Strong Interfacial Charge Transfer Research Articles

Enhancing Electron/Ion Transport in SnO2 Quantum Dots Decorated Polyaniline/Graphene Hybrid Fibers for Wearable Supercapacitors with High Energy Density.

Fiber-based supercapacitors are the potential power sources in the field of wearable electronics and energy storage textiles due to their unique advantages of electrochemical properties and mechanical flexibility, but achieving high energy density and practical energy supply still presents some challenges. In this study, we reported an approach of microfluidic assisted wet-spinning to fabricate SnO2 quantum dots encapsulated polyaniline/graphene hybrid fibers (SnO2 QDs@PGF) by incorporating uniformly polyaniline into graphene fibers and covalently bridging SnO2 quantum dots. The assembled SnO2 QDs@PGF fiber-typed flexible supercapacitors exhibit an ultralarge specific areal capacitance of 925 mF cm-2 in PVA/H2SO4, superior rate capabilities, and capacitance retention of 88% after 8000 cycles, indicating that the SnO2 QDs@PGF possess near-ideal capacitance properties, efficient ion transfer rate, and good cycling stability. In the EMITFSI/PVDF-HFP electrolyte system, SnO2 QDs@PGF realize a wide operating potential window of 2.5 V, a specific areal capacitance of 678.4 mF cm-2, and an energy density of 147.2 μWh cm-2 at 500 μW cm-2, which can be utilized to power an alarm clock, an electronic timer, and a desk lamp with a requirement of a 3 V battery. The exceptional performance of the SnO2 QDs@PGF can be attributed to the molecular-level homogeneous composite of granular polyaniline and graphene nanosheets and the interfacial C-O-Sn covalent coupling strategy employed between SnO2 QDs and PGF. These avenues not only effectively prevent the undesirable restacking of graphene nanosheets but also increase the interlayer electroactive sites, ordered ion diffusion channels, and strong interfacial charge transfer.

A single site ruthenium catalyst for robust soot oxidation without platinum or palladium

The quest for efficient non-Pt/Pd catalysts has proved to be a formidable challenge for auto-exhaust purification. Herein, we present an approach to construct a robust catalyst by embedding single-atom Ru sites onto the surface of CeO2 through a gas bubbling-assisted membrane deposition method. The formed single-atom Ru sites, which occupy surface lattice sites of CeO2, can improve activation efficiency for NO and O2. Remarkably, the Ru1/CeO2 catalyst exhibits exceptional catalytic performance and stability during auto-exhaust carbon particle oxidation (soot), rivaling commercial Pt-based catalysts. The turnover frequency (0.218 h−1) is a nine-fold increase relative to the Ru nanoparticle catalyst. We further show that the strong interfacial charge transfer within the atomically dispersed Ru active site greatly enhances the rate-determining step of NO oxidation, resulting in a substantial reduction of the apparent activation energy during soot oxidation. The single-atom Ru catalyst represents a step toward reducing dependence on Pt/Pd-based catalysts.

Controllable construction of NiFe MOF/LDH heterojunction with interfacial charge transfer as efficient oxygen evolution electrocatalyst

Herein, a facile partial hydrolysis strategy has been developed to construct NiFe MOF/LDH heterojunction using NiFe MOF as the precursor. While preserving the basic structure of MOF, LDH species along with electroactive phase interfaces were in-situ generated in NiFe MOF/LDH. The obtained catalyst exhibited an ultralow overpotential of 207 mV to reach the current density of 10 mA cm−2 and performed excellent stability towards OER. Both experimental and theoretical investigations demonstrated that the strong interfacial charge transfer in NiFe MOF/LDH heterojunction could improve the conductivity and optimize the adsorption of O-intermediates, thus enhancing the OER kinetics. This study may provide a novel platform to construct heterojunction materials with interfacial charge transfer for electrocatalytic applications.

Perylene diimide/iron phthalocyanine Z-scheme heterojunction with strong interfacial charge transfer through π-π interaction: Efficient photocatalytic degradation of tetracycline hydrochloride

The development of an all-organic Z-scheme heterojunction photocatalyst with the matched band structure, efficient electron transfer and excellent photocatalytic performance is valuable for a sustainable future. A novel perylene diimide/phthalocyanine iron (PDI/FePc) heterojunctions with strong π-π interaction were synthesized by a self-assembled method, which exhibited strong visible-light-driven photocatalytic degradation activities of tetracycline hydrochloride (TC). The TC removal rate over PDI/FePc was achieved three times and 87.5 times higher than that of PDI and FePc. PDI/FePc (131.1 mv·dec−1) presented a lower Taffel slope than that of PDI (228.6 mv·dec−1) for the oxidation. This may be due to the strong π-π interactions between PDI and FePc, which can reduce the layer spacing of the supramolecular structure and facilitate the separation and transfer of photogenerated carriers in the built-in electric field. In addition, radical quenching tests revealed that superoxide radicals (•O2−) acted as a dominant role in photocatalytic oxidation. An increscent specific surface area of PDI decorated by FePc also gave the rapid pathway for charge transfer and enhanced the adsorption ability. This provides a new idea for the formation of heterojunction to improve the photocatalytic activity of organic supramolecular materials.

Schottky barrier heights and mechanism of charge transfer at metal-Bi2OS2 interfaces

Strong Fermi-level pinning (FLP) always occurs at the two-dimensional (2D) semiconductor-metal interface due to the complex interfacial charge transfer. By using monolayer (ML) Bi2OS2, an emerging 2D semiconductor with the highest electron mobility, the Schottky barrier heights (SBHs) and origin of charge transfer at Bi2OS2-metal interfaces are systematically studied based on density functional theory calculations. In 3D metal-Bi2OS2 interfaces, the formation of chemical bonding and the effect of Pauli exchange repulsion are found to be responsible for the strong interfacial charge transfer, resulting in strong FLP, and the direction of charge transfer induced by the two factors is opposite. Besides, an extra interfacial charge transfer is expected to equilibrate the Fermi level when the work functions (WFs) of metal electrodes are out of the range of electron affinity energy and ionization energy of semiconductors. For 2D metal-ML Bi2OS2 interfaces, surprisingly, the FLP is found to be entirely suppressed, and thereby, the 2D metal-Bi2OS2 contacts obey the conventional Schottky-Mott model. Such intriguing behavior arises from the 2D metal electrodes chosen in this work can effectively shield the effect of Pauli exchange repulsion. Consequently, wide-range and linear-tunable SBHs can be obtained and the conversion from n-type Ohmic contact to p-type Ohmic contact can be achieved by using 2D metal electrodes with different WFs. This study not only provides a theoretical foundation for selecting favorable metal electrodes in devices based on ML Bi2OS2, but also helps to enhance the understanding of the mechanism of interface interaction between metals and 2D semiconductors.

Hierarchical Heterostructure Engineering of Layered Double Hydroxides on Nickel Sulfides Heteronanowire Arrays as Efficient Cathode for Alkaline Aqueous Zinc Batteries.

Aqueous alkaline rechargeable nickel-zinc (Ni-Zn) batteries possess great potential for large-scale energy storage systems because of their high output voltage, cheap cost, and intrinsic safety. However, the practical applicability of Ni-Zn batteries has been limited by traditional Ni-based cathodes with low capacity and poor cycle stability. Rational design of electrode structure and composition is highly desired but still significantly challenging. Herein, uniform self-supported hierarchical heterostructure composites interacting NiCo-layered double hydroxide with 1D nickel sulfides heteronanowire rooted on Ni foam (NF\Ni3 S2 /NiS@NiCo-LDH) are successfully developed by a hydrothermal sulfurization-electrodeposition process. The self-supported 3D hierarchical heterostructured composites nanoarray provides abundant reactive sites, rapid ion diffusion channels, and fast electron transfer routes, as well as strong structural stability. More significantly, the strong interfacial charge transfer between Ni3 S2 /NiS heteronanowire and NiCo-LDH effectively modifies the electronic structure of the composites and thereby improving the reaction kinetics. Consequently, the NF\Ni3 S2 /NiS@NiCo-LDH electrode presents a superior capacity of 434.5 mAh g-1 (1.73 mAh cm-2 ) at 3mA cm-2 . In addition, the fabricated NF\Ni3 S2 /NiS@NiCo-LDH//Zn battery can offer a maximal energy density and power density as large as 556.3Wh kg-1 and 26.3kW kg-1 , respectively, as well as an exceptional cycling performance.

Silver decorated hydroxides electrocatalysts for efficient oxygen evolution reaction

Electrocatalysts play a pivotal role in electrochemical water splitting, where the development of efficient oxygen evolution reaction (OER) electrocatalysts remains challenging. Here, we report a facile one-step blending approach to synthesize efficient and durable OER electrocatalysts of silver decorated hydroxides (Ag@hydroxides). The general efficacy of this methodology is demonstrated in five hydroxides, in form of powders or self-supported electrodes. The decoration of Ag lowers the overpotentials by 41–56 mV, rendering Ag@NiFe LDH among the most active OER catalysts. It requires an overpotential of 246 mV only to deliver a current density of 10 mA cm−2. Under industrial electrolysis conditions (30 wt% KOH and 80 °C), the cell voltage is 1.76 V for 500 mA cm−2. It is 270 mV lower than the intact nickel mesh, corresponding to a 9% improvement in the energy conversion efficiency. Furthermore, by combining spectroscopic analysis and theoretical calculation we unravel that the strong interfacial charge transfer is the root cause for the promoting catalytic activity, where the binding energies of catalytic intermediates are optimized. This work provides a facile and ease-to-scale-up approach for the synthesis of efficient and durable electrocatalysts and demonstrates the power of regulating the interface in improving electrocatalytic kinetics.

Novel AgI/BiSbO4 heterojunction for efficient photocatalytic degradation of organic pollutants under visible light: Interfacial electron transfer pathway, DFT calculation and degradation mechanism study

Herein, we constructed a novel AgI/BiSbO4 heterojunction via a hydrothermal-precipitation method. The heterojunction structure boosts the generation of hydroxyl and superoxide radicals for efficient degradation of organic pollutants. The photocatalytic activities of the optimal sample for ARG and TC degradation are 10 and 1.6 times higher than those of bare AgI, respectively. Characterizations and theoretical calculations together confirm a strong interfacial charge transfer exists between the interlayer in AgI and BiSbO4 by the formation of Ag‒O bond, making O atoms obtain rich free electrons from Ag atoms of AgI, thus forming an ultrahigh electron transfer tunnel, and ultimately accelerating the separation of photoinduced electrons. More interestingly, low amounts of Ag0 NPs formed during the photocatalytic process, enhancing the visible light absorption because of its SPR (surface plasmon resonance) effect and further promoting the separation of photoinduced carriers. Furthermore, photocatalytic degradation pathways were proposed in detail by analyzing intermediates and a reasonable photocatalytic mechanism was unearthed. This work extends the development of AgI-based heterojunction photocatalysts.

Strong interfacial charge transfer between hausmannite manganese oxide and alumina for efficient photocatalysis

Well crystalline manganese oxide (Mn3O4) nanoparticles anchored on gamma alumina (γ-Al2O3) have been successfully tailored via a proficient and cost effective chemical process as an efficient material for photo catalysis. XRD indicated the composite formation of γ-Al2O3 and hausmannite structure of Mn3O4. SEM and TEM revealed that hetero structure of Mn3O4/γ-Al2O3 exhibits an amalgam of aggregated nanoparticles and nanorods. XPS demonstrated the chemical states of binary nanocomposite. The band gap tuning has been performed with γ-Al2O3 nanoparticles by assimilating hausmannite Mn3O4 particles into flower like microstructure of Al2O3. The photoluminescence spectra affirmed the enhancement in charge separation in Mn3O4/γ-Al2O3 binary hybrid photocatalyst. The band gap becomes narrow with the increase in concentrations of Mn3O4. The narrowing of band gap is concorded with crystalline domains of primary aggregated particles. To elucidate the mechanism of the photocatalytic activity linear sweep voltammetry was performed. The results showed that Mn3O4/γ-Al2O3 nanocomposite revealed the enhancement in current density as compared to pure γ-Al2O3 which confirmed the electron transfer from Mn3O4 to γ-Al2O3 through the interfacial potential gradient in conduction bands. The optimum concentration of 6.0% Mn3O4/γ-Al2O3 for hybrid structure showed an excellent photocatalytic activity under visible light due to narrow band gap energy. High degree distribution of Mn3O4 nano architects overlying on γ-Al2O3 induces a significant synergic effect between γ-Al2O3 and hausmannite phase of manganese oxide (Mn3O4). This strong interfacial contact between γ-Al2O3 and Mn3O4 endures the quick transfer of photo generated charge carriers across interface.

Boosting interfacial charge separation of Ba5Nb4O15/g-C3N4 photocatalysts by 2D/2D nanojunction towards efficient visible-light driven H2 generation

To efficiently facilitate the charge transfer by constructing heterojunction photocatalysts is a promising strategy for improving solar-driven hydrogen generation. Herein, a novel 2D/2D nanojunction architecture of Ba5Nb4O15/g-C3N4 photocatalysts with powerful interfacial charge transfer are rationally designed. Advanced electron microscopy analysis elucidates the layered hexagonal nanosheets were coupled on the surface of ultrathin g-C3N4 forming a 2D/2D nanojunction. More importantly, such characterizations and theoretical calculations together illustrate that a strong interfacial charge transfer existed between the g-C3N4 layer and Ba-O layer of the Ba5Nb4O15 nanosheets, which fostered the efficient transfer and provided more massive reactive centers for photocatalytic hydrogen evolution. The unique 2D/2D structure in Ba5Nb4O15/g-C3N4 heterojunction leads to generate numerous charge transfer nanochannels, and which could accelerate the interfacial charge separation efficiency to a great extent. Ba5Nb4O15/g-C3N4 (1:20) sample displayed a remarkable photocatalytic H2 evolution rate (2.67 mmol h−1 g−1) in oxalic acid solution, nearly 2.35 times higher than that of single g-C3N4 under visible light and exhibits an outstanding photostability even after four cycles. This work would provide a new insight for the design of 2D/2D heterojunction photocatalyst with efficient interfacial charge transfer and separation for solar-to-H2 conversion.

Construction of trace silver modified core@shell structured Pt-Ni nanoframe@CeO2 for semihydrogenation of phenylacetylene

The Pt-Ni nanoframe catalysts have attracted great interest owing to their unique electronic structure and excellent catalytic performance. However, the stability of the tenuous edges of nanoframe-structures is dissatisfactory and their universal applications in catalytic market beyond electrocatalytic reactions are yet to be tapped and explored. Herein, we developed a new core@shell structured Pt-Ni nanoframe@CeO2 (Pt-Ni NF@CeO2) composite via etching the Ni from inhomogeneous Pt-Ni rhombic dodecahedra (Pt-Ni RD) by cerium(III) acetate hydrate (Ce(OAc)3). In this path, Pt-Ni RD was used as self-sacrificial template, while the Ce(OAc)3 serves as the provider of the Ce3+ source and OH− for the formation of CeO2 shell, etchant of Pt-Ni RD, and the surface modification agent. By this way, the etching of Pt-Ni RD and the formation of the CeO2 shell are simultaneously proceeded to form the final Pt-Ni NF@CeO2 in one step. The obtained Pt-Ni NF@CeO2 exhibits strong interfacial charge transfer interaction between Pt-Ni NF core and CeO2 shell even without reduction treatment, leading to enhanced catalytic activity in the hydrogenation of phenylacetylene. After introduction of trace silver, the Pt-Ni-Ag4.9 NF@CeO2 achieves remarkable catalytic performance for the selective conversion of phenylacetylene to styrene: high conversion (100%), styrene selectivity (86.5%), and good stability. It reveals that encapsulation noble metal nanoframes into metal oxide to form core@shell structured hybrids will indeed enhance their stability and catalytic properties. Particularly, this work expends the application of noble metal nanoframes materials to hydrogenation reactions.

Carbide-Supported Au Catalysts for Water-Gas Shift Reactions: A New Territory for the Strong Metal-Support Interaction Effect.

Strong metal-support interaction (SMSI) has been regarded as one of the most important concepts in heterogeneous catalysis, which has been almost exclusively discussed in metal/oxide catalysts. Here, we show that gold/molybdenum carbide (Au/MoC x) catalysts feature highly dispersed Au overlayers, strong interfacial charge transfer between metal and support, and excellent activity in the low-temperature water-gas shift reaction (LT-WGSR), demonstrating the active SMSI state. Subsequent oxidation treatment results in strong aggregation of Au nanoparticles, weak interfacial electronic interaction, and poor LT-WGSR activity. The two interface states can be transformed into each other by alternative carbonization and oxidation treatments. This work reveals the active SMSI effect in metal/carbide catalysts induced by carbonization, which opens a new territory for this important concept.

Electronic structures of TiO2–TCNE, –TCNQ, and –2,6-TCNAQ surface complexes studied by ionization potential measurements and DFT calculations: Mechanism of the shift of interfacial charge-transfer bands

Interfacial charge-transfer (ICT) transitions between inorganic semiconductors and π-conjugated molecules allow direct charge separation without loss of energy. This feature is potentially useful for efficient photovoltaic conversions. Charge-transferred complexes of TiO2 nanoparticles with 7,7,8,8-tetracyanoquinodimethane (TCNQ) and its analogues (TCNX) show strong ICT absorption in the visible region. The ICT band was reported to be significantly red-shifted with extension of the π-conjugated system of TCNX. In order to clarify the mechanism of the red-shift, in this work, we systematically study electronic structures of the TiO2–TCNX surface complexes (TCNX; TCNE, TCNQ, 2,6-TCNAQ) by ionization potential measurements and density functional theory (DFT) calculations.

The origin of the strong interfacial charge-transfer absorption in the surface complex between TiO2 and dicyanomethylene compounds

Interfacial charge transfer transitions between organic and inorganic materials are expected to be a potential photoinduced charge separation mechanism for photoenergy conversions. Recently, we reported that the hybrid material formed from TiO2 nanoparticles and an organic electron acceptor, 7,7,8,8-tetracyanoquinodimethane (TCNQ), shows strong interfacial charge transfer absorption in the visible region. In this work, we have theoretically studied the structure, and electronic and absorption properties in order to clarify the formation mechanism and the origin of the strong interfacial charge transfer absorption. Density functional theory (DFT) calculations employing an anatase Ti14O28H2(OH)2(H2O)2 nano-cluster unraveled that the surface complex is formed by a nucleophilic addition reaction between a surface hydroxyl group of TiO2 and the carbon atom of the methylene moiety in TCNQ with the drastic changes in the structure and electronic properties of TCNQ. In the formation process, owing to the high electron affinity of TCNQ, a negative charge of the surface oxygen atom is transferred to the TCNQ moiety. This leads to a significant electronic hybridization between TiO2 and TCNQ, which is the origin of interfacial charge transfer transitions.