Advancing overall water splitting via phase-engineered amorphous/crystalline interface: A novel strategy to accelerate proton-coupled electron transfer.

Traditional phase engineering enhances conductivity or activity by fully converting electrocatalytic materials into either a crystalline or an amorphous state, but this approach often faces limitations. Thus, a practical solution entails balancing the dynamic attributes of both phases to maximize an electrocatalyst's functionality is urgently needed. Herein, in this work, Co/Co2C crystals have been assembled on the amorphous N, S co-doped porous carbon (NSPC) through hydrothermal and calcination processes. The stable biphase structure and amorphous/crystalline (A/C) interface enhance conductivity and intrinsic activity. Moreover, the adsorption ability of water molecules and intermediates is improved significantly attributed to the rich oxygen-containing groups, unsaturated bonds, and defect sites of NSPC, which accelerates proton-coupled electron transfer (PCET) and overall water splitting. Consequently, A/C-Co/Co2C/NSPC (Co/Co2C/NSPC with amorphous/crystalline interface) exhibits outstanding behavior for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), requiring the overpotential of 240.0 mV and 70.0 mV to achieve 10 mA cm-2. Moreover, an electrolyzer assembled by A/C-Co/Co2C/NSPC-3 (anode) and A/C-Co/Co2C/NSPC-2 (cathode) demonstrates a low drive voltage of 1.54 V during overall water splitting process. Overall, this work has pioneered the coexistence of crystalline/amorphous phases in electrocatalysts and provided new insights into phase engineering.

Iron Active Center Coordination Reconstruction in Iron Carbide Modified on Porous Carbon for Superior Overall Water Splitting.

In this work, a novel liquid nitrogen quenching strategy is engineered to fulfill iron active center coordination reconstruction within iron carbide (Fe3C) modified on biomass-derived nitrogen-doped porous carbon (NC) for initiating rapid hydrogen and oxygen evolution, where the chrysanthemum tea (elm seeds, corn leaves, and shaddock peel, etc.) is treated as biomass carbon source within Fe3C and NC. Moreover, the original thermodynamic stability is changed through the corresponding force generated by liquid nitrogen quenching and the phase transformation is induced with rich carbon vacancies with the increasing instantaneous temperature drop amplitude. Noteworthy, the optimizing intermediate absorption/desorption is achieved by new phases, Fe coordination, and carbon vacancies. The Fe3C/NC-550 (550 refers to quenching temperature) demonstrates outstanding overpotential for hydrogen evolution reaction (26.3 mV at -10 mA cm-2) and oxygen evolution reaction (281.4 mV at 10 mA cm-2), favorable overall water splitting activity (1.57 V at 10 mA cm-2). Density functional theory (DFT) calculations further confirm that liquid nitrogen quenching treatment can enhance the intrinsic electrocatalytic activity efficiently by optimizing the adsorption free energy of reaction intermediates. Overall, the above results authenticate that liquid nitrogen quenching strategy open up new possibilities for obtaining highly active electrocatalysts for the new generation of green energy conversion systems.

Strain Engineering for Electrocatalytic Overall Water Splitting.

Strain engineering is a novel method that can achieve superior performance for different applications. The lattice strain can affect the performance of electrochemical catalysts by changing the binding energy between the surface-active sites and intermediates and can be affected by the thickness, surface defects and composition of the materials. In this review, we summarized the basic principle, characterization method, introduction strategy and application direction of lattice strain. The reactions on hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are focused. Finally, the present challenges are summarized, and suggestions for the future development of lattice strain in electrocatalytic overall water splitting are put forward.

Double-Shelled Porous g-C3 N4 Nanotubes Modified with Amorphous Cu-Doped FeOOH Nanoclusters as 0D/3D Non-Homogeneous Photo-Fenton Catalysts for Effective Removal of Organic Dyes.

Graphite phased carbon nitride (g-C3 N4 ) has attracted extensive attention attributed to its non-toxic nature, remarkable physical-chemical stability, and visible light response properties. Nevertheless, the pristine g-C3 N4 suffers from the rapid photogenerated carrier recombination and unfavorable specific surface area, which greatly limit its catalytic performance. Herein, 0D/3D Cu-FeOOH/TCN composites are constructed as photo-Fenton catalysts by assembling amorphous Cu-FeOOH clusters on 3D double-shelled porous tubular g-C3 N4 (TCN) fabricated through one-step calcination. Combined density functional theory (DFT) calculations, the synergistic effect between Cu and Fe species could facilitate the adsorption and activation of H2 O2 , and the separation and transfer of photogenerated charges effectively. Thus, Cu-FeOOH/TCN composites acquire a high removal efficiency of 97.8%, the mineralization rate of 85.5% and a first-order rate constant k = 0.0507 min-1 for methyl orange (MO) (40 mg L-1 ) in photo-Fenton reaction system, which is nearly 10 times and 21 times higher than those of FeOOH/TCN (k = 0.0047 min-1 ) and TCN (k = 0.0024 min-1 ), respectively, indicating its universal applicability and desirable cyclic stability. Overall, this work furnishes a novel strategy for developing heterogeneous photo-Fenton catalysts based on g-C3 N4 nanotubes for practical wastewater treatment.

Novel Strain Engineering Combined with a Microscopic Pore Synergistic Modulated Strategy for Designing Lattice Tensile-Strained Porous V2C-MXene for High-Performance Overall Water Splitting.

Transition metal carbon/nitride (MXene) holds immense potential as an innovative electrocatalyst for enhancing the overall water splitting properties. Nevertheless, the re-stacking nature induced by van der Waals force remains a significant challenge. In this work, the lattice tensile-strained porous V2C-MXene (named as TS(24)-P(50)-V2C) is successfully constructed via the rapid spray freezing method and the following hydrothermal treatment. Besides, the influence of lattice strain degree and microscopic pores on the catalytic ability is reviewed and explored systematically. The lattice tensile strain within V2C-MXene could widen the interlayer spacing and accelerate the ion transfer. The microscopic pores could change the ion transmission path and shorten the migration distance. As a consequence, the obtained TS(24)-P(50)-V2C shows extraordinary hydrogen evolution reaction and oxygen evolution reaction activity with the overpotential of 154 and 269 mV, respectively, at the current density of 10 mA/cm2, which is quite remarkable compared to the MXene-based electrocatalysts. Moreover, the overall water splitting device assembled using TS(24)-P(50)-V2C as both anode and cathode demonstrates a low cell voltage requirement of 1.57 V to obtain 10 mA/cm2. Overall, the implementation of this work could offer an exciting avenue to overcome the re-stacking issue of V2C-MXene, affording a high-efficiency electrocatalyst with superior catalytic activity and desirable reaction kinetics.

Liquid nitrogen quenching inducing lattice tensile strain to endow nitrogen/fluorine co-doping Fe3O4 nanocubes assembled on porous carbon with optimizing hydrogen evolution reaction.

In this work, the lattice tensile strain of nitrogen/fluorine co-doping ferroferric oxide (Fe3O4) nanocubes assembled on chrysanthemum tea-derived porous carbon is induced through a novel liquid nitrogen quenching treatment (named as TS-NF-FO/PCX-Y, TS: Tensile strain, NF: Nitrogen/Fluorine co-doping, FO: Fe3O4, PC: Porous carbon, X: The weight ratio of KOH/carbon, Y: The adding amount of porous carbon). Besides, the electrocatalytic activity influenced by the adding amount of porous carbon, the type of dopant, and the introduction of lattice tensile strain is systematically studied and explored. The interconnected porous carbon could improve electrical conductivity and prevent Fe3O4 nanocubes from aggregating. The induced nitrogen/fluorine could cause extrinsic defects and tailor the intrinsic electron state of the host materials. Lattice tensile strain could tailor the surface electronic structure of Fe3O4 via changing the dispersion of surface atoms and their bond lengths. Impressively, the designed TS-NF-FO/PC5-0.25 delivers a low overpotential of 207.3 ± 0.4 mV at 10 mA/cm2 and demonstrates desirable reaction dynamics. Density functional theory calculations illustrate that the electron structure and hydrogen adsorption free energy (ΔG*H) are optimized by the synergistic effect among porous carbon, nitrogen/fluorine co-doping and lattice tensile strain, thus promoting hydrogen evolution reaction (HER) catalytic activity. Overall, this work paves the way to unravel the enhancement mechanism of HER on transition metal oxide-based materials by electronic structure and phase composition modulation strategy.

g-C3N4-wrapped nickel doped zinc oxide/carbon core-double shell microspheres for high-performance photocatalytic hydrogen production.

The development of efficient heterojunctions with enhanced photocatalytic properties is considered a promising approach for photocatalytic hydrogen production. In this study, graphitic carbon nitride (g-C3N4)-wrapped nickel-doped zinc oxide/carbon (Ni-ZnO@C/g-C3N4) core-double shell heterojunctions with unique core-double shell structures were employed as efficient photocatalysts through an innovative approach. Ni doping can enhance the intensity and range of visible light absorption in ZnO, and the carbon core coupled with the hollow double-shell structure can accelerate the charge transfer rate and improve the photon utilization efficiency. Meanwhile, the construction of the Z-scheme heterojunction extended the electron-hole pair transport path. In addition, the Z-scheme charge-transfer mechanism of Ni-ZnO@C/g-C3N4 under simulated sunlight was verified by photoluminescence (PL) and electron spin resonance (ESR) experiments. As a result, the obtained photocatalyst acquired a high hydrogen evolution rate of 336.08 µmol g-1h-1, which is 36.49 times higher than that of pristine ZnO. Overall, this work may provide a pathway for the construction of highly efficient photocatalysts with unique core-double shell structures.

A novel composite anode via immobilizing of Ce-doped PbO2 on CoTiO3 for efficiently electrocatalytic degradation of dye.

The exploitation of efficient electrocatalyst is significantly important for degradation of refractory organic pollutants. Herein, a novel Ti/CoTiO3/Ce-PbO2 composite electrocatalyst (abbreviated as CTO/CP) is successfully constructed via facile consecutive immersion pyrolysis and electro-deposition method and then systematically characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier Transform infrared spectroscopy (FT-IR), energy dispersive spectroscopy (EDS) and near infrared chemical imaging (NIR-CI). Importantly, the electrochemical measurements demonstrate that the CTO/CP possesses numerous prominent properties such as lower charge transfer resistance, larger electroactive area, higher oxygen evolution potential than those of the pristine Ti/CoTiO3 (CTO) and Ti/Ce-PbO2 (CP). Thereby, the CTO/CP exhibits an enhanced electrocatalytic degradation performance with the degradation efficiency as high as 90.0% and COD removal rate of 88.3% at 180 min for the optimal CTO/CP (denoted as 10 layers of CTO and 1 h electrodeposition of CP), in which the ·OH is the major reactive species. Additionally, the optimal CTO/CP also shows a higher ICE/ACE together with lower EEC and desirable stability, universal applicability for many different dyes and reusability. Overall, this work offers a promising approach for enhancing the electrocatalytic properties of CTO via introducing CP.

Structure-designed synthesis of hollow/porous cobalt sulfide/phosphide based materials for optimizing supercapacitor storage properties and hydrogen evolution reaction.

Cobalt-based transition metal phosphides/sulfides have been viewed as promising candidates for supercapacitor (SCs) and hydrogen evolution reaction (HER) featured with their intrinsic merits. Nevertheless, the sluggish reaction kinetics and drastic volume expansion upon electrochemical process hinder their commercial application. In this work, the hollow/porous cobalt sulfide/phosphide based nanocuboids (C-CoP4 and CoS2 HNs) with superior specific surface area are achieved by employing a novel chemical etching-phosphatization/sulfuration strategy. The hollow/porous structure could offer rich active sites and shorten electrons/ions diffusion length. In virtue of their structural advantage, the obtained C-CoP4 and CoS2 HNs perform superior specific capacitance, fast charge/discharge rate and beneficial cycling stability. The advanced asymmetrical supercapacitors assembled by C-CoP4 and CoS2 HNs deliver exceptional energy density, respectively. Furthermore, when employed as hydrogen evolution reaction electrocatalysts, C-CoP4 and CoS2 HNs yield favorable electrocatalytic activity. These findings shed fundamental insight on the design of dual-functional transition metal phosphide/sulfide based materials for optimizing hydrogen evolution reaction and supercapacitor storage properties.

3D Hollow Flower-like CoWO4 Derived from ZIF-67 Grown on Ni-foam for High-Performance Asymmetrical Supercapacitors.

A three-dimensional (3D) hollow CoWO4 composite grown on Ni-foam (3D-H CoWO4 /NF) based on a flower-like metal-organic framework (MOF) is designed by utilizing a facile dipping and hydrothermal approach. The 3D-H CoWO4 /NF not only possesses large specific areas and rich active sites, but also accommodates volume expansion/contraction during charge/discharge processes. In addition, the unique structure facilitates fast electron/ion transport of 3D-H CoWO4 /NF. Meanwhile, a series of characterization measurements demonstrate the appropriate morphology and excellent electrochemical performance of the material. The 3D-H CoWO4 /NF possesses a high specific capacitance of 1395 F g-1 , an excellent cycle stability with 89% retention after 3000 cycles and superior rate property. Furthermore, the 3D-H CoWO4 /NF can be used as a cathode to configurate an asymmetric supercapacitor (ASC), and 3D-H CoWO4 /NF//AC shows a good energy density (29.0 W h kg-1 ). This work provides a facile method for the preparation of 3D-hollow electrode materials with high electrochemical capability for advanced energy storage devices.

A novel dual-tasking hollow cube NiFe2O4-NiCo-LDH@rGO hierarchical material for high preformance supercapacitor and glucose sensor.

Binary transition metal oxides as electroactive materials have continuously aroused grumous attention due to their high theoretical specific capacitance, high valtage window, and multiple oxidation states. However, the tiny specific surface area, poor conductivity and unsatisfactory cycle stability limit their practical application. Hence, a synthetic strategy is designed to fabricate a dual-tasking hollow cube nickel ferrite (NiFe2O4) - based composite (NiFe2O4-NiCo-LDH@rGO) with hierarchical structure. The composite is constructed by firstly preparing hollow NiFe2O4 from cube-like Ni - Fe bimetallic organic framework (NiFe-MOF), and then integrating nickel cobalt layered double hydroxide (NiCo-LDH) nanowires, together with reduced graphene oxide (rGO) via pyrolysis in conjuction with hydrothermal method. The NiFe2O4 possessing cubic hollow structure contributes to a huge accessible surface area, meanwhile alleviates large volume expansion/contraction effect, which facilitates suffcient permeation of the electrolyte and rapid ion/charge transport, and results in high cycling stability. The introduction of layered NiCo-LDH results in hierarchical structure and thus offers maximum contact areas with electrolyte, which heightens the specific capacitance of obtained composite and enhances the electro-catlytic activity towards oxidation of glucose. Furthermore, rGO layer greatly improves the electrical conductivity and ion diffusion/transport capability of composite. Benefiting from the unique structure and individual components of NiFe2O4-NiCo-LDH@rGO composite, the electrode delivers a high specific capacitance (750 C g-1) and superb durability. Simultaneously, the asymmetrical device based on NiFe2O4-NiCo-LDH@rGO as positive electrode delivers remarkable energy density (50 Wh kg-1). Moreover, NiFe2O4-NiCo-LDH@rGO exhibits good sensing performance with a sensitivity of 111.86 µA/µM cm-2, the wide linear range of 3.500 × 10-5 - 4.525 × 10-3 M, and the detection limit of 12.94 × 10-6 M with a signal to noise ratio of 3. Consequently, the NiFe2O4-NiCo-LDH@rGO could provide a prospective notion constructing bifunctional materials with hollow-cube hierarchical structure in the field of supercapacitors and electrochemical sensors.

Facile Dual-Ligand Modulation Tactic toward Nickel-Cobalt Sulfides/Phosphides/Selenides as Supercapacitor Electrodes with Long-Term Durability and Electrochemical Activity.

The use of high electrochemical active binary nickel-cobalt sulfides/phosphides/selenides (Ni-Co-X, X = S, P, Se) as electrochemical energy storage materials still has a space for improvement because they become electrochemically unstable during long-term use. Herein, a facile and cost-effective dual-ligand synergistic modulation tactic is described to substantially improve the durability of Ni-Co-X (X = S, P, Se) at the atomic level by partially substituting S, P, and Se ligands into the nickel-cobalt hydroxide precursor, respectively. Remarkably, the dual-ligand electrodes on Ni-foam achieve superior durability and high electrochemical activity when used as positive electrodes in supercapacitors. Impressively, the density functional theory calculations demonstrate that the OH ligand in NiCo2(MOH)x (M = S, P, Se) could attract electrons from metal-S/metal-P/metal-Se bonds to the metal-O bond, enhancing the binding energy of metal-S/metal-P/metal-Se bonds and improving the long-term durability of Ni-Co-X (X = S, P, Se) in alkaline electrolytes. Moreover, OH and S/P/Se ligands could effectively alter the electron structure and result in favorable electrochemical activity. Overall, this tactic could offer an exciting avenue to achieve long-term durability and electrochemical activity of supercapacitor electrodes simultaneously.

Freestanding hierarchical nickel molybdate@reduced graphene oxide@nickel aluminum layered double hydroxides nanoarrays assembled from well-aligned uniform nanosheets as binder-free electrode materials for high performance supercapacitors.

Herein, the hierarchical nickel molybdate@reduced graphene oxide@nickel aluminum layered double hydroxides (NiMoO4@rGO@NiAl-LDHs) architecture assembled from well-aligned nanosheets is successfully constructed on Ni-foam through a three-step strategy. For the first time, ultrathin graphene nanosheets are introduced by a novel spraying process to avoid the stack. NiAl-LDHs is prepared via situ growth procedure in which NiAl-LDH self-assembles on the surface of graphene to prevent graphene from aggregating, resulting in an enlarged specific surface area. Electrochemical analysis manifests that NiMoO4@rGO@NiAl-LDHs yields exceptional specific capacitance (3396 Fg-1 at 1 Ag-1), favorable charge/discharge rate and approving long-term stability. Furthermore, the NiMoO4@rGO@NiAl-LDHs//AC device delivers superior specific capacitance (137.2 Fg-1 at 1 Ag-1), high energy density (48.7 Whkg-1) associated with pleasurable power output (7987 Wkg-1). Importantly, the well-aligned NiMoO4@rGO@NiAl-LDHs provides a prospective conception constructing hierarchical structural materials in the area of supercapacitor.

Metal-Organic Framework Template-Directed Fabrication of Well-Aligned Pentagon-like Hollow Transition-Metal Sulfides as the Anode and Cathode for High-Performance Asymmetric Supercapacitors.

Given the exceptional specific surface area, geometry, and periodic porosity, transition-metal sulfides derived from crystalline metal-organic frameworks have spurred great interest in energy storage systems. Herein, employing a different sulfurization process, well-aligned NiCo2S4 and CoS2 nanoarrays with a hollow/porous configuration derived from pentagon-like ZIF-67 are successfully designed and constructed on Ni foam. The hollow/porous structure grown on a conductive matrix can significantly improve electroactive sites, shorten charge/ion diffusion length, and enhance mass/electron transfer. Consequently, the obtained NiCo2S4 possesses an excellent specific capacitance of 939 C/g, a fast charge/discharge rate, and a favorable life span. An advanced asymmetrical supercapacitor is fabricated by engaging NiCo2S4 and CoS2 as cathode and anode materials, respectively, with a well-separated potential window. The obtained device delivers an exceptional energy density of 55.8 W h/kg at 695.2 W/kg, which is highly considerable to the recent transition metal sulfide-based devices. This facile tactic could be employed to construct other electrode materials with superior electrochemical properties.