Electroactive Sites Research Articles

Mesoporous Amorphous Bulk Material Electrodes for Ultrahigh Volumetric Capacity Electrochemical Capacitors.

Retaining satisfactory electrochemical performances under high-mass electrode-active-matter loadings is important for energy storage. However, the performance decreases with increasing mass loadings due to a reduction in the ion/electron transport. In this study, a novel mesoporous amorphous bulk (MAB) material strategy is proposed. Co-based hydroxide KCo1.3 (OH)3.6 is directly electro-deposited on the Ni foam for cathode. Comprehensive structural characterizations confirm the mesoporous, amorphous, and bulk features for KCo1.3 (OH)3.6 . The fabricated whole MAB-KCo1.3 (OH)3.6 @Ni electrode exhibits an ultrahigh full volumetric capacity (123.7 mAh cm-3 ) with high KCo1.3 (OH)3.6 mass loading (11.7mg cm-2 ) and excellent cycling stability. Along with the MAB-KCo1.3 (OH)3.6 , the mesoporous amorphous features enable fast ion diffusion and provide sufficient electroactive sites for redox reactions. In addition, the bulk nature not only facilitates the electron mobility but also guarantees structural and chemical stability. Therefore, the proposed MAB strategy and explored KCo1.3 (OH)3.6 material demonstrate considerable prospects for designing electrode materials and practical applications.

Nanoporous Nonprecious High‐Entropy Alloys as Multisite Electrocatalysts for Ampere‐Level Current‐Density Hydrogen Evolution

Developing robust nonprecious metal‐based electrocatalysts toward hydrogen evolution reaction is crucial for large‐scale hydrogen production via electrochemical water splitting. Herein, surface high‐entropy NiFeCoCuTi alloy on column‐nanostructured nanoporous Ni skeleton is reported as multisite electrocatalyst for highly efficient hydrogen evolution in nonacidic environments by making use of surface heterogeneous atoms with distinct hydrogen and hydroxyl adsorption behaviors to accelerate water dissociation and mediate adsorption of hydrogen intermediates for combination into molecules. Associated with the column‐nanostructured nanoporous Ni skeleton that facilitates electron transfer/mass transportation and enables highly accessible and abundant electroactive sites, self‐supported monolithic nanoporous high‐entropy NiFeCoCuTi alloy electrode exhibits superior nonacidic hydrogen evolution reaction (HER) electrocatalysis, with low onset overpotentials and Tafel slopes. It only takes overpotential of as low as ≈209 mV to deliver ultrahigh current density of 2 A cm−2, along with exceptional stability for more than 240 h, in 1 m KOH electrolyte. These outstanding properties make nanoporous NiFeCoCuTi high‐entropy alloy (HEA) electrode attractive candidate as cathode material in the water electrolysis for large‐scale hydrogen production and suggest HEAs as ideal platform to develop multisite electrocatalysts.

Mixed-phase MoTe2 with exposed edges and rich defects for catalyzing hydrogen evolution reaction with noble-metal-like performance

Exploring low-cost electrocatalysts for the hydrogen evolution reaction (HER) is important in the development of renewable energy storage and conversion technology. Transition metal dichalcogenides, such as MoX2 (X = S, Se or Te), are a promising class of electrocatalysts for HER. However, MoX2 shows poorer catalytic performance than the commercially used platinum catalyst. In this study, we prepared MoTe2 with rich electroactive sites by morphology and defect engineering and investigated its electrocatalytic performance for the HER. The MoTe2 was grown on the surface of a Mo mesh and comprises the 2H and 1T’ phases of MoTe2 mixed evenly in the microscale. The morphology of MoTe2 depends on the cooling rate after its formation on the Mo mesh. A fast cooling process results in volcano-shaped protrusions and a large amount of defects in MoTe2, which facilitates the electrochemical reaction. The mixed-phase MoTe2 delivers better performance than does the commercial 5% Pt/C catalyst in an acidic medium, especially at high current densities. Density functional theory calculations reveal that the Gibbs free energy change for H atom adsorption is close to thermoneutral for both, the 2H and 1T’ phases of MoTe2. Their edges and Te vacancies can serve as active sites for catalyzing HER. This study provides a new strategy for developing inexpensive HER electrocatalysts that function optimally at high current densities.

Three-dimensional porous AuNPs-decorated polyaniline array for ultrasensitive determination of trace Cd(II) and Pb(II) in drinking water

Herein, a three-dimensional porous nanomaterials AuNPs-decorated polyaniline nanowire arrays/carbon nanotube (Au-PANI-array@CNT) was constructed by modified dilute polymerization and redox reaction. The Au-PANI-array@CNT exhibited a larger specific surface area (50.03 m2 g−1) and abundant mesopores (average pore size: 19.6 nm), due to the vertical growth of PANI nanowire arrays on CNT. The Au-PANI-array@CNT composite with a three-dimensional interconnected porous structure exhibited abundant electroactive sites and high adsorption capacity, significantly enhancing the deposition and electrochemical reaction process of heavy metals. The AuNPs embedded on PANI nanowries can provide high catalytic activity and multidimensional electron transport channels, further improving the detection sensitivity. A sensing platform with ultra-high sensitivity (2091, 3890 μA μM−1 cm−2) and lower limit of detection (0.18, 0.15 nM) for Cd(II) and Pb(II) determination was developed based on the three-dimensional porous PANI composite. Furthermore, the sensing mechanism of Au-PANI-array@CNT with Cd(II) was explored by XPS and FTIR spectroscopy. The current response only decreased by 5% after being stored at room temperature for 2 months, indicating that the sensor has high reproducibility and stability. Finally, the analysis of drinking water samples verified the excellent practicability of the sensor for the simultaneous measurement of trace levels (nM) of Cd(II) and Pb(II).

2D coordination unsaturated Ni-MOFs hierarchical nanosheets with internal electric fields for high-performance hybrid supercapacitors

The poor intrinsic electronic conductivity and low-exposure electroactive sites of MOFs limit their practical application in energy storage. Herein, the coordination unsaturated nickel-based metal organic frameworks (Ni-MOFs) were prepared by one-step solvothermal method via adjusting the molar ratio of metal salts to organic ligands (RM/L). The coordination unsaturated degree and morphology of the materials can be controlled by adjusting RM/L. When the RM/L is 2, the obtained Ni-MOF 2:1 is a two-dimensional (2D) hierarchical nanosheets made of interwoven ultra-thin nanoribbons. The 2D hierarchical nanosheets structure of Ni-MOF 2:1 can not only expose more electroactive sites, but also promote ions diffusion. The density functional theory (DFT) simulations reveal that the coordination unsaturated centers can narrow the band gap, thus resetting the internal electric field and improving the conductivity of Ni-MOF 2:1. Benefit from abundant electroactive sites, rapid ions diffusion and improved electrical conductivity, the Ni-MOF 2:1 shows a high specific capacity of 746 C g−1 at 1 A g−1 and excellent cycling stability of 89.7 % capacity retention after 10,000 cycles at 10 A g−1. The hybrid supercapacitor (HSC) assembled with Ni-MOF 2:1 as cathode and activated carbon (AC) as anode has a maximum energy density of 53.1 Wh Kg−1 at 799.9 W Kg−1. This work provides a promising strategy for the rational design of MOFs-based electrode materials for high performance HSC. Moreover, compared with the studies using MOFs derivatives as electrode materials, the direct use of Ni-MOFs as electrode materials in this study is of great significance to avoid energy waste and maintain the inherent advantages of MOFs.

Portable smartphone‐based microfluidic electrochemical immunosensor for ultrasensitive detection of alpha‐fetoprotein in human serum

AbstractRapid and accurate tracing of biomarkers is essential for early detecting and diagnosing of cancer. Therefore, a valid and convenient strategy needs to be developed for efficient monitoring of cancer biomarkers. Herein, we constructed a portable microfluidic electrochemical immunosensor based on three‐dimensional reduced graphene oxide (3D rGO) doped with gold nanoparticles (Au NPs) for ultrasensitive determination of alpha‐fetoprotein (AFP). The designed microfluidic chip, with the advantages of small injection volume, detachable structure and high integration, was fabricated by 3D printing, which only needed 9 μL of reagent to realize the high sensitivity detection. In addition, the 3D Au NPs‐rGO composites with high specific surface area and electrons transfer capacity can effectively increase electroactive sites and enhance electrochemical signals. Benefiting from these features, the 3D Au NPs‐rGO microfluidic electrochemical immunochip showed a wide detection range between 0.1 pg/mL–200 ng/mL and a best detection limit of 0.045 pg/mL with the high sensitivity of 175.008 μA (ng/mL)−1 cm−2. Meanwhile, the proposed immunosensor exhibited reliable AFP detection in human serum samples, which demonstrated that this portable smartphone‐based microfluidic electrochemical immunosensor hold great promises in clinical detection and huge potential in personalized healthcare.

Copper tungstate deposited reduced graphene oxide nanocomposite for highly efficient capacitive deionization

Copper tungstate (CuWO4) decorated 2-dimensional reduced graphene oxide (CWO/rGO) has been successfully fabricated via solvothermal synthesis at 180 °C for 12 h, and then utilized for capacitive deionization (CDI) applications. After deposition of 20 – 40 nm spherical CuWO4 nanoparticles onto few-layered rGO nanosheets, the specific surface area can be up to 338 m2 g−1 with abundant 2 – 10 nm mesopores, which can accelerate the ion transport to augment the electrochemical performance. The CWO/rGO nanocomposite also exhibits high specific capacitances of 380 and 327 F g−1 at 0.5 A g−1 and 5 mV s−1, respectively. Furthermore, the specific electrosorption capacity (SEC) of CWO/rGO is highly dependent on environmental parameters including NaCl concentration, flow rate, applied potential, and solution temperature. An excellent SEC of 54.1 mg g−1 is achieved when 1000 mg L-1 NaCl was used at 1.4 V. Both Faradaic and electric double layer capacitances contribute the electrosorption capacity to the CDI performance of CWO/rGO where CuWO4 provides electroactive sites and rGO enhances the electric conductivity as well as offers mesoporous channels for electrosorption of ions. Meanwhile, the high charge efficiency of 95 %, lower energy consumption of 0.32 kWh m−3, and long-term stability of 50 charging-discharging cycles make the CWO/rGO a potential material for brackish water desalination, which can elucidate on the development of highly efficient desalination technologies.

Hierarchical Ni@CNTs-bridged MoxC/Ni2P heterostructure micro-pillars for enhanced seawater splitting and Mg/seawater battery

In this study, a high-efficiency hybrid catalyst of Ni nanoparticles-encapsulated carbon nanotubes-bridged molybdenum carbide/nickel phosphide heterostructures (Ni@CNTs-MoxC/Ni2P) is prepared via a facile synthesis route. The catalyst having hierarchical structure with rich heterogeneous interfaces of MoxC/Ni2P micro-pillars bridged with Ni@CNTs offers an efficient connection among different active phases to guarantee good conductivity and stability. It also results in large electroactive surface with abundant multiple electroactive sites and creates unique modified electronic properties to effectively increase density of states near the Femi level and well adjust adsorption free energy, thus highly beneficial to simultaneously promote bifunctional OER and HER performances. The Ni@CNTs-MoxC/Ni2P only requires small overpotentials of 54 mV for HER and 228 for OER at 10 mA cm–2 in alkaline electrolyte, superior to recently reported bifunctional catalysts. The electrolyzer cell of Ni@CNTs–MoxC/Ni2P(+,-) requires a low operating voltage of 1.53 and 1.56 V at 10 mA cm–2 in alkaline freshwater and natural seawater, respectively. The Mg/seawater battery from Ni@CNTs–MoxC/Ni2P-based cathode exhibits a high peak power density of 7.01 mW cm−2 with a stable discharge period of 100 h. The results suggest that Ni@CNTs-MoxC/Ni2P is a promising candidate for future seawater splitting and prospective Mg/seawater battery application.

L-Cysteine anchored Co-MOF derived cobalt-nitrogen-carbon hierarchical architecture as an efficient sensor for the electrochemical detection of catecholamine

Dopamine (DA) is considered a critical neurotransmitter related to different neurological disorders. Therefore, finding a sensitive and selective technique for the early diagnosis of these diseases is important. Herein, we used a cobalt-nitrogen and sulfur-doped carbon hierarchical architecture (Co-N,S-C) as a sensor for the detection of DA. The synthesized materials were characterized by various physicochemical techniques. The obtained hierarchical material doped with heteroatoms not only provided sufficient electroactive sites but also enhanced the conductivity of the materials. The electrochemical properties and catalytic activity of the Co-N,S-C-modified glassy carbon electrodes were investigated using cyclic voltammetry, impedance spectroscopy, linear swift voltammetry (LSV), and square wave voltammetry (SWV). The SWV indicates that the sensor provides a wide linear range of 5–115 µM and a lower limit of detection (0.43 µM) for DA. The developed sensor was successfully utilized for the electrochemical detection of DA in human urine samples, with high accuracy and reliability. Hopefully, our method will be helpful for the detection of other neurotransmitters in the near future.

Nanorod Array-Based Hierarchical NiO Microspheres as a Bifunctional Electrocatalyst for a Selective and Corrosion-Resistance Seawater Photo/Electrolysis System

Utilizing earth-abundant seawater over scarce freshwater for hydrogen fuel production via water electrolysis is a promising/sustainable strategy. However, the serious anodic corrosion due to the competing chloride oxidation reaction significantly hampers the overall stability of the electrolyzer. Therefore, it demands an efficient and robust catalyst with high selectivity and corrosion resistance for direct seawater splitting. Here, we present a bifunctional catalyst developed by morphology engineering to form nanorod array-based hierarchical NiO microspheres (NRAHM-NiO) as a three-dimensional (3D) hierarchical oxide/hydroxide urchin-like structure material for highly selective seawater splitting against chloride oxidation. Benefitting from highly intrinsic electroactive sites, good charge transferability, fast-releasing gas bubbles, and corrosion resistance as well as hydrophilic surface, the NRAHM-NiO exhibits outstanding bifunctional hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalytic activity toward selective and durable overall seawater splitting. The system requires small cell voltages of 1.66 and 2.01 V to drive current densities of 100 and 500 mA cm–2 at room temperature, respectively. Such catalytic activity is superior compared to the benchmark Pt/C(−)||Pt/C(+) and Pt/C(−)||IrO2(+) pair systems. Importantly, this device demonstrates specific stability as well as selectivity toward the OER in seawater with 99% faradaic efficiency without forming any chlorine species. The experimental results are well supported by density functional theory (DFT) calculations. Powered by a single solar cell, the integrated photolysis system shows 9.9% solar-to-hydrogen (STH) efficiency.

MOF-derived flower-like ZnCo2O4/ZnO nanoarchitecture as a high-performance battery-type redox-active electrode material for hybrid supercapacitor applications

Implementing a facile and efficient strategy to fabricate the multi-component metal oxide nanocomposites as the high-efficient electroactive electrode materials have gathered the limelight for effective energy storage applications. However, the reasonable design and development of such materials is still a significant challenge to meet the energy storage capability. Herein, we report a bottom-up strategy to fabricate a flower-like ZnCo2O4/ZnO (ZCO/ZnO) nanoarchitecture via thermal decomposition of a metal-organic framework (MOF). The unique flower-like ZCO/ZnO nanoarchitecture provides a fruitful channel for rapid electron and ion transportation and offers abundant electroactive sites for the battery-type Faradaic charge storage process. Interestingly, the multi-component ZCO/ZnO electrode reveals a specific capacitance of (Csp) of 803 F g−1 at a specific current of 1 A g−1 as compared to its counterparts (ZCO and ZnO). Even at a high specific current of 20 A g−1, a superior Csp of 538 F g−1 can be achieved, signifying the high-rate performance of the ZCO/ZnO electrode. In addition, the hybrid supercapacitor of ZCO/ZnO//AC depicts the Csp of 161 F g−1 at a specific current of 1 A g−1. It delivers a high specific energy of 50.41 Wh kg−1 at a specific power of 710.49 W kg−1, with excellent cyclic retention of around 91.04% over 10,000 cycles. Hence, this strategy could enlighten a pathway to fabricate promising electrode materials for high-performance electrochemical energy devices.

Manganese oxide embedded graphene nanohybrid for pH-universal electrochemical overall water splitting

Efficient non-noble metal bifunctional electrocatalysts for overall water splitting in pH universal is highly desired in application. Herein, MnO2/graphene composition are applied as efficient electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in pH-universal electrolytes with the help of plasma dc arc method. The couple of MnO2 and graphene highly benefits to the H2O, H+ and OH− absorption respectively. The defects and stable Mn3+ contribute to the transfer of electron and charge. The low overpotentials and small Tafel slopes reveal attractive activities of HER and OER. The good electrocatalytic performances are attributed to the synergistic effect and abundant heterogeneous interfaces in MnO2/graphene. These can offer rich electroactive sites and accelerate electron transfer. Thus, it may provide facile route for developing nonprecious electrocatalysts of water splitting.

Hollow 1D carbon tube core anchored in Co3O4@SnS2 multiple shells for constructing binder-free electrodes of flexible supercapacitors

The design of the core@multi-shell metal sulfide hollow tube is of great importance for various supercapacitor electrodes. Herein, a hollow carbon tube (HCT) core@multi-shell with rich pores is developed for constructing the binder-free flexible electrodes (HCT-x@Co3O4@SnS2). The inner core–shell is derived from the zeolitic imidazole framework (ZIF)-8@ZIF-67 porous carbon tube and is engineered with vertically aligned SnS2 nanosheets. The unique inner core–shell and the outer-shell SnS2 contribute to the excellent characteristics, including abundant pores and channels for the rapid ion transport and storage, high specific surface area, improved electrical conductivity, and additional electroactive sites for the faradaic reaction. Thanks to the synergies between the unique 1D porous hollow structure and the different components, the as-fabricated HCT-2@Co3O4@SnS2 electrode exhibits a high specific capacitance of 439 F/g at 1 A/g. Moreover, the assembled flexible supercapacitor also demonstrates a remarkable energy density of 40.22 Wh kg−1, the corresponding power densities of 750.22 W kg−1, and long cycle life. In addition, no structural deformation and capacitance loss are observed in the bended devices. The developed approach provides a facile structure design route for the flexible binder-free electrode preparation of flexible energy storage applications.

Advanced hybrid supercapacitors assembled with beta-Co(OH)2 microflowers and microclews as high-performance cathode materials

Supercapacitors (SCs) have received increasing attention thanks to their high power density, cyclic stability, and quick charging capability. Herein, a battery-type beta-Co(OH)2 electrode materials including two types of microstructures of nanosheets-assembled microflowers (MFs) and nanowires-based microclews (MCs) have been prepared through a three-step synthetic method, which contains an initial solvothermal reactions, aging the precursor in water, and final hydrothermal treatment. The mixed solvent of glycerol and isopropanol with different volume ratio in the first solvothermal stage has a crucial impact on the formation of different microstructures. Both the MFs and MCs possess huge surface area, and may provide abundant electro-active sites for further Faradic reactions. After they were tested in different electrode systems, it was found that the β-Co(OH)2 MFs presented a specific capacity of 396.5 C g−1 (1 A g−1) along with a rate of 81.2% at 10 A g−1, and the MCs exhibited an inferior capacity of 303.9 C g−1. In order to further assess the potential of practical applications in SCs, a hybrid supercapacitor (HSC) device was designed by choosing activated carbon (AC) as negative electrode. The β-Co(OH)2 MFs//AC device exhibited 158.6 C g−1 and an energy density (Ed) of 43.6 W h kg−1. In contrast, the β-Co(OH)2 MCs//AC HSC showed lower Ed of 34.1 W h kg−1 at 954.7 W kg−1. Both HSCs exhibited brilliant cycling stability over 5000 continuous cycles at 6 A g−1. Such impressive electrochemical response of β-Co(OH)2 MFs & MCs makes them the suitable candidates to assemble advanced HSC devices with high-performance, and may anticipate their promising application prospect in the near future.

Impact of cation substitution in NiCo2O4 spinel on morphology and electrochemical performance

Nanostructured NiCo2O4 spinel is the most appealing candidate to be used as the electrode for supercapacitors due to its significant merits such as eco-friendliness, low cost and easy availability. Introduction of a secondary metal cation into the host NiCo2O4 could provide more electroactive sites with rich redox chemistry. Herein we report the influence of cation (Zn/Mn) doping on the physicochemical and electrochemical properties of easily synthesized NiCo2O4 spinel. After being doped with Zn/Mn the morphology of NiCo2O4 was notably changed and specific capacitance of NiCo2O4 was greatly enhanced. Mn doped NiCo2O4 nanorod bundles store more internal surface charge than Zn doped NiCo2O4 flowers. A maximum specific capacitance of 1494 F/g was delivered by Mn doped NiCo2O4 nanorod bundles with a good rate capability (capacity retention of 64 % from 1 to 20 A/g) and excellent cycling stability (88.6% of initial value after the completion of 5000 cycles). An asymmetric device fabricated using Mn substituted NiCo2O4 as the positive electrode achieved an energy density of 12 Wh/kg at a power density of 427 W/kg and could efficiently light up a light emitting diode.

Mixed-phase composites derived from cobalt terephthalate as efficient battery-type electrodes for high-performance supercapattery

Interfacial engineering of two-dimensional (2D) monometallic phosphides enables remarkable structural and electrochemical properties in energy storage devices. Herein, 2D nanosheets (NSs) of FeP2/Co2P were grown on Ni-foam (FCP) using a solution-based and phosphorization approach to be used as freestanding for high-performance energy storage devices. An effective phosphorization strategy is successfully developed to improve the overall crystalline phase, tailor the morphology, and boost the electrochemical performances of electrodes. The FCP NSs electrode exhibits a battery-type redox behavior with a maximum high areal capacity of 1.96 C cm–2 at 4 mA cm–2 in 6 M KOH aqueous electrolyte compared to the other counterparts. The superior electrochemical performance was achieved by increasing the electroactive sites and high conductivity via surface tailoring and fast redox reactions. Moreover, a supercapattery was assembled utilizing FCP and activated carbon (AC) electrodes and it revealed maximum specific energy (Es) and specific power (Ps) of 41.2 Wh kg–1 and 7578 W kg–1 with good cycling stability of 91% after 10,000 cycles at 5 A g–1. Eventually, the supercapattery has been explored in practical applications by lighting up light-emitting diodes (LEDs), representing the real-time performance of superior energy storage devices.

Direct growth of cobalt-doped nickel vanadate shelf-like architectures on Ni foam electrodes for solid-state alkaline battery

Controlled-engineering on the phase and morphology of the metal vanadates is thought of as an impactful protocol for boosting electrochemical properties in terms of generating active sites and increasing intrinsic conductivity. A new perspective on a high-performance solid-state alkaline battery made of Co-doped Ni3V2O8 (NCV) directly grown on Ni foam (NF) and Bi2O3-NiO composite electrodes, prepared by a simple hydrothermal method, is presented here. Incorporating Co dopants into high-crystalline nickel vanadate with a novel shelf-like architecture enables more electroactive sites, strengthens the electronic conductivity, as well as enriches redox chemistry. The optimized NCV/NF electrode demonstrated consistent cycling behavior and a high discharge specific capacity of 255.82 mAh g−1 at 1 A g−1. Moreover, the counter electrode of the Bi2O3-NiO composite exhibits a nest-like morphology (consisting of NiO nanowires embedded in Bi2O3 nanoflakes) and provides a very high surface area and an optimum discharge specific capacity of 204.76 mAh g−1 (@ 1 A g−1), with good cycling stability. In particular, the solid-state alkaline battery (SSAB) configuration of NCV/NF//Bi2O3-NiO achieves an ultrahigh energy density of 80.4 Wh kg−1 at a power density of 900.86 W kg−1 with nearly 90% of specific capacity retention even after 8000 cycles. The superior performance of the SSAB device indicates promise in the portable electronics and industrial sectors.

Hybrid of pyrazine based π-conjugated organic molecule and MXene for hybrid capacitive deionization

In this work, we report a hybrid material of pyrazine based π-conjugated organic molecule, hexaazatrinaphthalene (HATN), and MXene. In this hybrid, MXene serves as a conductive substrate and HATN provides multiple electroactive sites, which are jointly combined to build a unique 3D structure with more ion transport channels for accelerating the charge transfer and ion diffusion rates. The as-obtained HATN/MXene composite displays a superior desalination capacity of 57.5 mg g−1 with an excellent desalination rate of 13.2 mg g−1 min−1 and good long-term stability. This work provides a meaningful guidance for designing and applying organic molecules in capacitive deionization field.

Fabrication of CoS2-MoS2 heterostructure via interface engineering toward efficient dual-pH hydrogen evolution

Modulation of electronic structure via heterointerface engineering is regarded as an appealing strategy to promote the hydrogen evolution reaction (HER) performance of a pH-universal electrocatalyst. Herein, the CoS2-MoS2 heterostructure is synthesized, where MoS2 nanosheets are vertically anchored on CoS2 microflakes. Plentiful heterogeneous nanointerfaces generated between MoS2 and CoS2 phases not only provide sufficient electroactive sites and structural defects, but also afford a hierarchically porous structure. The synergistic modulation of electronic and geometric structures accounts for a superb catalytic activity and long-durability of CoS2-MoS2 toward HER in acidic and alkaline solutions simultaneously, in terms of the overpotential in 0.5 M H2SO4 (218 mV versus RHE) and 1.0 M KOH (251 mV) at a current density of 10 mA cm−2. This work offers an exciting avenue for fabricating transition metal sulfides as efficient wide-pH electrocatalysts through an interface-induced strategy.

Interface engineering of a hollow core-shell sulfur-doped Co2P@Ni2P heterojunction for efficient charge storage of hybrid supercapacitors

Transition metal phosphides (TMPs) are widely used as supercapacitor energy storage materials due to their abundant valence and high theoretical capacity, but their poor electrical conductivity and low active material utilization lead to low actual capacity and slow kinetics. Herein, we demonstrate the excellent electrochemical properties of sulfur-doped Co2P@Ni2P heterojunction materials prepared using a combination of hydrothermal, ion-exchange and low-temperature annealing approaches. For sulfur-doped Co2P@Ni2P, hollow core-shell microstructures increase the number of electroactive sites and provides a shortcut for electron transport, while sulfur doping promotes the transfer and rearrangement of interfacial charge from Co2P to Ni2P, optimizing the redox ability of the active component. In addition, the S doping and the highly electrochemically active nickel-cobalt phosphide synergistically accelerate the charge transfer, which leads to fast reaction kinetics. Therefore, the obtained S-Co2P@Ni2P exhibits an optimal specific capacity of 1200 C g−1 at 1 A g−1 and excellent rate performance. Furthermore, when combined with activated carbon (AC) for hybrid supercapacitor (HSC), the S-Co2P@Ni2P//AC device shows an excellent energy density of 41.5 Wh kg−1 and a high-capacity retention of 93 % after 15,000 cycles. This work provides a novel approach for the exploration of high-performance and stable phosphorus-based battery-like supercapacitor materials.