Binder-free Electrode Research Articles

Layer‑by‑layer assembled binder-free hydrated vanadium oxide-acetylene black electrode for flexible aqueous zinc ion battery

Vanadium oxides are potential positive electrode materials for aqueous zinc ion batteries (ZIBs) owing to their advantages of high theoretical capacity, low cost, and so on. Developments of methods for preparing binder-free vanadium oxide electrodes on a large scale and further investigation of their Zn2+ storage mechanisms are essential for expanding their uses in large-scale energy storage systems and wearable electronics. In this work, binder-free electrodes with hydrated vanadium oxide (V2O5·nH2O, denoted as VOH)-acetylene black (AB) on carbon cloth (VOH-AB/CC) are fabricated by a simple and scalable method which combined low-temperature hydrothermal treatment with layer-by-layer drop/spray-coating process. The AB can greatly improve the electrical conductivity of VOH, thereby enhancing the electrochemical performance. The as-prepared electrode with 20 wt% of AB (VOH-AB2/CC) delivers a high capacity of 280 mA h g−1 at 1 A/g and a good rate capability of 205 mA h g−1 at 4 A/g, which is better than many of the reported binder-free vanadium base electrodes. Besides, excellent cycling performance with 89 % retention rate after 3000 cycles at 4 A/g is achieved on the VOH-AB2/CC electrode. Furthermore, a storage mechanism of Zn2+/H+/H2O insertion accompanied by the formation of basic zinc salt precipitate during the discharging process is proposed by the aid of ex-situ XRD and XPS techniques. Additionally, the flexible Quasi-Solid-State ZIB constructed using VOH-AB/CC as positive electrode can work well at different bending states and two ZIBs connected in series can lighten a light-emitting diode even under bending state. This work provides a low-cost, time-saving, environmental-friendly and scalable method to fabricate binder-free hydrated vanadium oxide electrodes for flexible aqueous ZIBs.

Binder-free all-carbon composite supercapacitors

Carbon-based electrode materials have widely been used in supercapacitors. Unfortunately, the fabrication of the supercapacitors includes a polymeric binding material that leads to an undesirable addition of weight along with an increased charge transfer resistance. Herein, binder-free and lightweight electrodes were fabricated using powder processing of carbon nanofibers (CNFs) and graphene nanoplatelets (GNPs) resulting in a hybrid all-carbon composite material. The structural, morphological, and electrochemical properties of the composite electrodes were studied at different concentrations of GNPs. The specific capacitance (Cs) of the CNFs/GNPs composite was improved by increasing the concentration of GNPs. A maximum Cs of around 120 F g−1 was achieved at 90 wt% GNPs which is around 5-fold higher in value than the pristine CNFs in 1 M potassium hydroxides (KOH), which then further increased to 189 F g−1 in 6 M KOH electrolyte. The energy density of around 20 Wh kg−1 with the corresponding power density of 340 W kg−1 was achieved in the supercapacitor containing 90 wt% GNPs. The enhanced electrochemical performance of the composite is related to the presence of a synergistic effect and the CNFs establishing conductive/percolating networks. Such binder-free all-carbon electrodes can be a potential candidate for next-generation energy applications.

Preparation of binder-free MoP/SnO2 carbon fiber composites with Cu-mediated surface modification for high-rate sodium ion storage

Nanofiber webs stacking with circular cross-section generally suffer from insufficient inter-fiber connection and thus poor electrical contact. Beyond regular 1D nanofibers, electrospinning is able to fabricate nanobelt webs with reinforced electron transfer for energy storage and conversion. Previously, we prepared quasi-2D belt-like fiber through electrospinning of PMo12-PPy-SnCl2-PVP-based solution (phosphomolybdic acid /polypyrrole /SnCl2 /polyvinylpyrrolidone) with freestanding property. Here, to boost the electrochemical performance, we proposed Cu-mediated surface engineering for construction of accessible active sites with balanced material components of MoP/SnO2 and carbon. As a result, thinner and porous belt-like fibers were obtained with high specific surface area (above 100 m2 g−1). The interfacial charge transfer was improved by superficial phosphides, as binder-free electrode the Cu-mediated MoP/SnO2 carbon fiber composite can deliver capacity above 200 mAh g−1 at 0.2 A g−1 under low mass loading (1.5–2.5 mg cm−2) and sustain capacity above 1.0 mAh cm−2 with loading around 5 mg cm−2 at 2 mA cm−2. Combined with ex-situ characterization, the sodiation process was probed.

Binder-free CaMoO4 nanostructured anode electrodes for Li-ion battery applications

A straightforward hydrothermal technique was employed to develop binder-free CaMoO4 electrodes that can be utilized as electrodes in Li-ion batteries. Structural analysis was employed to validate the tetragonal scheelite structure and exceptional crystallinity of the electrodes. Examination with scanning electron microscopy revealed that the electrodes exhibited diverse morphologies, including nanorods, sheets, and flowers. The composition of CaMoO4 was confirmed by analyzing the X-ray photoelectron spectroscopy data, which revealed distinct binding energy peaks corresponding to Ca, Mo, and O. The presence of these elements in the nanostructures was further confirmed by transmission electron microscopy and energy dispersive spectroscopy mapping. Electrochemical tests showed that CaMoO4 (DIW@EG sample electrode) composite electrodes demonstrated an impressive primary discharge specific capacity of 2383 mAh g−1 and a high rate capacity of 1034 mAh g−1 at 0.5 A g−1 current density. Additionally, a full cell combining LCO with CaMoO4 achieved a remarkable capacity of 321 mAh g−1 at a current density of 0.5 A g−1, presenting it as a viable substitute for the traditional LCO//graphite system.

Doping effect and oxygen vacancy engineering in nickel-manganese layered double hydroxides for high-performance supercapacitors

Design of electrode materials with high electrochemical capacitance and long lifetime remains a challenging issue for high-performance supercapacitors. Herein, we successfully synthesized a binder-free composite electrode comprising oxygen vacancy-abundant NiMnMg-layered double hydroxides grown on 3D graphene foam (Vo-NiMnMg-LDH@3DG) by Mg doping during hydrothermal process and subsequently Ar plasma etching. Thanks to the incorporation of electrochemically inert Mg element, the enhanced charge transfer capability, and enriched active sites that induced by plentiful oxygen vacancies, Vo-NiMnMg-LDH@3DG manifests a high specific capacity of 374.8 mAh g−1 at a current density of 1 A g−1 and satisfactory rate performance (74.26% at 20 A g−1). Furthermore, the asymmetric supercapacitor (ASC) assembled with Vo-NiMnMg-LDH@3DG cathode and activated carbon anode exhibits a specific capacitance up to 171 F g−1 at 1 A g−1, achieving a maximum energy density of 53.62 Wh kg−1 and the highest power density of 7500 W kg−1. This work not only provides innovative approaches for preparing oxygen vacancy-rich LDH materials, but also offers insights for the design and improvement of energy storage devices based on transition metal-based LDH.

N, O-codoped porous carbon fiber cloth synthesized by molecular dispersed CaCl2·6H2O in situ activation for high performance supercapacitors

In this study, a nitrogen/oxygen co-doped carbon fiber cloth with a hierarchical porous structure was synthesized by one-step carbonization and in situ activation method and acted as binder-free electrode materials for supercapacitors. Cotton fiber cloth served as the carbon precursor, while molecular dispersed CaCl2·6H2O and urea functioned as activator and N dopant, respectively. The influence of molar concentration of CaCl2·6H2O and urea on the microstructure and capacitive performance of the resulting products were investigated. CaCl2·6H2O has an expansion effect on pores, resulting in reduction of micropores. Hence, the specific surface area of the resulting porous carbon increased first and then decreased with the increase of CaCl2·6H2O concentration. In addition, the erosion of NH3 and CO2 (produced by the decomposition of urea) at high temperature on the surface of the samples promoted the formation of porous structure. Urea plays the dual role of doping and activation agent. The morphology and structure analysis shown that the activated samples exhibited hierarchical pore structure, large specific surface area, and high heteroatom content. The optimal sample NAC-20 exhibited good capacitive performance, including high specific capacitance of 260.9 F g−1 at 0.1 A g−1 and good rate performance. Moreover, the symmetric supercapacitor exhibited a maximum energy density and power density of 16.2 Wh kg−1 and 19.0 kW kg−1, respectively, in 6 M KOH electrolyte. In this work, a green, low-cost molten salt activation method was proposed to synthesis biomass derived porous carbon materials for energy storage devices.

Prussian blue analogues-Derived Iron-Cobalt carbon fiber Binder-Free electrodes for electrocatalytic nitrate reduction

Developing a highly selective and efficient electrocatalytic system for nitrate reduction reaction (NO3RR) is of great significance but still remains challenging for environmental remediation and energy utilization. Herein, we constructed a binder-free cathode consisted of iron-cobalt Prussian blue analogues-based bimetal derived carbon fiber (FC-PBAFC) to enhance NO3RR performances. Significantly, high NO3−-N removal capacity of 169.1 mgN h−1 gcat-1, excellent ammonia Faradic efficiency (FE) of 83.2 ± 0.7 % and high ammonia selectivity of 99.3 ± 0.6 % were achieved by FC-PBAFC binder-free cathode. The excellent NO3RR performance was attributed to the rational polymer tethering strategy for the binder-free cathode construction. The introduction of polyacrylonitrile for electrospinning shaping essentially regulated the structural and compositional distribution of binder-free electrode during followed pyrolysis. The in-situ infrared spectroscopy and DFT calculation demonstrated that the Fe and Co regulation optimized the adsorption energy of key intermediate products with suppressing the side reactions. The bimetal binder-free cathode offers a promising strategy for selective and effective electroreduction of nitrate for ammonia synthesis.

Growth of CQD/PPy on cotton cloth as a binder-free high-performance flexible electrode for symmetric supercapacitor

Benefited from the continuous development of nanomaterials, wearable microelectronics with flexible and miniaturized features are booming, and smart textiles are attracting more attentions because of their superior flexibility and perfect safety. The combination of conductive polymers and flexible substrates has created a new field for flexible supercapacitors. Herein, cotton cloth (CC), which is commonly used in daily life, was selected as the flexible substrate and a layer of CQDs was uniformly grown on the CC fibers, and then pyrrole was directly grown on CC by in-situ polymerization under Fe3+ initiation to realize the tight bonding between the conductive polymer and the flexible substrate. The electrochemical properties of the composite electrode could be controlled by changing the amount of CQD. The obtained CC@CQD@PPy electrode has a high specific capacitance (C) of 537.9 F/g at 0.5 A/g. The assembled symmetric CC@CQD@PPy supercapacitor exhibits an excellent energy density (E) of 18.7 Wh/kg at a power density (P) of 125.0 W/kg, and a supreme cycling stability with a capacitance retention of 77.9 % after 10,000 cycles. In addition, the CC@CQD@PPy supercapacitor has excellent flexibility, with almost unchanged electrochemical performance under different bending angles, and the assembled all-solid-state supercapacitor has good electrochemical properties.

In situ patterning of nickel/sulfur-codoped laser-induced graphene electrode for selective electrocatalytic valorization of glycerol

The electrocatalytic valorization of glycerol is an emerging upcycling process for the biomass utilization. In this work, nickel/sulfur-codoped laser-induced graphene (LINiSG) on flexible polyimide film was fabricated and demonstrated as a self-supported and binder-free monolithic electrode for electrocatalytic glycerol oxidation reaction (EGOR) towards the selective generation of value-added three-carbon (C3) chemicals. The laser-induced in-situ and synchronous carbonization of polysulfone and Ni precursor was demonstrated to remarkably promote both the electrochemical surface area and Ni loading of LINiSG electrode. These synergistic merits are considered as the main origin for its enhanced EGOR activity and stability, showing much smaller Tafel slope and 2-fold enhanced current density, as compared to LINiG electrode without the co-carbonization of polysulfone. The influence of experimental parameters has been systematically investigated by the product analysis, achieving an average 94.7 % C3 selectivity and 76.1 % C3 Faradaic efficiency with a high selectivity of dihydroxyacetone (ca. 67.7 %) in near-neutral conditions, which is better than most of the reported EGOR electrodes operated in near-neutral conditions. This work demonstrated the viability of using flexible self-supported and binder-free LIG electrode with rational design and preparation approach for electrocatalytic valorization of biomass.

Design of Na3MnZr(PO4)3/Carbon Nanofiber Free-Standing Cathodes for Sodium-Ion Batteries with Enhanced Electrochemical Performances through Different Electrospinning Approaches.

The NASICON-structured Na3MnZr(PO4)3 compound is a promising high-voltage cathode material for sodium-ion batteries (SIBs). In this study, an easy and scalable electrospinning approach was used to synthesize self-standing cathodes based on Na3MnZr(PO4)3 loaded into carbon nanofibers (CNFs). Different strategies were applied to load the active material. All the employed characterization techniques (X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), thermal gravimetric analysis (TGA), and Raman spectroscopy) confirmed the successful loading. Compared to an appositely prepared tape-cast electrode, Na3MnZr(PO4)3/CNF self-standing cathodes demonstrated an enhanced specific capacity, especially at high C-rates, thanks to the porous conducive carbon nanofiber matrix. Among the strategies applied to load Na3MnZr(PO4)3 into the CNFs, the electrospinning (vertical setting) of the polymeric solution containing pre-synthesized Na3MnZr(PO4)3 powders resulted effective in obtaining the quantitative loading of the active material and a homogeneous distribution through the sheet thickness. Notably, Na3MnZr(PO4)3 aggregates connected to the CNFs, covered their surface, and were also embedded, as demonstrated by TEM and EDS. Compared to the self-standing cathodes prepared with the horizontal setting or dip-drop coating methods, the vertical binder-free electrode exhibited the highest capacity values of 78.2, 55.7, 38.8, 22.2, 16.2, 12.8, 10.3, 9.0, and 8.5 mAh/g at C-rates of 0.05C, 0.1C, 0.2C, 0.5C, 1C, 2C, 5C, 10C, and 20C, respectively, with complete capacity retention at the end of the measurements. It also exhibited a good cycling life, compared to its tape-cast counterpart: it displayed higher capacity retention at 0.2C and 1C, and, after cycling 1000 cycles at 1C, it could be further cycled at 5C, 10C, and 20C.

Evaluation of the effect of precursor ratios on the electrochemical performances of binder-free NiMn-phosphate electrodes for supercapattery

Binary metal phosphate electrodes have been widely studied for energy storage applications due to the synergistic effects of two different transition elements that able to provide better conductivity and stability. Herein, the battery-type binder-free nickel-manganese phosphate (NiMn-phosphate) electrodes were fabricated with different Ni:Mn precursor ratios via microwave-assisted hydrothermal technique for 5 min at 90 °C. Overall, NiMn3P electrode (Ni:Mn = 1:3) showed an outstanding electrochemical performance, displaying the highest specific (areal) capacity at 3 A/g of 1262.4 C/g (0.44 C/cm2), and the smallest charge transfer resistance of 108.8 Ω. The enhanced performance of NiMn3P electrode can be ascribed to the fully grown amorphous nature and small-sized flake and flower structures of NiMn3P electrode material on the nickel foam (NF) surface. This configuration offered a higher number of active sites and a larger exposed area, facilitating efficient electrochemical reactions with the electrolyte. Consequently, the NiMn3P//AC electrode combination was chosen to further investigate its performance in supercapattery. The NiMn3P//AC supercapattery exhibited remarkable energy density of 105.4 Wh/kg and excellent cyclic stability with 84.7% retention after 3000 cycles. These findings underscored the superior electrochemical performance of the battery-type binder-free NiMn3P electrode, and highlight its potential for enhancing the overall performance of supercapattery.

A 2.5V In-Plane Flexi-Pseudocapacitor with Unprecedented Energy and Cycling Efficiency for All-Weather Applications.

As electronic devices for aviation, space, and satellite applications become more sophisticated, built-in energy storage devices also require a wider temperature spectrum. Herein, an all-climate operational, energy and power-dense, flexible, in-plane symmetric pseudocapacitor is demonstrated with utmost operational safety and long cycle life. The device is constructed with interdigital-patterned laser-scribed carbon-supported electrodeposited V5O12·6H2O as a binder-free electrode and a novel high-voltage anti-freezing water-in-salt-hybrid electrolyte. The anti-freezing electrolyte can operate over a wide temperature range of -40-60°C while offering a stable potential window of ≈2.5V. The device undergoes rigorous testing under diverse environmental conditions, including rapid and regular temperature and mechanical transition over multiple cycles. Additionally, detailed theoretical simulation studies are performed to understand the interfacial interactions with the active material as well as the local behavior of the anti-freeze electrolyte at different temperatures. As a result, the all-weather pseudocapacitor at 1Ag-1 shows a high areal capacitance of 234.7mFcm-2 at room temperature and maintains a high capacitance of 129.8mFcm-2 even at -40°C. Besides, the cell operates very reliably for over 80950 cycles with a capacitance of 25.7mFcm-2 at 10Ag-1 and exhibits excellent flexibility and bendability under different stress conditions.

Unlocking the potential of optimal etching and ion exchange concentration in post-synthesis of binder-free NiCo-MOFs for high-performance supercapacitors

In this study, we synthesized binder-free NiCo-MOFs electrodes on a flexible stainless-steel substrate (abbreviated as NCMS) using a post-synthesis approach that involves etching and an ion-exchange method. Herein, different concentrations of the nickel precursor, specifically 0.01 M (NCMSA), 0.05 M (NCMSB), 0.10 M (NCMSC), and 0.15 M (NCMSD), were employed to optimize the concentrations of the nickel precursor involved in etching and ion exchange method for Supercapacitors (SCs). Structural, morphological, compositional, and electrochemical characteristics of NCMS electrodes were studied. Morphological investigation unveiled a porous interconnected sheet-like architecture of NiCo-MOFs electrodes which is highly advantageous for SCs. Notably, the NCMSB electrode exhibited outstanding electrochemical performance, achieving a highest specific capacity (Csp) of 206 mAh/g (1487 F/g) at 5 mV/s; along with a 54.42 % retention rate after 3000th cycles at 100 mV/s. Additionally, NCMSB demonstrated superior power density (Pd) and energy density (Ed) of 2500 W/kg and 43.68 Wh/kg respectively. The power law was employed to examine the charge storage kinetics of the NCMSB electrode. Moreover, a symmetric aqueous device fabricated and evaluated for its electrochemical performance, exhibiting maximum Cs of 22 F/g (9.01 mAh/g) at 10 mV/s. The device exhibited a good Pd of 389 W/kg and Ed of 3.14 Wh/kg at 1 A/g, maintaining 69 % retention over 3000th cycles at 15 A/g. The current findings highlight the significance of etching and ion-exchange concentrations of nickel precursor during the post-synthesis of NiCo-MOFs electrode to achieve high supercapacitive performance.

Porous tungsten carbo-nitride supported Pt nanoparticles with high conductivity for efficient and stable hydrogen evolution reaction

Designing low-cost catalysts that offer both high mass activity and high cycling stability is crucial. Herein, a binder-free 3D self-supporting electrode composed of carbo-nitride tungsten supporting Pt nanoparticles (Pt@3DP-WNxC1-x/W) has been successfully synthesized for hydrogen evolution reaction in acid electrolyte. The tungsten carbo-nitride synthesized via a one-step heat treatment exhibits enhanced conductivity as a result of the carbonization process and optimizes the adsorption and desorption properties of WC towards H atoms through the incorporation of N atoms, thereby achieving an effective balance. Simultaneously, the N–Pt bond enhances electron transfer efficiency. This electrode exhibits outstanding electrochemical performance with a 219 mV overpotential at a current density of −300 mA cm−2. Its current density and mass activity is up to 75 mA cm−2 and 7.5 A·mgPt−1 at an overpotential of 100 mV, respectively, which are both 2.6 times higher than those of the 40% Pt/C electrode. In addition, it reveals a low Tafel slope of 38.3 mV dec−1 indicating rapid kinetics. Furthermore, the electrocatalyst shows only 3 mV day at −100 mA cm−2 after 10,000 cycles. Both theoretical calculation and experimental results show the promotion of catalytic efficiency of Pt@3DP-WNxC1-x/W brought by carbo-nitrition. This study offers a novel, efficient, and stable electrode design strategy.

Designing core-shell heterostructure arrays based on snowflake NiCoFe-LTH shelled over W2N-WC nanowires as an advanced bi-functional electrocatalyst for boosting alkaline water/seawater electrolysis

The pursuit of efficient and sustainable hydrogen production through water splitting has led to intensive research in the field of electrocatalysis. However, the impediment posed by sluggish reaction kinetics has served as a significant barrier. This challenge has inspired the development of electrocatalysts characterized by high activity, abundance in earth's resources, and long-term stability. In addressing this obstacle, it is imperative to meticulously fine-tune the structure, morphology, and electronic state of electrocatalysts. By systematically manipulating these key parameters, the full potential of electrocatalysts can unleash, enhancing their catalytic activity and overall performance. Hence in this study, a novel heterostructure is designed, showcasing core–shell architectures achieved by covering W2N-WC nanowire arrays with tri-metallic Nickel-Cobalt-Iron layered triple hydroxide nanosheets on carbon felt support (NiCoFe-LTH/W2N-WC/CF). By integrating the different virtue such as binder free electrode design, synergistic effect between different components, core–shell structural advantages, high exposed active sites, high electrical conductivity and heterostructure design, NiCoFe-LTH/W2N-WC/CF demonstrates striking catalytic performances under alkaline conditions. The substantiation of all the mentioned advantages has been validated through electrochemical data in this study. According to these results NiCoFe-LTH/W2N-WC/CF achieves a current density of 10 mA cm−2 needs overpotential values of 101 mV for HER and 206 mV for OER, respectively. Moreover, as a bi-functional electrocatalyst for overall water splitting, a two-electrode device needs a voltage of 1.543 V and 1.569 V to reach a current density of 10 mA cm−2 for alkaline water and alkaline seawater electrolysis, respectively. Briefly, this research with attempting to combination of different factors try to present a promising stride towards advancing bi-functional catalytic activity with tailored architectures for practical green hydrogen production via electrochemical water splitting process.

3D-printed pyramid nickel-based electrode enabling directional bubble traffic and electrolyte flow for efficient hydrogen evolution

For efficient and stable large-scale water electrolysis, practical industrial electrodes should meet the following characteristics: high activity, structural stability, and fast bubble removal. Here we report a structured electrode (NiS–Co–NiP) prepared via 3D printing of nickel-based substrate and subsequent electrodeposition for the hydrogen evolution reaction (HER). With unique 3D nanosheets, the NiS–Co–NiP electrode exhibits large electrochemical surface area (ECSA), strong hydrophilicity, high mechanical strength and electrical conductivity, delivering outstanding HER activity. It requires low overpotentials of 134 mV and 169 mV to achieve the current densities of 100 mA cm−2 and 300 mA cm−2, respectively. Moreover, rational design of the NiS–Co–NiP electrode in pyramidal geometry facilitates directional bubble transport and electrolyte flow, resulting in superior stability of 350 h at a current density of 150 mA cm−2. This work demonstrates a new approach for manufacturing binder-free structured electrode of excellent HER performance at high current densities.

Simple and affordable synthesis of a binder-free nickel-zinc sulfide electrode for high-performance supercapacitors

Due to the increasing demand for renewable energy solutions, aqueous energy systems have emerged as promising and sustainable technologies. Nanostructured transition metal sulfides, renowned for their exceptional properties, are prime candidates for electrochemical supercapacitors. In this study, we present the synthesis of nickel-zinc sulfide (Ni-Zn-S) as a binder-free supercapacitor material using the affordable successive ionic layer adsorption and reaction simple technique. The active nanomaterial was directly deposited onto a 3D Ni foam current collector substrate, negating the need for a binder. The synergistic combination of Ni and Zn enhances the electrode capacitance. Various electrochemical techniques were used to evaluate the loaded active material as a binder-free supercapacitor electrode in a 6 M KOH electrolyte. Results indicate pseudocapacitive performance, achieving a high specific capacitance of 400F/g at 0.7 A/g. This material retains 97 % of its capacity, even after 2000 cycles, showcasing exceptional long-term cycling stability. These findings underscore the potential of the Ni-Zn-S electrode for delivering low-cost, high-performance supercapacitors.

Construction of hydrophilic-hydrophobic domains in Bi2O3/nitrogen-doped carbon electrode to boost CO2-to-formate conversion

Bi has drawn attention in catalyzing the electrochemical CO2-to-formate conversion due to promising selectivity and low cost, but the process suffers from low activity. Herein, we introduce nitrogen-doped carbon (NC) support with hydrophobicity modification to enhance the activity of a binder-free Bi2O3 electrode. Formate partial current on the NC supported Bi2O3 electrode almost doubles compared to Bi2O3 on unmodified support. Furthermore, the hydrophobicity modification with polytetrafluoroethylene (PTFE) significantly extends the stability of NC supported Bi2O3 by diminishing flooding. It also maintains >90% formate selectivity at a broad potential range from −0.87 to −1.27 V (vs. RHE) and shows a formate partial current density of −100 mA cm−2 at −1.37 V (vs. RHE) in 0.5 M KHCO3. The improvement is attributed to the synergetic effects of the hydrophilic active sites and the hydrophobic PTFE modified NC support. The unique structure promotes the reactants transport and thus maximizes the active site utilization at the triple-phase interface. This facile microenvironment regulation can be extended to other applications involving gaseous-aqueous phases.

NiMnCo-LDH in-situ derived from ZIF-67@ZnO as self-supporting electrode for asymmetric supercapacitor device

Metal-organic frameworks have attracted much attention due to their abundant redox sites and tunable characteristics, which are advantageous for energy storage applications. However, the low electrical conductivity, poor physical strength and undesirable capacity seriously hinder their applications. Therefore, designing effective and convenient strategies to build composites with unique structures will be of practical significance. Herein, we successfully generate NMC-LDH/ZnO@CC nanocomposites by growing ortho-hexagonal nickel–cobalt layered double hydroxide (NMC-LDH) nanosheets in-situ on ZIF-67 precursor covering vertical arrays of ZnO nanorods. As a result of the unqiue ortho-hexagonal structure, highly ordered arrangement of active substances and multi-dimensional spaces of the prepared NMC-LDH/ZnO@CC binder-free electrode, its capacitance is as high as 9258 mF cm−2 at a current density of 2 mA cm−2 and the capacitance retention is maintained at 87.5 % after 5000 cycles. Furthermore, in order to explore the practical value of the prepared binder-free electrode, the NMC-LDH/ZnO@CC//AC solid-state asymmetric supercapacitor device is assembled. The energy density of the assembled supercapacitor is 24.6 W h kg−1 at a power density of 170 W kg−1 and 1020 W kg−1 at an energy density of 11.8 W h kg−1. In addition, a versatile instrument for monitoring air humidity, time and ambient temperature in portable environments can be powered by a single ultracapacitor unit for more than 30 min. Overall, this study provides a unique strategy for synthesizing ZIF derivatives with novel morphologies for electrochemical energy storage applications.

PPy-PdO modified MXene for flexible binder-free electrodes for asymmetric supercapacitors: Insights from experimental and DFT investigations

Binder-free, flexible electrodes of V2C MXene, V2C-PPy, and V2C-PPy-PdO (a ternary composite of vanadium carbide, polypyrrole, and palladium oxide) were fabricated using a simplified, one-step electrodeposition method. A comprehensive assessment has subsequently been conducted on the microstructural and electrochemical attributes of these electrode materials when utilized in supercapacitors with a 1 M H2SO4 electrolyte. Notably, an impressive specific capacitance of 487F g−1 is achieved for V2C-PPy-PdO ternary composite at 1 A/g. This exceptional performance is due to the considerable active surface area and inherent structural stability of the host material. These factors significantly enhanced the electrochemical reaction kinetics and cyclic reversibility. Furthermore, the V2C-PPy-PdO composite demonstrated a notable specific capacitance of 250F g−1 when integrated into an asymmetric coin cell configuration alongside activated porous carbon under a current density of 1 A/g. Remarkably, it maintained an outstanding capacitance retention of 92 % across 10,000 charge–discharge cycles. Our experimental discoveries were additionally substantiated through the Density Functional Theory calculations, which unveiled that the inclusion of PdO within the V2C-PPy-PdO composite led to an augmentation of electronic states near the Fermi level. This increase in electronic states ultimately improved the quantum capacitance, rendering the V2C-PPy-PdO composite a highly promising candidate for supercapacitor applications.