly desired for enhancing polysulfide conversion to address the above issue. Here, the one-step flash-Joule-heating route is employed to synthesize a W-W2C heterostructure on the graphene substrate (W-W2C/G) as a catalytic interlayer for this purpose. Theoretical calculations reveal that the work function difference between W (5.08eV) and W2C (6.31eV) induces an internal electric field at the heterostructure interface, accelerating the movement of electrons and ions, thus promoting the sulfur reduction reaction (SRR) process. The high catalytic activity is also confirmed by the reduced activation energy and suppressed polysulfide shuttling by in situ Raman analyses. With the W-W2C/G interlayer, the Li-S batteries exhibit an outstanding rate performance (665 mAh g-1 at 5.0 C) and cycle steadily with a low decay rate of 0.06% over 1000 cycles at a high rate of 3.0 C. Moreover, a high areal capacity of 10.9 mAh cm-2 (1381.4 mAh g-1) is obtained with a high area sulfur loading of 7.9mg cm-2 but a low electrolyte/sulfur ratio of 9.0 µL mg-1.

The study on influence factors of contact properties of metal-MoS2 interfaces

The metal and two-dimension (2D) semiconductor contact interfaces have a more considerable contact resistance hindering carrier injection, which makes the performance of 2D semiconductor devices less than the theory. The contact properties of Ni, Au, and Mo with MoS2 are simulated by the first-principles method. The interface dipole caused by the interface charge redistribution changes the work function difference at the metal-MoS2 interface, so the interface charge redistribution is one of the important factors for correctly evaluating the contact properties. Due to the metal-induced gap states (MIGS) at metal-monolayer (ML) MoS2 interfaces, the Fermi level is strongly pinned to fixed energy, and the Schottky barrier height (SBH) cannot be regulated efficiently by the metal work function. Although the work function of Au is bigger than Ni, the Fermi level of Au is pinned at a higher position. In the meantime, the bandgap of MoS2 narrows and metallization occurs due to the larger MIGS. In the Mo-MoS2 interface, the Fermi level is pinned near the conduction band minimum of MoS2. The contact resistances (Rc) of the three structures are tested by the Circular Transfer Length Method (CTLM), which is consistent with the prediction of the simulation. The Mo-MoS2 has the smallest Rc. The results indicate that contact resistance of 2D semiconductors cannot be simply predicted by soled work functions or Fermi level pinning, but is determined by several factors.

Construction of MoS2/NiS2 heterostructure with fast interfacial reaction kinetics for ultrafast sodium storage

Constructing heterostructure is a valid method to reinforcing sodium storage performance of transition metal chalcogenides materials. Herein, a simple, safe and controllable one step hydrothermal method is proposed to synthesize MoS2/NiS2 heterostructure. Due to the difference in band gaps and work functions of MoS2 and NiS2, the charges are redistributed at the MoS2/NiS2 heterointerfaces, thereby accelerating the migration of electrons and Na+. The heterointerfaces provide extra active sites for storing Na+, thus increasing the sodium storage capacity of the heterostructure. Furthermore, the distinct redox potentials of NiS2 and MoS2 promote the structural stability of MoS2/NiS2 heterostructure during the electrochemical reaction processes. Consequently, the obtained MoS2/NiS2 heterostructure exhibits superior rate properties (339.4 mAh g−1 at 10 A g−1) and ultra-stable cycling stability (480.5 mAh g−1 after 350 cycles at 1 A g−1). This paper presents a valid strategy for creating heterostructure anodes with excellent sodium storage properties.

Synergistic defect and heterojunction engineering of carbonized MOF@MoS2 for self-powered sensing micro-system with photothermal therapy

Electrically conductive hydrogel with photothermal therapy (PTT) is highly desired in assembling self-powered sensing micro-system for personalized healthcare. However, the poor electrical conductivity and low photothermal conversion efficiency (PCE) of carbonized metal–organic framework (CMOF) restricted their practical application. Herein, a unique CMOF@MoS2 heterojunction with abundant defects was elaborately designed via the in situ growth of MoS2 on CMOF for constructing functional hydrogel. The presence of numerous defective sites in MoS2 thin layer accelerated the electrons transport, accompanied with the enhanced electrical conductivity of CMOF@MoS2 hydrogel. Moreover, originating from the spontaneous electrons transfer from MoS2 to CMOF due to the difference of work function, the built-in electric field at CMOF@MoS2 interface driven the fast separation of electron-hole in MoS2 excited by photon, boosting the PCE and PTT performances. When CMOF@MoS2 hydrogel was assembled into micro-system, the flexible sensors delivered ultra-sensitivity (GF = 97.1), fast response behavior (23 ms) and excellent durability over 10,000 cycles. After healthcare monitoring, the damaged tissues can be effectively and timely healed under near-infrared laser irradiation. Our findings provided a sort of novel strategy to rational design and construct advanced sensing micro-system with excellent PTT behavior.

Long‐Range Charge Carrier Transport in Planar Polymer Bulk‐Heterojunction Photovoltaic Cells

One‐dimensional scanning optical beam‐induced current (OBIC) measurements have been carried out on polymer bulk heterojunction (BHJ) photovoltaic cells with a planar, or lateral configuration. The planar P3HT:PCBM cells have parallel aluminum or gold electrodes that are 390 to 560 micrometers apart. When a focused laser beam is scanned across the electrode gap, photocurrent or photovoltage is recorded as a function of beam position along with the transmission of the excitation beam. Despite the large electrode gap size, cells with symmetric Al/Al electrodes exhibit significant photocurrent and photovoltage which are the highest at the electrode interfaces and null at the cell center. The OBIC in these large planar polymer BHJ cells is attributed to the metal/BHJ blend Schottky junction. The larger Schottky barrier of the Al/BHJ junction gives rise to a stronger OBIC response than the Au/BHJ junction. The photocurrent and photovoltage always have opposite signs and are antisymmetric about the cell center. In asymmetric Al/Au cells, the electrode work function difference contributes an additional built‐in field/potential drop and significantly modifies the photocurrent and photovoltage profiles. The depletion width of the Al/BHJ Schottky junction is 110–120 μm, while the minority electron diffusion length is determined to be 43.8 μm.

How liquids charge the superhydrophobic surfaces

Liquid-solid contact electrification (CE) is essential to diverse applications. Exploiting its full implementation requires an in-depth understanding and fine-grained control of charge carriers (electrons and/or ions) during CE. Here, we decouple the electrons and ions during liquid-solid CE by designing binary superhydrophobic surfaces that eliminate liquid and ion residues on the surfaces and simultaneously enable us to regulate surface properties, namely work function, to control electron transfers. We find the existence of a linear relationship between the work function of superhydrophobic surfaces and the as-generated charges in liquids, implying that liquid-solid CE arises from electron transfer due to the work function difference between two contacting surfaces. We also rule out the possibility of ion transfer during CE occurring on superhydrophobic surfaces by proving the absence of ions on superhydrophobic surfaces after contact with ion-enriched acidic, alkaline, and salt liquids. Our findings stand in contrast to existing liquid-solid CE studies, and the new insights learned offer the potential to explore more applications.

87‐4: Control of LTPS Flat‐Band Voltage to Improve the Short‐Term Image Sticking of AMOLED Displays

In this paper, the certain relation between threshold voltage and flat‐band voltage to improve the image sticking for AMOLED display was investigated. Flat band state generally refers to a state in which the energy bands of each region in an ideal MOSFET system are flattened. However, it is requiring an additional voltage to flatten the energy band for actual MOS systems due to the difference in metal and semiconductor work function, which is called the flat‐band voltage. It is investigated that this flat‐band voltage is strongly linked to the short‐term image sticking.

Bridging microscopic phase and defect manipulation with macroscopic core-sheath-shell structure for polarization-dominated electromagnetic wave absorption

Manipulating phases and defects brings boundless vitality to the design of electromagnetic wave (EMW) absorption (EMA) materials. However, current manipulations often prioritize the improvement in the overall EMA performance without distinguishing the effects of individual polarizations. Therefore, the design of EMA materials is result-oriented and limited by reliance on semi-empirical rules. Herein, we synthesized carbon cloth (CC)@MoS2@carbon nanotubes (CNTs) (CMSC) by self-assembly of MoS2 on CC, followed by in-situ growth of CNTs through high-temperature annealing. This synthesis process not only created a hierarchical core-sheath-shell structure consisting of an MoS2 intermediate sheath and a CNT outer shell but also introduced tunable vacancy defects and phases (2 H and 1 T). Density Functional Theory calculations revealed an enhanced carrier influx from the CNTs into the 2 H/1 T MoS2 due to the substantial difference in work function between the 1 T and 2 H phases, which promoted charge redistribution and subsequent polarization at defect sites and interfaces in CMSC. Therefore, defect-induced and interfacial polarizations dominated the EMW-attenuation mechanisms for CMSC, distinguishing it from CC@MoO2@CNTs, where conduction loss predominated. Owing to these enhanced polarizations and core-sheath-shell structure, CMSC exhibited a minimum reflection loss of −43.9 dB at 2.1 mm, even with a filler ratio of 3 wt%. This study highlights the potential for designing and tailoring polarization-dominated EMA materials through the manipulation of defects and phases.

Enhancing Z-scheme {001}/{110} junction in BiOCl with {110} surface oxygen vacancies for photocatalytic degradation of Rhodamine B and tetracycline

Since photocatalysis relies on surface reactions, the exposed facets and surface defects of the catalyst play important roles. In this study, we investigate the influence of oxygen vacancy creation on various exposed facets on the electronic structure and photocatalytic properties of {001}/{110}-bismuth oxychloride (BiOCl) with plate-like morphology prepared via a facile co-precipitation technique. Our experiments demonstrated that the ratio of different exposed facets could be controlled by adjusting HCl concentration in the precipitation process. Although the obtained BiOCl samples have a large band gap energy, oxygen vacancies (OV) induce defect states within the bandgap, enhancing the photocatalytic performance under visible light. Experiments and calculations have revealed that formation of OV is easier on the (110) facet than on the (001) facet. Consequently, the sample with a higher portion of (110) exposed facet exhibits higher OV. While {001}/{110} Z-scheme is created in all samples, higher OV enhance the work function difference (ΔΦ) between the two facets. As a result, an internal electric field is stronger, leading to improved carrier separation and photocatalytic degradation of Rhodamine B and Tetracycline. Therefore, this systematic investigation contributes to the advancement of understanding BiOCl photocatalysts and offers valuable insights for designing and optimizing photocatalytic materials for environmental remediation applications.

Weak interlayer interactions and nearly temperature independent electrical transport in p-type 1T′-MoTe2/Sb2Te3 superlattice-like films

Thermoelectric superlattices (SLs) are one of the important focuses in the thermoelectric field due to their ordered stacking structure and the potential to obtain extremely high thermoelectric performance. To understand the critical effects of interlayer interactions, this work fabricates p-type (1T′-MoTe2)x(Sb2Te3)y SLs and investigates their electrical properties as functions of SL period and temperature. The results discovered that the weak interlayer interactions could be driven by both the small work function difference and temperature. This brings forth hole donation and energy filtering and leads to increased hole density and the carrier effective mass of (1T′-MoTe2)x(Sb2Te3)y SLs. Strikingly, the SL structure is beneficial for achieving temperature independent electrical properties, owing to the temperature driven interlayer interaction. Several SLs acquire the largest average power factor among all SLs, which is about 1.10 mWm−1K−2 within 300∼473 K, favorable for thermoelectric applications near room temperature. This work points out the beneficial effect of the SL structure on obtaining high thermoelectric properties in a wide temperature range.

Hydrogen spillover inspired bifunctional Platinum/Rhodium Oxide-Nitrogen-Doped carbon composite for enhanced hydrogen evolution and oxidation reactions in base

The poor activity of Pt-based-catalysts for alkaline hydrogen oxidation/evolution reaction (HOR/HER) encourages scientific society to design an effective electrocatalyst to develop alkaline fuel cells/electrolyzers. Herein, platinum/rhodium oxide-nitrogen-doped carbon (Pt/Rh2O3-CNx) composite is prepared for alkaline HER and HOR inspired by hydrogen spillover. The HER performance of Pt/Rh2O3-CNx is ∼ 6 times higher than Pt/C. In HOR, Pt/Rh2O3-CNx possesses an exchange current density of 657.60 mA/mgmetal, which is ∼ 3.4 times higher than Pt/C. Hydrogen and hydroxyl binding energy (HBE and OHBE) contribute equally to alkaline HOR/HER. The experimental and theoretical evidence suggests that the enhanced HER and HOR activity of Pt/Rh2O3-CNx may be due to hydrogen spillover from Pt to Rh2O3. Small work function difference [0.08 eV] of the system suggested hydrogen-spillover is feasible, which has been justified by reaction-free energy calculations. We proposed that the dissociation of hydrogen (H2) and water (H2O) occurs at Pt to form Pt-adsorbed hydrogen species (Pt-Had). Then, some Had moves to Rh2O3 through hydrogen spillover and reacts with neighboring Had or adsorbed hydroxyl species (OHad) to form H2 or H2O, which enhances the HER and HOR activity, respectively. The role of water-metal-hydroxyl species in the electrical double layer was also demonstrated on alkaline HOR/HER. This work may help to design the hydrogen-spillover-based catalysts for several renewable energy technologies.