Diffusion Of Electrolyte Ions Research Articles

Copper(II)-Tannic Acid@Cu with In Situ Grown Gold Nanoparticles as a Bifunctional Matrix for Facile Construction of Label-Free and Ultrasensitive Electrochemical cTnI Immunosensor.

Sensitive detection of cardiac troponin I (cTnI) is of great significance in the diagnosis of a fatal acute myocardial infarction. A redox-active nanocomposite of copper(II)-tannic acid@Cu (CuTA@Cu) was herein prepared on the surface of a glassy carbon electrode by electrochemical deposition of metallic copper combined with a metal stripping strategy. Then, HAuCl4 was in situ reduced to gold nanoparticles (AuNPs) by strong reductive catechol groups in the TA ligand. The AuNPs/CuTA@Cu composite was further utilized as a bifunctional matrix for the immobilization of the cTnI antibody (anti-cTnI), producing an electrochemical immunosensor. Electrochemical tests show that the immunoreaction between anti-cTnI and target cTnI can cause a significant reduction of the electrochemical signal of CuTA@Cu. It can be attributed to the insulating characteristic of the immunocomplex and its barrier effect to the electrolyte ion diffusion. From the signal changes of CuTA@Cu, cTnI can be analyzed in a wide range from 10 fg mL-1 to 10 ng mL-1, with an ultralow detection limit of 0.65 fg mL-1. The spiked recovery assays show that the immunosensor is reliable for cTnI determination in human serum samples, demonstrating its promising application in the early clinical diagnosis of myocardial infarction.

Improved-quality graphene films via the synergism of large nanosheet aligning and nanotube bridging for flexible supercapacitors.

Scalable production of reduced graphene oxide (rGO) films with high mechanical-electrical properties are desirable candidates for wearable electronics devices and energy storage applications. Removing structural incompleteness such as wrinkles or voids in the graphene films generated from the assemble process would greatly optimize their mechanical properties. However, the densely stacked graphene sheets in the films degrades their ionic kinetics and thus limits their development. Here, a horizontal-longitudinal-structure modulating strategy is demonstrated to produce enhanced mechanical, conductive and capacitive graphene films. Typically, two-dimensional (2D) large graphene sheets (LGS) induce regular stacking of GO during assembling process to reduce wrinkles, while one-dimensional (1D) single-walled carbon nanotubes (SWCNT) bridge with graphene sheets to strengthen the multidirectional intercalation and reduce GO layer restacking. The simultaneous incorporation of LGS and SWCNT synergistically makes fine microstructure with improving the alignment of graphene sheets, increasing continuous conductive pathways to facilitate electron transport, and enlarging interlayer spacing to promote the electrolyte ion diffusion. As a result, the obtained graphene films are flat and exhibit signally reinforced mechanical properties, electrical conductivity (38727 S m-1), as well as specific capacitance (232 F g-1) as supercapacitor electrodes than those of original rGO films. Moreover, owing to the comprehensive improved properties, the flexible gel supercapacitor assembled by the graphene film-based electrodes shows high energy density, good flexibility and excellent cycling stability (93.8% capacitance retention after 10000 cycles). This work provides a general strategy to manufacture robust graphene structural materials for energy storage applications in flexible and wearable electronics.

Self-discharge suppression by composite regenerated cellulose ion-selective separator for high-energy aqueous supercapacitors

Aqueous supercapacitors exhibit the advantage of high cycling stability, inherent safety and appealing energy density, and thus have long been considered an exceptional technology for efficient energy storage. However, in the absence of an electric field, the spontaneous transmembrane diffusion of ions leads to self-discharge or energy decay of supercapacitors. Herein, we propose a phase transformation strategy to design a porous regenerated cellulose and polyvinylidene difluoride composite separator with ion selectivity by utilizing cellulose dissolution regeneration with PVDF enhancement. Specifically, the anion selective property of PVDF screens the transmembrane diffusion of electrolyte ions, thereby suppressing the self-discharge of supercapacitors. The in-depth characterization indicated that the RC@PVDF separator applied to aqueous supercapacitors demonstrated high performance by maintaining a capacitance of 173 F g−1 after 20,000 cycles. After 24 h of self-discharge, the supercapacitor retained 59 % of its energy. In addition, the cross-linked network of regenerated cellulose provides critical properties for the ion-selective separator, including strong mechanical stability, excellent thermal stability (220 °C) and uniform pore structure (31 nm). This work is anticipated to provide considerable insight into the creative design of self-discharge suppression separators for long-term energy storage supercapacitors.

Electrochemical evaluation of low crystalline CoFe2O4@Reduced graphene oxide nanocomposite for hybrid supercapacitor application

The development of high-performance and cost-effective energy storage materials remains of significant scientific interest. Here, low-crystalline (LC) binary transition metal oxide (BTMO) CoFe2O4 is studied for its application in a hybrid supercapacitor. This disordered LC CoFe2O4 material was prepared by the co-precipitation method, and to improve the electron transport property of the LC CoFe2O4, a composite was prepared with reduced graphene oxide (RGO). LC CoFe2O4@rGO interconnected network enhances the electrolyte ion diffusion within the material. This CoFe2O4@RGO shows an electrochemical performance of 2247.82 mF cm−2 at a current density of 1 mA cm−2. The cyclic stability study is performed to CF@RGO 20 % electrode for 2000 cycles at 30 mA cm−2 current density. Further, to understand the charge storage mechanism, Dunn analysis is done, the capacitive and diffusion contributions to charge storage are studied. Besides, the charge transfer and diffusion characteristics of the material were studied using electrochemical impedance spectroscopy. So, these LC CoFe2O4@RGO based materials with improved ion diffusivity and flexibility in synthesis make them attractive candidates for the development of high-performance and cost-effective supercapacitor.

Waste-to-energy material: Winery-waste derived heteroatoms containing graphene-like porous carbon for high-voltage supercapacitor

Recycling industrial waste to produce energy and storage materials provides the best means of addressing its environmental impact and achieving economic benefits. This study used solid industrial winery waste to prepare an innovative heteroatom containing graphene-like porous carbon (HGPC) by simple heat treatment and chemical activation using KOH. The prepared N and S containing HGPC had a thin sheet-like structure, a high specific surface area (925.00 m2/g), and a micro-meso-porosity suitable for sustainable energy storage applications. A density functional theory investigation indicated that the synergistic effects of N and S co-doping enhanced both conductivity and electrolyte ion (Na+) diffusion kinetics in HGPC samples. When the solid winery waste-derived HGPC was used in a supercapacitor (SC) cell assembly with a diglyme-based electrolyte, it delivered an operating voltage window of 2.0 V, which was about twice as wide as those reported for symmetric SCs and compared well with those of asymmetric/hybrid SCs. In addition, it had a specific capacitance of 32 F/g (at the cell level) with a high energy density of 17.7 Wh/kg at a power density of 303.42 W/kg and excellent cycling stability over 10,000 charge/discharge cycles. This work shows that the solid winery waste-derived HGPC can be utilized for future SCs technology by replacing costly commercial YP-50F carbon to provide enhanced energy storage in a sustainable, green manner.

Hierarchical porous carbon originated from the directing associated with activation as high-performance electrodes for supercapacitor and Li ion capacitor

A template-directing methodology combined with post-activation methodology is developed to synthesize hierarchical porous carbon (HPC) with a unique nanocage-like morphology and exceptional structural integrity, utilizing light MgO nanocapsules as templates and coal pitch as precursor. The specific surface area and pore volume of HPC can be precisely adjusted by varying the mass ratio between the chemical activator and PC. This optimized pore structure significantly enhances the kinetics of electrolyte ion diffusion, which is a crucial point for the high-performance supercapacitors. The superior capacitive energy-storage behavior with respect to capacitance and rate capability (168 and 160 F g−1 at 1 and 100 A g−1) can be delivered by HPC electrode as compared to commercial activated carbon and pristine PC. The great compatibility to high gravimetric and areal capacitances (173 F g−1 and 1391 mF cm−2) can still be achieved even at 8 mg cm−2 for HPC electrode. Moreover, a full hybrid Li ion capacitor fabricated using HPC, delivers outstanding rate capability, excellent Ragone performance, and exceptional cyclability, establishing the potential of this material for advanced energy storage systems. The successful integration of template-directed synthesis with activation techniques presents a scalable approach to convert coal pitch into high-performance electrode materials.

Synthesis and Electrochemical Characterization of ZnMoS4 Nanorods on Nickel Foam Substrate for Advanced Hybrid Supercapacitor Applications.

A single-step hydrothermal method was utilized to grow ZnMoS4 (ZMS) nanorods uniformly. Initially, [MoS4]2- and Zn2+ ions interacted to create active nucleation centers, which then led to the formation of primary particles. These particles then underwent spontaneous aggregation and self-assembly on the nickel foam (NF) substrate, which served as a superior 3D interconnecting network template. This aggregation occurred nearly perpendicular to the NF and promoted the uniform growth of ZMS nanorods. The nanorods structure ensures efficient and rapid electrolyte accessibility and ion diffusion, resulting in an increased specific capacitance (Cs) of 2,116 Fg1- (846.4 C g-1) at 1 A g-1 and maintaining about 90% of their capacitance after 10,000 cycles of galvanic charge-discharge (GCD). In a hybrid supercapacitor configuration, ZMS@NF//AC@NF achieved a peak specific power of 7.2 kW.kg-1 and a specific energy of 40.3 Wh.kg-1. Remarkably, it preserved 93% of its initial capacitance after more than 20,000 cycles. These findings affirm the potential of binder-free ZMS nanorods as effective positive electrodes in advanced hybrid supercapacitors.

Nano ZIF-67/PBA derived core-shell sulfides or phosphides for enhanced electrochemical performance of supercapacitors

Metal-organic frameworks (MOFs) possess large specific surface area, high porosity, and adjustable pore size, exhibiting a broad prospect in the field of supercapacitors. However, the poor stability and conductivity of MOFs limited their application in energy storage. The structure of MOF composites and their derivatives are beneficial for storing electric charge and boosting the diffusion of electrolyte ions. In this study, we prepared heterostructured ZIF-67/Prussian blue analogues (PBA) derived sulfides and phosphides using the hydrothermal and solid-phase phosphating method, respectively. The ZIF-67/PBA composites with an average particle size of approximately 1100 nm, retained the rhombic dodecahedral shape of ZIF-67. Compared with MOF-derived phosphides, MOF-derived sulfides more completely retained the rhombic dodecahedron morphology of ZIF-67/PBA and demonstrated good electrochemical performance, especially ZPS-3. The unique core-shell nanostructure provides more active sites and suitable ion transport paths for reversible oxidation-reduction reactions. In three-electrode system, the ZPS-3 electrode exhibited a specific capacity of 603.9 F g−1 at a current density of 0.5 A g−1, superior rate performance, and excellent cycle stability. This study established a new synthesis paradigm for the development of MOF derivatives as a potential class of electrode materials for supercapacitors.

Hierarchical heterostructures of MXene and mesoporous hollow carbon sphere for improved ion accessibility and rate performance

The development of electrode materials with a hierarchically porous structure and good electrical connection is key to improving the charging-discharging rate and energy density of supercapacitors. However, the restacking issue of two-dimensional nanomaterials, such as MXene, seriously hinders the diffusion of electrolyte ions. Different from the extensively used sacrificing template method, a hierarchical heterostructure of electrically conducting mesoporous hollow carbon spheres (MHCS) and MXene composite electrode is designed and achieved through simple vacuum filtration without further template removing procedures. This direct preparation strategy not only effectively improves the specific surface area of the electrode but also enhances the abundant surface pores and good conductivity of MHCS, improving the penetration of the electrolyte solution and shortening the ion transport path, leading to a pronounced improvement in specific capacitance and rate performance of the electrodes. Additionally, the influence of sheath thickness of MHCSs on ion transfer rate is deeply discussed. The introduction of carbon nanotubes (CNTs) further improves conductivity and stability while maintaining good flexibility. Consequently, the MXene/MHCS/CNT film delivers a high specific capacitance (395F g−1 at 2 mV s−1), outstanding rate performance (70.9 % at 1000 mV s−1), and excellent cycling stability (98.3 % capacity retention after 10,000 cycles). Furthermore, the assembled symmetric supercapacitor provides a maximum energy density of 14.48 Wh kg−1. This work provides a quick and effective approach for constructing high performance 3D MXene architectures for fast ion transfer electrodes.

Cathode|Electrolyte Interface Engineering by a Hydrogel Polymer Electrolyte for a 3D Porous High-Voltage Cathode Material in a Quasi-Solid-State Zinc Metal Battery by In Situ Polymerization.

This work highlights the development of a superior cathode|electrolyte interface for the quasi solid-state rechargeable zinc metal battery (QSS-RZMB) by a novel hydrogel polymer electrolyte using an ultraviolet (UV) light-assisted in situ polymerization strategy. By integrating the cathode with a thin layer of the hydrogel polymer electrolyte, this technique produces an integrated interface that ensures quick Zn2+ ion conduction. The coexistence of nanowires for direct electron routes and the enhanced electrolyte ion infiltration and diffusion by the 3D porous flower structure with a wide open surface of the Zn-MnO electrode complements the interface formation during the in situ polymerization process. The QSS-RZMB configured with an integrated cathode (i-Zn-MnO) and the hydrogel polymer electrolyte (PHPZ-30) as the separator yields a comparable specific energy density of 214.14Whkg-1 with that of its liquid counterpart (240.38Whkg-1, 0.5MZn(CF3SO3)2 aqueous electrolyte). Other noteworthy features of the presented QSS-RZMB system include its superior cycle life of over 1000 charge-discharge cycles and 85% capacity retention with 99% coulombic efficiency at the current density of 1.0Ag-1, compared to only 60% capacity retention over 500 charge-discharge cycles displayed by the liquid-state system under the same operating conditions.

Vertically aligned ReS2 on MOF deorived CoS2–C hybrid as core-shell catalyst for promoting overall water splitting

The rational design of a core-shell structured electrocatalyst is important to improve the efficiency of electrocatalytic hydrogen production through water splitting. Herein, the catalyst is composed of rhenium disulfides (ReS2) vertically grown on cobalt sulfides/carbon hybrid by hydrothermal and activation treatment (CoS2–C@ReS2/CFP). The core-shell structure is constructed by sulfurizing the cobalt-based metal-organic framework, preventing the restacking of the ReS2 nanosheet, exposing more active sites, and facilitate electrolyte ion diffusion. Moreover, the CoS2–C@ReS2/CFP catalyst shows exceptional performance during the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) process in an alkaline electrolyte. At ·10 mA cm−2, the overpotentials of the CoS2–C@ReS2/CFP catalyst are 85 and 257 mV during the HER and OER processes with the small Tafel slope, low charge transfer resistance and exceptional catalytic stability. The combination of the CoS2 core and ReS2 shell is designed to adjust the adsorption energy of water molecules, promoting water dissociation, and enhancing the catalytic activity of CoS2–C@ReS2/CFP catalyst. This work provides an efficient strategy for developing the core-shell structured catalysts, potentially advancing the practical application into water splitting for hydrogen production.

An insight Into Surface and Diffusion Characteristics of UiO‐66@ZIF‐8 Core–Shell MOF for Asymmetric Supercapacitors with Unprecedented Energy Density

AbstractIn this study, nanosized zeolitic imidazolate framework‐8 (ZIF‐8) crystal has been produced on the universitetet i oslo‐66 (UiO‐66) metal–organic framework (MOF) to make core–shell structure using a layer‐by‐layer deposition method. In comparison to the pristine UiO‐66 and ZIF‐8, the core–shell MOF exhibits superior performance in terms of specific capacitance. This enhanced performance is attributed to its remarkable ability to facilitate the rapid diffusion of electrolyte ions through nanosized ZIF‐8 and enhance the electron transfer process involving the inner and outer metal ions within the UiO‐66@ZIF‐8 structure. Remarkably, the core–shell structure achieves an impressive specific capacitance of 588.8 F g−1 at a current density of 0.5 A g−1 using 1 m sulfuric acid (H2SO4) aqueous electrolyte. Additionally, the UiO‐66@ZIF‐8 core–shell material is demonstrated as a positive electrode, coupled with activated carbon (AC) derived from waste tissue paper serving as the negative electrode, in the fabrication of an asymmetric supercapacitor (ASC) device. At a power density of 400 W kg−1, this assembled asymmetric device delivers a notably high energy density of 53 Wh kg−1 along with a cyclic stability of 94.8% after 10 000 cycles. This study substantiates the superior performance of the UiO‐66@ZIF‐8 core–shell MOF structure as a highly effective supercapacitor electrode material, surpassing the performance of its pristine MOF counterparts.

MnCo2O4 Spinel Nanorods for Highly Sensitive Electrochemical Detection of Nitrite.

The rational design of nitrite sensors has attracted significant research interest due to their widespread use and the associated risks of methemoglobinemia and carcinogenicity. The undisclosed nitrite-sensing performance of the spinel cobaltite MnCo2O4 (MCO) prepared by an oxalate-assisted coprecipitation method is reported in this study. Spectroscopy and microscopy investigations revealed the formation of uniform MCO nanorods with a high aspect ratio. The electrocatalytic nitrite oxidation at the MCO-coated glassy carbon electrode (MCO/GCE) indicated the promising performance of the synthesized material for nitrite sensing. MCO/GCE detects nitrite in a concentration range of 5 μM to 3 mM and has a limit of detection of 0.95 μM with a higher sensitivity of 857 μA mM-1 cm-2 in a response time of 4 s. In MCO, the mixed-valence states of Co2+/Co3+ confer a high electrical conductivity, and higher valent redox couples of Mn and Co impart remarkable electrocatalytic activity toward nitrite oxidation. MCO spinel undergoes facile and ultrafast faradaic reactions to mediate nitrite oxidation. Additionally, the mesopores of MCO nanorods facilitate the rapid diffusion of electrolyte and nitrite ions. Employing the electrode in sensing nitrite in milk, lake, and tap water samples further validates its potential application in real-life testing. MCO spinel nanorods showcase promising scope for utilization in the electrochemical sensing of nitrite and inspire further exploration of transition-metal oxide-based mixed-spinel materials.

Electrodeposited three-dimensional hierarchical architecture of MgO anchored with Ag nanoparticles for high-performance symmetric supercapacitors

A blossom-like, three-dimensional (3D) hierarchical architecture of MgO anchored with silver nanoparticles (Ag NPs) is developed using a simple galvanostatic electrodeposition method. This study shows how electrochemical performance is improved by the incorporation of Ag NPs within a 3D framework. The 3D blossom-like scaffold comprises thin 2D petals, whose porous lace-like patterns provide a large surface area and many channels for the rapid diffusion of electrolyte ions. The anchored Ag NPs increase the electrical conductivity of the MgO structure and enhance redox reactions. An optimum Ag loading of 10 vol% on MgO (MgO@Ag-10) affords a 100-fold enhancement in specific capacitance over that of MgO. This hybrid MgO@Ag-10 electrode on a stainless-steel substrate yields a specific capacitance of 388.6 F.g−1 (134.85 mF.cm−2) at a current density (CD) of 1 mA.cm−2, whereas pure MgO delivers only 3.72 F.g−1 (3.1 mF.cm−2) at the same CD in a three-electrode system. The MgO@Ag-10 electrode also exhibits 88.6 % capacitance retention over 5000 charge–discharge cycles. A symmetric supercapacitor device comprising two MgO@Ag-10 electrodes exhibits a specific capacitance of 42 F.g−1, an energy density of 23.33 Wh.kg−1, and a power density of 8000 W.kg−1 at 4 mA.cm−2 in aqueous KOH.

NiFe2O4@NiCo2O4 hollow algae-like microspheres enabled by Mott-Schottky for electrochemical energy storage

Designing hybrid structure of transition metal oxides (TMOs) with controlled morphology can adjust the electronic structure and create more kinetics reactions. Herein, a new kind of NiFe2O4@NiCo2O4 nanocomposite was synthesized with one pot hydrothermal route. The unique hollow algae-like microspheres with plenty nanowires and the synergistic effect factors promote high electroactive sites and generate a built-in electric field. The constituted Mott-Schottky heterostructure creates strong interfacial interaction, paves the way for the electrolyte ions diffusion and results high charges transfer abilities by reducing the energy barriers in the heterointerfaces. As cathode material, the NiFe2O4@NiCo2O4 presents satisfactory specific capacity of 996C·g−1 at 0.5 A·g−1 and maintains ultrahigh capacity retention of 81 % at 30 A·g−1 with marvellous stability of only 6 % loss during 20,000 cycles. Interestingly, asymmetric hybrid supercapacitor device based NiFe2O4@NiCo2O4//active carbon (AC) provides tremendous energy density of 117.6 Wh·kg−1 at 438 W·kg−1 power density. What’s more, all-solid-state device offers ultra-low self-discharge process of 9.5 % through 24 h. Therefore, the combination of NiFe2O4@NiCo2O4 to form Mott-Schottky heterojunction was a promising strategy to develop electrode material with high energy storage performance.

Fabrication of spinel SrBi2O4 nanomaterials anchored on g-C3N4 nanosheets with enhanced performance of electrode material for energy storage application

Graphitic carbon nitride (g-C3N4) material with a similar structural phase to graphite opens new opportunities in energy conversion storage systems. The g-C3N4 sheets offered many defected sites that enhanced the adsorption and diffusion of electrolyte ions. High nitrogen concentration in g-C3N4 was ideal for increasing the binding energy between metals and carbon. The stability of pseudo-active metal oxides/chalcogenides supported by carbon results in improved capacitive performance. This study used a hydrothermal route to fabricate binary SrBi2O4/g-C3N4 composite onto g-C3N4 sheets. The SrBi2O4/g-C3N4 nanocomposite was characterized through various techniques including different analytical analyses. Among all evaluated electrodes for the electrochemical experiment binary composite SrBi2O4/g-C3N4 demonstrated the highest electrochemical activity and showed the capacitive of 777.2 F g−1 at 1 A g−1. Moreover, binary composite SrBi2O4/g-C3N4 was shown to have a lesser charge transfer resistance (Rct) of 0.87 Ω as compared to other bare fabricated materials. The exceptional electrochemical capability of SrBi2O4/g-C3N4 can be due to the combined effect of SrBi2O4 and g-C3N4 which included various redox state enhanced electrode wettability and superior structural and chemical stability. The composite material shows excellent power and high energy density of 319.95 W Kg−1 and 44.20 Wh Kg−1. Based on the findings our study suggested a practical approach to fabricated hybrid electrode materials that have optimum properties for use in energy storage devices in future supercapacitors.

Hierarchically Structured Graphene Aerogel Supported Nickel-Cobalt Oxide Nanowires as an Efficient Electrocatalyst for Oxygen Evolution Reaction.

The rational design of a heterostructure electrocatalyst is an attractive strategy to produce hydrogen energy by electrochemical water splitting. Herein, we have constructed hierarchically structured architectures by immobilizing nickel-cobalt oxide nanowires on/beneath the surface of reduced graphene aerogels (NiCoO2/rGAs) through solvent-thermal and activation treatments. The morphological structure of NiCoO2/rGAs was characterized by microscopic analysis, and the porous structure not only accelerates the electrolyte ion diffusion but also prevents the agglomeration of NiCoO2 nanowires, which is favorable to expose the large surface area and active sites. As further confirmed by the spectroscopic analysis, the tuned surface chemical state can boost the catalytic active sites to show the improved oxygen evolution reaction performance in alkaline electrolytes. Due to the synergistic effect of morphology and composition effect, NiCoO2/rGAs show the overpotential of 258 mV at the current density of 10 mA cm-2. Meanwhile, the small values of the Tafel slope and charge transfer resistance imply that NiCoO2/rGAs own fast kinetic behavior during the OER test. The overlap of CV curves at the initial and 1001st cycles and almost no change in current density after the chronoamperometric (CA) test for 10 h confirm that NiCoO2/rGAs own exceptional catalytic stability in a 1 M KOH electrolyte. This work provides a promising way to fabricate the hierarchically structured nanomaterials as efficient electrocatalysts for hydrogen production.

Flexible films with three-dimensional ion transport channels: Carbon nanotubes@MnO2 as interlayer spacers in porous graphene electrodes for high-performance supercapacitors

Flexible supercapacitors have a high potential for application in wearable electronics and microdevices, but their commercial appeal is limited because of low energy density. To overcoming this challenge, this paper proposes a strategy to fabricate dense films with high specific capacitance. A composite film with rapid ion diffusion channels and a high density of 0.86 g cm–3 was synthesized by combining porous graphene nanosheets (PGNs), carbon nanotubes (CNTs), and MnO2 nanosheets. The incorporation of CNTs@MnO2 between graphene layers effectively mitigated aggregation and enhanced electrolyte ion diffusion within the dense graphene structure. PGNs and CNTs synergistically established a three-dimensional pathway for efficient ion transport while optimizing electron dynamics. In 1 mol L–1 Na2SO4 electrolyte, the material exhibited a gravimetric capacitance of up to 320 F g–1 at 1 A g–1 and a volumetric capacitance reached 275 F cm–3. Furthermore, the assembled asymmetric supercapacitors, PGNs-CNTs@MnO2//PGNs-CNTs, exhibited a gravimetric energy density of up to 26.4 Wh kg–1 and a volumetric energy density of up to 22.7 Wh L–1. These findings offer insights into advancing flexible supercapacitor technology for diverse applications.

Core-Shell CoS2@MoS2 with Hollow Heterostructure as an Efficient Electrocatalyst for Boosting Oxygen Evolution Reaction.

It is imperative to develop an efficient catalyst to reduce the energy barrier of electrochemical water decomposition. In this study, a well-designed electrocatalyst featuring a core-shell structure was synthesized with cobalt sulfides as the core and molybdenum disulfide nanosheets as the shell. The core-shell structure can prevent the agglomeration of MoS2, expose more active sites, and facilitate electrolyte ion diffusion. A CoS2/MoS2 heterostructure is formed between CoS2 and MoS2 through the chemical interaction, and the surface chemistry is adjusted. Due to the morphological merits and the formation of the CoS2/MoS2 heterostructure, CoS2@MoS2 exhibits excellent electrocatalytic performance during the oxygen evolution reaction (OER) process in an alkaline electrolyte. To reach the current density of 10 mA cm-2, only 254 mV of overpotential is required for CoS2@MoS2, which is smaller than that of pristine CoS2 and MoS2. Meanwhile, the small Tafel slope (86.9 mV dec-1) and low charge transfer resistance (47 Ω) imply the fast dynamic mechanism of CoS2@MoS2. As further confirmed by cyclic voltammetry curves for 1000 cycles and the CA test for 10 h, CoS2@MoS2 shows exceptional catalytic stability. This work gives a guideline for constructing the core-shell heterostructure as an efficient catalyst for oxygen evolution reaction.

Doping Ti3C2Tx with Sn to enhance the stability of electrode for supercapacitor

The chemical instability and self-restacking have become major hurdle to the practical application of Ti3C2Tx although it is considered to be the promising candidates for energy storage. Herein, one-step process is developed to increase the stability and inhibit the self-agglomeration of Ti3C2Tx by using SnCl2 in ethanol to intercalate Ti3C2Tx. Characterization results demonstrate that Sn has doped into Ti3C2Tx (termed Ti3C2Tx-Sn). The obtained Ti3C2Tx-Sn shows an enlarged interlayer spacing to facilitate the rapid diffusion of electrolyte ions, and improve the stability by reducing its oxidation rate. In 1.0 M H2SO4 solution, the optimal Ti3C2Tx-Sn sample (labelled as Ti3C2Tx-Sn-2) can retain 93.5 % of its initial capacitance after 10,000 cycles, but Ti3C2Tx electrode only 51.2 %. Especially, after storage for 120 days in a refrigerator at −18 °C, the Ti3C2Tx-Sn-2 sample still exhibits excellent cycle stability (84.6 % capacitive retention after 10,000 cycles) while Ti3C2Tx sample remains negligible capacitance retention (only 2.7 % of its initial capacitance). It is believed that this work provides a simple and mild strategy to prepare high-stability Ti3C2Tx-based electrodes for energy storage.