Electrodes For Energy Storage Research Articles

Carbonization of bacterial cellulose with structure retention and Nitrogen/Sulfur/Oxygen doping for application in supercapacitors electrode

Bacterial cellulose (BC) presents great potential as an economical and sustainable biomass for the preparation of porous carbon electrodes for electrochemical energy storage. However, it is a challenge to maintain the natural structural advantages of BC and regulate the chemistry during the carbonization, significantly hindering the practical application. This study proposes a straightforward and efficient approach to rationally control the carbonization process of BC for improving structure retention and endowing multiple atomic doping, contributing an advanced electrode for supercapacitors. The addition of ammonium sulfate ((NH4)2SO4) is instrumental in promoting the early dehydration carbonization, forming a carbon layer with thermal insulation. This thermal barrier suppresses the volatile organic compound formation, resulting in the inhibition of volume shrinkage and boosted carbon yield. Moreover, the air activation combined with the addition of (NH4)2SO4 contributes to a Nitrogen/Sulfur/Oxygen-doped carbon electrode. The well-maintained hollow structure and diverse chemistry provide sufficient active sites and enhanced ion diffusion, resulting in a specific capacitance of 268.2 F/g at a current of 0.5 A/g and outstanding capacitance retention of 99.46 % after 10,000 cycles at 5 A/g. This work provides a deep insight into the development of cost-effective biomass in developing advanced carbon electrodes for efficient energy storage.

Tuning the active plane and crystallinity of GaN microcrystals for high-performance supercapacitors through potassium nitrate-mediated synthesis

The surface atomic structure and crystallinity have an important effect on the electrochemical energy storage of electrode materials, in addition to the surface chemistry and textural properties. We report here for the first time that the surface atomic structure and crystallinity of GaN, a renowned electrode material for energy storage, can be tuned by controlling the annealing time via potassium nitrate-mediated synthesis. The underlying mechanism for GaN microcrystals with enhanced intensity ratios of I(002)/(100) and I(101)/(100) manifesting excellent rate performance has been revealed by theoretical computations. The energy storage mechanism and electrode kinetics of the GaN electrodes have been clarified. In addition, the GaN microcrystals-based symmetric supercapacitors empowered by 52 wt% H3PO4 can deliver an output voltage of 1.5 V and volumetric specific energy of 11.6 and 40.2 W h L−1 at a specific power of 392.2 W L−1 when operating at −60 and 60 °C, respectively, with electrode material on a commercial loading level.

Synthesis of Binder-Free, Low-Resistant Randomly Orientated Nanorod/Sheet ZnS-MoS2 as Electrode Materials for Portable Energy Storage Applications.

The scientific community needs to conduct research on novel electrodes for portable energy storage (PES) devices like supercapacitors (S-Cs) and lithium-ion batteries (Li-ion-Bs) to overcome energy crises, especially in rural areas where no electrical poles are available. Herein, the nanostructured MoS2 and ZnS-MoS2 E-Ms consisting of nanoparticles/rods/sheets (N-Ps-Rs-Ss) are deposited on hierarchical nickel foam by a homemade chemical vapor deposition (H-M CVD) route. The X-ray diffraction patterns confirm the formation of polycrystalline films growing along various orientations, whereas the field-emission scanning electron microscope analysis confirms the formation of N-Ps-Rs-Ss. The change in structural and microstructural parameters indicates the existence of defects improving the energy storage ability of the deposited ZnS-MoS2@Ni-F electrodes. The specific capacitances of MoS2@Ni-F and ZnS-MoS2@Ni-F electrodes are found to be 1763 and 3565 F/g at 0.5 mV/s and 1451 and 3032 F/g at 1 A/g, respectively. The growing behavior of impedance graphs indicates their capacitive nature; however, the shifting of impedance curves toward y-axis indicates that the increasing diffusion rates due to the formation of nanostructures of ZnS-MoS2 results in low impedance. An excellent energy storage performance, minimum capacity fading, and improved electrical conductivity of the deposited E-Ms are due to the combined contributions of the electrical double layer and pseudocapacitor nature, which is again confirmed by theoretical Dunn's model. The absence of charge transfer resistance and good capacitance retention (95%) even after 10,000 cycles indicates that the deposited E-Ms are better for PES devices like S-Cs and Li-ion-Bs than MoS2 E-Ms. The assembled asymmetric supercapacitor device exhibited the maximum specific capacitance = 996 F/g, energy density = 354-285 W h/kg, power density = 2400-24,000 W/kg, capacitance retention = 95% and Coulombic efficiency = 100% even after a long charging-discharging of 10,000 cycles.

Plasma-induced, N-doped, and reduced graphene oxide–incorporated NiCo–layered double hydroxide nanowires as a high-capacity redox mediator for sustainable decoupled water electrolysis

Although the recent emergence of decoupled water electrolysis prevents typical H2/O2 mixing, the further development of decoupled water electrolysis has been confined by the lack of reliable redox mediator (RM) electrodes to support sustainable H2 production. As energy storage electrodes, layered double hydroxides (LDHs) possess inherently poor conductivity/stability, which can be improved by growing LDHs on graphene substrates in situ. The proper modification of the graphene surface structure can improve the electron transport and energy storage capacity of composite electrodes, while current methods are usually cumbersome and require high temperatures/chemical reagents. Therefore, in this study, dip coating was adopted to grow graphene oxide (GO) on nickel foam (NF). Then, the GO was reduced using nonthermal plasma (NTP) to reduced GO (rGO) in situ while simultaneously implementing N doping to obtain plasma-assisted N-doped rGO on NF (PNrGO/NF). The uniform conductive substrate ensured the subsequent growth of less-aggregated NiCo-LDH nanowires, which improved the conductivity and energy storage capacity (5.93 C/cm2 at 5 mA/cm2) of the NiCo-LDH@PNrGO/NF. For the decoupled system, the composite RM electrode exhibited a high buffering capacity for 1300 s during the decoupled H2/O2 evolution, and in the conventional coupled system, the necessary input voltage of 1.67 V was separated into two lower ones, 1.42/0.33 V for H2/O2 evolutions, respectively. Simultaneously, the RM possessed outstanding redox reversibility and structural stability during long-term cycling. This work could offer a feasible strategy for using NTP to synthesize excellent RM electrodes for application to decoupled water electrolysis.

Carbon nanotube interweaved Fe7Se8 nanosheet/nanorod hybrids on expanded graphite for high-performance sodium storage

The construction of nano-micro scale hybrid structures by carbon materials is an effective strategy to address the issues of metal chalcogenides when used as anodes of sodium-ion batteries. Herein, we develop a carbon nanotube (CNT)-interweaved Fe7Se8/expanded graphite (EG) composite by means of a facile one-step gas-phase pyrolysis route with ferrocene, selenium and EG as the starting materials. The ex-situ monitoring of the pyrolysis process indicates that the selenium as a promoter facilitates the formation of CNTs and the carbon coated Fe7Se8 nanosheet/nanorod mixture. A competing reaction between CNT growth and the evolution of Fe7Se8 nanostructures occurs, which could be dominated by the concentration of selenium vapor. By optimizing the feeding ratio and the pyrolysis condition, the nanocomponents are homogeneously deposited on the surface of the EG matrix to realize a well-developed nano-micro hybrid configuration. The constructed three-dimensional conductive network, rich mesopores and high specific surface area (107.1 m2 g−1) contribute to substantially enhanced sodium-storage performance in ester electrolyte. Remarkably, the optimized composite electrode exhibits high reversible capacity retention of 97.5 % after 1000 cycles at 1.0 A g−1 and improved rate performance of 325 mAh g−1 at 2.0 A g−1. This study provides new avenues to develop high-performance metal chalcogenide electrodes for electrochemical energy storage.

Synthesis and performance of novel n-type EC/AIE energy storage electrode materials containing triphenylamine and quinazolin groups

Synthesis and performance of novel n-type EC/AIE energy storage electrode materials containing triphenylamine and quinazolin groups

Heterointerfaces: Unlocking Superior Capacity and Rapid Mass Transfer Dynamics in Energy Storage Electrodes.

Heterogeneous electrode materials possess abundant heterointerfaces with a localized "space charge effect", which enhances capacity output and accelerates mass/charge transfer dynamics in energy storage devices (ESDs). These promising features open new possibilities for demanding applications such as electric vehicles, grid energy storage, and portable electronics. However, the fundamental principles and working mechanisms that govern heterointerfaces are not yet fully understood, impeding the rational design of electrode materials. In this study, the heterointerface evolution during charging and discharging process as well as the intricate interaction between heterointerfaces and charge/mass transport phenomena, is systematically discussed. Guidelines along with feasible strategies for engineering structural heterointerfaces to address specific challenges encountered in various application scenarios, are also provided. This review offers innovative solutions for the development of heterogeneous electrode materials, enabling more efficient energy storage beyond conventional electrochemistry. Furthermore, it provides fresh insights into the advancement of clean energy conversion and storage technologies. This review contributes to the knowledge and understanding of heterointerfaces, paving the way for the design and optimization of next-generation energy storage materials for a sustainable future.

Restricted and epitaxial growth of MnO2-x nano-flowers in/out carbon nanofibers for long-term cycling stability supercapacitor electrodes

Carbon nanofibers (CFs) have been widely applied as electrodes for energy storage devices owing to the features of increased contact area between electrodes and electrolyte, and shortened transmission route of electrons. However, the poor electrochemical activity and severe waste of space hinder their further application as supercapacitors electrodes. In this work, MnO2−x nanoflowers restricted and epitaxial growth in/out carbon nanofibers (MnO2/MnO@CF) were prepared as excellent electrode materials for supercapacitors. With the synergistic effect of uniquely designed structure and the introduction of MnO and MnO2 nanoflowers, the prepared interconnected MnO2/MnO@CF electrodes demonstrated satisfactory electrochemical performance. Furthermore, the MnO2/MnO@CF//activated carbon (AC) asymmetric supercapacitor offered an outstanding long-term cycle stability. Besides, kinetic analysis of MnO2/MnO@CF-90 was conducted and the diffusion-dominated storage mechanism was well-revealed. This concept of “internal and external simultaneous decoration” with different valence states of manganese oxides was proven to improve the electrochemical performance of carbon nanofibers, which could be generalized to the preparation and performance improvement of other fiber-based electrodes.

Preparation and properties of two-dimensional Ti2CT x MXene based on electroetching method

The continuous advancements in wearable electronics have drawn significant attention toward 2D MXenes materials for energy storage owing to their abundant availability, adaptability, and distinctive physicochemical properties. Two unresolved concerns currently revolve around environmental pollution by F-containing etching and finite kinetics caused because of re-stacking of nanosheets. In this study, Al was electrochemically etched from porous Ti2AlC electrodes without the use of fluorine, through a selective electrochemical etching process in dilute hydrochloric acid. Subsequently, Ti2CT x MXene was vertically grown on carbon fiber (CF) substrates. The resulting Ti2CT x @CF electrodes are lightweight, thin, and flexible, exhibiting a surface capacitance of 330 mF cm−2 at a constant current density of 1 mA cm−2 after 2000 cycles. They display a surface capacitance retention of 96.16% and a high energy density of 45.3 μWh cm−2 at a power density of 0.497 mW cm−2. These metrics underscore the Ti2CT x @CF electrode’s commendable multifunctionality, electrochemical performance, ion transport efficiency, and charge storage capacity. Moreover, a flexible energy storage electrode material with a high area capacity was developed by combining Ti2CT x MXene nanosheets, possessing a large specific surface area, with a flexible carbon fabric substrate.

Enhancing Capacitance of Carbon Cloth Electrodes via Highly Conformal PEDOT Coating Fabricated by the OCVD Method Utilizing SbCl5 Oxidant

AbstractCarbon cloth shows potential for flexible energy storage electrodes but encounters challenges such as low specific capacitance and limited wettability. This study addresses these limitations by fabricating a highly conformal coating of poly(3,4‐ethylenedioxythiophene) (PEDOT) around 3D carbon fibers via the oxidative chemical vapor deposition (oCVD) method, employing antimony pentachloride (SbCl5) as the oxidant. The oCVD stands out as a robust manufacturing technique for fabricating highly conformal conducting polymer films on porous structures, ensuring the preservation of geometric features and the maintenance of active sites for redox reactions. The resulting PEDOT‐coated carbon cloth electrodes exhibit improved pseudocapacitance and specific capacitance compared to their pristine counterparts. Particularly, oCVD PEDOT‐coated carbon cloth fabricated at various deposition temperatures exhibit a substantial 1.5‐ to 2.3‐fold enhancement in specific capacitance compared to pristine carbon cloth. The highest specific capacitance (170.94 F g⁻¹) is attained in the oCVD PEDOT‐coated carbon cloth fabricated at a deposition temperature of 80 °C, representing a 2.3‐fold enhancement over its pristine counterpart. The PEDOT‐coated carbon cloths demonstrate lower charge transfer resistance compared to their pristine counterparts, further confirming their superior electrochemical performance. This investigation highlights oCVD's effectiveness in fabricating highly conformal PEDOT coating on carbon cloth electrodes for electrochemical energy storage devices.

Heteroatom(S) (N, S, P) Co‐Doped Reduced Graphene Oxide‐Based Binder‐Free Novel Energy Storage Electrode Material for High Energy Density Supercapacitor

AbstractThis manuscript reports a one‐pot synthesis of ternary heteroatoms (N/S/P) co‐doped reduced graphene oxide as an electrode material by simultaneous reduction/doping of/into graphene oxide employing eco‐friendly natural molecule(s) (thiamine monophosphate (TM) and thiamine pyrophosphate (TP)) under mild heating (≤60 °C) and near‐neutral pH (≤8) conditions. It produces N, S, P co‐doped rGO‐TM and N, S, P co‐doped rGO‐TP nanohybrids displaying a well‐connected porous microstructure with significantly doped atomic(%) ‐N (10.0%), S (4.1%), P (0.1%) and N (6.7%), S (2.0%), and P (0.5%), respectively. The symmetric supercapacitor designed using N, S, P‐rGO‐TM‐10 in water‐in‐salt 17 m NaClO4 electrolyte exhibits stable cell voltage of 3.0 V, superb gravimetric energy density (areal energy density) of 47.9 Wh kg−1@522.8 W g−1 (0.2363 Wh cm−2@ 2.5 W cm−2); the excellent cyclic stability (88.8 %) and Coulombic efficiency (99.2%) even after 20 000 cycles. Their energy storage capability is corroborated by the illumination of 109 white LEDs upon lighting a single SSC for 50 s each, driving a motor to run a fan, and forming the tandem device by joining three such cells in series.

Scaling to practical pouch cell supercapacitor: Electrodes by electrophoretic deposition

The scale-up of supercapacitors by electrophoretic deposition (EPD) from coin cell to pouch cell with commercially relevant mass loadings and thicknesses is reported. The use of EPD in electrode fabrication mainly reduces the interfacial resistance and increases the mechanical flexibility of the electrodes. The cycling performance or conversion efficiency can also be improved due to the highly porous EPD coatings. An exemplary investigation of activated carbon (AC) electrodes with an electrolyte comprising of tetraethylammonium tetrafluoroborate in acetonitrile is carried out. According to the general literature, EPD of AC on metal substrates has not performed well for supercapacitor electrodes unless they were thinner and with lower mass loadings than commercial requirements. As a consequence, and to redress this research gap, all the electrodes prepared in this work demonstrate high mass loadings (8 mg cm−2) and practical layer thicknesses (125 µm) and contain polyvinylidene fluoride binders with electrically conductive carbon black particles. Research investigations include: (a) impact of EPD of AC onto small (10 cm2) and large areas (50 cm2) of aluminum foil current collectors, (b) scaling-up of coin to pouch cells, and (c) the preparation of electrode coatings on both sides of the current collector for the first time using EPD for pouch cell investigations. Our research learning shows the evidence of practical cell performance, including current loading (40 A g−1), tens of thousands of successive charge and discharge operation (150,000 cycles), power (30 kW kg−1) and energy densities (10 W h kg−1), capacitance (154 F g−1), capacitance retention (80%) and coulombic efficiency (relatively close to 100%). Based upon the success of the pouch cells investigated in this work, further research studies on the use of EPD for preparing energy storage electrodes for commercial cylindrical types of supercapacitors is envisaged.

Modulating charge storage mechanism of cobalt-tungsten nitride electrodes using in situ formed metal-p-n heterojunction for ultrahigh energy density supercapattery

Supercapatteries combine both diffusion-controlled and capacitive charge storage mechanisms to simultaneously deliver exceptional power density and energy density. Though developing materials that combine both charge storage mechanisms for use as supercapattery electrodes is difficult, one solution has been to modify a material that inherently has one of these mechanisms so that it also exhibits the other form of charge storage. In the present study, we modulate the electrochemical reconstruction of a W5N4 electrode to modify its charge storage from pure battery-type to pseudocapacitive, thus enhancing its specific capacity and cyclic stability. This modulation was carried out by embedding Co in W5N4 (Co-W5N4), leading to the formation of W and N-doped Co(OH)2 as an active phase and producing a high specific capacity of 2211 C g−1 at 2 A g−1. The incorporation of a thin layer of TiO2 (Co-W5N4/TiO2) through atomic layer deposition minimized tungsten dissolution during reconstruction, thus generating in-situ a dynamic metal–p-n junction heterostructure (Co-W5N4||Co(OH)2||TiO2) that modulated the charge flow, achieving high-rate capability (retaining 53.1 % at 50 A g−1 compared to 2 A g−1) and cyclic stability (82.8 % after 100,000 cycles at a high current density of 40 A g−1). As illustrated by operando electrochemical impedance spectroscopy and physicochemical analysis, the dynamic response of metal–p-n junction sustains the pseudocapacitive charge storage mechanism at high current rate. This study thus demonstrates the formation of metal-p-n heterojunction and describes its dynamic response under actual charge/discharge operating conditions, providing useful information for the design of energy storage electrodes and energy conversion catalysts.

Regulating intramolecular hydrogen bonds of p-phenylenediimidazole-based small-molecule compounds towards the enhanced lithium storage capacity

The use of redox-active organic electrode materials in energy storage is restricted due to their inferior solvent resistance, abysmal conductivity, and the resultant low practical capacity. To address these issues, a class of bipolar p-phenylenediimidazole-based small-molecule compounds are designed and fabricated. The π-conjugated backbone of these small molecules allows for electron delocalization on a big conjugation plane, endowing them with good conductivity and reaction reversibility. Furthermore, when the para-positions of phenylene are occupied by hydroxyl groups, as-formed intramolecular hydrogen bonds (N–H…O) between phenolic hydroxyl groups and the –NH groups of imidazole rings further enhance the structural planarity, resulting in higher π-conjugation degree and better conductivity, and thus higher utilization of active sites and electrode capacity, proved by both experimental results and theoretical calculations. The optimized composite electrode DBNQ@rGO-45 shows a high specific capacity (∼308 mA h g−1 at 100 mA g−1) and a long cycling stability (112.9 mA h g−1 after 6000 cycles at 2000 mA g−1). The significantly better electrochemical properties for hydroxyl group-containing compounds than those without hydroxyl groups attributed to intramolecular hydrogen bond-induced conjugation enhancement will inspire the structure design of organic electrodes for better energy storage.

Layer-by-layer assembling redox wood electrodes for efficient energy storage

The exploration of redox-active organic materials and low tortuous thick-electrodes is attractive for energy storage. The in-situ valorized lignin on raw wood surface accompanied by layer-by-layer deposition of electro-active materials endow such spatially distributed wood electrodes with high specific capacitance. Here, we report a layer-by-layer assembled ca.1.5 mm-thick redox wood hybrid electrode with 20 mg cm-2 electro-active mass loading for efficient energy storage. The in-situ modified surface lignin in treated wood (TrW) holds promise as redox-active material with enriched nanoporosity, carbonyl functionalities, and multi-phase ionic transport structure. The carbon nanotubes (CNTs) networking with in-situ polymerized polypyrrole (PPy) nanorods three-dimensionally in the lumen of TrW afford a wool-like, highly porous nanostructure. Such a hierarchical structured PPy@CNTs@TrW electrode offers a high areal capacitance of 1.46 F cm-2 with an extraordinary energy density of 0.983 mWh cm-3 (3.68 Wh kg-1) and power density of 5.4 mW cm-3 (20.25 W kg-1). Here, the valorized surface lignin contributes contributes to electrochemical energy storage accompanied by spatially distributed PPy@CNTs in low tortuous electrodes. The electrode offers extremely low electrochemical impedance of 0.61 Ω electrode resistance and 1.57 Ω electrolyte resistance. The hybrid wood electrode showcases even higher conductivity and energy/power density than thin carbonized wood and other state-of-the-art thin electrodes made of highly conductive three-dimensional networks. This work highlights the potential of in-situ valorized lignin in developing high-performance eco-friendly thick-electrodes for electrochemical energy storage applications.

Fabrication of Fe@Ni-orotate coordination polymer composite: iron doping provokes the colorimetric recognition efficiency for naproxen drug and energy storage magnitude

Coordination polymers have emerged as promising materials for various applications due to their unique properties and structural versatility. Making a composite with coordination polymers may broaden their applications. In this study, we developed Iron doped Nickel Coordination polymer Fe@Ni-CP from previously synthesized nickel orotate coordination polymer and explored its efficacy in sensing Naproxen (NPX) and also as an electrode material for energy storage devices. Photoluminescence sensing investigations exhibited a notable enhancement in NPX sensing efficiency, whereby the Fe@Ni-CP composite displayed a sensing efficiency of 94.05 %, surpassing the 6.42 % efficiency observed when utilizing the Ni-Orotate coordination polymer alone. Moreover, both materials showed significant differences in specific capacitance when tested as energy storage electrodes using Cyclic Voltammetry (CV) and Galvanostatic Charge Discharge (GCD). The Fe@Ni-CP has specific capacitance of 810.83 F/g, compared to 468.00 F/g for the Ni-CP. In Cyclic Voltammetry, Fe@Ni-CP retained 91.07 % specific capacitance after 4000 cycles. These findings underscore the potential of Fe@Ni-CP for multifunctional applications in sensing and energy storage.

Electrochemical Investigation of Lithium Perchlorate-Doped Polypyrrole Growing on Titanium Substrate

Lithium perchlorate-doped polypyrrole growing on titanium substrate (LiClO4-PPy/Ti) has been fabricated to act as electroactive electrode material for feasible electrochemical energy storage. A theoretical and experimental investigation is adopted to disclose the conductivity, electroactivity properties and interfacial interaction-dependent capacitance of LiClO4-PPy/Ti electrode. The experimental measurement results disclose that LiClO4-PPy/Ti reveals lower ohmic resistance (0.2226 Ω cm−2) and charge transfer resistance (2116 Ω cm−2) to exhibit higher electrochemical conductivity, a more reactive surface, and feasible ion diffusion to present higher double-layer capacitance (0.1930 mF cm−2) rather than LiClO4/Ti (0.3660 Ω cm−2, 65,250 Ω cm−2, 0.0334 mF cm−2). LiClO4-PPy/Ti reveals higher Faradaic capacitance caused by the reversible doping and dedoping process of perchlorate ion on PPy than the electrical double-layer capacitance of LiClO4/Ti caused by the reversible adsorption and desorption process of the LiClO4 electrolyte on Ti. Theoretical simulation calculation results prove that a more intensive electrostatic interaction of pyrrole N···Ti (2.450 Å) in LiClO4-PPy/Ti rather than perchlorate O···Ti (3.537 Å) in LiClO4/Ti. LiClO4-PPy/Ti exhibits higher density of states (57.321 electrons/eV) at Fermi energy and lower HOMO-LUMO molecule orbital energy gap (0.032 eV) than LiClO4/Ti (9.652 electrons/eV, 0.340 eV) to present the enhanced electronic conductivity. LiClO4-PPy/Ti also exhibits a more declined interface energy (−1.461 × 104) than LiClO4/Ti (−5.202 × 103 eV) to present the intensified interfacial interaction. LiClO4-PPy/Ti accordingly exhibits much higher specific capacitances of 0.123~0.0122 mF cm−2 at current densities of 0.01~0.10 mA cm−2 rather than LiClO4/Ti (0.010~0.0095 mF cm−2, presenting superior electroactivity and electrochemical capacitance properties. LiClO4-PPy/Ti could well act as the electroactive supercapacitor electrode for feasible energy storage.

Surface exsolved NiFeOx nanocatalyst for enhanced alkaline oxygen evolution catalysis

A synergistically improved alkaline oxygen evolution catalyst of the NiFeOx nanoalloy oxide structure is introduced using an in-situ exsolution method. The separately doped Ni and Fe ions are exsolved on the surface of the perovskite as homogeneously distributed NiFeOx oxide alloy catalysts via following reduction and oxidation processes. The incorporation of additional Fe into the surface embedded NiFeOx catalyst improved the inherent oxygen evolution reaction (OER) property with fast reaction kinetics. Density functional theory (DFT) result indicates the lowest OER overpotential of NiFeOx catalyst is originated from the reduced energy barrier of surface *O formation from *OH group. The NiFeOx exsolved catalyst shows the smallest overpotential of 0.49 V (j = 10 mA∙cm−2) and Tafel slope (93 mV∙dec-1), compared with that of single NiO (0.54 V, 132 mV∙dec-1) and Fe3O4 catalyst. This study provides an effective method for developing nanosized OER catalysts for various energy conversion and storage electrode materials.

The hierarchical dense structure induced high stability to NiCoB-based electrode for electrochemical energy storage

The construction of stable hierarchical surfaces through structural engineering is the key to improve reactive active sites and cycle stability to achieve high cycle performance of supercapacitors (SCs). In this work, the NiCo-LDH nanoflower as a structure guide agent was used to support NiCoB nanosheets to form a dense and stable hierarchical structure, thereby exposing more active sites and improving cycle stability. Due to the hierarchical stable surface structure, the NiCoB-0.3@NiCo-LDH-30 electrode has an excellent specific capacitance of 2710F g−1 at 1 A/g due to the excellent electrochemical active surface area (1259 mF cm−2), improving the OH– diffusion coefficient (2.4 × 10−9 cm2 s−1) and decreasing ionic diffusion barrier. After 5000 cycles, NiCoB-0.3@NiCo-LDH-30 electrode still has 92.6 % initial specific capacitance. In order to balance the energy density decrease caused by the capacitance imbalance between positive and negative electrodes, the cubed carbon (Co-C) derived from cobalt metal organic frameworks (Co-MOFs) as cathode with a good specific capacitance of 220F g−1 at 1 A/g is prepared. The assembled NiCoB-0.3@NiCo-LDH-30//Co-C hybrid SCs (HSCs), which are assembled with NiCoB-0.3@NiCo-LDH-30 electrode as anode and Co-C electrode as cathode, displays an energy density of 75 Wh kg−1 at a power density of 741 W kg−1.

A Highly Robust and Conducting Ultramicroporous 3D Fe(II)-Based Metal-Organic Framework for Efficient Energy Storage.

Exploitation of metal-organic framework (MOF) materials as active electrodes for energy storage or conversion is reasonably challenging owing to their poor robustness against various acidic/basic conditions and conventionally low electric conductivity. Keeping this in perspective, herein, a 3D ultramicroporous triazolate Fe-MOF (abbreviated as Fe-MET) is judiciously employed using cheap and commercially available starting materials. Fe-MET possesses ultra-stability against various chemical environments (pH-1 to pH-14 with varied organic solvents) and is highly electrically conductive (σ=0.19Sm-1) in one fell swoop. By taking advantage of the properties mentioned above, Fe-MET electrodes give prominence to electrochemical capacitor (EC) performance by delivering an astounding gravimetric (304Fg-1) and areal (181mFcm-2) capacitance at 0.5Ag-1 current density with exceptionally high cycling stability. Implementation of Fe-MET as an exclusive (by not using any conductive additives) EC electrode in solid-state energy storage devices outperforms most of the reported MOF-based EC materials and even surpasses certain porous carbon and graphene materials, showcasing superior capabilities and great promise compared to various other alternatives as energy storage materials.