The electrochemical route to sustainable transport

With rapid development of the global economy, increasing environmental pollution and the depletion of fossil fuels, there is a vital need for clean, sustainable and efficient sources of energy as well as new technologies allied with energy conversion and storage (1). Among many application fields, some of the most practical and efficient technologies for electrochemical energy conversion and storage are fuel cells, batteries and electrochemical supercapacitors. In recent years, these devices have attracted significant attention, each with recognized advantages. Driven by this need and the promise of the technology, significant progress in practical and theoretical research and development of these devices has taken place. One of the challenges of developing these electrochemical energy conversion and storage technologies is the use of low cost and readily available materials that possess complex requirements of different applications. To overcome obstacles of high costs of raw materials and avoid usage of depleting sources, bio-based carbon materials are believed to lead the next generation of many industries including aerospace, sports equipment and electrochemical devices due to their abundance, high chemical stability, electrical conductivity, low cost and non-toxicity, high specific surface area and wide operating temperature range (2). The feasibility of the carbon precursors in different electrochemical devices for practical applications including hybrid power sources in electrical vehicles, burst-power generation in electronic devices, back-up power sources, portable and stationary equipment has been demonstrated. Cellulosic fibers in nano and micro scale, the green and most abundant material, have eco-friendly attributes that are economically and technically feasible to replace man-made fibers (3). Carbonization of cellulose yields carbons, including charcoal, activated carbon and graphite fibers. The process comprises of introducing the fibers in an inert atmosphere, preheating and drying the fibers, treating the dried fibers up to a certain temperature at which they carbonize by evolution of a purging gas and finally cooling the carbonized residues (4). The produced carbon materials have been investigated as a potential material in different electrochemical devices and have proved to have prospect as electrode materials for supercapacitors, catalyst supports in fuel cells and membrane separators in lithium-ion batteries. In this project, bio-based cellulosic starting materials have been investigated as a candidate for supercapacitor electrode materials. The produced activated carbon materials upon carbonization of the cellulose fibers have been functionalized and characterized by different techniques to study the effect of the morphology and surface area of the carbonaceous residues on their performance in the electrochemical device. This work has been coupled with a range of electrochemical tests in two and three-electrode systems including cyclic voltammetry, electrochemical impedance spectroscopy and charge-discharge loop tests. The work highlights the importance of relating the different characterization techniques of the raw and produced materials and the effect of each on the performance of the activated carbons as electrode materials in supercapacitors.

Synergistic effect of La2o3 -Nio nanocomposite based electrode for electrochemical high-performance asymmetric supercapacitor applications

Nanosized hyperbranched cobalt and metal-free phthalocyanine intercalated with Pd–C matrix using PVA-TEOS as binder for admirable supercapacitor properties

The low cost and profusion of sodium resources make sodium-ion batteries (SIBs) a potential alternative to lithium-ion batteries for grid-scale energy storage applications. However, the use of conv...

The intermittent nature of many renewable energy sources such as wind and solar, coupled with fluctuations in energy demand, creates a pressing need for efficient, low-cost energy storage technologies. Supercapacitors are promising candidates to play a role in next-generation energy storage systems. They have a higher power density and better cycle life (although lower energy density) than batteries making them ideal for rapid energy storage and deployment [1]. Activated carbon is a favoured electrode material due to high surface area, although low conductivity requires use of a conductive additive (often carbon black), reducing available surface area for charge storage. In contrast, the high conductivity and specific surface area of graphene has made it a promising material for electrochemical double layer supercapacitors (EDLCs) [2], however, performance is limited by restacking of the graphene sheets, reducing available surface area.In this work, high-shear exfoliated few layer graphene (FLG) [3] is investigated both as an electrode material and as a conductive additive/interfacial layer for EDLCs. FLG suspensions were produced under a variety of exfoliation conditions, with platelet thickness and linear dimension determined from Raman spectroscopy based on metrics developed by Backes et al. [4] and through scanning electron microscopy (SEM).The FLG suspensions were used in three ways: i) to create thin ‘graphene paper’ electrodes; ii) as a conductive additive, mixed into the activated carbon electrode material; iii) deposited onto the back of (and diffused within) activated carbon electrodes. These electrodes were investigated by Raman spectroscopy and Scanning Electron Microscopy, before being assembled into symmetric two-terminal aqueous cells then evaluated by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS), and their electrochemical performance related to structure and composition.As expected, pure FLG electrodes often showed excellent low series resistance values, however specific capacitance was low, due to restacking. Directly mixing 5% FLG into activated carbon as a conventional conductive additive led to a specific capacitance of 63 F/g (from CV at 10 mV/s), and a series resistance of 19 W (from GCD at 1 A/g) - markedly inferior to those with 5% carbon black as a conductive additive (95 F/g and 2 Ohm) and inferior even to electrodes with no conductive additive (87 F/g and 10 Ohm).However, post fabrication deposition/infusion of FLG offers comparable performance to carbon black (90 F/g and 1 Ohm) at 7% FLG by weight. As the quantity of FLG is increased the specific capacitance decreases sharply. This behaviour is attributed to FLG restacking on the rear of the electrode, so adding mass whilst providing limited additional capacitance, and compression of the electrode.Adding high-shear exfoliated FLG to activated carbon electrodes shows promise for obtaining the benefits of both materials. At present, FLG/activated carbon electrodes can match the performance of those produced from activated carbon with a carbon black conductive additive and, with further optimization, we expect will be able to exceed them.Figure: a) Cross sectional SEM image of activated carbon electrode with graphene interfacial layer; b) magnified cross sectional SEM image of graphene interfacial layer; c) cyclic voltammograms at 10 mV/s of the different electrodes mentioned in the abstract.

Techno-economic analysis of long-duration energy storage and flexible power generation technologies to support high-variable renewable energy grids

Nowadays, renewable and sustainable energy sources are being explored and promoted to curb global pollution and to solve the issue of depleting fossil fuel resources. However, these renewable energy sources are intermittent in supply, therefore, it becomes necessary to store them for future usage. The traditional storage devices for electrical energy storage are different kinds of batteries but the sluggish performance of batteries, use of toxic heavy metals, issues pertaining to safety and low cycling efficiency are some of its major drawbacks. Recent proliferation of portable, wearable and flexible electronics and adoption of electric vehicles have forced the scientists to look for fast charging, light weight, leak proof, safe, toxic material free, durable energy storage devices like supercapacitors. Supercapacitors possess fast charge-discharge characteristics, high cycling stability and eco-friendliness in comparison to batteries. But they suffer from extremely low energy density (<10 Wh kg-1), high cost, bulk size, high self-discharge and significant drop in power density while increasing its energy density. The rational synthesis of electrode-materials has a significant impact on the development of high-performance electrodes for energy storage devices. Traditionally semiconducting materials like transition metal oxides are used as pseudocapacitive materials but transition metal oxides have very low electronic and ionic conductivity. Recently, transition metal sulfides, another class of semiconductors, are being investigated as they exhibit better conductivity and reaction kinetics compared to oxides. In this work, α-MnS is selected as an alternative to transition metal oxides. α-MnS is the most stable polymorph among other possible crystal structures of MnS, and has a hexagonal sheet like structure along with high operational potential window than many other metal sulfides. Although it is more conducting than transition metal oxides, it still needs conductivity enhancers like activated carbon, graphene, multiwall carbon nanotubes (MWCNT) etc. External mixing of conductivity enhancers is not effective enough to enhance the conductivity. Hence, MWCNT is mixed during the synthesis step to have a better bonding with α-MnS and create high conductivity channels. α-MnS + MWCNT composite shows a specific capacitance of 115 F g-1 at 1 A g-1 in 3 M KOH electrolyte under 3 electrode configuration. α-MnS + MWCNT composite is deposited on flexible conducting carbon cloth as cathode material and Vulcan carbon is deposited on carbon cloth as anode material. A mixture of poly vinyl alcohol PVA+ 3 M KOH is used as the gel type electrolyte. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), galvanostatic charge discharge (GCD), electrochemical impedance spectroscopy (EIS), cycling stability are performed to characterize the active material and the device performance. The assembled device shows a potential window of 1.4 V, alongside a specific capacitance of 27.7 F g-1 at 1 A g-1 and with 80% of capacity retention after 10,000 cycles. These results prove that transition metal sulfides can be viable alternative materials for supercapacitor application. This quasi-solid state or gel type electrolyte significantly reduces the conductivity and specific capacitance. Enhancing the ionic conductivity of the gel and finding out the optimum thickness of gel electrolyte layer between the electrodes are expected to open new pathways in enhancing the performance of the device. Figure 1

Rational design of pyrene and thienyltriazine-based conjugated microporous polymers for high-performance energy storage and visible-light photocatalytic hydrogen evolution from water

Conjugated microporous polymers (CMPs) have found extensive applications in various fields, such as optoelectronics, CO2 capture, and catalysis. However, their potential in electrochemical supercapacitors as energy storage and H2 production systems remains relatively unexplored. This limited exploration can be attributed to certain challenges, including issues related to structural and electrochemical stability, as well as the relatively modest specific capacitance. Additionally, many of the CMPs discovered thus far have exhibited lower energy densities, further contributing to this underexplored aspect of their utility. In this study, we prepared two different CMPs [TPET-TTh and PyT-TTh CMPs] containing thienyltriazine units (TTh) for the redox mechanism and constructed electrodes for supercapacitor applications. The synthesized TPET-TTh and PyT-TTh CMPs displayed exceptionally high specific surface areas of 545 and 528 m² g⁻¹, respectively. Furthermore, their pore sizes were very similar, centered at approximately 0.39 and 0.36 nm, respectively. To evaluate their electrochemical properties, the TTh-CMPs were examined using cyclic voltammetry (CV) and galvanostatic charge/discharge (GCD). The resulting CV curves exhibited rectangular shapes, indicative of the characteristic behavior of electric double-layer capacitors, across a range of potential and scan rates. These TPET-TTh and PyT-TTh CMPs delivered nominal specific capacitances of 74 and 76 F g−1 at 0.5 A g−1, respectively. In addition, they exhibited outstanding capacity retentions of 95.2 and 97.30 % even after 2000 cycles [analyzed at 10 A g−1]. The TTh-CMPs also exhibited excellent light-capture capabilities. The PyT-TTh CMP has faster charge separation and lower charge recombination rates than TPET-TTh CMP. This results in a higher hydrogen evolution rate from the water decomposition reaction. The H2 production rate of PyT-TTh CMP could be as high as 18,533 μmol g−1 h−1, which is approximately 4-fold that of TPET-TTh CMP. This study offers a strategy for the design of TTh-containing CMPs that exhibit exceptional energy storage application and photocatalytic efficiency for H2 evolution. Figure 1

Chapter 1 - MOF-based nanostructures and nanomaterials for next-generation energy storage: an introduction

The world dependence on portable electronic devices has increased the demand for high-performance energy storage devices. The use of transition metal sulfides as faradaic electrode materials for electrochemical energy storage is rapidly increasing due to their high energy density. Herein Zinc Cobalt Sulfide (ZCS) with graphene oxide (GO) and carbon nanotubes (CNT) were used to create an interconnected ZCS composite network using a solvothermal technique. The materials were characterized by utilizing XRD, FT-Raman, TGA, FESEM/EDX, XPS, and BET. The electrochemical performance of the materials was examined using cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS). The prepared electrodes exhibited both pseudocapacitor behavior and double-layer capacitor behavior, indicating the hybrid nature. Furthermore, All the electrode ZCS, ZCS/GO, ZCS/CNT, and ZCS/GO/CNT electrodes demonstrated higher capacitance behavior, with values of 420, 551, 585 and 811 F g−1 at 1 A/g. Among these ZCS/GO/CNT electrode exhibits outstanding electrochemical properties, with a notable retention of 81.08% at 10 Ag−1 because Combining ZCS nanoparticles with interconnected GO and CNT provides excellent electronic conductivity and stability. The assembled ZCS/GO/CNT//graphene oxide asymmetric coin cell (ACC) supercapacitor showed a high energy density of 33.3 Wh kg–1 at a power density of 624 W kg–1. The 3D nanostructure of ZCS/GO/CNT/Graphene oxide has great potential for developing foldable energy storage devices.

Facile hydrothermal synthesis of high-performance binary silver-cobalt-sulfide for supercapattery devices

Exploration of La2O3-CuO nanocomposite as an effective electrode material for asymmetric supercapacitor applications

The demand for improved energy storage technologies will increase significantly in coming years, as global ambitions move towards a net-zero future and intermittent renewable energy sources make up a larger proportion of the total energy mix. To meet this demand, worldwide storage technologies must be diversified to include modern electrochemical energy storage, such as batteries and supercapacitors, at handheld-, household- and grid-scale capacities.Supercapacitors represent a promising alternative and complementary electrochemical storage method to traditional batteries. They possess cycle lifetimes and power densities far superior to batteries, allowing much faster charging and discharging, but currently lag behind in energy density. Additionally, they are more environmentally friendly than batteries through having no reliance on toxic metals such as lithium. However, the most common formulations for supercapacitor electrode coatings in the literature continue to use hazardous solvents. One of the most common polymer/solvent combinations is polyvinylidene fluoride (PVDF) in N-methyl-2-pyrrolidone (NMP). NMP is very hazardous to human health and has recently been classified as a “Substance of Very High Concern” by the European Chemicals Agency, leading to use restrictions within the EU. As such, there is an urgent requirement for greener alternatives.This work explores a variety of alternative, greener solvents for PVDF dissolution, examining their effects on the properties and performance of electric double-layer capacitor (EDLC) electrodes, in comparison to NMP. The research aims to find a green solvent with comparable electrochemical performance and physical properties, alongside a much lower health and environmental impact. Dimethyl sulfoxide (DMSO), γ-valerolactone (GVL), triethyl phosphate (TEP) and Cyrene (dihydrolevoglucosenone) have been investigated; chosen based on their Hansen Solubility parameters and position within the Hansen solubility sphere for PVDF. The electrodes have been analysed morphologically using scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX), and nitrogen adsorption-desorption analysis (BET), to identify any differences in coating performance and pore structure. A particular focus has been placed on electrochemical testing of EDLC electrodes fabricated using these coatings. Three-electrode testing in aqueous electrolyte has comprised cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), electrochemical impedance spectroscopy (EIS) and electrode cycling over 2000 charge-discharge cycles. In this work we show that electrodes produced using Cyrene outperformed the specific capacitance and capacitance retention of all tested solvents, including control NMP samples, across the whole range of current densities from 0 to 200 Ag-1.Electrodes have also been produced for each solvent using either activated carbon or graphene nanoplatelets as the active material, to confirm that the results are comparable for different carbon structures. This has allowed comparison of the electrochemical properties between the two carbon materials. In addition, each solvent has been assessed for suitability for carbon-incorporated polymer nanowires production for supercapacitor electrode application. This could open the doors to developing environmentally friendly, freestanding electrodes for fast-charging electrical energy storage devices. Figure 1

With the depletion of traditional fossil fuels, rising pollution levels and fast growth of the global economy. New technology for energy conversion and storage, as well as efficient, sustainable energy sources, are all urgently needed. The development of supercapacitors (SCs) as an energy storage device has received a lot of interest in recent years. SCs are comparable to dielectric capacitors in terms of their high-power density, cyclic stability, and discharge rate. In addition, a high energy density that is comparable to batteries. In this chapter, polyaniline (PANI) based materials for electrochemical supercapacitor (ESs) electrodes are thoroughly reviewed. Pure PANI electrodes have low cycle life, low power density, and poor mechanical stability resulting from the swelling and shrinkage during the charging and discharging processes. Nevertheless, the development of nanocomposite of PANI with carbon materials or metal compounds could overcome the drawbacks of pure PANI and achieve higher electrochemical performance. Capacitance, energy, power, cycle performance, and rate capability have all been used to evaluate the performance of nanocomposites.