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Bismuth vanadate (BVO) having suitable band edges is one of the effective photocatalysts for water oxidation, which is the rate-determining step in the water splitting process. Incorporating cocatalysts can reduce activation energy, create hole sinks, and improve photocatalytic ability of BVO. In this work, the visible light active nickel tellurium oxide (NTO) is used as the cocatalyst on the BVO photoanode to improve photocatalytic properties. Different NTO amounts are deposited on the BVO to balance optical and electrical contributions. Higher visible light absorbance and effective charge cascades are developed in the NTO and BVO composite (NTO/BVO). The highest photocurrent density of 6.05 mA/cm2at 1.23 V versus reversible hydrogen electrode (VRHE) and the largest applied bias photon-to-current efficiency (ABPE) of 2.13% are achieved for NTO/BVO, while BVO shows a photocurrent density of 4.19 mA/cm2at 1.23 VRHEand ABPE of 1.54%. Excellent long-term stability under light illumination is obtained for NTO/BVO with photocurrent retention of 91.31% after 10,000 s. The photoelectrochemical catalytic mechanism of NTO/BVO is also proposed based on measured band structures and possible interactions between NTO and BVO. This work has depicted a novel cocatalytic BVO system with a new photocharging material and successfully achieves high photocurrent densities for catalyzing water oxidation.

Structure directing agent (SDA) can tailor morphology of active materials with preferable surface properties. Ammonium fluoroborate has been proposed as an effective SDA to synthesize metal organic framework (MOF) derivatives in previous reports, where fluoroborate ions play as morphology regulators by providing steric hindrance. Nickel and cobalt hydroxides are intensively used as active materials in battery supercapacitor hybrids (BSHs), owing to high theoretical capacitances and durability. However, previous studies rarely investigate metal specie effects on energy storage and compare electrochemical performance of nickel and cobalt hydroxides particularly in unique synthesis environments. In this study, nickel tetrafluoroborate (Ni(BF4)2) and cobalt tetrafluoroborate (Co(BF4)2) are respectively used as nickel and cobalt sources to synthesize hydroxides as active materials of BSHs. Tetrafluoroborate ions act as SDAs to design favorable morphologies, while 2-methylimidazole is incorporated to control the pH value for facilitating precipitations. The Ni(OH)2and Co(OH)2electrodes respectively show specific capacitances (CF) of 1118.5 and 334.3 F/g at 20 mV/s, owing to the preferable alpha-type hydroxide and larger pore volume/width for Ni(OH)2. A BSH consisted of a Ni(OH)2positive electrode shows a maximum energy density of 64.0 Wh/kg at 700.0 W/kg, and the CFretention of 116% and Coulombic efficiency of 94% after 5000 cycles.

Iron oxide (Fe2O3) with a high theoretical capacitance, wide potential ranges and easy availability has attracted much attentions as the electrode material of battery supercapacitor hybrids (BSH). Metal–organic framework (MOF) is one of the promising potential energy storage materials due to its large surface area and controllable pore structures. In this work, novel iron oxide/iron organic framework composites (Fe2O3/FeMOF) are in-situ grown on the Ni foam as efficient energy storage electrodes of BSH. By tuning the solvothermal durations, the morphology changes from random sizes of sheets, regular grown vertical sheets, to flower-like structures. The d-spacing also increases for the Fe2O3/FeMOF synthesized using longer solvothermal durations. The optimal Fe2O3/FeMOF electrode synthesized using 9 h shows a high areal capacitance of 10.97 F/cm2along with an areal capacity of 5.49 F/cm2at the current density of 35 mA/cm2, owing to the most regular growth of sheets, the large d-spacing, and the smallest charge-transfer resistances. A BSH composed of the Fe2O3/FeMOF positive electrode and a graphene negative electrode shows a maximum energy density of 0.76 mWh/cm2at 22.5 mW/cm2. The excellent long-term cycling stability with the capacitance retention of 85% and Coulombic efficiency of 98% are also achieved after 10,000 charge/discharge cycles.

The zeolitic imidazolate framework 67 (ZIF67) derivative is a potential active material of supercapacitors (SC), owing to high specific surface area and porosity and possible formation of cobalt compounds. A novel ZIF67 derivative is synthesized using a one-step solution process with cobalt precursor 2-methylimidazole (2-Melm) and ammonia fluoride in our previous work. Due to its facile synthesis and excellent electrocapacitive behavior, it is crucial to understand the competition between ammonia fluoride and 2-Melm on forming derivatives with cobalt ions and to create more efficient ZIF67 derivatives for charge storage. In this work, several ZIF67 derivatives are designed using a one-step solution process with 2-Melm and ammonia fluoride incorporated in different sequences. The reaction durations for a single ligand and two ligands are controlled. The largest capacity of 176.33 mAh/g corresponding to the specific capacitance of 1057.99 F/g is achieved for the ZIF67 derivative electrode prepared by reacting ammonia fluoride and a cobalt precursor for 0.5 h and then incorporating 2-Melm for another 23.5 h of reaction (NM0.5). This derivative composed of highly conductive CoF2, NiF2, Co(OH)F, and Ni(OH)F presents high specific surface area and porosity. The relevant SC presents a maximum energy density of 19.5 Wh/kg at 430 W/kg, a capacity retention of 92%, and Coulombic efficiency of 96% in 10000 cycles.

Two-dimensional layered double hydroxide (LDH) has promising open spaces for efficient Na+diffusion/migration. Also, cobalt-based materials have high theoretical capacities and molybdenum incorporations can enhance electrical conductivity. Therefore, cobalt and molybdenum LDH is considered as an efficient anode material of sodium-ion battery (SIB). Nevertheless, volume expansion of LDH may limits the electrochemical performance of SIB. In this work, polydopamine (PDA) derived carbon coated cobalt molybdenum LDH (CoMoLDH) is synthesized via the hydrothermal, polymerization and carbonization processes as a novel anode material of SIB. Hydrothermal and polymerization durations are optimized to regular the morphology of CoMoLDH and achieve the suitable thickness of carbon layer. The optimal carbon coated CoMoLDH (CoMoLDH-C-PDA) anode shows a high specific capacity of 779.9 mAh/g at 0.05 A/g. After 100 cycles, the CoMoLDH-C-PDA anodes still presents a specific capacity of 310.9 mAh/g corresponding to capacity retentions of 70.0%. High specific capacity, excellent rate performance and long-term cyclic ability of CoMoLDH-C-PDA are attributed to the higher Na+diffusion coefficient and smaller charge-transfer resistances. This study brings a blueprint for modifying novel bimetallic LDH with well-designed carbon coating, which is worthy to apply on other bimetallic LDH for enhancing rate performance and cycle life of SIB in the future.

Zeolitic imidazolate framework-67 (ZIF-67) derivatives are designed with large surface area, high porosity and numerous redox states, which are beneficial for an efficient active material for charge storage. Incorporating structure directing agents (SDA) such as ammonium fluoroborate (NH4BF4) or ammonium bifluoride (NH4HF2) during synthesis is one of the effective methods for designing ZIF-67 derivatives. To simplify the environment and understand the function of fluorine-based complex, it is worthy to use a single metal precursor and 2-methylimidazole (2-Melm) to synthesize ZIF-67 derivatives. In this work, a novel cobalt precursor, cobalt tetrafluoroborate (Co(BF4)2), is used as the cobalt source and SDA to design new ZIF-67 derivatives (CoMel) for energy storage. Effects of Co(BF4)2and 2-Melm ratios on material and electrochemical properties of CoMel are investigated. The optimal CoMel electrode shows a specific capacitance (CF) of 605.5 F/g at 20 mV/s, owing to large contacts to electrolyte with sheet-like structures and favorable cobalt compound compositions. A battery supercapacitor hybrid composed of the optimal CoMel electrode and the carbon electrode presents a maximum energy density of 45 Wh/kg at the power density of 410 W/kg. Excellent long-term stability with the CFretention of 95% and Coulombic efficiency of 98% after 7000 charge/discharge cycles are also achieved for this system. The novelty is to propose a single cobalt precursor as both cobalt ion source and SDA to design efficient active materials for energy storage. The same concept can be further used in other metal compounds for electrochemical applications.

Zeolitic imidazolate framework (ZIF-67) with high surface area and tunable pore size are considered as a promising active material for energy storage, but the low electrical conductivity restricts its performance. Developing ZIF67 derivatives with improved electrical conductivity is necessary to broaden its application in electrochemical fields. In this work, two strategies are applied to improve electrical conductivity and electrochemical performance of ZIF67. Novel structure directing agents of NH4BF4and NH4HF2are used to synthesize ZIF67 derivatives with higher theoretical capacitances and favorable layered structures. Self-assembled MXene with different amounts is further incorporated in ZIF67 derivatives to establish composites. The optimal composite electrode shows a high specific capacitance (CF) of 1410.4 F/g (775.6C/g) at 20 mV/s, while the ZIF67 derivative electrode without MXene only shows a CFvalue of 942.3 F/g (518.3C/g), due to the high surface area and better pore structure as well as the close combination of MXene and the layered ZIF67 derivative for the former case. An energy storage device with the optimal composite and carbon electrodes shows the maximum energy density of 32.40 Wh/kg at 375 W/kg. The Coulombic efficiency of 100% and the CFretention of 77.4% are also achieved after 10,000 cycles.

Zeolitic imidazolate framework 67 (ZIF67) have been intensively applied as efficient active materials for energy storage. Structure directing agents (SDA) play important roles on morphology and electrochemical performance of active materials. Incorporating SDA in synthesis is expected to confine growth of ZIF67 derivatives and create efficient active materials. Ammonium fluoride (NH4F) has been widely applied as an effective SDA for synthesizing active materials in electrochemical systems. Inspired by the confiner of NH4+and the conductive agent of F−, two novel SDA of ammonium hydrogen fluoride (NH4HF2) and ammonia borane fluoride (NH4BF4) are introduced to synthesize Ni-based or Co-based ZIF67 derivatives via a one-step solution process at room temperature. Substituting 2-methylimidazole with HF2−and BF4−improves conductivity of ZIF67. Effects of NH4HF2to NH4BF4ratio for synthesizing ZIF67 derivatives are investigated. The main compositions of ZIF67 derivatives are cobalt and nickel hydroxides. The largest specific capacitance (CF) of 1112.4 F/g is attained for the optimized Ni-based ZIF67 derivative (NiHB) at 20 mV/s. An asymmetric supercapacitor with the NiHB and activated carbon electrodes shows a maximum energy density of 32 Wh/kg at the power density of 750 W/kg, and the CFretention of 70% and Coulombic efficiency of 90.6% after 10,000 cycles.

Sodium-ion battery (SIB) is attractive and cost-effective for energy storage due to the high abundance of sodium. Anodes with complex electrochemical mechanisms significantly impact the performance and safety of battery systems. In recent times, cobalt-based binary metal sulfides have received enormous attention in energy storage applications. However, high volume expansion, limited cycle life, and low initial Coulombic efficiency are major problems of SIB in a practical application perspective. Herein, a novel binder-free electrode is designed by synthesizing polypyrrole-coated zinc cobalt sulfide nanosheets on carbon cloth (PPy/ZnCoS@CC) as the anode of SIB via a hydrothermal process for the first time. The PPy coating on the ZnCoS surface is to control the volume expansion and solve the long-term stability issue. The thickness of PPy on ZnCoS is controlled by using different polymerization reaction times. The optimal PPy/ZnCoS@CC electrode demonstrates a high areal capacity of 2.33 mAh/cm2at 0.1 mA/cm2and retains 75 % of the areal capacity after 100 cycles. The galvanic intermittent titration technique analysis is also used to measure the diffusion coefficient of anodes. This work brings a blueprint on enhancing the conducing property and control the volume expansion during the charge-discharge process by coating conductive polymer on metallic compounds.

Battery supercapacitor hybrids (BSH) comprising battery and supercapacitor-type electrodes can attain high energy/power densities and long cycle life. Copper oxide is regarded as a promising battery-type active material, due to low-cost, high chemical stability and good electrochemical properties. However, poor electrical conductivity and insufficient active sites should be improved to attain high energy storage ability. In this work, a novel battery-type material composed of Ni(OH)2nanosheets decorated on Cu2O cages is synthesized via a facile solution process for the first time. Less deposition of Ni(OH)2leads to sparse distribution on Cu2O cages, and full coverage of Ni(OH)2is achieved via depositing four Ni(OH)2layers on Cu2O cages. The largest specific capacitance (CF) of 389.1 F/g is achieved at 20 mV/s for the optimized Ni(OH)2and Cu2O (Ni(OH)2@Cu2O) composite, while the Cu2O electrode shows a smaller CFvalue of 79.7 F/g. Coating Ni(OH)2on Cu2O can induce active site formation and enhance electrical conductivity. The Ni(OH)2@Cu2O positive electrode and the active carbon negative electrode are used to assemble a BSH, which presents a maximum energy density of 4.09 Wh/kg at 500 W/kg and excellent cycling ability with CFretention of 70% and Coulombic efficiency higher than 97% after 10,000 charge/discharge cycles.

A vital aspect of energy storage devices is the development of novel materials with excellent electrical conductivity and rational structures. In combination with alkaline electrolytes, the manganese-cobalt layered double hydroxide (MnCo-LDH) cathode material has long been recognized as a highly desirable cathode material. Nevertheless, the synthesis of MnCo-LDH is time-consuming and required high temperatures. Therefore, it is important to find simple routes for the synthesis of MnCo-LDH. Herein, we propose a synthesis of metal organic framework (MOF)-derived MnCo-LDH nanosheets on conductive nickel foam (NF) for the supercapacitor (SC) application. The CoMOF decorated NF was fabricated by simple precipitation method, and then it was converted to MnCo-LDH by etching process at 80 °C for 5 min (MnCo-LDH/80 °C). The MOF-derived MnCo-LDH/80 °C electrode provides large accessible regions for electrolytes, low charge transfer resistance, and rich electroactive sites. Therefore, the MnCo-LDH/80 °C electrode demonstrates preferable energy storage property with a high areal capacitance of 2.62 F/cm2at 20 mV/s. In this study, an asymmetric supercapacitor (ASC) is constructed using MnCo-LDH/80 °C and activated carbon (AC) on NF as the positive and negative electrodes, respectively. The optimized MnCo-LDH//AC device provides the maximum energy of 0.116 mWh/cm2at the maximum power density of 2.49 mW/cm2. Added to that, the ASC has excellent cyclic stability with 78% as the capacitance retention and Coulombic efficiency of 94.3% after 5000 charge-discharge cycles.

Copper cobalt sulfide (CuCo2S4) has received intensive attentions as one of effective battery-type materials of battery supercapacitor hybrids (BSH), because of numerous redox states and large conductivity. Morphology has been widely reported to play important roles on energy storage ability. Tube-like structure is beneficial for providing large surface area at inner/outer surface, and efficient charge transfer paths in one-dimensional directions. In this study, the CuCo2S4particle-decorated tube-like structure is firstly designed on nickel foam via the hydrothermal process at different temperatures. The effects on morphology, composition and electrochemical performance are examined. The CuCo2S4synthesized at 160 °C shows the most uniform rod size and regularly distributed particles on surface. The highest specific capacitance (CF) of 831.7 F/g corresponding to the capacity of 115.6 mAh/g is achieved for the optimal CuCo2S4electrode, due to the largest electrochemical surface area with multiple active sites. A BSH is fabricated by using the CuCo2S4positive electrode and the activated carbon negative electrode. A wide potential window of 1.5 V and the maximum energy density of 32.1 Wh/kg at power density of 1.1 kW/kg are achieved. The CFretention of 78.8% and Coulombic efficiency of 95.5% are also attained after 10,000 charge/discharge cycles for the BSH.

Transition metal sulfides (TMS) are considered as the efficient battery-type material due to high theoretical capacity, redox reversibility, and electrical conductivities. The Ni3S2with a high theoretical capacity and abundant sources is one of the efficient energy storage materials, but high contact resistances and poor cyclic stability of Ni3S2restrict its electrochemical performance. The binder-free design, morphology regulation, composite development, and conductive polymer incorporation are useful strategies for solving the problems of Ni3S2. In this study, a novel lavandula-like manganese oxide, Ni3S2and polyaniline composite (PANI/MnOx/Ni3S2) is synthesized on Ni foam as the binder-free battery-type electrode of battery supercapacitor hybrid (BSH) as clean energy sources at the first time. The Mn amounts and aniline electropolymerization durations play important roles on active sites and electrical conductivity. The functions of MnOxand PANI are analyzed by comparing physical and electrochemical properties of Ni3S2, MnOx/Ni3S2, PANI, PANI/Ni3S2and PANI/MnOx/Ni3S2electrodes. The largest specific capacitance (CF) of 9.5 F/cm2at 30 mA/cm2is achieved for the optimized PANI/MnOx/Ni3S2electrode. A BSH assembled using activated carbon and PANI/MnOx/Ni3S2electrodes presents the maximum energy density of 2.31 Wh/m2at 65 W/m2, and the CFretention of 78.5 % and Coulombic efficiency of 95.8 % after 10,000 times repeatedly charging and discharging process.

Bimetallic sulfide has attracted much attentions as efficient electroactive materials of battery supercapacitor hybrid (BSH), because of numerous redox states, high conductivity and good energy efficiency. Developing composites having excellent chemical and electrochemical properties is necessary to enhance the energy storage features of bimetallic sulfides. In this study, CuCo2S4and Ni(OH)2composites (CuCo2S4@Ni(OH)2) are designed on Ni foam via the facial hydrothermal process and chemical bath deposition as the electroactive material of BSH at first time. Effects of Ni(OH)2amounts on CuCo2S4on electrochemical and physical properties of CuCo2S4@Ni(OH)2are investigated. The physical mixed CuCo2S4and Ni(OH)2composite is also fabricated to verify synergistic effects of CuCo2S4@Ni(OH)2. A higher specific capacitance (CF) of 1583.9 F/g along with the capacity of 220.0 mAh/g are got for optimal CuCo2S4@Ni(OH)2electrode, respectively comparing to 831.7 and 1063.3 F/g of CuCoS4and Ni(OH)2electrodes. A BSH is fabricated by the CuCo2S4@Ni(OH)2electrode and the activated carbon electrode. The potential window of 1.6 V and maximum energy density of 32.1 Wh/kg at 1.1 kW/kg are achieved. The CFretention of 78% and Coulombic efficiency higher than 97% in 8000 charge/discharge cycles are also obtained for this BSH.

Metal organic framework (MOF) with large surface area and pore tunability has been intensively applied on energy storage. Tubular structure is one of promising configurations due to abundant contacts to electrolyte at inner/outer surface and straight charge transfer paths. Bimetallic compounds with multiple redox states are favorable for generating redox reactions. Possible conversions to oxides or sulfides can also induce additional active sites and enhance conductivity. In this study, cobalt and manganese bimetallic MOF (CoMn-MOF) tubular structures are firstly synthesized using polypyrrole nanotubes as the template. Effects of metal ratio on energy storage is investigated to understand contributions from Co and Mn. The CoMn-MOF derived oxide and sulfide are further synthesized to enhance energy storage ability. A larger specific capacitance (CF) of 670.1 F/g is attained for CoMn-MOF derived sulfide (S-CoMn-MOF) electrode, respectively compared to those of 247.0 and 426.7 F/g for the CoMn-MOF and oxidized CoMn-MOF electrodes, because of surface connected tubular structure and balanced components of MOF and sulfides for S-CoMn-MOF. An energy storage device with S-CoMn-MOF and graphene electrodes shows a maximum energy density of 17.9 Wh/kg at 785.7 W/kg. The CFretention of 78 % and Coulombic efficiency of 97 % after 10,000 charge/discharge cycles are also obtained.

Metal organic framework is often post-treated to increase electrical conductivity and electroactivity for application on battery supercapacitor hybrids (BSH). An in-situ modification is previously proposed to replace post-treatments via incorporating ammonium fluoride (NH4F) during synthesizing zeolitic imidazolate framework-67 (ZIF67) to develop derivatives with excellent energy storage ability. Inspired by structure directing ability of ammonium group, high electronegativity of fluorine-based group, and time and money-saving process of in-situ modification, a novel structure directing agent (SDA), ammonium bifluoride (NH4HF2), is proposed in this study to design ZIF67 derivatives via the facile one-step solution process for the first time. The amounts of NH4HF2and 2-methylimidazole are varied to fabricate a series of ZIF67 derivatives, and the SDA effects on physical and electrochemical properties are investigated. The highest specific capacitance (CF) of 1116.7 F/g and the capacity of 217.1 mAh/g are achieved for the optimal ZIF67 derivative at 20 mV/s, because of the thinnest layers with large surface area and abundant electrolyte contacts. The ZIF67 derivative and carbon electrodes are applied to fabricate a BSH, which displays a CFretention of 84.8 % and Coulombic efficiency of 96.1 % after measuring the charge/discharge curves at 1.0 A/g for 10,000 cycles, as well as the maximum energy density of 7.3 Wh/kg at the power density of 714.3 W/kg.

Photoelectrochemical catalytic capability mainly relies on light absorption and charge transfer efficiency. TiO2nanotube array (TNA) having suitable band edges and one-dimensional hollow structure is regarded as one of efficient photoelectrocatalysts toward water reduction. In this study, two strategies are firstly applied to modify TNA as the photocatalyst of water reduction. Ti foils are etched by acid to produce multiple light reflections planes for improving light absorption, and Cu is doped in TNA to enhance charge transfer efficiency. The optimal Cu-doped TNA electrode on the acid-etched Ti foil presents a much smaller overpotential of 91 mV at 10 mA/cm2compared with that of the undoped TNA (524 mV). A smaller Tafel slope of 134 mV/dec is obtained for the optimal Cu-doped TNA electrode than that of the undoped TNA (167 mV/dec). After measuring the photoelectrochemical performance for 1000 cycles, overpotential and charge-transfer resistance of modified TNA are largely reduced owing to activation. Current retention of 96.7 % is achieved after continuously illuminating for 10 h. Highly improved photoelectrochemical catalytic ability of TNA modified by acid etching and Cu doping provides new pages for material modifications on substrate and active material.

Cobalt and nickel oxides with large theoretical capacitance, high redox activity and low-cost features are widely applied as electroactive material of battery supercapacitor hybrids (BSH) to reduce energy consumption and create renewable energy. Synthesizing cobalt and nickel oxides using zeolitic imidazolate framework 67 (ZIF67) can enhance conductivity and electroactivity and maintain surface area and porosity of ZIF67. Structure directing agent (SDA) can control morphology and improve electrochemical performance. It is attractive to apply SDA for controlling morphology of oxidized ZIF67 and achieving excellent energy storage. In this work, ammonium tetrafluoroborate (NH4BF4) is firstly applied as SDA to synthesize ZIF67 derivative, which is then annealed to form leaf-like cobalt and nickel oxides as electroactive material. The optimal oxidized ZIF67 derivative shows a larger specific capacitance (CF) of 828.9 F/g than those of 519.9 and 5.0 F/g respectively for the oxidized ZIF67 and pristine ZIF67 electrodes, due to preferable leaf-like structure and (311) facet for the former case. A BSH with oxidized ZIF67 derivative positive electrode and graphene negative electrode shows maximum energy density of 10.2 Wh/kg at 357 W/kg, and CFretention of 91 % and Coulombic efficiency of 97 % after 10,000 cycles. The novel SDA of NH4BF4is expected to design other efficient electroactive materials for effective energy storage.

Nickel and cobalt layered double hydroxide (NiCo-LDH) is one of promising active materials of battery supercapacitor hybrids (BSH) as the clean renewable energy. Designing composites and doping heteroatoms are widely applied to solve poor conductivity, serious agglomeration, and structural defects of NiCo-LDH. In this work, manganese cobalt LDH (MnCo-LDH) is firstly incorporated in sulfur-doped NiCo-LDH (S-NiCo-LDH) on Ni foam (NF) via the hydrothermal process as a binder-free electrode of BSH. Favorable morphology with nanowires covered on the vertical grown nanosheet array is successfully designed for MnCo-LDH/S-NiCo-LDH with the large specific surface area and the well-established pore structure. The specific capacitances (CF) of 681.4, 953.9 and 1581.3 F/g are respectively achieved for the NiCo-LDH, S-NiCo-LDH, MnCo-LDH/S-NiCo-LDH electrodes at the current density of 1 A/g. The larger CFvalue of MnCo-LDH/S-NiCo-LDH is due to larger conductivity and effective charge transfer paths. A BSH assembled using MnCo-LDH/S-NiCo-LDH/NF and graphene/NF electrodes shows a wide potential window of 1.6 V, a large maximum energy density of 46.6 Wh/kg at 0.8 kW/kg, and an excellent cyclic stability with the CFretention of 81% and the Coulombic efficiency higher than 87% after 10,000 times charge/discharge process at the current density of 7 A/g.

Metal organic framework (MOF) derivatives have attracted intensive attention as the active material of energy storage devices. Layered double hydroxide (LDH) with large surface area, high redox capability and good cycling stability is regard as one of efficient active materials. Developing MOF-derived LDH with multiple metals can possibly achieve excellent surface properties, high electrical conductivity and abundant redox reactions. However, synthesizing MOF-derived LDH is time-consuming and requires high temperature environments. In this work, a simple and time-effective precipitation and etching process is proposed to synthesize MOF-derived LDH on nickel foam (NF) as binder-free electrodes of energy storage devices. The cobalt, nickel and manganese are utilized to design MOF-derived LDH with different metal species and numbers. The trimetallic MOF-derived LDH based on Co, Ni and Mn presents a high specific capacitance (CF) of 1113.7 F/g at 20 mV/s, due to abundant electroactive sites and multiple redox states for carrying out large numbers of redox reactions. The energy storage device composed of the trimetallic MOF-derived LDH and carbon on NF as electrodes presents the maximum energy density of 61.5 Wh/kg at the power density of 750 W/kg, and the CFretention of 92.5 % and Coulombic efficiency of 95 % after 10,000 charge/discharge cycles.

Zeolitic imidazolate framework-67 (ZIF67) derivatives are intensively applied as the active material of battery supercapacitor hybrids (BSH) as clean renewable energy. Binder-free electrodes without insulated binders possessing high electrical conductivity can be fabricated with less time and money. In this work, carbonized ZIF67 (C-ZIF67) is fabricated on Ni foam using in-situ binder-free technique. The C-ZIF67 electrode is applied as battery-type electrode of BSH for the first time. Using Ni foam as a conductive substrate of binder-free electrodes is beneficial for generating nickel compounds with multiple redox states. The electrocapacitive nitrogen-doped carbon can be generated from ZIF67 after thermal treatments. Carbonization temperature for synthesizing C-ZIF67 electrodes is optimized regarding morphology and defect to graphitic intensity ratios of C-ZIF67. The C-ZIF67 electrode prepared using 600 °C presents the highest specific capacitance (CF) of 914.0 F/g along with capacity of 126.9 mAh/g at 20 mV/s, due to tightly attached active material with favorable vertical grown sheet array on Ni form and suitable defect to graphitic intensity ratio. A BSH composed of reduce graphene oxide negative electrode and carbonized ZIF67 positive electrode presents a maximum energy density of 15.15 Wh/kg at 600 W/kg, and the CFretention of 71% and Coulombic efficiency higher than 85% after 6000 charge/discharge cycles.

β-Ni(OH)2is one of the effective battery-type active materials of battery supercapacitor hybrid (BSH). Two-dimensional structure can supply large surface area for conducting redox reactions and abundant open spaces for ion diffusion. It is promising to design favorable morphology of β-Ni(OH)2as the active material of BSH. In this study, the novel β-Ni(OH)2layered structure decorated with nanoparticles is synthesize on a nickel foam using the hydrothermal process and post treatments. Pure terephthalic acid is verified to be indispensable for synthesizing nickel metal organic framework (Ni-MOF) in the hydrothermal process. Ultrasonication is used to break the large accordion-like structure of Ni-MOF into small pieces. Alkalization is applied to fully convert Ni-MOF into β-Ni(OH)2. Better electrochemical performance is achieved for β-Ni(OH)2synthesized from Ni-MOF, which presents the largest specific capacitance (CF) of 1171 F/g at 3 A/g. A BSH is assembled using the Ni-MOF derived β-Ni(OH)2on a nickel foam as the positive electrode and the activated carbon on a nickel foam as the negative electrode. The maximum energy density of 6.50 Wh/kg at 0.14 kW/kg, and excellent cyclic stability with the CFretention of 82% and Coulombic efficiency higher than 96% after 8000 charge/discharge cycles are achieved for the BSH.

Metal organic framework derivatives are intensively applied as the active material of battery supercapacitor hybrids (BSH) as clean energy technology because of their high surface area and tunable pore sizes. Cobalt and nickel sulfides are promising battery-type materials with multiple redox states for conducting abundant redox reactions and with conductive sulfur for transferring electricity efficiently for energy development. Binder-free electrodes fabricated without insulated binders in the facile synthesis are widely investigated for reducing time and money costs. In this work, it is the first time to fabricate binder-free electrodes with sulfurized zeolitic imidazolate framework 67 (ZIF67) on nickel foam (S-ZIF67/NF) as the battery-type electrode of BSH. The temperature and duration of the hydrothermal process for synthesizing S-ZIF67/NF electrodes are investigated. Based on 100 °C and 4 h, the S-ZIF67/NF electrode shows the largest specific capacitance (CF) of 2744.6 F/g along with the capacity of 533.7 mAh/g at 10 A/g, due to the formation of cobalt and nickel sulfides respectively from the cobalt precursor and the NF as well as the favorable sheet-assembled flower-like structures with large surface area and regular assembly. A BSH composed of the reduced graphene oxide negative electrode and the S-ZIF67/NF positive electrode shows a maximum energy density of 38.5 Wh/kg at 750 W/kg, and CFretention of 71% and Coulombic efficiency higher than 85% after 8000 cycles.

Bimetallic fluorides are widely applied as the electroactive material of the supercapacitor (SC) due to abundant redox states and high electrical conductivity as clean renewable energy. Ammonia fluoride is regarded as the structure-directing agent for modulating morphology as well as providing F−and NH4+to respectively form fluoride and hydrogen bonding with promoted electricity transfer routes. In this study, ammonium-decorated cobalt molybdenum fluoride (CoMoFN) is firstly synthesized using the molybdenum salt and the zeolitic imidazolate framework 67 (ZIF67) derived perovskite prepared using NH4F in the hydrothermal process as the active material of the SC. Molybdenum can enhance electrical conductivity and cyclic stability, as well as confines NH4+in the framework. Hydrogen bond between NH4+and F−could promote charge transfer, but the steric hindrance of NH4+could prohibit ion diffusion. The optimal CoMoFN presents the preferable one-dimensional nanowires-embedded film-like structure, and achieves a specific capacity (CF) of 33.7 mAh/g at 20 mV/s, while the electrode synthesized without Mo shows a smaller CFvalue of 17.8 mAh/g. A symmetric SC composed of CoMoFN electrodes shows a maximum energy density of 6.44 Wh/kg at 0.7 kW/kg. Excellent cycling stability with the CFretention of 73% and the Coulombic efficiency higher than 99% after 6500 times charge/discharge processes are also achieved. This work provides significant information about functions of NH4+on energy storage. It is expected to synthesize more efficient materials based on NH4+for the energy storage devices.

Conductive agent can increase conductivity and construct pore structure in supercapacitor (SC) electrode as clean renewable energy. Carbon black (CB) is common conductive agent but its zero dimension hinders efficient charge-transfer conductive bridge. Combining CB with other carbon materials can possibly solve this issue. Graphene quantum dot (GQD) with high hydrophilicity and stable doping features is easier and cheaper to develop. Previous synthesis of GQD requires complex process and lacks large-scale production. In this study, novel one-step thermal treatment was provided to synthesize N-doped GQD. Citric acid and urea ratios were varied to synthesize N-doped GQD with different N-doping extents and electrical conductivities. CB and GQD mixtures, GQD and CB are used as conductive agent for fabricating SC electrodes. Activated carbon electrode with CB and GQD mixture shows the highest specific capacitance (CF) of 241.4 F/g at 20 mV/s, while electrodes without conductive agent and with CB conductive agent respectively shows CFof 41.5 and 108.6 F/g, due to more functional groups, defects, hydrophilic sites and electrochemical surface area of the former case. Symmetric SC with CB and GQD shows a maximum energy density of 10.54 Wh/kg at 550 W/kg, and CFretention of 85% and Coulombic efficiency of 80% after 5000 charging/discharging cycles.

Cobalt based metal organic framework (Co-MOF) derivatives are regarded as attractive electroactive materials for energy storage, due to its high surface area, excellent pore structure and the possible formation of cobalt compounds. Cobalt sulfide with multiple redox states of Co and high electronegativity of S can produce numerous redox reactions for electron storage and provide high electrical conductivity for charge transfer. In this work, it is the first time to synthesize the novel binder-free sulfurized Co-MOF electrode as energy storage electrode of supercapacitor (SC). Three sulfur sources are used to sulfurize the Co-MOF electrode in hydrothermal process. The sulfurized Co-MOF prepared using thiourea (S67/CC-thiourea) shows wrinkles surface and particle connected aggregations, which can provide high surface area and electrical conductivity, respectively. The highest specific capacitance (CF) of 469.5 F/g at 4 A/g is achieved for the S67/CC-thiourea electrode. The untreated Co-MOF electrode merely shows a CFvalue of 8.0 F/g. An asymmetric SC is assembled using activated carbon negative electrode and S67/CC-thiourea positive electrode. A maximum energy density of 3.25 Wh/kg at 275 W/kg, and CFretention of 106 % and Coulombic efficiency higher than 91 % after 10,000 charge/discharges cycles are obtained for the asymmetric SC. This work opens new routes for creating novel MOF derivatives directly on conductive substrate using simple experimental processes.

Metal organic framework (MOF) derivatives have attracted much attention as efficient active material of energy storage device, due to large surface area, excellent pore structure and abundant redox states. Previously ammonia fluoride is used to control morphology of zeolitic imidazolate framework 67 (ZIF-67) and supply NH4+and F−to enhance charge transfer. More treatments are worthy to apply for improving energy storage ability of this ZIF-67 derivative. In this study, sulfurized ammonium-decorated cobalt fluoride (S-NH4-CoF) is firstly synthesized using ZIF-67 derivative and sulfur powder in the one-step annealing process at different temperatures as active material. The optimized S-NH4-CoF electrode prepared at 400 °C shows specific capacitance (CF) of 462.1 F g−1at 20 mV s−1, due to round particle-assembled sphere morphology with high surface area and large pore volume, and suitable ratio of cobalt fluoride and cobalt sulfide. The symmetric energy storage device composed of optimized S-NH4-CoF electrodes shows maximum energy density of 30.47 Wh kg−1at 800 W kg−1. The CFretention of 85% and Coulombic efficiency higher than 97% are obtained after 20,000 charge/discharge times. This study supplies important information about sulfurization on MOF derivatives. Other parameters like sulfurization precursor and duration are worthy to discuss for enhancing energy storage ability of S-NH4-CoF.

Metal organic framework (MOF) with high surface area and tunable porous size is largely used as active material of supercapacitor (SC). MIL-101(Fe) composed of iron ions and terephthalic acid ligand is candidate active material of SC owing to its possible formation of carbon and iron compounds. Combining carbon and metal compound is feasible to establish efficient active material with ion adsorption/desorption and redox reaction charge storage abilities. In this study, it is the first time to investigate physical and electrochemical properties of MIL101(Fe) derivatives synthesized using carbonization and successive carbonization/oxidation processes as active materials of SC. Carbonization temperature of MIL-101(Fe) is optimized regarding to morphology, composition and defect/graphization ratio. The highest specific capacitance (CF) of 95.7 F/g at 20 mV/s is obtained for the carbonized MIL-101(Fe) (MIL101(Fe)-C) prepared at 800 °C, due to rough surface, hollow structure and suitable defect to graphization ratio. The MIL-101(Fe) and the successive carbonization/oxidation synthesized derivative electrodes merely achieve CFvalues of 44.3 and 0.1 F/g, respectively. Symmetric SC fabricated using optimized MIL101(Fe)-C electrodes shows the maximum energy density of 1.13 Wh/kg at 400 W/kg and excellent cycling stability with CFretention of 96% and Columbic efficiency of 72% in 8000 times repeated charging/discharging cycles.

Activated carbon (AC) with low-cost, high surface area and pore volume properties is common active material of commercial supercapacitor (SC). Producing AC using cigarette filters (CF) cannot only reduce serious CF pollution but also decrease ingredient costs. Also, activating agents have been reported to play important roles on energy storage ability of home-made AC. In this work, it is the first time to use CF to synthesize AC with ZnCl2, KOH and H3PO4as activating agents. The CF-derived AC activated by KOH (CAC-KOH) shows abundant functional groups, larger surface area, well-constructed pore structure and suitable defect-to-graphene intensity. The CAC-KOH electrode achieves the largest specific capacitance (Csp) of 106.5 F/g at 0.5 A/g, while the CF-derived AC electrodes fabricated using ZnCl2and H3PO4show smaller Cspvalues of 4.2 and 9.4 F/g, respectively. The symmetric SC assembled using CAC-KOH electrodes presents a maximum energy density of 5.15 Wh/kg at 325 W/kg and a Cspretention of 73 % after 11,000 charge/discharge cycles. Synthesizing AC with polluted CF successfully opens new blueprints for using wastes to produce efficient active material. It is expected to further enhance energy storage ability of wastes-derived AC by refining the activation process in near future.

Activated carbon (AC) is intensively applied as active material of supercapacitor (SC) due to high porosity and surface area. Incorporating battery-type materials in AC can enhance energy storage ability by generating redox reactions, but poor cycling stability of battery-type materials limits practical use of SC. Similar surface properties can be achieved by redox active organic compounds, which also possesses rich functional groups with extra redox ability. Unlike battery-type materials producing redox reactions from transition metals, incorporating organic molecule is expected to generate redox reactions without reducing cycling stability of AC. In this study, it is the first time to fabricate 1,4 benzene diboronic acid (DBA) and AC composite (DBA-AC) as active material of SC. The ratio of DBA and AC is optimized regarding to uniformity of DBA decoration. The optimized DBA-AC electrode presents a specific capacitance (CF) of 211.4 F/g at 20 mV/s, owing to the largest surface area and abundant functional groups. A flexible symmetric SC based on the optimized DBA-AC electrodes shows the maximum energy density of 0.761 Wh/kg at the power density of 400 W/kg. The CFretention of 110% and Coulombic efficiency higher than 95% after 10,000 times charge and discharge cycling process are also achieved.

Flexible supercapacitor (FSC) with high power density and cycle life has been considered as efficient energy storage device for soft electronics. Gel electrolyte is used in FSC to avoid electrolyte leakage. Titanium dioxide (TiO2) with high dielectric constant and abundant surface vacant sites is regarded as efficient inorganic filler in gel electrolyte. In this work, TiO2nanoparticles are incorporated in polyvinyl alcohol/H3PO4gel electrolyte for FSC. Different particle sizes and phases of TiO2are firstly used as inorganic filler in gel electrolyte to enhance ionic conductivity via reducing crystallinity of polymer. The FSC with P25 TiO2in gel electrolyte presents the best energy storage ability due to the smallest particle size and preferable phases. The highest specific capacitance (CF) of 69.2 F/g at 20 mV/s is obtained for FSC with optimized P25 TiO2amount in gel-electrolyte. This FSC also shows the maximum energy density of 5.9 Wh/kg at 300 W/kg, and CFretention of 94% after 3500 charging/discharging cycles. This work demonstrates feasibility of TiO2as efficient filler in gel electrolyte. It is worthy to study the relation between intrinsic property of TiO2and energy storage ability of FSC in other gel-electrolyte systems.