Kinetics Of Redox Reactions Research Articles

Bidirectional enhancement of Li2S redox reaction by NiSe2/CoSe2-rGO heterostructured bi-functional catalysts

The high activity barriers of Li2S nucleation and deposition limit the redox reaction kinetics of lithium polysulfides (LiPSs), meanwhile, the significant shuttle effect of LiPSs hampers the advancement of Li-S batteries (LSBs). In this work, a NiSe2/CoSe2-rGO (NiSe2/CoSe2-G) sulfur host with bifunctional catalytic activity was prepared through a hard template method. Electrochemical experiment results confirm that the combination of NiSe2 and CoSe2 not only facilitates the bidirectional catalytic function during charge and discharge processes, but also increases the active sites toward LiPSs adsorption. Simultaneously, the highly conductive rGO network enhances the electronic conductivity of NiSe2/CoSe2-G/S and provides convenience for loading NiSe2/CoSe2 catalysts. Benefitting from the exceptional catalytic-adsorption capability of NiSe2/CoSe2 and the presence of rGO, the NiSe2/CoSe2-G/S electrode exhibits excellent electrochemical properties. At 1C, it demonstrates a low capacity attenuation of 0.087 % per cycle during 500 cycles. The electrode can maintain a discharge capacity of 927 mAh/g at a sulfur loading of 3.3 mg cm−2. The bidirectional catalytic activity of NiSe2/CoSe2-G offers a prospective approach to expedite the redox reactions of active S, meanwhile, this work also offers an ideal approach for designing efficient S hosts for LSBs.

Enhancing lithium-sulfur battery performance through electronic/ionic co-conductive multi-walled carbon nanotubes/lithium lanthanum titanium oxide separator modification

As one of the most promising energy storage devices, lithium-sulfur batteries (LSBs or Li-S batteries) are still facing obstacles due to the notorious shuttling of soluble polysulfide intermediates, accompanied by low S utilization, corrosion of the lithium anode, and rapid capacity fading, leading to a short cycling life. To overcome these issues and achieve high-performance LSBs, we introduce a modified separator composed of multi-walled carbon nanotubes/lithium lanthanum titanium oxide (MWCNTs/LLTO). The proposed MWCNTs/LLTO-modified separator improves the redox reaction kinetics from soluble higher-order lithium polysulfides to insoluble lower-order ones and ultimately to Li2S, thereby reducing the polysulfides dissolved in the electrolyte. It also serves as a physical barrier to adsorb polysulfides, efficiently preventing their diffusion from the cathode to the anode. LSBs adopting the MWCNTs/LLTO-modified separator exhibit higher ionic and electronic conductivity than their un-modified counterparts, leading to an initial specific capacity of 1496 mA/h/g (∼90% of the theoretical capacity) at 0.1 C, excellent rate capability performance, and a remarkable capacity retention of 80% after 200 cycles. Furthermore, the cells with S loading reaching up to 4.18 mg/cm2 further confirmed the beneficial impact of the MWCNTs/LLTO-modified separator.

Synergistic improvements on capacity and Coulombic efficiency of lithium-sulfur batteries with NiSe-Ni2P/C modification on PP separators

Lithium-sulfur batteries (LSBs) emerge as promising energy storage devices due to their high theoretical energy density. So far, there are constrained issues that need to be urgently addressed, such as the shuttle effect of lithium polysulfides (LiPS) and the sluggish kinetics of redox reactions. Herein, NiSe-Ni2P/C composite was synthesized and casted on the cathode side of polypropylene (PP) separator. This investigation reveals that the adsorption-catalysis synergistic effect of NiSe-Ni2P/C composite, accelerates the reduction of LiPS to lithium sulfide (Li2S) as well as the oxidation of Li2S. The synergistic effect effectively mitigates the shuttle effect of LiPS, reduces concentration polarization, and improves Coulombic efficiency (CE) throughout the entire lifespan. At a current density of 0.05 C, LSBs with NiSe-Ni2P/C modified PP separators exhibit a remarkable high initial CE of 97.0% and a substantial discharge specific capacity of 1205.4 mAh gs−1. Even under conditions of a high sulfur loading (4.3 mg cm−2) and a limited electrolyte dosage (10 μL mgs−1), the LSBs maintained a reversible specific capacity of 804 mAh gs−1, a CE of 94%, and an energy density of 1232.1 Wh kgs−1 after 720 h of continuous cycling at 0.05 C. This work provides a solution for achieving long-time, high-capacity, and high-CE electrochemical performance in LSBs with a high sulfur loading and a limited electrolyte dosage.

Defect engineering of a TiO2 anatase/rutile homojunction accelerating sulfur redox kinetics for high-performance Na-S batteries.

Room-temperature sodium-sulfur (RT Na-S) batteries have the drawbacks of the poor shuttle effect of soluble sodium polysulfides (NaPSs) as well as slow sulfur redox kinetics, which result in poor cycling stability and low capacity, seriously affecting their extensive application. Herein, defect engineering is applied to construct rich oxygen vacancies at the interface of a TiO2 anatase/rutile homojunction (OV-TRA) to enhance sulfur affinity and redox reaction kinetics. Combining structural characterizations with electrochemical analysis reveals that OV-TRA well alleviates the shuttle effect of NaPSs and precipitates the deposition and diffusion kinetics of Na2S. Consequently, S/OV-TRA provides excellent electrochemical performance with a reversible capacity of 870 mA h g-1 at 0.1 C after 100 cycles and a long-term cycling capability of 759 mA h g-1 at 1 C after 1000 cycles. This work provides an effective interfacial defect engineering strategy to promote the application of metal oxides in RT Na-S batteries.

Nickel and nickel oxide nanoparticle-embedded functional carbon nanofibers for lithium sulfur batteries.

Lithium-sulfur (Li-S) batteries are attracting tremendous attention owing to their critical advantages, such as high theoretical capacity of sulfur, cost-effectiveness, and environment-friendliness. Nevertheless, the vast commercialisation of Li-S batteries is severely hindered by sharp capacity decay upon operation and shortened cycle life because of the insulating nature of sulfur along with the solubility of intermediate redox products, lithium polysulfides (LiPSs), in electrolytes. This work proposes the use of multifunctional Ni/NiO-embedded carbon nanofibers (Ni/NiO@CNFs) synthesized by an electrospinning technique with the corresponding heat treatment as promising free-standing current collectors to enhance the kinetics of LiPS redox reactions and to provide prolonged cyclability by utilizing more efficient active materials. The electrochemical performance of the Li-S batteries with Ni/NiO@CNFs with ∼2.0 mg cm-2 sulfur loading at 0.5 and 1.0C current densities delivered initial specific capacities of 1335.1 mA h g-1 and 1190.4 mA h g-1, retrieving high-capacity retention of 77% and 70% after 100 and 200 cycles, respectively. The outcomes of this work disclose the beneficial auxiliary effect of metal and metal oxide nanoparticle embedment onto carbon nanofiber mats as being attractively suited up to achieve high-performance Li-S batteries.

Reduced graphene oxide/MXene hybrid decorated graphite felt as an effective electrode for vanadium redox flow battery.

Vanadium redox flow battery (VRFB) is a highly suitable technology for energy storage and conversion in the application of decoupling energy and power generation. However, the sluggish reaction kinetics of redox couples is one of the bottlenecks hindering the commercialization of VFFBs. Developing efficient electrode is a promising method to improve the battery performance. In this work, a reduced graphene oxide/Mxene hybrid-decorated graphite felt (rGO/Mxene@GF) is designed to facilitate the kinetics of redox reaction. The electrocatalytic activity and mass transfer of the prepared electrode are investigated through experiment and simulation methods. The results indicate that the favorable mass transfer and the synergistic effect between rGO and Ti3C2Tx Mxene remarkably improve the performance of electrode. The flow cell with rGO/Mxene@GF delivers a good stability up to 100 cycles with a coulombic, voltage, and energy efficiency of 91.6%, 82.7%, and 75.8%, respectively, at a current density of 80 mA cm-2. These findings suggest that the as-prepared rGO/Mxene@GF holds a good application potential in VRFB and provides a promising approach to design efficient electrode for electrochemical devices.

Design of a sulfur host with CuCo2O4 supported on carbon cloth for lithium sulfur batteries.

A high-efficiency sulfur host with bimetallic oxide CuCo2O4 cubes supported on carbon cloth has been designed and used in lithium sulfur batteries, which can suppress the "shuttle effect" and boost the redox reaction kinetics. The unique three-dimensional cube-based structure realized a high sulfur loading of 7.1 mg cm-2, and the corresponding assembled lithium sulfur battery delivered excellent cycling stability over 100 cycles at 0.1C.

Facile preparation of a lightweight multifunctional interlayer for high-performance Li-S batteries.

The construction of functional interlayers for separator modification in Li-S batteries has been proven to be a feasible and effective strategy to alleviate the shuttle effect. However, several challenging issues in interlayer design and fabrication, including the tedious material preparation process and high weight loading of the interlayer on the pristine separator, jeopardize the battery energy density. In this work, a nitrogen-abundant nanoporous carbon/graphene (NC/G) composite was synthesized by a facile method and fabricated into a lightweight membrane, which was investigated as a multifunctional interlayer in a Li-S battery. The abundant nitrogen sites and nanoporous structure of NC/G can effectively anchor and trap polysulfides; graphene (G) can create an excellent conductive network in NC/G. These attributes of NC/G are able to efficiently boost the sulfur redox reaction kinetics and significantly suppress the shuttle effect, leading to superb battery performance. More importantly, the low density of NC/G was conducive to reducing the load on the separator, thus reducing the decline in battery energy density, which is promising for practical applications. Even at an ultra-low loading of NC/G on the pristine separator (0.08 mg cm-2), the battery showed a competitive electrochemical performance compared with many reported materials. We believe this work provides a strategic guidance for the future fabrication of promising functional interlayers for practical Li-S battery applications.

Defect Strategy‐Regulated MoSe2‐Modified Self‐Supporting Graphene Aerogels Serving as Both Cathode and Interlayer of Lithium‐Sulfur Batteries

AbstractThe severe shuttle effect and the sluggish redox reaction kinetics are the two most urgent issues with lithium‐sulfur batteries (LSBs). In this work, Se vacancy‐rich molybdenum selenide‐modified graphene aerogels are designed to serve as both cathode host (MoSe2‐x@GA/S) and freestanding interlayers (MoSe2‐x@GA) for LSBs. The graphene network‐supported binder‐free sulfur host maximizes electron conductivity/Li+ migration rate and alleviates bulk expansion. The defect‐rich MoSe2‐x with sulfiphilic‐lithiophilic properties accelerates the nucleation and dissociation of Li2S, while the insertion of a bifunctional interlayer not only facilitates the adsorption and conversion of polysulfides but also regulates the uniform lithium deposition and inhibit the growth of lithium dendrites. As a result, the assembled MoSe2‐x@GA/S+interlayer electrode obtains good feedback in terms of capacity enhancement and cycling stability, possessing a high initial discharge capacity of 1256.9 mA h g−1 at 0.2 C and a slow decay ratio of 0.024% per cycle at a high current density of 1 C after 1000 long‐term cycling, and achieve high specific capacity (720.6 mA h g−1) at high sulfur loading (4.8 mg cm−2) and lean electrolyte (5.5 µL mg−1) conditions. This insightful work contributes new ideas for the design of binder‐free sulfur host and the application of defective electrocatalytic engineering.

Tungsten oxide nanostructures for all-vanadium redox flow battery: Enhancing the V(II)/(VIII) reaction and inhibiting H2 evolution

Vanadium redox flow batteries (VRFBs) offer remarkable performance capabilities for renewable energy power plants. However, the kinetics of the VRFBs' redox reactions are slow and the efficiency is low due to parasitic reactions such as the hydrogen evolution reaction (HER). In this work, to overcome these limitations, the effect of modifying the carbon cloth electrode with tungsten oxide nanowires, nanoflakes, and nanospheres prepared was elucidated for the negative half-cell reaction V(II)/V(III). The physical and chemical properties of those nanostructures were characterized using FESEM, XPS, XRD, FTIR, and contact angle measurements. The effect of the catalyst loading and structure, pH and composition of the synthesis solution, and the presence of binder on catalytic activity was evaluated using CV and EIS. The results showed that the effective loading of all three structures is ~2 mg/cm2, with all of the structures showing a significant enhancement of the V(II)/(VIII) reaction kinetics in comparison to the untreated carbon cloth and greater stability than the thermally treated carbon cloth. The tungsten oxide nanostructures prepared at pH 2 showed the best catalytic activity, with the suppression of hydrogen evolution reaction (HER) being inversely proportional to the number of defects. Tungsten oxide nanoflakes prepared at pH 2 using water as a solvent exhibited the optimum balance between promoting the V(II)/(VIII) reaction kinetics and suppressing the HER. The performance evaluation in a two-electrodes setup of all‑vanadium RFB revealed that the WNFs structure have the highest charge/discharge capacity and energy efficiency at a relatively high current density of 60 mA/cm2 due to its improved kinetics.

(Invited) Effect of Electrochemical Treatment and pH on the Kinetics of VII-VIII Reactions on Glassy Carbon Electrodes

Vanadium flow batteries (VFBs) are known for their long cycle life, high efficiency, and scalability, which make them suitable for various energy storage applications, including grid-scale energy storage, renewable energy integration, and remote power systems. There are several areas of active research on VFBs. These include electrolyte chemistry, electrode materials, cell design, system integration, modeling and simulation, performance optimization, scale-up and commercialization1.Carbon felts are often used as electrodes in VFBs due to their high electrical conductivity, chemical stability, and availability2. However, the surface properties of carbon materials can be influenced by the surrounding environment, leading to changes in their surface chemistry and reactivity. These changes in the environment can alter the kinetics of the vanadium reactions at the carbon surfaces, which in turn can impact the performance and efficiency of the battery system. Various electrochemical, chemical, and thermal treatments have been reported to have a significant impact on the carbon electrode kinetics3. It is thus important to investigate electrode kinetics to improve the performance of VFBs.Previously our group has reported that electrochemical treatments of carbon electrodes at different potentials significantly affect the electrode kinetics of VIV-VV and VII-VIII redox reactions4,5. The cathodic treatment of carbon electrode enhances the kinetics of VIV-VV redox reaction but inhibits the kinetics of VII-VIII redox reaction, while anodic treatment inhibits the kinetics of the VIV-VV redox reaction but enhances the kinetics of the VII-VIII redox reaction6-9. We have further investigated the effect of electrochemical treatment on the VIV-VV kinetics at glassy carbon electrodes following treatment in electrolytes of various pH. For all pHs investigated (pH 0 – pH 6), VIV-VV kinetics are enhanced by cathodic treatment of the electrode and inhibited by anodic treatment. The activating effect of cathodization increased markedly with increasing pH, whereas the deactivating effect of anodization appears approximately the same for all pHs. The observed effects are attributed to changes to electrode surface states by electrochemical polarization reactions, the rates of which appear to be pH dependent10.We have extended our investigation into the VII-VIII reaction kinetics. We will present results on the effect of electrochemical treatment and pH on the kinetics of VII-VIII reactions on glassy carbon electrodes. The kinetic rates for the VII-VIII couple on these electrodes are measured and compared using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Acknowledgements Varsha Sasikumar S P would like to thank the Irish Research Council (IRC) for a postgraduate scholarship to perform this research and acknowledge facilitation of this research by University of Limerick (UL), Ireland and South East Technological University (SETU), Ireland. References Aluko and A. Knight, IEEE Access, 11, 13773-13793 (2023).Kim et al., Scientific Reports, 4, 6906 (2014).K. Sankaralingam et al., Journal of Energy Storage, 41, 102857 (2021).N. Buckley et al., ECS Transactions, 98(9), 223-239 (2020).N. Buckley et al., Electrodes for Vanadium Flow Batteries (VFBs) In Flow Batteries: From Fundamentals to Applications, Chapter 24, Edited by. C. Roth et al., Wiley-VCH, ISBN 978-3-527-34922-7 (2023).Bourke et al., Journal of Electrochemical Society, 163, A5097 (2016).Bourke et al., Journal of Electrochemical Society, 162, A1547 (2015).A. Miller. et al., Journal of Electrochemical Society, 163, A2095-A2102, (2016).Bourke et al., Journal of Electrochemical Society, 170, 030504 (2023).Sasikumar et al., ECS Transactions, 109, 107 (2022).

An Optical-Electronic-Catalytic Coupled Multi-Physical Simulation for Sunlight-Driven CO2 Reduction Device Based on Light Absorbers Patterned with Island Electrocatalysts

Photoelectrochemical (PEC) reduction of CO2 to value-added chemicals is a promising approach to convert solar energy but it is often suffered from sluggish kinetics and photocorrosion at the semiconductor-electrolyte interface.1, 2 In general, there are two requirements for a good performing solar-driven CO2 reduction: i) effective catalysts for a fast surface redox reaction and ii) an effective semiconductor/catalyst interface for rapid charge transfer across interfaces.3 The deposit of a continuous electrocatalyst layer on the photoabsorber surface can reduce kinetic overpotentials for CO evolution reaction (COER) and can enhance the photoelectrode stability. However, the optical obscuration significantly attenuates the magnitude of the incident illumination. Reducing the coverage (f c) of the catalyst on the photoabsorber surface can reduce the optical obscuration but worsen the reaction kinetics. Moreover, the pinch-off effect occurs as the size of the catalyst is small enough to provide a facile path for carriers to transport across interfaces. The PEC CO2 reduction with the utilization of the pinch-off effects could potentially be advantageous to balance the kinetics and the optical absorption. Understanding the trade-offs between the reduction in photocurrent density due to optical obscuration and the decrease in kinetic overpotentials due to improved active area is important in optimizing PEC CO2 reduction devices.To elucidate the effects of the optical performance, interfacial carrier transport, and electrochemical activity for the PEC CO2 reduction, three possible interfacial configurations in PEC were considered in this study: i) Bare p-Si photocathode case. The bare p-Si photocathode immersed in aqueous electrolyte and CO2R occurs at the semiconductor-electrolyte (SC/E) interface; ii) Layered catalyst case. The continuous layer catalyst is deposited on the surface of p-Si photocathode and forms a semiconductor-metal (SC/M) interface; iii) Patterned catalyst case. Producing a patterned catalyst with a low geometric coverage fraction on the surface of p-Si photocathode. The Schottky junctions with a low barrier height formed by the SC/M are surrounded by the Schottky junctions with a high barrier height formed by the SC/E. We developed a multiphysics model based on the finite element method, including electromagnetic wave propagation, charge transport in bulk semiconductor, species transport in the electrolyte, and charge-transfer kinetics of surface redox reactions.The optical performance and electrochemical performance of CO2R reduction were compared in the three cases. Under the bare p-Si case, the saturation photocurrent densities (J sa) and the onset potential (V on) were -13.40 mA/cm2 and -0.80 V vs. RHE at -1 mA/cm2, respectively. Under the layered catalyst case, the J sa and the V on were -0.84 mA/cm2 and -0.50 V vs. RHE at -0.10 mA/cm2, respectively. Under the patterned catalysts case (f c is 0.1 in this case), the J sa is -12.30 mA/cm2 and V on is -0.69 V vs. RHE at -1 mA/cm2. The magnitude of J sa is influenced by the extent of light obscuration and the magnitude of V on is influenced by the photoelectrode activity and the pinch-off effects. The V on for the patterned case is higher than that of the bare p-Si case due to the improved electrode activity combined with the pinch-off effects. In the bare p-Si case and the patterned catalyst case, the CO2 mass transfer limits the CO partial current density (J CO) to further increase due to high J sa while CO2 mass transfer is not the limitation for COER at high overpotentials for the layered catalyst case due to significant light obscuration. The pinch-off effect also increased the applied voltage corresponding to the maximum J CO for the patterned case (-1.21 V vs. RHE) compared to that for the bare p-Si case (-1.35 V vs. RHE) due to the deceased transport resistance of electrons.The influence of different interfacial configurations, solar concentration ratio, different coverage of catalysts, and different sizes of catalysts for optical loss, pinch-off effect, CO2 mass transfer, current distribution at interfaces, and electrochemical performance are discussed in detail for the optimal design photoelectrode. This framework allows us to provide design guidelines for PEC CO2 reduction devices.

(Invited) Relationship of Pseudo-Capacitive Current in Sulphuric Acid and Vanadium Flow Battery Reaction Kinetics at Carbon Electrodes

Flow battery technologies are promising solutions to the need for electricity storage driven by the increasing demand for energy supply at the same time as the electricity grid becomes more and more dependent on renewable sources such as solar, wind and ocean energy. Vanadium flow batteries (VFBs) are perhaps the most promising of these technologies and a growing number of commercial systems are in operation worldwide.The energy efficiency of vanadium flow batteries (VFBs) largely depends upon the performance of the electrodes. Poor electrode kinetics cause large overpotentials, which reduce the voltage efficiency. They can also lead to side reactions, such as hydrogen evolution at the negative electrode and oxidation of the positive electrode, which reduce the coulombic efficiency and the overall performance and durability.There is considerable variation in the data regarding the kinetics of vanadium redox reactions at carbon electrodes. We have previously reported that cathodic treatment enhances the kinetics of the positive (VIV-VV) electrode in VFBs but inhibits the kinetics of the negative (VII-VIII) electrode, while anodic treatment inhibits the kinetics of the positive electrode but enhances the kinetics of the negative electrode1-3. We also showed that the activity of carbon-based material is strongly dependent on the surface history, in particular the most positive and the most negative potential used to treat an electrode4. In this presentation we will further investigate the effect of electrochemical treatment of the carbon surface and show the relationship between the observed pseudo-capacitive behavior and the kinetics of the different vanadium redox couples. References Bourke, M. A. Miller, R. P. Lynch, X. Gao, J. Landon, J. S. Wainright, R. F. Savinell and D. N. Buckley, J. Electrochem. Soc. 163, A5097 (2016). A. Bourke, M. A. Miller, R. P. Lynch, J. S. Wainright, R. F. Savinell and D. N. Buckley, J. Electrochem. Soc., 162, A1547 (2015). M. A. Miller, A. Bourke, N. Quill, J. S. Wainright, R. P. Lynch, D. N. Buckley and R. F. Savinell, J. Electrochem. Soc., 163, A2095 (2016). M. Al Hajji Safi, A. Bourke, D. N. Buckley, R. P. Lynch, ECS Trans., 109, 67-84 (2022).

Use of Surface Features with Controlled Kinetics to Verify Fits of Scanning Electrochemical Microscopy Images

Scanning Electrochemical Microscopy (SECM) is a promising technique for measuring kinetics of redox reactions at surfaces. The conversion of the current map - produced by rastering an electrode over the surface - to a maps of the rate constant of reactions at the surface requires computer modelling and statistical techniques. Experimentally obtained SECM images are necessary to validate computer models that will be used to test these fitting procedures.The largest challenge was finding or creating samples that have reactive sites of known kinetics that were sufficiently slow to be activation-limited. This was achieved by producing small precious metal electrodes embedded in an insulating surface. The exchange currents of these electrodes were characterized using cyclic voltammetry at high scan rates[1,2] so that the rate constant of the electrodes could be effectively controlled by the potential at which they were poised. SECM images of these electrodes can compared to computer simulations to verify that they produced correct results. [1] Nicholson, R.S. Theory and Application of Cyclic Voltammetry for Measurement of Electrode Reaction Kinetics. Anal. Chem. 1965, 37, 11, 1351–1355[2] Mirkin, M.V.; Bard, A.J. Simple Analysis of Quasi-Reversible Steady-State Voltammograms. Anal. Chem. 1992, 64, 19, 2293–2302

(Invited) A Sustainable and Reliable Electrolyte Toward Safe Zn-MnO2 Alkaline Rechargeable Batteries

Zinc-Manganese Dioxide (Zn-MnO2) rechargeable batteries has spurred interest due to lower cost, high specific capacity, increased safety while using in small electronic devices and wearable technology. Zn-MnO2 alkaline batteries form inactive compounds during charging and discharging that hinder their ability to be utilized in rechargeable settings. Design and development of functional electrolyte to replace traditional electrolyte have become an effective way to inhibit irreversible compound formations and Zn dendrite growth, avoid leakage issues and metallic packaging. However, many challenges such as reliable and reproducible ionic conductivity and ion transference number of free-standing electrolyte films at lower thickness (150 µm), and interfacial contact resistance between electrolyte and electrode layer still exist. Our assumption is producing reliable and consistent ionic conductivity and ion transference number of electrolytes at lower thickness (150 µm) will help in providing the faster redox reaction kinetics at electrolyte-electrode interface. Moreover, by reducing the interfacial contact resistance between electrolyte and electrode interface will help in reducing the charge transfer resistance and zincate ion movements and results in improving the reversible life cycle of batteries. Many electrolytes fabricated utilize two different solutions that are mixed separately, forming either a liquid or a solid electrolyte after curing. Due to separate mixing, both solutions are never fully incorporated into one another, causing discrepancies in the consistency of the electrolyte. Here, we propose to use sustainable chitosan, which utilized 5:1 ratio of naturally occurring Chitosan (Chi) and Polyvinyl Alcohol (PVA) respectively. The Chi and PVA solution were premixed using ultrasonic bath and vacuum suction was used to remove extra bubbles formation due to mixing of Chi and PVA. This new process of electrolyte formation was compared between different thickness (120 µm, 150 µm, and 250µm), and the best electrolyte was then compared to the old process of mixing the solutions separately for electrolyte formation. The different thickness electrolytes were soaked into Potassium Hydroxide (KOH) and compared on their Ionic Conductivity, Ionic Conductance, Ion Transference Number, PH, and Swelling Ratio. To reduce the interfacial contact resistance between electrolyte and electrode, free standing electrolyte layer will be dipped into Chi solution and then put in contact with electrodes. These electrolytes were then used in the fabrication of Zn-MnO2 batteries and measure their performance using cyclic voltammetry and galvanostatic charge-discharge.

Zn-BTC MOF as Self-Template to Hierarchical ZnS/NiS2 Heterostructure with Improved Electrochemical Performance for Hybrid Supercapacitor.

Zn-BTC (H3BTC refers to 1, 3, 5-benzoic acid) MOF was used as a self-template and a zinc source to prepare ZnS/NiS2 with a layered heterogeneous structure as a promising electrode material using cation exchange and solid-phase vulcanization processes. The synergistic effect of the two metal sulfides enhances the application of ZnS/NiS2. And the high specific surface area and abundant active sites further promote the mass/charge transfer and redox reaction kinetics. In the three-electrode system, the specific capacitance was as high as 1547 F/g at a current density of 1 A/g, along with satisfactory rate capability (1214 F/g at 6 A/g) and cycling performance. Coupled with activated carbon (AC), the prepared hybrid device (ZnS/NiS2 as the positive electrode and AC as the negative electrode) (ZnS/NiS2/AC) can be operated under a potential window of 1.6 V and provides a high energy density of 26.3 Wh/kg at a power density of 794 W/kg. Notably, the assembled ZnS/NiS2//AC showed little capacity degradation after 5000 charge/discharge cycles.

Accelerated Redox Reactions Enable Stable Tin-Lead Mixed Perovskite Solar Cells.

The facile oxidation of Sn2+ to Sn4+ poses an inherent challenge that limits the efficiency and stability of tin-lead mixed (Sn-Pb) perovskite solar cells (PSCs) and all-perovskite tandem devices. In this work, we discover the sustainable redox reactions enabling self-healing Sn-Pb perovskites, where their intractable oxidation degradation can be recovered to their original state under light soaking. Quantitative and operando spectroscopies are used to investigate the redox chemistry, revealing that metallic Pb0 from the photolysis of perovskite reacts with Sn4+ to regenerate Pb2+ and Sn2+ spontaneously. Given the sluggish redox reaction kinetics, V3+ /V2+ ionic pair is designed as an effective redox shuttle to accelerate the recovery of Sn-Pb perovskites from oxidation. The target Sn-Pb PSCs enabled by V3+ /V2+ ionic pair deliver an improved power conversion efficiency (PCE) of 21.22 % and excellent device lifespan, retaining nearly 90 % of its initial PCE after maximum power point tracking under light for 1,000 hours.

Accelerated Redox Reactions Enable Stable Tin‐Lead Mixed Perovskite Solar Cells

AbstractThe facile oxidation of Sn2+ to Sn4+ poses an inherent challenge that limits the efficiency and stability of tin‐lead mixed (Sn−Pb) perovskite solar cells (PSCs) and all‐perovskite tandem devices. In this work, we discover the sustainable redox reactions enabling self‐healing Sn−Pb perovskites, where their intractable oxidation degradation can be recovered to their original state under light soaking. Quantitative and operando spectroscopies are used to investigate the redox chemistry, revealing that metallic Pb0 from the photolysis of perovskite reacts with Sn4+ to regenerate Pb2+ and Sn2+ spontaneously. Given the sluggish redox reaction kinetics, V3+/V2+ ionic pair is designed as an effective redox shuttle to accelerate the recovery of Sn−Pb perovskites from oxidation. The target Sn−Pb PSCs enabled by V3+/V2+ ionic pair deliver an improved power conversion efficiency (PCE) of 21.22 % and excellent device lifespan, retaining nearly 90 % of its initial PCE after maximum power point tracking under light for 1,000 hours.

Understanding synergistic catalysis on Pt–Cu diatomic sites via operando X-ray absorption spectroscopy in sulfur redox reactions

Sulfur redox reactions render lithium–sulfur (Li–S) batteries with an energy density of > 500 ​Wh ​kg−1 but suffer a low practical capacity and fast capacity fade due to sluggish sulfur redox reaction (SRR) kinetics, which lies in the complex reaction process that involves a series of reaction intermediates and proceeds via a cascade reaction. Here, we present a Pt–Cu dual-atom catalyst (Pt/Cu-NG) as an electrocatalyst for sulfur redox reactions. Pt/Cu-NG enabled the rapid conversion of soluble polysulfide intermediates into insoluble Li2S2/Li2S, and consequently, it prevented the accumulation and shuttling of lithium polysulfides, thus outperforming the corresponding single-atom catalysts (SACs) with individual Pt or Cu sites. Operando X-ray absorption spectroscopy and density functional theory calculations revealed that a synergistic effect between the paired Pt and Cu atoms modifies the electronic structure of the Pt site through d-orbital interactions, resulting in an optimal moderate interaction of the metal atom with the different sulfide species. This optimal interaction enhanced charge transfer kinetics and promoted sulfur redox reactions. Our work thus provides important insights on the atomic scale into the synergistic effects operative in dual-atom catalysts and will thus pave the way to electrocatalysts with enhanced efficiency for high-performance Li–S batteries.

A Facilely Synthesized NiCo2S4 with Two Mutually Reinforcing Active Sites for High-Performance Lithium-Sulfur Batteries.

The shuttle effect and slow conversion kinetics of soluble polysulfides hinder the commercial application of lithium-sulfur batteries (LSBs). In this context, we propose a three-dimensional lamellar-stacked nanostructure of nickel cobalt sulfide (D-NiCo2S4) enriched with lattice defects by manipulating the cations in spinel sulfides. It has an obvious synergistic promotion mechanism for the adsorption and catalysis of lithium sulfides. Specifically, Ni3+ on tetrahedral (Td) sites with strong Ni-S covalency anchors LiPSs, whereas Co3+ on octahedral (Oh) sites promotes a highly efficient catalytic conversion of LiPSs, which is confirmed by experimental results and density functional theory (DFT) calculations. Besides, the crystal defects and distortions in the lamellar region could expose more active sites and enhance the redox reaction kinetics of polysulfides. Hence, Li-S batteries with D-NiCo2S4@S as the cathode show outstanding cycle stability; upon cycling at 1 A/g, the battery achieves a high initial specific capacity of 1001.12 and 655.31 mAh g-1 after 1000 cycles (decay rate as low as 0.05% per cycle), as well as a high initial areal capacity of 3.15 mAh cm-2 under high S loading (4.2 mg cm-2). This work provides a viable scheme for designing efficient bimetal sulfide catalysts and furnishes a rational strategy for constructing LSB cathodes with high specific capacity and high area capacity.