Conductive Ni Foam Research Articles

Learning from Nature: Constructing a Smart Bionic Structure for High‐Performance Glucose Sensing in Human Serums

AbstractTraditional noble metal‐based catalysts for glucose sensing usually suffer from easy deactivation by halides and weak sensing properties. To unravel these limits, herein, a novel nature‐inspired design concept (mimicking a “rock–soil–grass” geotexture system) is purposed to build a free‐standing hierarchical micro‐nano architecture. Thanks to the design (rigid and conductive Ni foam) (“rock”, underlayer, rough and highly disordered graphene nanosheets (GNSs) (“soil”, middle‐layer), and strong catalytic activity of multiscale grass‐like Co3O4 (“grass”, top‐layer), the bionic structure achieves ultra‐high sensitivity, a low limit of detection (120 × 10−9 m), an extremely short response time, broad linear ranges (two stages: 1–10 000 and 10 000–30 040 µm), good anti‐Cl−‐poisoning and anti‐interference properties, and long‐term stability. Besides the structural design, the “gotong‐royong” effects (the strong interface coupling and charge transfer between GNSs and Co3O4 and energetically favorable glucose adsorption on Co3O4) also contribute to the high sensing properties, as verified by kinetic studies and density functional theory simulation. To determine human blood glucose levels, the self‐made glucometer with the self‐developed software demonstrates an ultra‐high recovery rate (99.0–100.9%), validating the potential for high‐performance blood‐glucose sensing.

Self-supported hierarchical P,Cu-codoped cobalt selenide nanoarrays for enhanced overall water splitting

Highly efficient electrocatalysts with low cost for electrochemical water splitting is important for the intermediate energy conversion. In the present work, P and Cu dual-doped cobalt selenide nanoarrays with hierarchical structure were fabricated via a facile hydrothermal method, involving in-situ growth on a self-supported conductive Ni foam substrate (P,Cu-Co0.85Se/NF). The overall water splitting (OWS) performance of the catalysts was systematically studied in alkaline solution. Compared to single-ion-doped or pure Co0.85Se, dual incorporation of the anion and cation can contort the lattice and induce powerful electronic interactions, thereby exposing abundant catalytic sites and optimizing the adsorption energy of the reaction intermediates. Benefiting from the merits of P, the Cu-co-doped Co0.85Se/NF electrode exhibited outstanding catalytic activity towards hydrogen evolution reaction (HER), generating a 10 mA cm−2 current density at the overpotential of 96.8 mV in 1 M KOH, and the overpotential is 300 mV towards oxygen evolution reaction (OER) with the current density of 100 mA cm−2. Furthermore, when applied it to fabricate OWS cell, the cell voltage is as low as 1.57 V at the current density of 10 mA cm−2. This present work broaden the potential application of the electrocatalytic performance of transition metal dichalcogenides.

Highly electrochemically‐active surface area of Ni (OH)2 with petal structure in situ grown on conductive Ni foam for efficient hydrogen evolution reaction

An highly electrochemically active surface area and the efficient carrier transfer between catalysts and their carriers are the basis of an efficient hydrogen evolution reaction (HER). Here, petal‐like Ni (OH)2 nanosheets with tunable size and thickness, which represent controllable electrocatalytically active areas, are directly grown on conductive Ni foam. As a result, the optimized in situ‐grown Ni (OH)2 nanosheets (NSNs) show optimum HER performance and stability compared to step‐by‐step‐grown NSNs with similar surface areas due to the enhanced carrier transfer efficiency. The in situ NSNs show high HER activity with overpotentials of 187 and 137 mV with respective current densities of 20 and 10 mA cm−2 in alkaline solution. Our work affords a simple and reliable method for future catalyst design.

Metal-organic framework derived Co9S8/Ni3S2 composites on Ni foam with enhanced electrochemical performance by one-step sulfuration strategy for supercapacitors electrode

Electrode materials with excellent performance are urgently demanded for supercapacitors. Herein, heterogeneous nanostructure Co9S8/Ni3S2 supported on conductive Ni foam (Co9S8/Ni3S2/NF) is fabricated using zeolite imidazole frameworks (ZIFs) as the sacrificial template. The Co9S8/Ni3S2/NF electrode shows an outstanding specific capacitance of 1356 F g−1 at a current density of 1 A g−1 and still remained 1145 F g−1 at 10 A g−1. The enhanced electrochemical performance should be attributed to the superior structural characteristics, the abundant active sites, the rich redox reactions, the strongly synergistic effect in heterogeneous sulfide composition and the good conductivity resulted from the NF and the Co9S8/Ni3S2/NF. Meanwhile, to further evaluate the practical application value of the Co9S8/Ni3S2/NF electrode, a hybrid supercapacitors (HSCs) device is constructed using Co9S8/Ni3S2/NF as positive electrode and activated carbon (AC) as negative electrode, and it displays a high energy density of 48.2 Wh kg−1 at a power density of 799.6 W kg−1 and a superior long-term cycling stability with 82% of initial capacitance after 8000 cycles. In addition, two as-assembled capacitors in series can light 7 LED bulbs. This strategy of obtaining multi-metal sulfides from Co/Ni-ZIF precursor provides a new perspective to design and develop electrode materials for high-performance hybrid supercapacitors.

The in-situ construction of NiFe sulfide with nanoarray structure on nickel foam as efficient bifunctional electrocatalysts for overall water splitting

Developing high-efficiency, stable and cost-effective non-noble metal-based bifunctional electrocatalysts is crucial for the overall water splitting to produce clean hydrogen energy. Nanoarray structures electrocatalysts have attracted increasing research interests due to its structural advantages. Herein, Ni3S2/Fe9S10 with two dimensions (2D) nanosheet arrays in-situ growth on three dimensions (3D) nickel foam (Ni3S2/Fe9S10@NF) was prepared by step-wise hydrothermal method. Ni3S2/Fe9S10@NF was derived from NiFe layered double hydroxides, and the as-prepared Ni3S2/Fe9S10@NF electrode was directly served as a bifunctional catalyst for electrolysis of water. Benefiting from the directly contact with conductive Ni foam substrate, the positive synergy effect between Ni and Fe in the Ni3S2/Fe9S10@NF catalyst and its open 3D porous structure, the binder-free and integrated Ni3S2/Fe9S10@NF electrode displayed excellent catalytic activities towards hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), the overpotential for HER and OER are only 56 and 147 mV at 10 mA cm−2, respectively. Particularly, when the prepared Ni3S2/Fe9S10@NF further employed as both the cathode and anode electrocatalysts a symmetric cell Ni3S2/Fe9S10@NF|| Ni3S2/Fe9S10@NF, a low cell voltage of 1.43 V was achieved at 10 mA cm−2, with good stability. This work not only illustrated that non-noble metal-based electrocatalysts have tremendous potential applications for electrocatalytic electrolysis of water but also provided a feasible strategy to prepare high-efficiency and stable non- precious metal catalysts.

NiMoO4@Ni3S2 core–shell composites grown in situ on nickel foam for applications in supercapacitors

A binder-free Ni3S2 nanosheets wrapped NiMoO4 nanorods hybrid electrode (NiMoO4@Ni3S2) was prepared on conductive Ni-foam via a simple two-step hydrothermal process. The microstructure and chemical composition of as-prepared NiMoO4@Ni3S2 core–shell hybrid electrode was confirmed by means of SEM, TEM, XRD, and XPS. The SEM analysis results demonstrated that the NiMoO4@Ni3S2 composites consisted of NiMoO4 nanorods in the core, which were surrounded by a myriad of Ni3S2 nanosheets in the shell. Electrochemical characterization revealed that the integrated structure of the NiMoO4@Ni3S2 electrode exhibited a high areal capacitance (2.3 F cm−2 at areal current density of 1 mA cm−2), which was 1.8 times than the NiMoO4 nanorods, excellent rate performance and outstanding cycling performance (84.4% retention at 30 mA cm−2 after 6000 cycles). An asymmetric capacitor assembled with NiMoO4@Ni3S2 core–shell composites and AC as the positive and negative electrodes, respectively, delivered a maximum area energy density of 158.4mWhcm−2 at an area power density of 2.199 W cm−2, and exceptional capacitance retention of 93.1% after 20k cycles. With such outstanding electrochemical performance, this NiMoO4@Ni3S2 electrode material will have a potential application value in the field of portable and flexible energy storage equipment.

3D heterogeneous ZnCo2O4@NiMoO4 nanoarrays grown on Ni foam as a binder-free electrode for high-performance energy storage

3D heterogeneous ZnCo2O4@NiMoO4 core-shell nanowire/nanosheets nanoarrays (3D ZnCo2O4@NiMoO4 NAs) grown on the conductive Ni foam substrate was successfully synthesized by a two-step simple water bath heating method. The prepared composites were characterized by XRD, FESEM, and TEM and were found to ZnCo2O4 nanowires acted as the core and the NiMoO4 nanosheets covered as the shell. Using as a supercapacitor electrode, 3D ZnCo2O4@NMioO4 NAs/Ni foam demonstrate a high specific capacitance 1912 F g−1 (at the current density of 1 A g−1) and excellent rate capability (55% initial capacity retention at 20 A g−1). Furthermore, the asymmetric supercapacitors constructed with the anode (carbon nanotubes/Ni foam) and the cathode (3D ZnCo2O4@NiMoO4 NAs/Ni foam) exhibit excellent performances in energy storage. This solid-state device shows high specific energy 57.5 Wh∙Kg−1(at specific power density of 900 W∙Kg−1) and high specific power 18000 W∙Kg−1(at specific energy of 30 Wh∙Kg−1) by broaden the potentials range from 0 V to 1.8 V. These superior results of 3D ZnCo2O4@NiMoO4 NAs mainly comes from the synergistic effect of 3D array microstructure of the conductive ZnCo2O4/Ni foam and the nanosheet structure of NiMoO4. The ZnCo2O4/Ni foam can provide facial routes for the transfer of the ions and electrons and the nanosheet structure is benefit for the intercalation-deintercalation processes of OH− ions in the NiMoO4. This work provides a new strategy for the preparation of high-performance supercapacitor electrode.

Dual Improvement of β‐MnO2 Oxygen Evolution Electrocatalysts via Combined Substrate Control and Surface Engineering

AbstractThe development of catalysts with high intrinsic activity towards the oxygen evolution reaction (OER) plays a critical role in sustainable energy conversion and storage. Herein, we report on the development of efficient (photo)electrocatalysts based on functionalized MnO2 systems. Specifically, β‐MnO2 nanostructures grown by plasma enhanced‐chemical vapor deposition on fluorine‐doped tin oxide (FTO) or Ni foams were decorated with Co3O4 or Fe2O3 nanoparticles by radio frequency sputtering. Upon functionalization, FTO‐supported materials yielded a performance increase with respect to bare MnO2, with current densities at 1.65 V vs. the reversible hydrogen electrode (RHE) up to 3.0 and 3.5 mA/cm2 in the dark and under simulated sunlight, respectively. On the other hand, the use of highly porous and conductive Ni foam substrates enabled to maximize cooperative interfacial effects between catalyst components. The best performing Fe2O3/MnO2 system provided a current density of 17.9 mA/cm2 at 1.65 V vs. RHE, an overpotential as low as 390 mV, and a Tafel slope of 69 mV/decade under dark conditions, comparing favorably with IrO2 and RuO2 benchmarks. Overall, the control of β‐MnO2/substrate interactions and the simultaneous surface property engineering pave the way to an efficient energy generation from abundant natural resources.

Trimetal-based N-doped carbon nanotubes arrays on Ni foams as self-supported electrodes for hydrogen/oxygen evolution reactions and water splitting

Rational design of non-noble metal-based bifunctional electrocatalysts for hydrogen evolution reactions (HER) and oxygen evolution reactions (OER) is still a challenge in water splitting. Herein, a MOF-on-MOF (MOF = metal-organic framework) strategy is developed to obtain trimetal-based nitrogen-doped carbon nanotubes arrays loaded on nickel foams (denoted as FeNiCo@NC/NF). Benefiting from the superior compositional and structural feature, FeNiCo@NC/NF self-supported electrodes exhibit excellent bifunctional HER and OER activity with a low overpotential of 145 and 245 mV at 10 mA cm−2. When simultaneously used as cathode and anode for water splitting, it only requires 1.61 V to achieve 10 mA cm−2 and even outperforms the benchmark electrode couple of Pt/C||RuO2 at higher current densities. Studies discover that trimetallic FeNiCo nanoparticles can provide more synergetic metal active sites, interconnected N-doped carbon nanotubes arrays can offer more effective electron transports channels, and conductive Ni foam substrate can reduce the internal impedance of the material. Density functional theory (DFT) calculations also demonstrate that FeNiCo@NC/NF electrode possesses a favorable Gibbs free energy of hydrogen adsorption (ΔGH*) value of −0.13 eV, which is benefit for its superior HER activity. Overall, our work reports an efficient self-supported electrode for hydrogen/oxygen evolution reactions and water splitting.

Improved H2 production of ZnO@ZnS nanorod-decorated Ni foam immobilized photocatalysts

ZnO@ZnS nanorod-decorated Ni foam was prepared as a self-supported photocatalyst for hydrogen generation through a two-step method, including the formation of the ZnO nanorod core by a hydrothermal method, and the fabrication of the ZnS shell by a sulfidation method. The impact of the ZnS shell thickness was studied, including the influence on the optical properties, surface wettability, separation of photoexcited charge carriers, and photocatalytic hydrogen generation performance. Formation of the core-shell ZnO@ZnS structure and the incorporation of the conductive Ni foam substrate can enhance the separation of photoexcited carriers of the immobilized photocatalyst. The formation of ZnO@ZnS nanorods on the Ni foam resulted in a change in the surface from hydrophobic to superhydrophilic. The porous texture of the Ni foam facilitates the effective contact between the sacrificial agent and the immobilized photocatalyst. The ZnO@ZnS/Ni foam photocatalyst that was synthesized using a sulfidation time of 4 h, (namely, NZS4), exhibited H2 generation activity of 5860 μmol g−1 h−1, which is approximately three-fold that of the ZnO/Ni foam photocatalyst (named NZ). After being reused for three cycles, with a simple washing between cycles, the NZS4 photocatalyst retained 90% of its hydrogen generation activity.

In situ direct growth of flower-like hierarchical architecture of CoNi-layered double hydroxide on Ni foam as an efficient self-supported oxygen evolution electrocatalyst

Exploring economical, efficient and robust electrocatalysts toward the oxygen evolution reaction (OER) is one of the key issues in water splitting technology. Nanostructure engineering of electrocatalysts and hybridizing active species with a conductive support represent powerful strategies to enhance the electrocatalytic performance. Herein, we report a facile one-step solvothermal method to directly grow 3D CoNi-layered double hydroxide (LDH) flower-like architectures onto porous and conductive Ni foam (NF) substrate (denoted as CoNi-LDH(2:1)@NF hereafter). The flower-like hierarchical architecture of CoNi-LDHs with open configurations endows CoNi-LDH microflowers with sufficient accessible active sites and efficient mass diffusion paths. Moreover, the in situ direct growth manner ensures an intimate contact between the electroactive CoNi-LDHs and NF substrate and thus the charge transfer resistance is reduced. Consequently, the as-formed self-supported and binder-free electrode of CoNi-LDH(2:1)@NF exhibits an outstanding OER performance with a small overpotential of 283 mV at a relatively large current density of 50 mA cm−2 and a remarkable long-term electrochemical durability in 0.1 M KOH solution, holding great promise in practical scale-up water electrolysis. The present study may open a new avenue to design and fabricate cost-effective and high-efficiency electrocatalysts for energy conversion applications.

A High-Energy-Density Hybrid Supercapacitor with P-Ni(OH)2 @Co(OH)2 Core-Shell Heterostructure and Fe2 O3 Nanoneedle Arrays as Advanced Integrated Electrodes.

Transition metal hydro/oxides (TMH/Os) are treated as the most promising alternative supercapacitor electrodes thanks to their high theoretical capacitance due to the various oxidation states and abundant cheap resources of TMH/Os. However, the poor conductivity and logy reaction kinetics of TMH/Os severely restrict their practical application. Herein, hierarchical core-shell P-Ni(OH)2 @Co(OH)2 micro/nanostructures are in situ grown on conductive Ni foam (P-Ni(OH)2 @Co(OH)2 /NF) through a facile stepwise hydrothermal process. The unique heterostructure composed of P-Ni(OH)2 rods and Co(OH)2 nanoflakes boost the charge transportation and provide abundant active sites when used as the intergrated cathode for supercapacitors. It delivers an ultrahigh areal specific capacitance of 4.4 C cm-2 at 1 mA cm-2 and the capacitance can maintain 91% after 10 000 cycles, showing an ultralong cycle life. Additionally, a hybrid supercapacitor composed with P-Ni(OH)2 @Co(OH)2 /NF cathode and Fe2 O3 /CC anode shows a wider voltage window of 1.6 V, a remarkable energy density of 0.21 mWh cm-2 at the power density of 0.8 mW cm-2 , and outstanding cycling stability with about 81% capacitance retention after 5000 cycles. This innovative study not only supplies a newfashioned electronic apparatus with high-energy density and cycling stability but offers a fresh reference and enlightenment for synthesizing advanced integrated electrodes for high-performance hybrid supercapacitors.

Hierarchical nickel–cobalt oxide and glucose-based carbon electrodes for asymmetric supercapacitor with high energy density

Combining hierarchical nickel–cobalt oxides (NCO) with cost-effective glucose-based carbons could be attractive electrode materials for high-performance supercapacitor. The bimetallic nickel (Ni) and cobalt (Co) hydroxide was directly electrodeposited for 120, 180, 300, 480, and 600 s, respectively, on a conductive Ni foam as the NCO/Ni electrodes. The (NCO/Ni)-480 electrode showed the highest capacitance among NCO/Ni electrodes. Furthermore, an asymmetric supercapacitor (ASC) was assembled by utilizing (NCO/Ni)-480 as a positive electrode and glucose-based activated-carbon coated on Ni foam, (G-AC)/Ni, as a negative electrode in solid state carboxymethyl cellulose-lithium nitrate (CMC-LiNO3) gel electrolyte. At the potential window of 1.5 V, the device exhibits a prominent energy density of 45.3 Wh kg−1 at a power density of 0.743 kW kg−1 (1 A g−1) and excellent cycling stability of 89.7% of the initial capacity retention over 10,000 cycles. The outstanding electrochemical performances of the ASC can be ascribed to the synergistic effect of hierarchical Ni–Co oxides, mesoporous G-AC, three-dimensional Ni foam collector, and binder-free preparation, which facilitates a faster diffusion of the electrolyte ion into the electrode material and provides a stronger adhesion of active materials with the current collector.

Preparation and performances of 3D hierarchical core-shell structural NiCo2S4@NiMoO4·xH2O nanoneedles for electrochemical energy storage

Elaborate design and controllable synthesis of 3D hierarchical structure electrode materials, which overcome the single role of pure materials and generate interface effect between structures, are crucially important for enhancing the electrochemical performance of supercapacitor. Herein, we develop a facile synthesis route for novel 3D electrode material of supercapacitor with hierarchical core-shell structure NiCo2S4@NiMoO4•xH2O nanoneedle-like arrays immobilized on conductive Ni foam substrate. The self-supported NiCo2S4@NiMoO4•xH2O electrode can effectively enhance the conductivity between NiCo2S4 and NiMoO4, avoiding the agglomeration of NiMoO4•xH2O nanosheets, which enables much more electroactive sites for faradaic reactions. Therefore, the as-prepared NiCo2S4@NiMoO4•xH2O electrode acquires a high specific capacity of 830.2 F g−1 at 2 A g−1, which is much higher than that of single NiCo2S4 or NiMoO4•xH2O. Subsequently, the NiCo2S4@NiMoO4•xH2O electrode is assembled into an asymmetric supercapacitor, which shows a high energy density of 19.3 Wh kg−1 at 795.7 W kg−1. Besides, it also exhibits an outstanding cycling stability with 89.9% capacitance retention after continuous 5000 cycles at 1 A g−1, indicating its promising applications in high-performance supercapacitors.

Molybdenum Selenide nanosheets Surrounding nickel Selenides Sub-microislands on nickel foam as high-performance bifunctional electrocatalysts for water Splitting

Transition metal selenides supported on three-dimensional metal foams have attracted extensive attention as promising electrocatalysts for water splitting. Herein, the direct growth of misaligned and intertwined molybdenum selenide nanosheets surrounding nickel selenide sub-microislands on nickel foam (denoted as Mo–Ni–Se@NF) was demonstrated via a simple one-step hydrothermal approach. The as-prepared Mo–Ni–Se@NF demonstrates excellent electrocatalytic activity for hydrogen evolution reaction (HER) in alkaline electrolyte, demanding a low overpotential of 113 mV to achieve the current density of 10 mA cm−2, and a small Tafel slope of 85.7 mV dec−1. It also displays good catalytic performance towards oxygen evolution reaction (OER) with an overpotential of 397 mV at the current density of 100 mA cm−2, and a Tafel slope of 44.9 mV dec−1. Moreover, when applied as both anode and cathode in a two-electrode electrolyzer for overall water splitting, low voltages of 1.583 and 2.098 V are allowed to reach the current densities of 20 and 100 mA cm−2, respectively. Large electrochemical surface area, low electron-transfer resistance, and good stability were demonstrated during the test. The superior activity of Mo–Ni–Se@NF is largely attributed to the seamless integration of the three-dimensional and conductive Ni foam substrate, the direct growth of molybdenum selenide nanosheets on Ni foam with sufficient active sites, and the metallic nickel selenide sub-microislands with good activity and electronic conductivity for the electrons transfer from the substrate to the active sites on molybdenum selenide nanosheets during electrocatalytic process. This work can inspire the optimal design of bimetal selenides on metal foam as efficient and low-cost electrocatalysts for overall water splitting.

Engineering RuO2 on CuCo2O4/CuO nanoneedles as multifunctional electrodes for the hybrid supercapacitors and water oxidation catalysis

Abstract Currently, designing and constructing multifunctional electrodes is highly desirable for energy conversion and storage devices. Spinel cobaltites have attracted considerable attention owing to the relative high conductivity and rich redox chemistry, but the limited electroactive sites and poor surface chemical reactivity are the highly concerned issues. Taking Co–Cu oxides as the model material, here we demonstrate that a surface restructuring strategy by constructing core-shell arrays can achieve simultaneous modulation of electroactive sites and surface chemical reactivity. Strating from the hydrothermal and annealing process, CuCo2O4/CuO nanoneedles are synthesized directly on the conductive Ni foam, and followed by electrodeposited RuO2 nanoparticles (denoted as CuCo2O4/CuO@RuO2). Core-shell CuCo2O4/CuO@RuO2 arrays show a high areal capacity up to 862.5 mAh cm−2 and a high capacity retention of about 90.1% after 8000 cycles. Moreover, the hybrid supercapacitor by CuCo2O4/CuO@RuO2 and activated carbon can achieve 0.84 mWh cm−2 energy density at 8 mW cm−2 power density, as well as good long-term stability. In addtion, working as water oxidation catalysis, CuCo2O4/CuO@RuO2 shows the low overpotential of 279 mV at 10 mA cm−2, as well as a low Tafel slope and stable long-term performance. This work provides a novel strategy to engineer surface nanostructure for energy conversion and storage devices.

Designing hierarchical NiCo2S4 nanospheres with enhanced electrochemical performance for supercapacitors

Hierarchical nanostructure materials have attracted significant attention due to their fascinating structural features for the application of high-performance supercapacitors. In this report, nanosheets interconnected hierarchical NiCo2S4 (NCS) nanospheres were synthesized by a facile hydrothermal method. The growth process was explored by performing different reaction temperature conditions (140, 150, 160, and 170 °C), and their electrochemical properties were studied. The electrochemical properties of NCS products (coated on conductive Ni foam substrate) at different reaction temperatures were measured in a traditional three-electrode electrochemical system. The optimized hierarchical NCS nanospheres (prepared at 150 °C) delivered better electrochemical results due to their synergetic morphological features and higher specific surface area. The NCS-150 nanospheres–based electrode exhibited its maximum specific capacity of 155 mA h g−1 at 2 A g−1 and further showed a good capacity retention value of 115 mA h g−1 at a higher current density of 5 A g−1. Besides, cycling analysis was proceeded up to 4000 cycles to test the practical ability of the designed electrode, and it retained 76% of capacity after performing the cycles. These results demonstrate that the nanosheets interconnected hierarchical NCS nanospheres (prepared at 150 °C) could be a promising electrode material for high-performance supercapacitors.

Rational rope-like CuCo2O4 nanosheets directly on Ni foam as multifunctional electrodes for supercapacitor and oxygen evolution reaction

Transition metal oxides have shown promising candidates for energy storage and conversion devices, but the limited electroactive sites may greatly limit the further improvement. Herein, we successfully achieve rope-like CuCo2O4 nanosheets directly on Ni foam, which acts as multifunctional electrodes for supercapacitor and oxygen evolution reaction (OER). The rope-like nanosheets with the ultrathin thickness and large surface areas can effectively increase the number of active sites, resulting in enhanced electrochemical performances. In addition, directly growing nanostructures on conductive Ni foam can endows the electrode materials with higher conductivity and richer active sites. Consequently, obtained rope-like CuCo2O4 nanosheets show the superior electrochemical performances toward supercapacitor and OER. In detail, obtained rope-like CuCo2O4 nanosheets display a high capacity of 5.84 F cm−2 (0.65 mAh cm−2) at 5 mA cm−2, as good as good stability. The asymmetric supercapacitor made of CuCo2O4 (positive electrode) and activated carbon (negative electrode) also show a high energy density of 0.55 mWh cm−2 at 8 mW cm−2 power density. In addition, obtained rope-like CuCo2O4 nanosheets only require a low overpotential of 220 mV at 10 mA cm−2 for OER, and also maintain the outstanding long-term durability. These remarkable performances of rope-like CuCo2O4 hold great promise for energy storage and conversion devices.

Heteromorphic Ni Foam@Ni(OH)2/MnO2 as a Self-Standing Electrode for Electro-Fenton Reactions

Developing effective and economical materials for emerging electrochemical remediation of persistent organic pollutants has attracted significant research interest. In this study, a heteromorphic self-standing nickel foam@Ni(OH)2/MnO2 (NF@Ni(OH)2/MnO2) electrode was synthesized by a simple solvothermal method and employed for the remediation of persistent organic pollutants. The prepared NF@Ni(OH)2/MnO2 electrode exhibited better performance for the electro-catalytic degradation of tetracycline (TC) than that of the NF and NF@Ni(OH)2. In optimized conditions, the NF@Ni(OH)2/MnO2 electrode exhibited the highest TC degradation efficiency (90%) and total organic carbon(TOC) removal (59.02%) among the prepared electrodes. In addition, a higher mineralization current efficiency (MCE) and lower energy consumption (EC) for the NF@Ni(OH)2/MnO2 electrode was achieved. The enhancement occurs primarily because the active MnO2 anchored to the porous and highly conductive Ni foam substrate surface boosts the electron transfer and the generation of hydroxyl radicals, as proved by a free radical trapping experiment and fluorescence spectrum analysis. This study suggests the possibility of a new paradigm in designing effective and practical electro-Fenton electrodes for environmental remediation.

Spinel-type oxygen-incorporated Ni3+ self-doped Ni3S4 ultrathin nanosheets for highly efficient and stable oxygen evolution electrocatalysis

Spinel-type structured materials have attracted considerable attention and been regarded as promising alternative catalysts for oxygen evolution reaction (OER). However, the regulation of catalytically active octahedral sites in spinel structure to realize high activity and good stability for OER electrocatalysis is still a great challenge. Herein, we propose a self-doping strategy to boost OER performance of spinel-type Ni3S4 enriched high valence Ni3+ as active sites. By sacrificing Ni-based metal-organic framework, the ultrathin Ni3S4 manosheets are topologically grown on conductive Ni foam substrate and realize the simultaneous Ni3+ self-doping and surface oxygen incorporation during in situ sulfidation conversion process. These compositional and structural characteristics endow it with enhanced adsorption binding strength, enabling the highly efficient OER. As a result, the Ni3S4/NF exhibits excellent activity and outstanding stability toward OER electrocatalysis in alkaline medium, which only demands an ultralow overpotential of 266 mV to deliver a current density of 10 mA cm−2 and manifests the stable OER process for at least 75 h. Moreover, when used as an effective overall water splitting electrolyzer, the Ni3S4/NF achieves a current density of 10 mA cm−2 at only 1.638 V with good long-term stability.