Integrating intermittent renewable energy with alkaline water electrolysis causes reverse current-driven performance degradation under dynamic operating conditions during green hydrogen production.

Metal‐organic framework (MOF)–carbon composite materials are promising candidates for use as electrocatalysts in zinc‐air batteries (ZAB). Electrospun carbon nanofibers (CNFs) are particularly advantageous as conductive substrates due to their porous and binder‐free architecture. However, achieving stable and efficient dispersion of MOFs on CNFs remains a significant challenge. In this study, we present the synthesis of a composite electrode comprising of nickel‐based metal‐organic framework decorated over cobalt oxide‐embedded carbon nanofibers (NM@CCNF), designed as a self‐standing bifunctional electrocatalyst for rechargeable ZABs. The NM@CCNF features a unique open flower petal‐like morphology providing abundant active sites for oxygen reduction (ORR) and oxygen evolution reactions (OER). Electrochemical testing demonstrated that NM@CCNF exhibited a low potential gap (Δ E ) between the ORR and OER of 0.794 V, surpassing individual noble metal catalysts and rivaling benchmark Pt/C and IrO₂ combinations. The assembled ZAB demonstrated a high specific capacity of 830 mA h g Zn −1 , and a peak power density of 77.36 mW cm −2 . Long‐term cycling stability tests over 200 cycles showed minimal voltage degradation, indicating excellent durability and rechargeability. Post‐mortem analysis confirmed the reversible formation of ZnO during operation, validating the battery's rechargeability. These findings highlight the potential of NM@CCNF as a promising candidate for next‐generation energy storage systems.

Metal-organic frameworks (MOFs) represent a promising class of electrode materials for electrochemical energy storage systems due to their tunable morphology, high surface area, and chemical composition. However, the poor electron transport characteristics of MOFs have hindered their application in supercapacitor electrodes. Here, we report the seed-assisted synthesis of a freestanding composite featuring hydrangea flower-like Ni-MOF structures anchored on cobalt oxide (CoO x )-embedded carbon nanofibers (Co-CNFs) as electrodes for superior asymmetric supercapacitors. The CoO x nanoparticles serve as seeds that promote nucleation and modulate the growth of the Ni-MOF particles over the Co-CNF surface. The resulting Ni-MOF@Co-CNF composite exhibits a significantly high specific capacitance of 491 F g-1 at a current density of 0.1 A g-1 in a three-electrode system, surpassing the performance of both the individual components and the Ni-MOFs deposited onto the CNFs without any seed. This enhancement is accredited to the synergistic effect between Co-CNF and Ni-MOF, facilitating efficient dispersion of reaction active sites and promoting fast electron transfer through the conductive CNF matrix. The asymmetric supercapacitor (ASC) device with Ni-MOF@Co-CNF as a positive electrode demonstrates a specific capacitance of 126 F g-1 (301 mF cm-2) at a current density of 0.5 A g-1. The ASC device exhibited a high energy density of 44.8 Wh kg-1 (428.4 Wh cm-2) at a power density of 0.4 kW kg-1 (3.82 kW cm-2). Furthermore, the quasi-solid-state ASC device (SASC) delivered a remarkable energy density of 35.6 Wh kg-1 (340 Wh cm-2) at a power density of 0.4 kW kg-1 (3.82 kW cm-2) with excellent cycling durability (similar to 89% capacitance retention after 10,000 charge/discharge cycles). This study highlights the significant potential of Ni-MOF@Co-CNF as electrodes in electrochemical energy storage applications.

Iodine-iodide redox reactions are pivotal in diverse energy storage and production technologies. The electrooxidation of iodide ions (I-) involves the formation of a solid I-2 film on the electrode surface that impedes the further electrooxidation process and therefore has a significant implication on the performance of iodine-iodide redox chemistry-based systems. In this work, we have illustrated the role of pore structure in the accumulation of the I-2 film and its consequent effect on charge storage capabilities. Freestanding electrospun carbon nanofibers (CNFs) with varying pore architectures were synthesized through strategic selection of sacrificial material. The mechanistic understanding of the I-2-film formation within these porous CNF electrodes is elucidated compared to that of a planar electrode. The cyclic stability tests demonstrated a loss in capacitance, attributed to gradual I-2-film accumulation on the CNFs over multiple redox cycles. A mathematical model has been proposed to simulate this capacitance loss and understand its dependence on the pore structure in the CNFs. It was deduced that while macropores contribute to an exponential reduction in capacitance, meso-/micropores result in a near-linear reduction in capacitance with cycling. This is attributed to the lower diffusional resistance to the transport of electroactive I- ions offered by the macropores and, thereby, a higher propensity toward I-2-film formation and accumulation. Furthermore, self-discharge studies revealed that surfaces with a higher fraction of meso-/micropores demonstrated relatively slower self-discharge compared to macropores.

Manganese oxides have attracted great interest as promising pseudocapacitive materials due to its low cost, variable oxidation states, and high theoretical capacitance. In this work, we report the in-situ syn-thesis of MnO-dispersed carbon nanofibers (CNFs) using electrospinning and a unique two-step car-bonization technique. While the single-step carbonization resulted in mixed MnxOy forms, however, by employing a suitable and optimized two-step carbonization, we were able to obtain CNFs assimilated with MnO nanoparticles (MnO-CNFs). The synthesized MnO-CNF electrodes achieved a high specific capacitance of 246 F g-1 at 0.5 A g-1 in a three-electrode system. A symmetric supercapacitor device assembled with these electrodes exhibited remarkable electrochemical performance with a maximum power density of 5000 W kg-1, maximum energy density of 14 W h kg-1, and an excellent cycling stabil-ity (97.5% retention after 10,000 cycles). The exceptional electrochemical performance of MnO-CNFs makes them promising electrode materials for practical energy storage applications.(c) 2022 Elsevier Ltd. All rights reserved.

Introducing KI as a redox additive in the electrolyte is a promising approach to enhancing the charge storage capacity of supercapacitors, bridging the gap between traditional electric double-layer capacitors and batteries. In this work, we have illustrated the role of pore structure in the accumulation of inhibiting I2-film and its consequent effect on charge storage capabilities. Freestanding electrospun carbon nanofibers (CNFs) with varying pore architectures were synthesized through strategic sacrificial material selection. The I2-film formation was studied in these porous CNF electrodes, and compared to a planar electrode, based on which mechanistic understanding is elucidated. The charge storage behaviour was found to be dependent on the pore structure of the CNF. The cyclic stability tests demonstrated a continuous loss in capacitance attributed to gradual I2-film accumulation on CNFs over cycles. A simplified mathematical model has been proposed to simulate this capacitance loss and understand its dependence on the pore structure in the CNFs. It was found that while macropores exhibit an exponential reduction in capacitance, meso/micropores show a near-linear reduction in capacitance with cycling. This is attributed to the lower diffusional resistance to the transport of electroactive I- ions offered by the macropores and, thereby, a higher propensity towards I2-film formation and accumulation. Self-discharge studies revealed that surfaces with a higher fraction of meso/micropores demonstrated slower self-discharge.

Adding potassium iodide (KI) as a redox additive to any non-faradaic electric double layer forming aqueous electrolyte (EE) has been shown to significantly enhance the charge storage capacity in a supercapacitor. However, whether the choice of EE is immaterial, or if there are advantages with any specific EE when used with KI is an open question. Herein, we demonstrate that the extent to which performance enhancement can be attained is dependent on the EE used in conjugation with KI. EEs as co-electrolyte in KI-EE systems influence (inhibit/promote) the specific redox reactions, their kinetics, solution conductivity as well as the wettability that dictates its pore penetration. While the pH of the electrolyte dictates the participating redox reactions, the kinetics and the solution conductivity are determined by the characteristic ions constituting the EEs. Our investigations reveal that H2SO4 (acidic) as EE when used with KI showed a synergistic enhancement in charge storage capacity, which was otherwise not obtained for other commonly used EEs such as Na2SO4 and KOH. The synergistic enhancement was found emanating from the enhanced reaction kinetics of the iodine-iodide redox reactions and augmented pore penetration through enhanced wetting resulting in the access to an increased electrochemical surface area. Conversely, Na2SO4 (neutral) as EE with KI offers impeding effect on the charge storage through iodine-iodide redox reactions along with poor wetting of the electrode, thereby resulting in a lower specific capacitance. While KOH (basic) as EE with KI, leads to suppression of the iodine-iodide redox reactions offered by KI thereby lowering the charge storage capacity as compared to KI.

The role of the collector properties in changing the fiber morphology in electrospinning has not been completely understood yet. In this work, we studied the effect of different collectors on the helicity of the magnetic polystyrene nanocomposite fibers containing superparamagnetic magnetite nanoparticles. Aluminum and ice were used as solid collectors. Ethanol, ethanol-deionized (DI) water mixture, sodium dodecyl sulfate, Triton X-100, deionized water, and NaCl baths were used as liquid collectors. Ice, when surrounded by a conductive foil, produced excellent fiber alignment, but increased local humidity, inhibiting the continuous jet formation. The deionized water and NaCl bath exhibited minimum helicity. The surfactant bath produced different structures such as coiled, helical, and zigzag with varied diameters. Ethanol and DI/Ethanol baths were found to retain the structure of the deformed fiber formed due to jet instability. The helicity of the fibers was observed to increase with decreasing surface tension. Incorporation of the magnetic phase affected the viscosity of the polymer solution and the hydrophobicity of the polystyrene fibers further influencing the obtained morphologies.

Meniscus-confined electrodeposition and electrodissolution are a facile maskless approach to generate controlled surface patterns and 3D microstructures. In these processes, the solid-liquid interfacial area confined by the meniscus dictates the zone on which the electrodeposition or the electrodissolution occurs. In this work, we show that the process of electrodeposition or electrodissolution in a meniscus-confined droplet system can lead to dynamic spreading of the meniscus, thereby changing the solid-liquid interfacial area confined by the meniscus. Our results show that the wetting dynamics depends on the applied voltage and the type of interface underneath the droplet, specifically a smooth surface with a homogeneous solid-liquid interface or a superhydrophobic surface with a heterogeneous solid-liquid and liquid-vapor interface. It is found that both electrodissolution and electrodeposition processes induced droplet spreading in the case of a smooth surface with a homogeneous interface. However, a superhydrophobic surface with a heterogeneous interface under the droplet produced nonlinear spreading during electrodissolution and spreading inhibition during electrodeposition. The underlying mechanisms resulting in the observed behavior have been explicated. The dynamic droplet spreading could modify the dimensions of the patterns formed and hence is of immense importance to the meniscus-confined electrochemical micromachining. The findings also provide fundamental insights into the spreading behavior and wetting transitions induced by electrochemical reactions.

Hypothesis: The superhydrophobic surfaces with re-entrant microstructures are known to provide robust superhydrophobicity by enhancing the energy barrier for Cassie-Baxter to Wenzel transition. However, the fabrication of such structured surfaces often involves sophisticated techniques and expensive ingredients. Experiments: Herein, a multifunctional, low-cost, and fluorine-free superhydrophobic coating with reentrant surface topology was fabricated using fly ash (FA) and room-temperature-vulcanizing silicone. A systematic study was performed to evaluate the coating properties and durability. The robustness was evaluated as a function of particle size and inter-particle spacing. The performance in selfcleaning, corrosion inhibition and oil-water separation has been presented. Findings: The synthesized coatings are substrate-versatile and demonstrate superhydrophobic behavior. The close-packed coating of re-entrant FA particles attained via vibration compaction was seen to provide high robustness. The coatings retain their superhydrophobicity after multiple cycles of tape-peeling and exposure to environmental factors including temperature, pH, and UV radiation. These coatings exhibit excellent corrosion inhibition (corrosion efficiency > 99.999%), outperforming the majority of the previously reported superhydrophobic coatings. It also displays excellent self-cleaning property and high separation efficiencies in oil-water separation (>99%). We envision that such FA-based superhydrophobic coatings can solve the issues of synthesizing cheaper, sustainable, and robust superhydrophobic surfaces while simultaneously opening new avenues for FA utilization. (c) 2021 Elsevier Inc. All rights reserved.

Electrospinning has emerged as one of the most versatile and extensively used approaches to synthesize nanofibers for a diverse range of applications. The production of custom nanofibrous assemblies with controlled fiber orientation, spatial deposition, and high productivity is desirable for emerging applications that demand new electrospinning system designs. The electric field plays a major role in determining the jet trajectory and thereby its manipulation can provide us with a tool to create desired fibrous architectures. In this work, we have systematically studied the three aspects of electrospinning system, specifically, collector/target designs, auxiliary electrodes, and multi-nozzle configurations using finite element simulation. The electric field distribution for different designs were analyzed and correlated with the literature-reported experimental studies to envisage the resultant macroscopic properties of the fibers. It was established that the alteration in electric field distribution can be exploited to control and enhance the fiber alignment, spatial deposition, and productivity. CO 2021 Elsevier Ltd. All rights reserved.

Polystyrene waste disposal is an environmental challenge and transforming it into value-added products such as submicron fibers is an attractive paradigm. In this work, we have reported a sustainable approach to deal with the twin issues of handling low-density polystyrene waste and its re-utilization. Using ethyl acetate as a cost-efficient environmentally preferable solvent, we have successfully demonstrated conversion of waste expanded polystyrene (WPS) into hydrophobic fibers via solution blow spinning technique and its application towards oil-water separation. The macroscale spray pattern analysis in combination with microscale analysis is reported as a facile tool for evaluating the effect of polymer solution properties and operating parameters on the spray morphology. Additionally, the fiber spinnability limits are identified that provide the operational parameters in which fibers without any undesirable structural features are obtained. Here, the lower fiber spinnability limits were identified as 6 wt% polymer concentration, 3 kg cm(-2) gas pressure and 10 cm nozzle-to-target distance, below which excessive beads or film formation was observed. The upper fiber spinnability limits were 14 wt% polymer concentration and 5 kg cm(-2) gas pressure beyond which the solution blow spinning was not feasible. Moreover, wettability studies showed the enhanced hydrophobic and superoleophilic behavior of the synthesized WPS fibrous mats with water contact angle as similar to 138 degrees and oil contact angle as similar to 0 degrees. The WPS fiber-coated membrane demonstrated a maximum separation efficiency of 97% for free oil (diesel)-water mixtures, indicating potential applications in oil recovery and treatment of oily wastewater.

Polystyrene foam (PF), commonly used in packaging and insulation purposes, has emerged as a recycling predicament due to its low density and is often found littering the natural environment. Herein, we have reported the utilization of discarded PF as a sacrificial material to synthesize porous carbon nanofibers (CNFs) as a sustainable technique to produce cost-effective, high-performance supercapacitor electrodes while addressing PF disposal. It was found that the solubility difference between PF and polyacrylonitrile (PAN) in N,N-dimethylformamide can be exploited to create micro-mesoporous multi-channel CNFs via electrospinning technique for enhanced ion adsorption leading to higher specific capacitance. CNF-40 (PF:PAN = 40:60) showed the best electrochemical performance with a specific capacitance of 271.6 F g−1 at a current density of 0.5 A g−1. Further, CNF-40 exhibited 100% capacitance retention after 5000 cycles, and the high energy and power densities of 18.8 Wh kg−1 and 8000 W kg−1, respectively. Moreover, in an all-solid-state supercapacitor, it demonstrated a high areal capacitance of 0.32 F cm−2, indicating great potential for application in solid-state devices.

With increasing buoyant plastic wastes entering into oceans and food chains, the disposal and recycling of waste expanded polystyrene (WPS) has become an imminent environmental problem. In this work, a recycling scheme for waste WPS is proposed that combines the polymer dissolution recycling approach with the solution blow spinning (SBS) technique that facilitates the high-volume bulk WPS transportation and the value-addition of WPS to nanofibers. Solvent selection is critical for an economical and environmentally favorable implementation of this recycling scheme at large scale. Here, the effect of three solvents with distinct volatility, viz. ethyl acetate, toluene, and N, N- dimethylformamide (DMF) have been studied on the fiber formation and the ease of the solvent recovery, in order to ascertain the practicability of using these solvents for the recycling process. The fiber formation is experimentally demonstrated for the WPS-solvent systems using the SBS process. It is found that the fiber morphology varies for the different WPS-solvent systems. A solvent recovery scheme to recover the solvent from the air-solvent mixture (leaving SBS) is evaluated using ASPEN Plus simulation. The % solvent recovery is determined as a function of the required energy input for different process parameters including compressor pressure and air to polymer solution feed ratio. The simulation studies show that a lower feed air to polymer solution ratio and higher compressor pressure are required to obtain > 70% solvent recovery for high volatility solvents (ethyl acetate and toluene) with lower energy input and optimal operating condenser temperature (~ 0 °C). Conversely, significant solvent losses occur in the SBS process with a lower volatility solvent (DMF), leading to a lower solvent recovery for the whole process. The % DMF recovery can be improved upon by using higher feed air to polymer solution ratio although at a higher energy penalty.

In the solar thermal electrochemical process (STEP), sunlight is split into visible (for photovoltaic electricity) and thermal (unused, sub-bandgap) radiation using the full solar spectrum to efficiently drive high temperature electrolyzes. Electrolysis conditions for STEP ammonia are investigated. A mixed molten carbonate/hydroxide electrolyte with iron oxide catalyzes ammonia formation from water (steam) and air (nitrogen) via an iron intermediate. The higher temperature required for effective iron formation needs to be balanced by the lower temperature for effective hydration of the electrolyte. STEP ammonia is illustrated at a nickel anode and steel cathode at 650 °C in Li1.6Ba0.3Ca0.1CO3 with 6m LiOH and 1.5m Fe2O3.

Efficient, low-cost, non-precious metal-based, and stable bifunctional electrocatalysts are key to various energy storage and conversion devices such as regenerative fuel cells and metal-air batteries. In this work, we report cobalt nanoparticle-embedded porous carbon nanofibers with inherent N- and F-doping as binder-free bifunctional electrocatalysts with excellent activity for both the oxygen reduction and oxygen evolution reaction (ORR/OER) in an alkaline medium. Single-step electrospinning of a solution of the polymer mixture (carbon precursor) and the cobalt precursor followed by controlled pyrolysis with an intermediate reduction step in H-2 (to reduce cobalt oxides to cobalt) was utilized to synthesize an integrated freestanding catalyst. The fabricated catalyst with effective structural and electronic interaction between the cobalt metal nanoparticles and the N- and F-doped carbon defect sites showed enhanced catalytic properties compared to the benchmark catalysts for ORR and OER (Pt, Ir, and Ru). The ORR potential at the current density of -3mAcm(-2) was 0.81 V-RHE and the OER potential at a current density of 10mAcm(-2) was 1.595 V-RHE, resulting in a E of only 0.785V.

This paper demonstrates a highly favored route for the synthesis of controlled nanostructures at high rate, high yield, and low cost by molten carbonate electrolysis splitting of CO2. We show the wide, portfolio of carbon nanotubes (CNTs) that can be produced by controlling the electrolysis conditions in this one-pot synthesis. For example solid core carbon nanofibers are formed with C-13 isotope CO2, whereas hollow core CNTs are formed with natural abundance CO2 (which contains 99% C-12 and 1% C-13). Shown are the first doped electrosynthesized carbon nanotubes, prepared with added electrolytic LiBO2 for boron doping, and salts for phosphorous, nitrogen or sulfur CNT doping is probed. Boron doping greatly enhances conductivity of the CNTs. Electrolytic CaCO3 produces thin-walled CNTs, while excess electrolytic oxide yields tangled CNTs. Addition of up to 50 mol% Na2CO3 to a Li2CO3 electrolyte, decreases electrolyte costs and improves conditions for intercalation in Na- ion CNT anodes. Addition of BaCO3 increases electrolyte density. Longer electrolysis time leads to proportionally wider diameter CNTs. Synthetic components (steel cathode, nickel anode and inorganic carbonate electrolyte) are available and inexpensive. Advantages include (1) production is limited only by the cost of electrons (electricity) providing a substantial cost reduction compared to conventional CVD and polymer spinning syntheses and (2) the only reactant consumed in the formation of the CNTs is CO2, transforming this greenhouse gas into a stable, valuable product and providing an economic incentive to the removal of anthropogenic CO2 from flue gas or from the atmosphere. (C) 2017 Elsevier Ltd. All rights reserved.

Rechargeable lithium-oxygen (Li-O2) batteries have received much attention because of their ultra-high theoretical energy density, about ten-times higher than that of current lithium-ion batteries.[1-4] However, the development of these batteries is still at its initial stage, owing to various technical challenges such as high overpotentials, low round-trip efficiency, poor rate capability, and low cycle life. Among various issues affecting Li-O2 battery performance, the low performance of the oxygen cathode has been identified as the dominating factor.[5, 6] The development of efficient cathode with nano-architectures, large accessible surface area, and bifunctional catalytic activity is a great challenge for high-performance lithium-air batteries.[7] In the present study, binder-free high surface area porous carbon nanofibers modified with cobalt nanoparticles (Co-PCNF) are presented as efficient cathodes for Li-O2 batteries. The macroporous inter-connected structure of carbon nanofibers with effective dispersion of cobalt nanoparticles serve as an efficient cathode with high electrocatalytic activity. Co-PCNF demonstrated much better performance as cathodes in Li-O2 batteries, with high discharge capacity, rechargeability, and rate capability, compared to non-cobalt-carbon cathodes. Li-air cells with Co-PCNF as cathode exhibit a high initial discharge capacity of 8800 mAhg-1 at the current density of 100 mA g-1, and can be recharged for more than 50 cycles with limited discharge capacity of 500 mAh g-1. Moreover, the synergistic role of N-and F- doped carbon defects and cobalt nanoparticles leads to faster electronic transfer and stabilize carbon surface, enhancing the reversibility. References: [1] M. Armand, J.M. Tarascon, Nature, 451 (2008) 652-657. [2] G. Girishkumar, B. McCloskey, A.C. Luntz, S. Swanson, W. Wilcke, J. Phys. Chem. Lett., 1 (2010) 2193-2203. [3] P.G. Bruce, S.A. Freunberger, L.J. Hardwick, J.-M. Tarascon, Nat. Mater., 11 (2012) 172-172. [4] N. Imanishi, O. Yamamoto, Materials Today, 17 (2014) 24-30. [5] L. Mai, X. Tian, X. Xu, L. Chang, L. Xu, Chem. Rev., 114 (2014) 11828-11862. [6] Z. Ma, X. Yuan, L. Li, Z.-F. Ma, D.P. Wilkinson, L. Zhang, J. Zhang, Energy Environ. Sci., 8 (2015) 2144-2198. [7] J. Wang, Y. Li, X. Sun, Nano Energy, 2 (2013) 443-467.