Hierarchical Heterostructures Research Articles

Surface Engineering of Copper Foam to Construct a Hierarchical Heterostructure for High Energy Efficient Supercapacitors.

As a unique pseudocapacitive material, the heterojunction-structured CuO@Cu combines the high conductivity of substrate Cu and the high capacity of active CuO together for structure-integral electrodes, however, its structural optimization and improved capacity are still the main challenges so far. In this study, an initial surface etching of copper foam (CF) is adopted to construct a primary heterostructure of CuO nanowires@CF (CuO NW@CF), and then, the surface decoration of CuO NW@CF via the deposition of cerium-2-methylimidazole based metal-organic frameworks (Ce-2MI) finally results in the current-collector-/binder-free electrodes of the hierarchical heterostructure Ce-2MI@CuO NW@CF. Compared to the structural properties of CuO NW@CF, both the introducing Ce-ion active sites and the enriched lattice oxygen vacancies cooperatively endow the pseudocapacitive electrodes of Ce-2MI@CuO NW@CF with a ultrahigh specific capacitance and excellent cycling stability. Within the potential window of 1.6 V, the asymmetric supercapacitor devices of activated carbon//Ce-2MI@CuO NW@CF acquire a high energy density of 56.8 Wh kg-1 at 725 W kg-1, which can light up a light-emitting diode (LED) bulb for 20 min. Therefore, constructing the hierarchically heterostructured Ce-2MI@CuO NW@CF is an effective approach to developing high-performance supercapacitors for potential application purposes.

Tailoring flower-like NiCo LDH/MoS2/HPC ternary hierarchical heterostructures electrodes with enhanced energy density for aqueous asymmetric supercapacitor

The imperative quest for renewable energy sources and advanced energy storage technologies has arisen amidst the escalating perils of climate change and dwindling fossil fuel reserves. In the realm of energy storage technologies, asymmetric supercapacitor (ASC) has garnered significant attention owing to its high energy density and power density. In the quest for advanced electrode materials for ASC, the integration of 2D layered heterostructures on hierarchical porous carbon (HPC) substrates has emerged as a promising approach to enhance the electrochemical performance. Herein, a highly innovative hierarchical NiCo LDH/MoS2/HPC heterostructure was successfully synthesized using a simple two-step hydrothermal method for the electrode materials of ASC. Benefiting from the unique hierarchical heterostructure of NiCo LDH/MoS2/HPC composite and the synergistic effect between the components, it reveals an exceptional specific capacitance of 2368 F/g at 0.5 A/g in a three-electrode system, which significantly exceeds that of conventional supercapacitor electrodes. Additionally, the ASC device of NiCo LDH/MoS2/HPC//HPC achieves remarkable specific capacitance of 236 F/g at 0.5 A/g and an impressive energy density of 84 Wh/kg at a power density of 400 W/kg, as well as superior cyclic stability. This study not only demonstrates the effectiveness of incorporating MoS2 and NiCo LDH into a carbon-based framework for supercapacitor applications but also opens avenues for designing more efficient energy storage devices.

Enhanced Adsorption Kinetics and Capacity of a Stable CeF3@Ni3N Heterostructure for Methanol Electro‐Reforming Coupled with Hydrogen Production

Alkaline methanol‐water electrolysis system is regarded as an appealing strategy for electro‐reforming methanol into formate and producing hydrogen with low energy‐consumption compared with alkaline water electrolysis. However, stability and selectivity under high current densities for practical application remain challenging. Herein, a CeF3@Ni3N nanosheets array anchored on carbon cloth (CeF3@Ni3N/CC) was fabricated. The gradual extrusion of F species from Ni(OH)2 lattices can stabilize hierarchical structure and construct abundant heterostructure interfaces. Moreover, CeF3 can modulate electron distribution of Ni3N, thus simultaneously enhancing the surface adsorption kinetics and capability of methanol and OH‐, which is conducive to enhanced methanol oxidation reaction (MOR) activity and selectivity. Therefore, bifunctional CeF3@Ni3N/CC exhibits low potential of 1.43 V at 500 mA cm‐2, along with high stability over 72 h and high faradaic efficiency (FEs) in MOR, as well as an overpotential of 76 mV to achieve 50 mA cm‐2 for hydrogen evolution reaction (HER). Furthermore, membrane‐free CeF3@Ni3N/CC||CeF3@Ni3N/CC cell for MOR||HER delivers high electrocatalytic activity, long‐term stability and FEs at high current density of 300 mA cm‐2. This study highlights the importance of optimizing surface adsorption behavior of active species, as well as rational design of highly efficient heterostructure electrocatalysts for methanol upgrading coupled with hydrogen production.

Enhanced Adsorption Kinetics and Capacity of a Stable CeF3@Ni3N Heterostructure for Methanol Electro-Reforming Coupled with Hydrogen Production.

Alkaline methanol-water electrolysis system is regarded as an appealing strategy for electro-reforming methanol into formate and producing hydrogen with low energy-consumption compared with alkaline water electrolysis. However, stability and selectivity under high current densities for practical application remain challenging. Herein, a CeF3@Ni3N nanosheets array anchored on carbon cloth (CeF3@Ni3N/CC) was fabricated. The gradual extrusion of F species from Ni(OH)2 lattices can stabilize hierarchical structure and construct abundant heterostructure interfaces. Moreover, CeF3 can modulate electron distribution of Ni3N, thus simultaneously enhancing the surface adsorption kinetics and capability of methanol and OH-, which is conducive to enhanced methanol oxidation reaction (MOR) activity and selectivity. Therefore, bifunctional CeF3@Ni3N/CC exhibits low potential of 1.43 V at 500 mA cm-2, along with high stability over 72 h and high faradaic efficiency (FEs) in MOR, as well as an overpotential of 76 mV to achieve 50 mA cm-2 for hydrogen evolution reaction (HER). Furthermore, membrane-free CeF3@Ni3N/CC||CeF3@Ni3N/CC cell for MOR||HER delivers high electrocatalytic activity, long-term stability and FEs at high current density of 300 mA cm-2. This study highlights the importance of optimizing surface adsorption behavior of active species, as well as rational design of highly efficient heterostructure electrocatalysts for methanol upgrading coupled with hydrogen production.

Enhanced interfacial charge transfer in WO3-Bi2WO6 heterostructures: Toward trace detection of mustard gas simulant

Developing reliable and portable sensors for detection of highly toxic mustard gas is extremely important for public security. However, gas sensors based on pristine metal oxide semiconductors often suffer from high working temperature, inferior response, and inadequate detection limit owing to their poor intrinsic conductivity and weak adsorption toward target gases, thereby hindering their wide application. Herein, hierarchical WO3-Bi2WO6 heterostructures were fabricated as sensing materials to comprehensively improve their sensing properties to 2-chloroethyl ethyl sulfide (2-CEES, a mustard gas simulant). The optimized sensor based on WO3-Bi2WO6-2 displayed short response time of 1.4 s and high sensing response (Ra/Rg = 63) to 50 ppm 2-CEES at 133 °C, together with an ultra-low detection limit of 10 ppb. The improvement of WO3-Bi2WO6-2 in sensing properties are synergistically attributed to the amount of heterojunction and surface adsorption sites, which were proved by DFT calculations and a series of characterizations. This work might pave the way for further developing heterostructure-based sensors for 2-CEES detection with superior sensing properties.

Hierarchical Flower Array NiCoOOH@CoLa‐LDH Nanosheets for High‐Performance Supercapacitor and Alkaline Zn Battery

AbstractNickel oxyhydroxide based energy storage materials have been largely confined by insufficient exposure of active sites which results in low energy efficiency and poor stability. In order to resolve the problems, hierarchical flower array heterostructure NiCoOOH@CoLa‐LDH (denoted as NC@CL) nanosheets are designed with NiCo oxyhydroxide (NiCoOOH, denoted as NC) being tightly covered on CoLa layered double hydroxide (CoLa‐LDH, denoted as CL) nanosheet. This rational design creates more active sites, enlarges the electrode‐electrolyte contact area, improves electron conductivity, and prevents agglomeration during the cycling charge–discharge processes. Density functional theory calculations and differential charges concurrently illustrate that heterostructure formation optimizes the reaction kinetics and promotes electron redistribution. Benefiting from the heterogeneous structure and rich electro‐active sites caused by NC, NC@CL displays outstanding reversible specific capacitance (3228 F g−1 at 1 A g−1). The aqueous rechargeable alkaline Zn battery NC@CL//Zn exhibits a high capacity of 381.1 mA h g−1 at 0.5 A g−1 and cycling durability (98% capacity retention after cycling at 5 A g−1 for 2000 cycles). The excellent electrochemical performances indicate that NC@CL has great application potential as electrode material for aqueous energy storage device.

A novel BCC-L21-BCC hierarchical heterostructure high entropy alloy with excellent corrosion resistance and mechanical properties in as-cast state

In this paper, a novel as-cast CrFeNiAl0.35Si0.1Ti0.1 high entropy alloy (HEA) with micron-to-nano hierarchical heterostructure was designed, and its microstructure, mechanical properties and corrosion resistance have been systematically investigated. It is found that, this novel HEA exhibits well-dispersed L21 phase with various sizes from micron-scale to nano-scale in the BCC matrix, while nano-sized BCC lamellas could also emerge in the L21 phase with large diameter. Moreover, this HEA exhibits not only excellent corrosion resistance in 3.5 wt% NaCl solution that close to super-stainless steels, but also high mechanical properties combining yield strength of 1712 ± 56 MPa, compressive plasticity of 21.2% ± 0.5% and hardness of ∼560 Hv. Such outstanding comprehensive properties for this HEA are possibly resulted from the complex hierarchical BCC-L21-BCC heterostructure with stable passive film and low diversity in work function between different phases. This work provides a novel route in the development of high-performance corrosion-resistant HEAs for structural and coating applications.

NiFe LDH/Fe2O3/Ni3S2 Heterostructure with a Superhydrophilic/Superaerophobic Surface for Solar-Driven Electrolytic Water Splitting.

The development of a bifunctional electrocatalyst with high efficiency, high stability, and low cost is of great significance in practical applications of electrocatalytic water splitting. Herein, a self-supporting bifunctional electrocatalyst with a NiFe layered double hydroxide/Fe2O3/Ni3S2 heterostructure (NiFe LDH/Fe2O3/Ni3S2/IF) for hydrogen evolution and oxygen evolution reactions (HER/OER) is synthesized by the self-corrosion of iron foam (IF) and hydrothermal strategies. The constructed NiFe LDH/Fe2O3/Ni3S2/IF hierarchical heterostructure was not only beneficial to expose active sites and promote charge/mass transfer but also generate a superhydrophilic/superaerophobic surface, thereby accelerating the reaction kinetics to improve the HER/OER activity. Therefore, NiFe LDH/Fe2O3/Ni3S2/IF exhibited superior overpotentials of 226.2 and 162.8 mV for the OER and HER at 100 mA cm-2, respectively. NiFe LDH/Fe2O3/Ni3S2/IF was employed as both the cathode and the anode to assemble a device for overall water splitting and displayed a voltage of 1.55 V at 10 mA cm-2. The overall water splitting device was coupled with a solar cell to simulate a solar-powered water splitting system, resulting in a superior solar-to-hydrogen conversion efficiency of 15.16%. This work can promote the development of clean energy sources such as solar hydrogen production.

Construction of ternary hierarchical heterostructures with favorable interfacial compatibility for ultrahigh photocatalytic H2O2 production

Sluggish charge transfer dynamics are still the key issue limiting the development of photocatalysis. In this study, CdS/ZnIn2S4/MIL-53-NH2 ternary hierarchical heterostructures were constructed via a building block approach, where ZnIn2S4 lamellae first grow on MIL-53-NH2 followed by CdS nanoparticle deposition. The favorable interfacial compatibility and ternary heterostructures contribute to rapid and multistep spatial charge transfer, which suppresses charge recombination. Therefore, ultrahigh H2O2 production of 1792 μmol·L−1 was obtained over CdS/Znln2S4/MIL-53-NH2 composites with visible light, pure water and ambient air, which is not only higher than that of each monomer and binary heterostructure but also better than those of most reported references. Notably, the apparent quantum yield reached 4.5 % at 400 nm, and the solar-to-H2O2 conversion efficiency was 0.081 % in pure water and ambient air. Additionally, H2O2 generation over CdS/Znln2S4/MIL-53-NH2 composites involves two-electron O2 reduction with ·O2- as an intermediate. This work may encourage heterostructure design for efficient photocatalytic H2O2 production.

Bimetal Metaphosphate/Molybdenum Oxide Heterostructure Nanowires for Boosting Overall Freshwater/Seawater Splitting at High Current Densities.

Exploring excellent non-noble bifunctional electrocatalysts for freshwater/seawater splitting at high current densities has attracted extensive interest owing to strong anodic oxidation and severe chloride corrosion challenges. Herein, hierarchical bimetal Ni-Co metaphosphate/molybdenum oxide heterostructure nanowires (NiCoMoPO) are rationally designed and fabricated to efficiently boost oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline freshwater/seawater, where the favorable electronic structure from heterostructures, signified by X-ray absorption spectra, endows NiCoMoPO with the enhanced intrinsic activity, while its hierarchical nanowire structure and heterostructures provide abundant active sites. Additionally, the PO3 - improves the chloride-corrosion resistance and efficiently facilitates the OER kinetics verified by theoretical and experimental studies. Therefore, NiCoMoPO drives 1000mA cm-2 at low overpotentials of 467 and 442mV for OER and HER in alkaline freshwater respectively, as well as a small cell voltage of 2.135V for overall freshwater splitting with robust durability of 300h. Impressively, due to the strong corrosion resistance, at 500mA cm-2 of overall seawater splitting, NiCoMoPO maintains almost 2.096V for 1200h, indicating promising practical applications. This work sheds light on the rational design and fabrication of outstanding electrocatalysts at high current densities of seawater/freshwater splitting.

Construction of COFs@MoS2-Pd Hierarchical Tubular Heterostructures for Enhanced Catalytic Performance.

Here, we report ternary COFs@MoS2-Pd hybrids with an innovative self-sacrificial approach. MoO3@Covalent organic frameworks (COFs) microcables were first prepared and then two-dimensional MoS2 nanosheets (NSs) were integrated onto the surface of COFs, as COFs@MoS2, after treatment with hydrothermal reaction. The MoS2 NSs were used as an excellent support to introduce Pd nanoparticles (NPs) thanks to their reducing ability for the formation of the ternary COFs@MoS2-Pd hybrids. While COF microtubes improved the electrical conductivity of the hybrid materials, they also decreased the aggregation of MoS2 NSs, as a contribution to the enhanced catalytic performance. The mild reaction between MoS2 and Pd2+ ions realized the dense distribution of Pd NPs onto COFs@MoS2 for abundant active sites to further improve the catalytic performance. Thus, the hierarchical MoS2-based ternary hybrids were prepared with the enhanced catalytical performance as validated with the enzyme-like catalysis and the reduction of 4-nitrophenol.

Hierarchical ferrous medium entropy with heterogeneous precipitates embedded in core-shell grain structure for superior mechanical properties

Superalloys designed for high-temperature applications, featuring a face-centered cubic matrix and L12 precipitates, have shown excellent tensile properties at both room and elevated temperatures. However, the substantial Ni and Co, necessary for generating a high fraction of the ordered L12 phase within the matrix, results in high mass density and cost, subsequently limiting their widespread industrial application. It is important to increase Fe content over Ni and Co while preserving outstanding mechanical properties at ambient and high temperatures. In this study, we propose a novel approach to introduce a hierarchical structure in a 60-at%-Fe-based medium entropy alloy. The heterogeneous nano-precipitates embedded in harmonic (core-shell) grain structure reinforce mechanical contrast between soft and hard domains, achieving an excellent heterostructure. The present alloy incorporates hierarchical heterogeneity at multi-scales, combining heterogeneous grain at micrometers, precipitates at tens of nanometers, and elemental fluctuation at nanometers. This hierarchical structure shows superior mechanical properties at room and high temperatures comparable to those of conventional superalloys. Further, the high content of Fe in this alloy system shows excellent performance in alloy cost and mass density. This work suggests the unique hierarchical heterostructure to overcome the trade-off dilemma in alloy cost, mass density, and mechanical properties in room/elevated temperatures.

Hierarchical 2D/1D MOFs/electrospun ZIF-67 modified carbon nanofibers heterostructure electrode for high-performance asymmetric supercapacitor

In this paper, a 2 dimensional (2D) metal–organic frameworks (MOFs) nanosheets grown on 1D ZIF-67 modified carbon nanofibers (CNFs) was designed and fabricated with a hierarchical heterostructure. The hierarchical 2D/1D MOFs/CCNF offers rich electrochemical active sites and favorable ion/electron diffusion pathways. The synergistic effect of Co, CNFs and MOFs from heterostructures contributes to superb electrochemical activities. Benefiting from the hierarchical heterostructures optimized by the mass ratio of ZIF-67/PAN and CCNF/NiMOF as well as the type of substrates, CCNF-20@MOF showed a specific capacity of 361.50 C g−1 at 0.5 A g−1, whose charge storage mechanism is dominated by diffusion control. Meanwhile, a bamboo-derived carbon material (BBC) was designed in the solid-state asymmetric supercapacitor (CCNF-20@MOF//BBC). The device exhibited an energy density of 38.89 Wh kg−1 at the power density of 800.02 W kg−1 and excellent cycling stability, that exceed many MOFs based devices. Moreover, it could be successfully used for LED light-emitting, demonstrating a good application prospect. This work provides a feasible strategy for the improved performance of MOFs and CNFs based materials in the field of energy storage.

Enhanced performance of hierarchical heterostructures CuS@ZnS-Ag-doped core–shell quantum dots towards photocatalytic degradation of pesticide contaminants in aqueous solution

ABSTRACT In recent years, the pollution of the water by pesticides has become a significant global concern due to the harmful effects these compounds have on human health and the environment. Therefore, removal of pollutants or making them ineffective is necessary for life. In this study, removal of agricultural pesticides such as Deltamethrin, Flumethrin and Phoxim was performed through photodegradation process using CuS@ZnS-Ag quantum dots as photocatalyst. The synthesised CuS@ZnS-Ag heterojunction nanocomposite has suitable charge separation and low electron–hole recombination rate with good optical properties. The synthesised photocatalyst was characterised by various techniques such as X-ray diffraction, Fourier transform infrared spectrometry, UV-Visible spectroscopy, field emission scanning electron microscopy and transmission electron microscopy. The effects of pH, temperature, photocatalyst dose and agitation rate on the degradation were investigated. The optimised conditions were obtained as follows: pH 7 (±0.5), temperature 30 (±2) °C, photocatalyst dose for Flumethrin 30 mg/L, Deltamethrin 10 mg/L and Phoxim 15 mg/mL and agitation rate 500 rpm. Results showed that under optimal conditions, the CuS@ZnS-Ag as photocatalyst can degrade 96% of the pollutants using light-emitting diode lamp. Kinetic studies indicated the pseudo-second-order model.

Synergy of active sites and charge transfer in (WO3/phosphotungstic acid)@MoS2 hierarchical heterostructures for highly sensitive and selective ppb-level NO2 sensing

In this paper, (WO3/phosphotungstic acid)@MoS2 core-shell hierarchical nanofibers were fabricated by coaxial electrospinning technology to construct a high-performance gas sensing material combining the synergy of active sites and charge transfer. Polyoxometalate (POMs), as electrons acceptor, can separate electrons and holes, and thus promote sensing performances. Under optimized test conditions, the WO3/PW12@MoS2 sensor exhibited sensitive response of 3.4 to 2 ppm NO2 gas. That is obviously enhanced than WO3@MoS2 sensor, and much higher than that of 100 ppm other interference gases, indicating a satisfactory selectivity. Repeatability, long-term stability and humidity resistance were systematically investigated. The heterojunctions formed between the three components can extend electron lifetime, while allowing more electrons to migrate towards the surface to react with oxygen molecules in the air, thus promote the gas response. This work provides meaningful information for the practical application of POMs in gas sensors.

In-situ compression tests and analysis of strength-ductility synergy in heterogeneous structured copper-tin composite joint

Copper-tin (Cu–Sn) serves as a prevalent alloy system in electronic packaging, envisioned for future high-power device applications. However, interdiffusion in Cu–Sn yields rigid and brittle Cu6Sn5 and Cu3Sn phases, causing joint hardening and embrittlement. This paper introduces a novel, non-homogeneous Cu–Sn composite employing heterostructure design. Through room temperature in-situ compression tests and molecular dynamics (MD) simulations, we investigate mechanical property degradation origins and Cu–Sn composite strength-ductility mechanisms. Our findings reveal hierarchical heterostructures in joints stimulate dynamic stress distribution at interfaces, generating a high density of geometrically necessary dislocations (GNDs). This enhances the material's work-hardening rate and imparts robust strain-hardening capabilities. This unique structural feature has altered the interaction between dislocations and interfaces, thereby effectively promoting the formation and driving force of dislocations. The combined effects of strain inhomogeneity induced by soft and hard phases, along with a hybrid mechanism involving stacking faults (SFs), Lomer-Cottrell (L-C) locking, and dislocation bypassing and shearing, realize exceptional strength-ductility synergies in Cu–Sn composite joints. This study presents a promising paradigm for designing microstructures in high-strength, deformable, and high-temperature-resistant soldered composites.

2D MXene-derived 3D TiO2-NiCoPx hierarchical heterostructures for efficient water splitting

Achieving efficient electrocatalytic activity in two-dimensional (2D) MXene for advanced water splitting remains a significant challenge. In this work, 2D MXene was derived into sea urchin-like TiO2 and used to load porous bimetallic phosphide (NiCoPx) nanorods to achieve three-dimensional (3D) TiO2-NiCoPx hierarchical heterostructures. The hierarchical heterostructures synthesized through hydrothermal and phosphating processes enable rich heterogeneous interfaces and fully exposed active sites, thereby facilitating efficient charge transfer and accelerating mass transfer rates. As a result, the TiO2-NiCoPx heterostructures inherit the low overpotential (311 mV at 10 mA cm−2) and long-term stability (current density retention of 94.1 % after 12 h) towards oxygen evolution reaction (OER). Importantly, the assembled TiO2-NiCoPx || Pt/C cell also exhibits remarkable water splitting performance. This contribution delivers a desirable opportunity for constructing efficient 2D MXene-based electrocatalysts with abundant active sites for water splitting.

Long-Lifespan Fibrous Aqueous Ni//Bi Battery Enabled by Bi2O3-Bi2S3 Hierarchical Heterostructures.

Bismuth oxide (Bi2O3) materials are considered as great promising anodes for aqueous batteries on account of the high capacity as well as wide potential plateau. Nevertheless, the low conductivity and severe volumetric change of Bi2O3 in the course of cycling are the main limiting factors for their application in energy-storage systems. Herein, we propose and design unique hierarchical heterostructures constructed by Bi2O3 and Bi2S3 nanosheets (NSs) manufactured immediately on the surface of carbon nanotube fibers (CNTFs). The Bi2O3-Bi2S3 (BO-BS) exhibits enhanced conductivity and increased stability in comparison with pure Bi2O3 and Bi2S3. The BO-BS NSs/CNTF electrode indicates exceptional rate capability and cycling stability, while creating a high reversible capacity of 0.68 mAh cm-2 at 4 mA cm-2, as anticipated. Additionally, the quasi-solid-state fibrous aqueous Ni//Bi battery that was built with the BO-BS NSs/CNTF anode delivers an exceptional cycling stability of 52.7% capacity retention after 4000 cycles at 80 mA cm-2, an ultrahigh capacity of 0.35 mAh cm-2 at 4 mA cm-2, and a high energy density of 340.1 mWh cm-3 at 880 mW cm-3. This work demonstrates the potential of constructing hierarchical heterostructures of bismuth-based materials for high-performance aqueous Ni//Bi batteries and other energy-storage devices.

Hierarchical NiCo2O4 needle-like heterostructure arrays anchored on WO3 as high- performance asymmetric supercapacitors for energy storage applications

The current work employs a novel approach to construct a composite nanostructure to improve the capacitive performance of a supercapacitor device. The work involved preparing cube-shaped WO3 particles and depositing them onto the surface of NiCo2O4 needles using a microwave technique. The structure of the composites enables efficient paths for ion transport and electron diffusion in supercapacitors. The hybrid composite electrode demonstrates a specific capacitance of 716 F g−1 at a current density of 5 Ag−1. The asymmetric capacitor device, which utilizes NiCo2O4@WO3 as the positive electrode and AC as the negative electrode, exhibits an energy density of 48.57 Wh kg−1 at a power density of 1120 W kg−1. In addition, the NiCo2O4@WO3//AC device has a favourable cycle life, maintaining 85.7 % of its capacitance retention after 10,000 cycles. The findings demonstrate the potential of NiCo2O4@WO3//AC to be used in the development of advanced hybrid electrodes for improved supercapacitors.

Rational design of spatial charge separation and targeted active site Cu for highly selective photocatalytic CO2 reduction to CH4

Photocatalytic CO2 reduction reaction (CO2RR) is usually constrained by sluggish kinetics and low product selectivity. Herein, a Cu-doping multi-tier hierarchical S-scheme heterostructure Cu-ZnIn2S4/ZIF-67 was fabricated, achieving highly efficient photocatalytic CO2RR under visible light without additional thermal input. At low pressure (absolute pressure 40 kPa), the optimized catalyst 2Cu-ZISF demonstrated a CH4 yield of 22.27 μmol g−1h−1 with a selectivity of 94.7 %. In situ XPS and EPR confirmed that the photogenerated charge transfer obeys an S-scheme mechanism, with Cu sites serving as electron-rich centers, facilitating spatial charge separation. In situ DRIFT detected reaction intermediates of photocatalytic CO2RR mechanism, and Gibbs free energy calculations via Density Functional Theory revealed that Cu incorporation significantly stabilizes surface CO* species, thus reducing CO(g) production and facilitating hydrogenation, thereby acting as targeted active sites for CH4 production. This work overcomes the limitations of slow reaction kinetics and offers an in-depth understanding of how to design effective S-scheme heterojunction photocatalysts and their charge transfer mechanisms.