Porous Carbon-based Electrodes Research Articles

MnO2-decorated flexible carbon nanofibers with controllable hierarchical porous nanostructures for high energy density supercapacitors

Constructing hierarchical porous structures and reducing material size enhance the electrochemical efficiency of porous carbon-based electrodes. In this study, ultrafine hierarchical porous carbon-based nanofibers were synthesized via electrospinning a blend of polyacrylonitrile, polymethyl methacrylate (PMMA), and zinc acetate dihydrate (ZAH), followed by pre-oxidation, carbonization, and acid washing. Adjusting the ZAH content allowed precise control of fiber diameters (300-600nm) and promoted significant hierarchical porous structures, achieving an optimal mesopore to micropore ratio (1.65) and a high specific surface area (SSA) of 599 m²/g. MnO2 nanosheets were in-situ modified on the carbon nanofibers, forming a hybrid electrode (MnO2@HPCNFs) with excellent flexibility, high SSA value, and rich pore structure. This electrode demonstrated a specific capacitance value equal to 1035 F/g at 0.5 A/g and maintained 80.7% capacitance at 10 A/g. The assembled asymmetric supercapacitor achieved an energy density of 54.81 Wh/kg. This study presents new possibilities for binder-free, self-supporting electrodes in electrochemical energy storage devices.

N, O and P co-doped hierarchically porous carbon fiber for high performance Zinc-ion hybrid capacitors

Multi-heteroatoms co-doped hierarchically porous carbon-based electrode is an effective strategy to solve the low energy density and poor cycle stability of Zn-ion hybrid capacitors (ZHCs). Herein, N/O/P co-doped porous carbon nanofiber (N-P-PCF) was prepared, which displays fibrous network hierarchically porous structure to fast electron/ Zn2+ transport and enhance Zn2+ adsorption sites. Meanwhile, rich N (9.47 at.%), O (11.29 at.%) and P (1.29 at.%) co-doping can be beneficial for the infiltration of electrode–electrolyte interface and provide an additional pseudocapacitance. The N-P-PCF based ZHCs can yield a large specific capacitance (205 mAh g−1 at 1 A g−1), high energy density (173 Wh kg−1 at 823 W kg−1) and excenllent cycle stability for 10,000 cycles (98.6 % capacity retention), which provides a reliable multi-heteroatoms co-doped porous carbon fiber for high-performance ZHCs.

Anthracite-derived porous carbon@MoS2 heterostructure for elevated lithium storage regulated by the middle TiO2 layer.

The rational design of MoS2/carbon composites have been widely used to improve the lithium storage capability. However, their deep applications remain a big challenge due to the slow electrochemical reaction kinetics of MoS2 and weak bonding between MoS2 and carbon substrates. In this work, anthracite-derived porous carbon (APC) is sequential coated by TiO2 nanoparticles and MoS2 nanosheets via a chemical activation and two-step hydrothermal method, forming the unique APC@TiO2@MoS2 ternary composite. The dynamic analysis, in-situ electrochemical impedance spectroscopy as well as theoretical calculation together demonstrate that this innovative design effectively improves the ion/electron transport behavior and alleviates the large volume expansion during cycles. Furthermore, the introduction of middle TiO2 layer in the composite significantly strengthens the mechanical stability of the entire electrode. As expected, the as-prepared APC@TiO2@MoS2 anode displays a high lithium storage capacity with a reversible capacity of 655.8 mAh g-1 after 150 cycles at 200 mA g-1, and robust cycle stability. Impressively, even at a high current density of 2 A g-1, the electrode maintains a superior reversible capacity of 597.7 mAh g-1 after 1100 cycles. This design highlights a feasibility for the development of low-cost anthracite-derived porous carbon-based electrodes.

Machine learning models for capacitance prediction of porous carbon-based supercapacitor electrodes

Energy storage devices and systems with better performance, higher reliability, longer life, and wiser management strategies are needed for daily technology advancement. Among these devices, the supercapacitor is the most preferable due to its high-limit capacitance that esteems more than different capacitors. Today, it is considered a significant challenge to design high-performance materials for supercapacitors by exploring the interaction between characteristics and structural features of materials. Because of this, it is essential to predict capacitance when assessing a material’s potential for use in constructing supercapacitor-electrode applications. Machine learning (ML) can significantly speed up computation, capture complex mechanisms to enhance the accuracy of the prediction and make the best choices based on detailed status data. We aimed to develop a new strategy for the assisted design of high-performance supercapacitor materials by applying ML to analyze the relationship between capacitance and structural features of porous carbon materials (PCMs) using hundreds of experimental data in the literature. In the present study, Linear Regression (LR), Regression Tree (RT), and Adaptive Neuro-Fuzzy Inference System (ANFIS) were used to estimate the supercapacitor’s capacitance. The effectiveness of the ML models was evaluated in terms of the root mean square error (RMSE), mean absolute error (MAE), and the correlation between expected yield and system-provided yield. The developed ANFIS model, with RMSE, MAE, and R values of 22.8, 39.7647, and 0.90004, respectively, compares favourably regarding prediction performance to other models built for this purpose.

Optimizing the application of high-performance supercapacitors: Utilizing 3D honeycomb mesoporous carbons derived from hybrid biomass

Biomass garbage convert into highly efficient porous carbon-based electrode materials for supercapacitors is of great significance to the current energy-friendly society. Herein, an efficient electrode material of three-dimensional honeycomb porous carbons is developed for supercapacitor by employing sunflower plate and rice husk as a precursor. Particularly, SiO2-rich rice husk plays a crucial role in the formation of porous structure and three-dimensional morphology. Benefiting from the high surface area and more defective carbon nano-framework, high contents of nitrogen and oxygen dopants, abundant porosity, the resultant optimal RSC-1-1 exhibits a specific capacitance of 448 F/g at 0.5 A/g in 6 M KOH. Furthermore, the capacitive performance of RSC-1-1 in acidic and neutral media are also analysed systematically. In addition, the energy densities of RSC-1-1 assembled supercapacitors 6 M KOH, 1 M Na2SO4 and PVA/KOH gels are 12.15 Wh/kg, 35.55 Wh/kg, and 29.06 Wh/kg, respectively. This study demonstrates the great potential of twin substance derived electrode materials in constructing high performance supercapacitor.

An artificial neural network model for capacitance prediction of porous carbon-based supercapacitor electrodes

Among energy storage devices, the last decades have witnessed the rapid spread of usage of carbon-based electrodes for electric double-layer capacitors (EDLCs) due to their large surface area, low cost, and high porosity. It is crucial to develop an accurate and efficient forecasting model for electrochemical performance to reduce the time needed for making suitable designs and choosing testing electrode materials. As a result, the use of machine learning (ML) approaches in creating a predicting model for the capacitance of carbon-based supercapacitors looks critical and provides the electrode characteristics' relative relevance. Data extracted from nearly a hundred published experimental research papers to select supercapacitors with certain electrode morphologies such as mesoporous, nanoporous, microporous, and hierarchical porous carbon electrode. The data was examined using machine learning techniques to predict the supercapacitor's specific capacitance (F/g). Electrode material structural qualities and various physicochemical test features such as electrolyte material, pore volume, and specific surface area. Electrochemical test features acquired via electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge (GCD) test investigations for the same purpose include: cell configuration, current density, applied potential window, charge-transfer resistance (RCT), and equivalent series resistance (ESR) were used as input features to predict the corresponding capacitance performance. In the present study, Lasso, Support Vector Machine Regression (SVMR), and Artificial Neural Networks (ANN) with different structures were examined to predict the capacitance of the supercapacitor. The exhibition of the ML models measured concerning the root mean square error (RMSE), the correlation between expected yield and yield provided by the system. The developed ANN model with RMSE, MAE, and R values of 30.82, 46.5624 and 0.89537, respectively, provides outcomes for the prediction that are highly accurate compared to other models created for this purpose. According to the analysis of the input features done using the SHAP (SHapley Additive exPlanations) framework, the specific surface area had the biggest impact on the ANN model.

Enhanced pseudocapacitive behaviour in laser-written graphene micro-supercapacitors decorated with nickel cobalt sulphide nanoparticles

The next generation of energy storage technologies requires enhanced fabrication techniques such as the use of CO2 infrared lasers to pattern micro-supercapacitor (MSC) electrodoes. This study reports direct-writen laser-induced graphene (LIG) micro-supercapacitors with electrodepositated NiCo2S4- nanoparticles on commercial polyimide sheets. X-ray photoelectron spectroscopy (XPS) combined with transmission electron microscopy (TEM) showed NiCo2S4 nanoparticles decorating the graphene, within a highly porous carbon-based electrode. The LIG/NiCo2S4 exhibited outstanding properties with a specific capacitance of 30.4 mF cm−2 at 0.75 mA cm−2 and an energy density of 16.9 µWh cm−2 at a power density of 367.5 µW cm−2. High capacitance retention of 1.22-fold was measured after 5000 cycles of charge/discharge, and of ∼90% when bent to 120˚ angle. Here, it is demonstrated that surface decoration is an effective route in improving LIG MSC storage properties, and that the LIG/NiCo2S4 MSC is suitable for use in next generation of flexible and miniaturized portable devices.

Electrochemical performance of aqueous electrolytes in porous carbon derived cassava peel electrode material-based for sustainable symmetrical supercapacitor

Electrolytes have been generally recognized as one of the most important components in enhancing the electrochemical performance of supercapacitors. On the other hand, aqueous electrolytes are considered prime candidates for the development of the next generation of symmetric supercapacitors due to their low-cost, environmentally friendly, high ionic conductivity, fine ionic size, and high capacitance. Herein, the symmetrical supercapacitor of the sustainable porous carbon-based electrode material was confirmed through various aqueous electrolytes consisting of neutral, basic, and acidic Na2SO4, KOH, and H2SO4. Activated carbon is obtained from high potential biomass sources of cassava peel waste. Activated carbon synthesis was performed with a comprehensive approach in order to obtain abundant pore structure, high porosity, and improved wettability through a combination of high-temperature chemical and physical activation. in addition, the electrode material is designed to resemble a solid disc without the addition of a synthetic binder. The evaluation of the disc dimensions showed high porosity in the obtained activated carbon. Furthermore, the symmetrical supercapacitor of the optimized electrode material exhibit excellent specific capacitances of 112, 150, and 183 F g-1 at 1 mV s-1 in the electrolytes Na2SO4, KOH, and H2SO4, respectively. In addition, the highest rate capability of 70% was confirmed in the H2SO4 acid electrolyte. Moreover, their coulombic efficiency can be maintained around 89% with low equivalent series resistance 0.21-0.42 ?. Therefore, the activated carbon-based supercapacitor symmetric cell device from cassava peel shows high performance for developing high-performance supercapacitor applications with guaranteed stability in aqueous electrolytes.

Toward better porous carbon-based electrodes by investigation of the viscoelastic properties of carbon suspension

In this article, an electrode slurry based on activated carbon, which is used to form electrodes of electrochemical capacitors, was assigned to a given group of rheological fluids. The interactions between the textural properties of carbon, the components of the slurry and their impact on the flow nature were explained. Moreover, the viscosity window and optimal ratio between components have been specified, which are necessary to form the right coating on the stainless steel foil as a current collector. The equation that correlates electrode thickness, viscosity, and composition of the slurry (mass of solid materials, solvent, and ratio between components) was obtained by mathematical consideration. Electrochemical measurements were performed to verify the impact of coating quality and thickness on device performance. Finally, the effect of the microstructure formed after slurry preparation and the phenomena accompanying the selected mixing technique are discussed. The paper ends with an economic analysis of electrode slurry production.

Novel Strategy for the Formulation of High-Energy-Density Cathodes via Porous Carbon for Li-S Batteries.

Porous carbon is considered an attractive host material for high-energy sulfur electrodes. This study concerns the design of a porous carbon-based sulfur electrode for the formulation of high-energy Li-S batteries. The porous carbon is impregnated with up to 80 vol.% of sulfur and a reduction in both the conductive agent and binder content. Therefore, less solvent can be used during slurry casting to inhibit crack formation following electrode drying. In addition, the utilization of two distinct electrically conducting networks enables reduced battery polarization, resulting in a battery with a capacity of 690 mAh g-1 (even after 100 cycles). Finally, pouch cells are prepared to characterize the practical performance of the optimized cathode. This yields a capacity of 741 mAh and a cathode energy density of 1001 Wh kg-1 . These findings are expected to guide the further development of high-energy-density cathode materials for Li-S batteries.

Carbon Gel-Based Self-Standing Membranes as the Positive Electrodes of Lithium–Oxygen Batteries under Lean-Electrolyte and High-Areal-Capacity Conditions

Lithium–oxygen batteries (LOBs) are promising next-generation rechargeable batteries due to their high theoretical energy densities. The optimization of the porous carbon-based positive electrode is a crucial challenge in the practical implementation of LOB technologies. Although numerous studies have been conducted regarding the relationships between LOB performance and the physicochemical properties of carbon electrodes, most of these studies evaluate the performances of the electrodes under unrealistic conditions with inappropriate technological parameters. In this study, we prepared carbon gel-based self-standing membranes as positive electrodes and evaluated their performances in LOBs under lean-electrolyte, high-areal-capacity conditions. We clarified the following three crucial points: (1) The nanometer-sized pores exhibited limited effects in improving the cycle performance, although they contributed in enhancing the discharge capacity. (2) The macro-sized pores displayed positive effects in enhancing the discharge capacity. (3) The crystallinity and/or surface functional groups influence the discharge potential and cycle life. The results of this study suggest the significance of controlling the physicochemical properties of a porous carbon-based positive electrode in preparing a LOB with a practically high energy density and an extended cycle life.

Identification and quantification of the distributed capacitance and ionic resistance in carbon-based supercapacitors using electrochemical techniques and the analysis of the charge-storage dynamics

This study reports the in-situ characterization of nanosized carbon-based electrodes to identify and quantify the distributed capacitance and resistances verified in the time domain during the charge-storage process in aqueous-based symmetric coin cells. A theoretical model was proposed to represent the electrochemical response considering the presence of the so-called ‘inner’/internal and ‘outer’/external surface regions. The derivative analysis of the galvanostatic findings revealed the presence of two distinct voltage plateaux that were ascribed to the progressive assessment of the ‘outer’ and ‘inner’ surface regions by the ionic species. For the first time, it was demonstrated a connection between the heterogeneous surface nature of carbon electrodes and the charge-storage process in supercapacitors where different charge-storage dynamics regarding the migration of the ionic species can be identified due to the progressive transfer of ions from the ‘outer’ to the ‘inner’ surface regions as a function of the polarization time. The synthesized carbon materials were ex-situ characterized by scanning electron microscopy, Raman, and X-ray photoelectron spectroscopies. Specifically, the surface-modified MWCNTs allowed us to focus on a fundamental approach for studying the overall capacitance characteristics of nanostructured carbon-based electrodes. Thus, the charge-storage mechanism in the time domain and the individual contribution of the pseudocapacitance in the frequency domain were studied to clarify the real electrochemical behavior exhibited by porous carbon-based electrode materials.

2,6-diaminoanthraquinone anchored on functionalized biomass porous carbon boosts electrochemical stability for metal-free redox supercapacitor electrode

The challenge of redox-active molecules for electrochemical capacitors is that they are easy to detach from the substrate during long-term charge-discharge cycles. In this work, redox-active molecule 2,6-diaminoanthraquinone (DAQ) is anchored on amino functionalized biomass porous carbon (FWS) via strong hydrogen bonding interaction. The protophilic C = O sites on the DAQ provide additional faradaic pseudocapacitance for biomass carbon-based electrode through fast redox reactions. In addition, the surface functionalization of porous carbon enhanced the interaction between the porous carbon and DAQ molecule, which inhibited the detachment of DAQ and significantly improved the electrochemical stability of the composite electrode. The optimized DAQ@FWS composite exhibits excellent specific capacitance of 424.9 F g−1 at 1 A g−1 with a stable capacity retention of 93.1% over 10,000 cycles at 10 A g−1, which is higher than unfunctionalized biomass porous carbon-based composite electrode (71.6% after 10,000 cycles). Meanwhile, DAQ@FWS composite maintains a high capacitance of 300.4 F g−1 even at 30 A g−1. Density functional theory calculations and detailed electrochemical analysis further elucidate the binding interactions of DAQ with FWS and charge storage mechanisms. Furthermore, coin-type symmetric supercapacitor based on DAQ@FWS exhibits excellent energy density (36.4 Wh kg−1 at 700.5 W kg−1), power density (7.001 kW kg−1 at 27.0 Wh kg−1) and durable cycling stability (capacitance retention is 88.3% after 10,000 cycles). Thus, amino functionalization of biomass porous carbon to anchor redox active organic quinones is promising as an effective strategy to fabricate superior performance supercapacitor electrode material.

Understanding the Parameters Influencing the Impedance Response of Sulfur-Carbon Composite Cathode in Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries, which in recent years have been aimed at a high gravimetric energy density of 500-600 Wh kg-1, indicate particular potential in aerospace applications such as aircraft, satellites and drones.1,2 In light of this, the German Aerospace Center (DLR) has been pursuing a strategy of developing and researching metal-sulfur batteries for a decade. Herewith, we present the results of a fundamental study on the investigation of structural and compositional parameters affecting the electrochemical performance of sulfur-carbon composite cathode.Highly porous carbon materials are widely employed in composite cathodes in Li-S batteries to compensate for the non-conductive property of the sulfur element. Indeed, this would have significant effects not only on the conductivity of the cathode, but also on the diffusion and charge transfer parameters. Herewith, we have systematically studied porous carbon-based electrodes employing electrochemical impedance spectroscopy. Using a suitable transmission-line model peculiar to the porous electrodes, the resistance of bulk and pore electrolyte, inter-particles, and charge transfer is defined and quantified. The dependence of the identified processes at the open circuit voltage on the fraction of the active material, the porosity of utilized carbon and thickness of the electrode is investigated elaborately. It is indicated that the electrolyte resistance in the pore increases on increasing the content of active material, electrode thickness and on reducing the pore size distribution of the C component.Additionally, an innovative symmetrical three-electrode cell configuration with an integrated Li-ring serving as counter electrode is implemented, enabling the investigation of the cathode impedance at different depths of discharge to shed light on the kinetics of the charge transfer depending on the infiltration method. To this end, various porous carbon materials such as Ketjenblack® (mesoporous) and carbon aerogel (microporous) in combination with different sulfur infiltration techniques including gas, melt and mechanical mixing have been employed as model systems3. The thermodynamic and kinetics of charge transfer mechanisms as a function of infiltration method as well as the variation of the charge transfer resistances upon discharge/charge are discussed in details4. A. Fotouhi, D. J. Auger, L. O’Neill, T. Cleaver and S. Walus, Energies, 2017, 10, 1937.Sripad S., Viswanathan V. (2017), ACS. Energy. Lett.2, 1669-1673M. Nojabaee, B. Sievert, M. Schwan, J. Schettler, F. Warth, N. Wagner, B. Milow, K. Andreas Friedrich, J. Mater. Chem. A, 2021,9, 6508-6519.Martina Gerle, Norbert Wagner, Joachim Häcker, Maryam Nojabaee, Andreas Friedrich J. Electrochem. Soc., 2022, 169, 030505.

Poly(norepinephrine) As a Functional Additive for Hybrid Cellulose/Agarose-Based Hydrogel Membranes: Application to Supercapacitors

A rapidly growing interest in renewable energy sources requires not only developing efficient energy storage systems but also incorporating a greater number of eco-friendly components. Electrochemical double-layer capacitors (EDLCs) are a class of energy storage devices capable to store the electrical charge due to the separation of oppositely charged ions in the electrical field which results in the formation of an electrical double layer (EDL) at the electrode/electrolyte interface. EDLCs consist in general of two porous carbon-based electrodes pre-soaked with electrolyte and separated with a membrane (separator). The simple electrostatic mechanism of energy storage, coupled with a lack of chemical changes and faradaic transitions during operation, results in high electrical capacitance compared to classical capacitors, significantly higher power density in contrast to batteries, and practically unlimited life span. Currently, commercial EDLCs typically rely on organic solvents, such as acetonitrile or propylene carbonate, with the addition of ionically-conductive salts. However, there are several drawbacks when it comes to practical applications involving particular low conductivity, toxicity, flammability and high cost. This resulted in an increased interest in aqueous electrolytes such as KOH, H2SO4 or simple inorganic salts, which although they have a limited potential window, exhibit many positive features including higher ionic conductivity, lower viscosity, increased safety, lower cost and ease of assembly under ambient atmosphere. Modern and technologically advanced charge storage devices often require high safety flexible and deformable devices for specific applications. However, at the current state-of-the-art, the EDLCs suffer from two prominent limitations (i) the possibility of electrolyte leakage and (ii) high standards of technology to safely encapsulate electrolytes in the device. Therefore, a lot of research is held to develop alternatives for currently used liquid (aqueous and organic) electrolytes. One of the solutions to overcome these limitations are solid-state EDLCs. Those systems use an ionically-conductive polymer or hydrogel membrane, which serves as both the separator and the electrolyte. Cellulose, built of β-(1→4)-linked D-glucose units, is one of the most prevalent and easily degradable biopolymers. Albeit, its wide availability, biodegradability and low cost, the usage of cellulose is limited due to insolubility in most common solvents. The recent alternative, to toxic and flammable organic compounds, such as N, N- dimethylformamide/N2O4, N-methylmorpholine oxide (NMMO), are ionic liquids (ILs), that have been gaining lately a lot of attention in energy storage systems. Various ILs based on imidazolium, pyridinium and ammonium cation paired with strongly basic anion (e.g., OAc-, HCOO-) were also recently used to dissolve cellulose. However, the requirements of high-purity syntheses and the cost of some of the cations/anions may affect a large scale application. Therefore, our research refers to an alternative route of chemical regeneration of microcrystalline cellulose, i.e. its dissolution using an aqueous mixture of NaOH/urea, and further processing into a hydrogel membrane in the presence of cross-linking agent epichlorohydrin. To improve the mechanical strength and electrolyte uptake, in-situ polymerized norepinephrine and agarose were subsequently incorporated obtaining an interpenetrating polymer network (IPN). The structure and morphology of the membranes were characterized with SEM/EDX, CP/MAS 13C-NMR, AT-FTIR, TGA, contact angle, and elementary analysis. The ionic conductivity was determined using impedance spectroscopy over a wide range of temperatures (5-60°C). The relation between stress and strain in the materials was also determined to diagnose the mechanical properties. The cellulose-based hydrogel membranes were further used as a support for various aqueous electrolytes, including H2SO4, Na2SO4, i.e. most commonly used for aqueous EDLCs. Also, the alternative electrolyte was used, i.e. silicotungstic acid, H4SiW12O40 which according to our recent results seems to be a promising candidate to replace conventional acidic electrolytes [1]. The designed systems were compared, in terms of energy, power and cycleability, with their analogues using conventional polypropylene separators and a liquid electrolyte.[1] N.H. Wisinska, M. Skunik-Nuckowska, S. Dyjak, P.J. Kulesza, Factors affecting the performance of electrochemical capacitors operating in Keggin-type silicotungstic acid electrolyte, Appl. Surf. Sci. 530 (2020) 147273, https://doi.org/10.1016/j.apsusc.2020.147273Acknowledgement Financial support was provided by the National Science Center under Preludium 19 grant no. 2020/37//N/ST4/01679. This work was implemented as a part of Operational Project Knowledge Education Development 2014–2020 co-financed by the European Social Fund, Project No POWR.03.02.00-00-I007/16-00 (POWER 2014-2020)

Novel Moringa oleifera Leaves 3D Porous Carbon-Based Electrode Material as a High-Performance EDLC Supercapacitor.

Biomass-based activated carbon has great potential in the use of its versatile 3D porous structures as an excellent electrode material in presenting high conductivity, large porosity, and outstanding stability for electrochemical energy storage devices. In this study, the electrode material develops through a novel consolidated carbon disc binder-free design, which was derived from Moringa oleifera leaves (MOLs) for electrochemical double-layer capacitor applications. The carbon discs are prepared in a series of treatments of precarbonized, chemical impregnation of zinc chloride, integrated pyrolysis of N2 carbonization, and CO2 physical activation. The physical activation temperatures applied at 650, 750, and 850 °C optimize the precursor potential. By optimizing the 3D hierarchical pore properties of the MOL750, the carbon disc binder-free design demonstrates optimal symmetric supercapacitor performance with a high specific capacitance of 307 F g–1 at a current density of 1 A g–1 in an aqueous electrolyte solution of 1 M H2SO4. Furthermore, the extremely low internal resistance (0.006Ω) of the carbon disc initiated excellent electrical conductivity. The supercapacitors also maintain their high capacitive properties in aqueous electrolyte solutions of 6 M KOH and 1 M Na2SO4, respectively. The results show that a novel consolidated carbon disc binder-free design can be obtained from biomass MOLs through a reasonable approach to develop superior electrode materials to enhance high-performance electrochemical energy storage devices.

Sustainable lignin precursors for tailored porous carbon-based supercapacitor electrodes

Sustainable materials are attracting a lot of attention since they will be critical in the creation of the next generation of products and devices. In this study, hydrogels were effectively synthesized utilizing lignin, a non-valorised biopolymer from the paper industry. This study proposes a method based on utilizing lignin to create highly swollen hydrogels using poly(ethylene) glycol diglycidyl ether (PEGDGE) as a crosslinking agent. The influence of different crosslinker ratios on the structural and chemical properties of the resultant hydrogels was investigated. Pore size was observed to be lowered when the amount of crosslinker was increased. The inclusion of additional hydrophilic groups in the hydrogel network decreased the swelling capacity of the hydrogels as the crosslinking density increases. These precursor materials were carbonised and electrochemically tested for application as electrodes for supercapacitors with capacitance characterized as a function of crosslinker ratio.

Bimetallic salts template-assisted strategy towards the preparation of hierarchical porous polyimide-derived carbon electrode for supercapacitor

Hierarchical porous carbon-based electrodes, benefiting from their facilitated ion diffusion and electron conduction, have demonstrated enormous potential in supercapacitors. The preparation of hierarchical carbons with uniformity and appropriate porosity, however, still remains a grand challenge, which hinders their widespread applications. Herein, a hierarchical porous polyimide-derived carbon electrode (CPC-Fe/Zn) has been fabricated by employing bimetallic salts (Fe/Zn) as precursor and template to activate the cellulose/polyimide (PI) carbon (CPC). Originating from suitable distribution of mesopores and micropores, the obtained CPC-Fe/Zn delivers a high specific capacitance of 420 F/g at a current density of 1 A/g. Moreover, a symmetric supercapacitor device assembled with CPC-Fe/Zn exhibits delivers an energy density of 35.5 Wh/kg at a power density of 800 W/kg. Even at a larger current density of 20 A/g, the specific capacitance retention of such device still remains 92.5 % after 10,000 cycles, showing the rate performance and stability. This work has proposed a bimetallic salts template-assisted strategy to precisely modulate of the pore structure of carbon electrodes, which provides a promising platform to design superior electrodes for various electrochemical systems.

Fungal hypha-derived freestanding porous carbon pad as a high-capacity electrode for water desalination in membrane capacitive deionization

Capacitive deionization (CDI) is an emerging technology for water desalination, especially low-salinity water. Freestanding porous carbon-based electrodes with rapid electron transfer rate and effective ion diffusion features are desired to achieve high desalination performance. Here, a porous carbon pad derived from the fungal hyphae of Aspergillus niger was prepared as a precursor of the electrode. After carbonization and activation, the intertwined and hierarchical porous structure of the fungal hypha pad was well-preserved, producing a freestanding fungal hypha activated carbon pad (FhACPad) electrode for MCDI. The interconnected carbon fibers and open pore structure of the FhACPad yielded an electrode with high electrical conductivity and rapid ion transport properties. The novel FhACPad exhibited a gravimetric salt adsorption capacity of 35.6 ± 2.3 mgNaCl/g with an average desalination rate of 1.2 mgNaCl/gelectrode/min from a 585 mg/L NaCl aqueous solution at a cell voltage of 1.2 V and a flow rate of 1 mL/min. As a result, the FhACPad outperformed conventional powdered activated carbon (PAC) electrodes and the most recently reported porous carbon electrodes under similar desalination conditions. This work also provides insights into the structure-performance relationships of CDI electrodes and shows a great potential of fungal biomass-derived porous carbon electrodes for high-performance MCDI applications.

Electrochemical hydrogen storage in porous carbons with acidic electrolytes: Uncovering the potential

Electrochemical hydrogen storage in porous carbon materials is emerging as a cost-effective hydrogen storage and transport technology with competitive power and energy densities. The merits of electrochemical hydrogen storage using porous conductive carbon-based electrodes are reviewed. The employment of acidic electrolytes in such storage systems is compared with alkaline electrolytes. The recent innovations of a proton battery for smaller-scale electricity storage, and a proton flow reactor system for larger (grid)-scale storage and bulk export of hydrogen produced from renewable energy, are briefly described. It is argued that such systems, along with variants proposed by others, all of which rely on electrochemical hydrogen storage in porous carbons, can contribute to the search for energy storage technologies essential for the transition to a zero-emission global economy.