Electrically conducting particle networks in polymer electrolyte as three-dimensional electrodes for hydrogenase electrocatalysis

Efficient H₂ oxidation and production by hydrogenase enzymes has attracted much interest because of the possibilities it raises for clean energy cycling without the need for precious metal catalysts. Although hydrogenases are extremely active electrocatalysts, high surface-area electrode structures will be necessary if the enzymes are to find application in energy technologies. Taking inspiration from fuel cell electrode assemblies, in which metal nanoparticles are commonly mounted on particulate carbon supports encased in polymer electrolyte, we show that high surface-area hydrogenase electrodes can be constructed from enzyme-loaded pyrolytic graphite particles in pH-neutralised Nafion. Pyrolytic graphite is the favoured surface for direct electrochemistry of many redox proteins, and on sanding, yields micron-dimension platelike particles. By modifying graphite platelets with hydrogenase before assembling the particles into a network, we ensure a high, uniform enzyme coverage. Incorporation of hydrogenases into high surface-area conducting network electrodes enhanced electrocatalytic H₂ oxidation currents by 30-times compared to values obtained for a planar hydrogenase electrode, while retaining efficient conductivity and H₂ mass transport through the network. This approach should make it possible to directly compare enzyme and precious metal electrocatalysis and to benchmark what opportunities are possible with selective enzyme catalysts.     

Electrochemical behaviour of olefins: oxidation at ruthenium–titanium dioxide and iridium–titanium dioxide coated electrodes

The electrocatalytic behaviour of a series of olefins was studied on thermally prepared Ti/MO₂ and Ti/M_0.3Ti_0.7O₂ electrodes (M = Ru, Ir) in 1.0 M HClO₄ in mixed solvent (AN/H₂O, 40/60v/v). The voltammetric investigation was limited to the potential region preceding the OER on these electrodes materials (E < 1.2 V vs SSCE). Aliphatic olefins (isophorone and cyclohexene) are inactive while the aromatic olefins show a single (safrole) or two (isosafrole) oxidation peaks. The overall catalytic activity of these electrode materials is about the same for both substrates. However, when morphological effects (differences in electrode surface area) are taken into account, normalizing the geometric current density (or faradaic charge) per surface site activity, a slightly better efficiency of the active surface sites is observed for Ru-based electrodes when compared to the equivalent Ir-based materials. Partial substitution of the noble metal catalysts by TiO₂ results in a synergetic effect depressing the efficiency of the active surface sites of the TiO₂-stabilized electrocatalysts. The decrease with potential cycling of the substrate oxidation current is attributed to dimeric/polymeric film formation blocking the electrode surface. Reflectance and FTIR spectroscopy as well as ohmic resistance data support film formation.     

Surface reconstruction of defective SrTi0.7Cu0.2Mo0.1O3-δ perovskite oxide induced by in-situ copper nanoparticle exsolution for high-performance direct CO2 electrolysis

Solid oxide electrolysis cell (SOEC) provides an effective solution to electrochemically convert CO₂ into valuable products with high efficiency, which is also developed as a promising way for the electricity utilization. However, the poor catalytic activity of the electrode material results in slow cathode kinetics for this technology. In this work, we propose a series of Sr_xTi_0.7Cu_0.2Mo_0.1O_3-δ (S_xTCM, x = 1, 0.975, 0.95) perovskite oxides as the cathodes of SOEC. By tuning the defects of the materials, abundant oxygen vacancies are stimulated in the perovskite lattice, which effectively improves the oxygen ion transport capacity and also act as the receptors of CO₂ molecule. Uniformly dispersed Cu nanoparticles on STCM substrate are in-situ generated after reduction treatment, leading to the formation of abundant active sites for CO₂ reduction reaction (CO₂RR). The results of this work demonstrate a general strategy for developing promising catalysts for efficient CO₂RR.     

PTFE-F-PbO2 电极在H2SO4溶液中的析氧行为

F-PbO2 electrode and polytetrafluoroethylene （PTFE） doped F-PbO2 electrode （PTFE-F-PbO2） were prepared on a plexiglas sheet substrate by a series of procedure including chemical and electrochemical depositions. The electrochemical activities of these two electrodes for oxygen evolution （OE） reaction were examined by electrochemical tests. In comparison with F-PbO2, PTFE-F-PbO2 electrode exhibited larger active surface area and higher oxygen vacancy deficiency, which resulted in its higher electrocatalytic activity for OE. In addition, both exchange current density and activation energy of the electrodes for OE were calculated in terms of active surface area. The values of exchange current density and activation energy in 0.5 mol·L^-1 H2SO4 aqueous solution were 1.125×10^ -3 mA·cm^-2 and 18.62 kJ·mol^-1 for PTFE-F-PbO2, and 8.384×10^-4 mA·cm^- 2 and 28.98 kJ·mol^-1 for F-PbO2, respectively. Because these values are calculated on the basis of the active surface areas of the electrodes, the enhanced activity of PTFE-F-PbO2 can be attributed to an increase in oxygen vacancy deficiency of PbO2 due to doping by PTFE. The influence of PTFE adulteration on the activity of PbO2 film electrode for OE was investigated in detail in this study.     

Enhanced electrochemical performance of hybrid composite microstructure of CuCo2O4 microflowers-NiO nanosheets on 3D Ni foam as positive electrode for stable hybrid supercapacitors

Self-assembled composite porous structures comprising CuCo₂O₄ microflowers and NiO hexagonal nanosheets were synthesized on a conducting 3D Ni foam surface [CCO/NO] using a simple hydrothermal method. This unique composite assembly was further characterized and electrochemically evaluated as a binder-free positive electrode for hybrid supercapacitor application. The study showed that the CCO/NO exhibited a maximum areal capacitance of 1444 mF cm^?2, significantly higher than the parent CuCo₂O₄ and NiO electrodes, with remarkable stability of 88.5% for 10,000 galvanostatic charge-discharge cycles. Key features for the enhanced electrochemical performance of CCO/NO can be related to a lowered diffusion resistance because the hybrid nanocomposite porous assembly generates short diffusion paths for electrolyte ions and more active sites for reversible faradaic transition for charge storage. The hybrid supercapacitor was assembled using activated carbon as a negative electrode and CCO/NO as a positive electrode in alkaline electrolyte, performed at an improved potential of 1.6 V. Device showed a maximum areal capacitance of 122 mF cm^?2, a maximum areal energy density of 43 μWh cm^?2, and a maximum areal power density of 5.1 mW cm^?2. This hybrid supercapacitor showed remarkable cyclic stability up to 98% for 10,000 cycles. This study encourages the development of low-cost, high-performance, durable electrode designs using hybrid composite for next-generation energy storage systems.     

Silver-coated ion exchange membrane electrode applied to electrochemical reduction of carbon dioxide

Silver-coated ion exchange membrane electrodes (solid polymer electrolyte, SPE) were prepared by electroless deposition of silver onto ion exchange membranes. The SPE electrodes were used for carbon dioxide (CO₂) reduction with 0.2 M K₂SO₄ as the electrolyte with a platinum plate (Pt) for the counterelectrode. In an SPE electrode system prepared from a cation exchange membrane (CEM), the surface of the SPE was partly ruptured during CO₂ reduction, and the reaction was rapidly suppressed. SPE electrodes made of an anion exchange membrane (SPE/AEM) sustained reduction of CO₂ to CO for more than 2 h, whereas, the electrode potential shifted negatively during the electrolysis. The reaction is controlled by the diffusion of CO₂ through the metal layer of the SPE electrode at high current density. Ultrasonic radiation, applied to the preparation of SPE/AEM, was effective to improve the electrode properties, enhancing the electrolysis current of CO₂ reduction. Observation by a scanning electron microscope (SEM) showed that the electrode metal layer became more porous by the ultrasonic radiation treatment. The partial current density of CO₂ reduction by SPE/AEM amounted to 60 mA cm⁻², i.e. three times the upper limit of the conventional electrolysis by a plate electrode. Application of SPE device may contribute to an advancement of CO₂ fixation at ambient temperature and pressure.     

Enhanced high-voltage performance of LiCoO2 cathode by directly coating of the electrode with Li2CO3 via a wet chemical method

Surface modification is an effective method for improving the high-voltage cycling stability of LiCoO₂. In this work, lithium carbonate (Li₂CO₃), the main component of solid electrolyte interphase (SEI) films, is selected as the coating material to modify LiCoO₂ composite electrodes by a wet chemical method, and the effect of the Li₂CO₃ coating time on the electrochemical performance of the LiCoO₂ electrode is investigated. Results show that the Li₂CO₃ coating significantly improves the cycling performances and initial coulombic efficiencies of the LiCoO₂ electrodes in the potential range of 3.0–4.5 V. The electrode with a coating time of 2 min exhibits the best electrochemical performance, in which the capacity retention rate is 90.9% after 100 cycles at 0.2C while the initial coulombic efficiency is 90.04%, whereas the capacity retention rate and initial coulombic efficiency of the uncoated electrode are only 73.11% and 74.66%, respectively. The capacity of the electrode with the 2-min coating reaches 134.3 mA h g^?1 after 500 cycles, while that of the uncoated electrode is only 37.7 mA h g^?1 under the same conditions. The results of cyclic voltammetry, electrochemical impedance spectroscopy, X-ray diffraction, and scanning electron microscopy show that the Li₂CO₃ coating stabilizes the electrode surface and structure to effectively inhibit the increase in electrode polarization.     

Improved performance of iron-chromium flow batteries using SnO2-coated graphite felt electrodes

Polyacrylonitrile-based graphite felt has the properties of high temperature resistance, corrosion resistance, low thermal conductivity, large surface area and excellent electrical conductivity. It has become the preferred material for flow battery electrodes, but its chemical activity is poor. In order to improve the electrochemical activity of graphite felt electrodes, the electrodes were prepared by SnO₂-coated graphite felt. Scanning electron microscopy and X-ray photoelectron spectroscopy were used to analyze the microscopic morphology of SnO₂-coated graphite felt electrodes. Electrochemical impedance spectroscopy, cyclic voltammetry and charge-discharge tests were performed using an electrochemical workstation to investigate the electrocatalytic activity of SnO₂-coated graphite felt electrodes and their cell performance. The results show that the SnO₂ coating on the graphite felt surface forms a convex and concave microstructure, which further increases the specific surface area of the electrode, and at the same time successfully introduces oxygen-containing functional groups to the electrode surface, increasing the electrochemically active spots on the surface. In addition, the presence of oxygen defects in the SnO₂ crystal structure provides more electrochemically active sites and improves the electrochemical performance of the graphite felt electrode. At a current density of 142 mA cm^?2, the charge-discharge capacity of the battery assembled with the SnO₂-coated graphite felt electrode was significantly improved; when the current density was 250 mAcm^?2, the Coulombic efficiency of the electrode (TGF-2) coated with a concentration of 0.1 M could reach 84%.     

Hierarchical FeC/MnO2 composite with in-situ grown CNTs as an advanced trifunctional catalyst for water splitting and Metal−Air batteries

In high demand is developing trifunctional electrocatalysts to simultaneously drive hydrogen evolution reaction (HER) and oxygen evolution/reduction reaction (OER/ORR) for metal-air batteries and water splitting. Here we develop the carbon nanotubes (CNTs)-grafted FeC/MnO₂ nanocomposite catalyst by carbonizing FeMn metal-organic frameworks. The synergistic effect between FeC and MnO₂ dominantly contributes the ORR, OER, and HER. The transition metal-mediated growth of CNTs by an in-situ catalysis mechanism enables high electrical conductivity, abundant active sites, as well as efficient reaction pathways. The optimized chemical composite and unique hierarchical structure endow the FeC/MnO₂ with low overpotentials for multiply electrochemical reactions. Consequently, the composite catalyst successfully serves as the bifunctional electrode for water splitting with a voltage of 1.66 V at 10 mA cm^?2 as well as the cathode for all-solid-state metal-air battery with Pt/C-comparable performance. The advanced transition metal composite presented in this work provides the guidance for rationally developing trifunctional electrocatalysts for efficient integrated energy conversion systems.     

Binder-less fabrication,some surface studies,and enhanced electrochemical performance of Co,Cu-embedded MnO2 thin film electrodes for supercapacitor application

We report the fabrication of nanocystalline MnO₂ thin film-based electrode on a predeposited indium tin oxide (ITO) film on the glass substrate, using a binderless and simple two-electrode electrofabrication approach. Effects of Co and Cu incorporation on microstructural and electrochemical performance of the electrode were optimally and extensively investigated. The experimental results for the optimum fabrication conditions for Co@MnO₂ and Cu@MnO₂ and pure MnO₂ thin film-based electrode samples showed uniqueness in microstructural features, degrees of crystallinity and roughness, and high electrochemical energy storage performance. Co@MnO₂ film electrode exhibited remarkable specific capacitance (1068 Fg^-1) and areal capacity (25.78 mAh cm^?2) as against other electrode films (Cu@MnO₂ and pure MnO₂) which exhibited specific capacitances 837 and 438 F g^?1 and areal capacities 10.6 and 4.9 mAh cm^?2, respectively. Exceptional stabilities were also recorded for the composite samples (87.2% and 84.4% for Cu@MnO₂ and Co@MnO₂ thin film electrodes, respectively) against the pure MnO₂ film electrode sample (77.8%), after 2000 cycles. In addition, the short time constants (1.27 s and 1.31 s) were respectively realized for the fabricated Co@MnO₂ and Cu@MnO₂ electrode films as against the pure MnO₂ electrodes (4.35 s). These features observed in the composite electrode samples demonstrated an exhibition of faster ion response and higher rate capability by the samples. Moreover, the incorporation of Co into the MnO₂ electrode material relatively improved the supercapacitive activeness by enhancing the charge transition and transport.     

Electrooxidation of acetaldehyde on platinum-modified Ti/Ru0.3Ti0.7O2 electrodes

In this study, the electrochemical oxidation of acetaldehyde was investigated at activated massive DSA^® electrodes in acid medium, using differential electrochemical mass spectrometry (DEMS) and high-performance liquid chromatography (HPLC). The electrodes were prepared either by platinum electrodeposition or by depositing a highly nanodispersive-supported catalyst (Pt and Pt-Ni) over electrode surfaces with a Ti/Ru_0.3Ti_0.7O₂ nominal composition. Bulk electrolysis shows evidence of CO₂ and acetic acid formation. The electrocatalytic efficiency of the electrode material was also investigated as a function of the amount of catalyst added over the DSA^® electrode surface. The presence of RuO₂-active sites on the DSA^® substrate plays an important role in the reaction overall efficiency. The addition of platinum to DSA^® enhances the oxidation of acetaldehyde to CO₂. The role of the substrate on the direct activation of acetaldehyde oxidation is discussed on the basis of the direct application of the metal nanoparticle catalyst over conductive oxide surface based on Magneli phase (mixture of Ti_nO_2n−1 and other phases) from Ebonex^®.     

Electrochemically created roughened lead plate for electrochemical reduction of aqueous CO2

Surface-roughened Pb electrodes were prepared through a facile oxidation–reduction cycle. Compared with their smooth surface counterparts, the electrodes exhibited significantly higher activity, selectivity, and energy utilization in the electrocatalytic reduction of CO₂ to HCOOH using water under ambient temperature and pressure. Furthermore, the modified electrodes maintained high activities after operating repeatedly for five batches. The enhanced performance of these electrodes is attributed to the enlarged active surface area and increased number of reactive species associated with the three-dimensional structure of the surface. Both the hydrogenation mechanism and the hydrogencarbonate mechanism were affected during the electrochemical CO₂ reduction.     

Anion doped bimetallic selenide as efficient electrocatalysts for oxygen evolution reaction

The development of highly efficient and low-cost electrocatalysts for the oxygen evolution reaction (OER) is of great importance in advancing the practical applications of green and sustainable hydrogen energy. Doping with either cations or non-metallic anions is a typical strategy used to improve the electrocatalytic activity for OER catalysts. In this study, an anion doped bimetallic selenide Co_0.75Fe_0.25(S_0.2Se_0.8)₂ solid solution is prepared via the simultaneous sulfuration and selenylation of a scalably produced CoFe-layered double hydroxide (CoFe-LDH) precursor, using commercially available sulfur and selenium powders as S and Se sources, respectively. Electrocatalytic test shows that the anion doped bimetallic selenide Co_0.75Fe_0.25(S_0.2Se_0.8)₂ electrode requires an overpotential of 293 mV and a low Tafel slope of 77 mV dec⁻¹ at a current density of 10 mA cm⁻² in an alkaline media, and it exhibits the significantly enhanced electrocatalytic performance for the OER compared with its counterparts of Co_0.75Fe_0.25S₂ and Co_0.75Fe_0.25Se₂. The enhanced electrocatalytic performance is supported experimentally by the results of charge-transfer resistance and electrochemically active surface area. Our LDH precursor-based protocol can provide a strategy to prepare non-metallic anion doped bimetallic selenides as efficient electrocatalysts for water splitting.     

Mechanistic study of the reduction of oxygen in air electrode with manganese oxides as electrocatalysts

Electrochemical reduction of oxygen (O₂) in air electrode with manganese oxides (MnOx) as electrocatalysts was studied with MnOx/Nafion-modified gold (Au) electrodes using cyclic voltammetry, potential-controlled amperometry and rotating ring-disk electrode (RRDE) voltammetry in alkaline aqueous solution. At Nafion-modified (MnOx free) Au electrode, O₂ reduction undergoes two successive two-electron processes with HO₂⁻ as intermediate. The presence of MnOx, including Mn₂O₃, Mn₃O₄, Mn₅O₈ and MnOOH, on Nafion-modified Au electrodes obviously increases the first reduction peak current of O₂ to hydrogen peroxide (HO₂⁻ in this case) and decreases the second one of HO₂⁻ to OH⁻, while does not shift the reduction potential. MnOx was found to show catalytic activity for the disproportionation reaction of HO₂⁻ to O₂ and OH⁻ and thus, the O₂ reduction in air electrode was considered to include an initial two-electron reduction of O₂ to HO₂⁻ followed by a disproportionation reaction of HO₂⁻ into O₂ and OH⁻ catalyzed by MnOx. The excellent activity of MnOx for the follow-up disproportionation reaction substantially results in an overall four-electron reduction of O₂ at MnOx/Nafion-modified Au electrodes in the first reduction step, depending on potential scan rate and the kind of MnOx. The present work provides a scientific significance of the mechanism of O₂ reduction in air electrode using MnOx as electrocatalysts to effect a four-electron reduction of O₂ to OH⁻.     

Effect of cathode binder IEC on kinetic and transport losses in all-SPEEK MEAs

The effect of ion exchange capacity (IEC) and loading of sulfonated polyether ether ketone (SPEEK) binder on PEFC cathode performance was studied. MEAs were prepared by decal transfer onto a SPEEK membrane (IEC-1.75 mequiv./g). The IEC of SPEEK binder in the MEA cathode was varied between 1.3 and 2.1 mequiv./g. Cathodes prepared with 30 wt.% SPEEK loading had an electrochemically active surface area (ECA) that was 25% lower than a Nafion^® bonded electrode with similar loading. Polarization curves were obtained at 80 °C and 75% RH with hydrogen as fuel and air and oxygen (O₂) as oxidants. Polarization data was analyzed to determine the relative contributions of different sources of polarization, namely membrane ohmic losses, electrode ohmic losses, and mass transport losses in the gas diffusion layer, binder film and electrodes. The electrode ohmic and mass transport losses decreased with increase in SPEEK IEC. However, even for the highest SPEEK IEC, these losses were higher than those obtained in a Nafion^® bonded electrode. This was attributed to the lower proton activity and O₂ permeability in SPEEK. The loading of SPEEK in the electrode was found to influence performance in the activation controlled region, with a loading of 7.5 wt.% giving the highest performance. However, gains in this region were negated at higher current densities due to enhanced ohmic and transport losses and MEAs with all binder loadings between 7.5 and 30 wt.% had similar limiting currents.     

Electrochemical degradation of phenol on the La and Ru doped Ti/SnO2-Sb electrodes

La and Ru doped Ti/SnO₂-Sb electrodes were prepared by thermal decomposition and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). It confirmed that the surface of the La and Ru doped Ti/SnO₂-Sb electrodes presents a certain microspherical structure formed by aggregates of nanoparticles, which increases the specific area greatly and provides more active sites. The enhanced performance of the La and Ru doped electrodes arose from the increased adsorption capacity of hydroxyl radicals. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) showed an improvement of the electrochemical capacity for the La and Ru doped Ti/SnO₂-Sb electrodes. The electrochemical oxidation performance of the prepared electrode was further studied using phenol as a model pollutant. UV scans revealed that both phenol and its intermediate products are more rapidly decomposed, especially in the early stage of oxidation on the La and Ru doped electrodes. The removals of chemical oxygen demand (COD) were 86.4% and 82.1% on the Ti/SnO₂-Sb-La and Ti/SnO₂-Sb-Ru electrodes, respectively, which were higher than that on the SnO₂-Sb/Ti electrode (60.1%). The doped electrodes are demonstrated to have superior electrochemical oxidation ability for phenol.     

Coordination-driven hierarchically structured composites with N-CNTs-grafted graphene-confined ultra-small Co nanoparticles as effective oxygen electrocatalyst in rechargeable Zn-air battery

Rational design and fabrication of optimal reversible oxygen electrocatalysts are essential yet still remain great challenges for rechargeable metal-air batteries. Supramolecular coordination polymer-derived strategy for transition metal–nitrogen–doped carbon (M–N/C, M = Co, Fe, etc.) composites catalysts has been deemed promising in preserving rich M–N_x coordination modes and enhancing their intrinsic activities. However, the closely packed and nonporous characteristics of coordination polymer usually lead to the serious agglomeration of metallic nanoparticles and lack of porous channels after pyrolysis, impacting the abundance and accessibility of the exposed active sites during electrocatalysis. In this work, we put forward a new tactic to obtain ultra-small Co nanoparticles confined within N-doped carbon nanotubes grafted to reduced graphene oxide (Co/N-CNTs@rGO) through a coordination-driven in situ self-assembly approach followed by pyrolysis. The integration of high intrinsic activity, enhanced conductivity, populated and richly exposed active species throughout the laminated hierarchical composite structure endows Co/N-CNTs@rGO with appealing bifunctional oxygen electrocatalysis properties. Impressively, Co/N-CNTs@rGO was subsequently fabricated as the air electrode in a rechargeable Zn−air battery, and the device achieves a maximum power density of 168 mW cm⁻², a large specific capacity of 765 mA h g⁻¹ while maintaining satisfying cycling durability. This work may provide valuable insights in regulating the coordination polymer derivatives and bring new perspectives for future design of promising composites electrocatalysts for electrochemical conversions and energy storage technologies.     

Free-standing SiOC/nitrogen-doped carbon fibers with highly capacitive Li storage

Silicon oxycarbide (SiOC) as a prospective electrode material for next-generation lithium ion batteries (LIBs) was restricted by the unsatisfactory discharge capacity and inflexibility used in flexible and wearable electronics. Herein, freestanding flexible SiOC/nitrogen-doped carbon fiber films are constructed through electrospinning process followed by carbonizing in NH₃ atmosphere. In this way, SiOC particles are tightly embedded in N-doped carbon fibers, forming a 3D conductive network to promote electron transport and faster reaction kinetics. The nitrogen dopants create more defects in carbon fibers matrix, which improve the electronic conductivity and electrochemical active sites of the electrodes. Owing to the above synergistic effect, SiOC/nitrogen-doped carbon fiber electrodes exhibit a high initial Coulombic efficiency of 73 % and a reversible remaining capacity of 595 mA h g⁻¹ at 200 mA g⁻¹ even after 200 cycles. The electrodes with good flexibility can successfully drive a light-emitting diode even when the package battery is bended to 180°.     

Interconnected SnO2/graphene+CNT network as high performance anode materials for lithium-ion batteries

As a metal oxide with a high theoretical capacity, SnO₂ is considered to be one of the promising alternative anode materials in lithium-ion batteries. However, the pulverization of electrodes caused by the large volume expansion of SnO₂ during repeated charge/discharge hinders its practical application. Here, SnO₂ nanoparticles decorated on a 3D carbon network structure formed by the interconnection of graphene and CNT (SnO₂/G + CNT), which is designed and successfully synthesized via in situ chemical synthesis and thermal treatment. In this structure, the SnO₂ with nanosized can increase energy storage points and decrease the ions transport length, the carbon network can build a high conductive network that facilitates electron transport and alleviate the volume expansion to prevent electrode pulverization. In addition, graphene has a high specific surface area effect that facilitates lithium-ion storage, and the CNT also supports the graphene frame to make the carbon skeleton structure more stable, and provides a large number of ion transport channels, increasing the active sites of the reaction. Due to this excellent structure with synergistic effects, the SnO₂/G + CNT electrode exhibits superior reversible capacity (1227.2 mAh g^-1 at 0.1 A g^-1 after 200 cycles), superior rate capacity (549.3 mAh g^-1 at 3.0 A g^-1) and long cycle stability (1630.1 mAh g^-1 at 0.5 A g^-1 after 1000 cycles).     

Three-dimensional carbon-based endogenous-exogenous MoO2 composites as high-performance negative electrode in asymmetric supercapacitors and efficient electrocatalyst for oxygen evolution reaction

It is not an easy way to design composite electrodes with a high concentration of the constituent. This study cleverly exploited the phase transformation of molybdenum oxide to synthesize three-dimensional carbon-based endogenous-exogenous MoO₂ composites (EEC) by a two-step process. MC-15 exhibited the most outstanding electrochemical performance among EEC, with a specific capacitance up to 411.1 F g^?1 in Na₂SO₄, due to the design of MoO₂, which could be highly loaded with three-dimensional carbon. In addition, the electrode capacitance remains up to 94.1% after 5000 cycles, attributed to the synergy effect of three-dimensional carbon and molybdenum dioxide by providing an abundance of active sites for MoO₂ and overcoming its stacking. In this way, the electrochemical properties of the EEC electrode are not compromised by the volume expansion during the electrochemical process. The energy density of the asymmetric supercapacitor using this material as the negative electrode and MnO₂@CC is 14 W h kg^?1 at a power density of 802 W kg^?1, showing a significant increase in energy density over the asymmetric supercapacitor with a conventional negative electrode (activated carbon, energy density of 3.36 W h kg^?1 and power density of 700 W kg^?1). Its specific capacitance remained 84.9% after 2500 cycles. In addition, an overpotential of only 348 mV was required to drive oxygen evolution in alkaline electrolytes with a Tafel slope as low as 88.7 mV dec^?1; the 20 h stability test retains almost 100%. The results show that the design optimization of the negative electrode material provides a simple and effective strategy to increase the energy density of supercapacitors, and EEC electrode materials are a great candidate to be utilized in supercapacitors with excellent performance as well as electrolytic water.