Carbon-based Electrode Materials Research Articles

Recent Advances in High-Performance Carbon-Based Electrodes for Zinc-Ion Hybrid Capacitors

Aqueous zinc-ion hybrid capacitors (ZIHCs) have emerged as a promising technology, showing superior energy and power densities, as well as enhanced safety, inexpensive and eco-friendly features. Although ZIHCs possess the advantages of both batteries and supercapacitors, their energy density is still unsatisfactory. Therefore, it is extremely crucial to develop reasonably matched electrode materials. Based on this challenge, a surge of studies has been conducted on the modification of carbon-based electrode materials. Herein, we first summarize the progress of the related research and elucidate the energy storage mechanism associated with carbon-based electrodes for ZIHCs. Then, we investigate the influence of the synthesis routes and modification strategies of the electrode materials on electrochemical stability. Finally, we summarize the current research challenges facing ZIHCs and predict potential future research pathways. In addition, we suggest key scientific questions to focus on and potential directions for further exploration.

The Impact of Supersaturated Electrode on Heterogeneous Lithium Nucleation and Growth Dynamics.

The concept of a lithiophilic electrode proves inadequate in describing carbon-based electrode materials due to their substantial mismatch in surface energy with lithium metal. However, their notable capacity for lithium chemisorption can increase active lithium concentration required for nucleation and growth, thereby enhancing the electrochemical performance of lithium metal anodes (LMAs). In this study, we elucidate the effects of the supersaturated electrode which has high active lithium capacity around equilibrium lithium potential on LMAs through an in-depth electrochemical comparison using two distinct carbon electrode platforms with differing carbon structures but similar two-dimensional morphologies. In the supersaturated electrode, both the dynamics and thermodynamic states involved in lithium nucleation and growth mechanisms are significantly improved, particularly under continuous current supply conditions. Furthermore, the chemical structures of the solid-electrolyte-interface layers (SEIs) are greatly influenced by the elevated surface lithium concentration environment, resulting in the formation of more conductive lithium-rich SEI layers. The improved dynamics and thermodynamics of surface lithium, coupled with the formation of enhanced SEI layers, contribute to higher power capabilities, enhanced Coulombic efficiencies, and improved cycling performances of LMAs. These results provide new insight into understanding the enhancements in heterogeneous lithium nucleation and growth kinetics on the supersaturated electrode.

Fabrication of Coconut Shell-Derived Graphitic Activated Carbon for Carbon-based Electrode Materials

This study aims to convert low-value plantation biomass waste into high-value materials. The process involves transforming coconut shell charcoal (CSC) into activated carbon and subsequently producing coconut shell graphitic-like activated carbon (CSGAC). Using a thermal graphitization method with a FeCl3 catalyst at 900°C for 1 hour in a nitrogen atmosphere, graphite microstructures (CSGAC) were formed on the coconut shell activated carbon (CSAC) framework. XRD, FTIR, SEM, and BET analyses confirmed the successful formation of CSGAC. The electrical conductivity of CSGAC, measured at 148 µS, highlights its potential as a cost-effective, renewable, and environmentally friendly raw material for carbon-based electrodes.

Understanding intra-pore electrolyte resistances and distributed capacitances in carbon electrodes used in supercapacitors using a robust modeling process to separate the charge-storage occurring into macro-, meso-, and micro-pore structures

In this study, a Modified Generic Electrochemical (MGE) model is introduced for studying rough/porous carbon-based electrode materials employed in electrical double-layer capacitors (EDLC) which contain different types of surface defects. Instead of adopting the common theoretical approach involving the use of transmission line models or ad hoc equivalent circuits, a rational equivalent circuit model has been devised, which permitted us to derive the different equations for each electrochemical technique. The MGE representing the overall electrochemical behavior of EDLCs obtained using the different techniques (e.g., cyclic voltammetry, chronoamperometry, chronopotentiometry, and impedance) is formally derived based on a simple premise considering that the different inhomogeneous surface defects, which are geometrically arranged under equipotential conditions, are not electrochemically equivalent. In this sense, the presence of hierarchically distributed charge-storage processes with different time constants, accounting for the ionic accumulation at the electrode/solution interface, can be ascertained. We verified that is imperative to avoid the determination of the specific capacitances and resistances in EDLCs using a single electrochemical technique or several techniques whose model equations are based on different theoretical premises. The use of the MGE model unequivocally revealed that isolated measurements of the specific capacitance in the absence of the associated intra-pore resistances are not sufficient to ensure the presence of rapid charge storage allied with high-power characteristics. With the appropriate choice of carbon-based materials with very low intra-pore resistances, substantial progress can be made in ushering in the next generation of EDCLs with very high-power characteristics.

Hierarchical porous self-supporting graphite carbon electrodes based on the biomimetic structure for supercapacitors

Regulating pore structure, improving conductivity, and reducing the influence of binders are considered important ways to improve the performance of carbon-based electrode materials for supercapacitors. This study successfully prepares a highly graphitized hierarchical porous self-supporting carbon electrode without the need for binders, conductive agents, and current collectors using low-cost and abundant pine wood as the precursor and K2FeO4 as the activator and catalyst. The self-supporting electrode inherits the biological structure of biomass and forms a large number of micro mesopores through activation, showing an excellent 3D interconnected pore structure, and achieves a high degree of graphitization with the ID/IG ratio of being only 0.47. The self-supporting electrode facilitates the effective transport of electrolyte ions and electrons, demonstrating excellent electrochemical performance. It achieves an area specific capacitance of 3.64 F cm−2 under a current density of 5 mA cm−2. Two identical self-supporting electrodes are employed to construct a symmetric supercapacitor. The supercapacitor exhibits an energy density of 148.61 μWh cm−2 at a power density of 1 mW cm−2, with a capacity retention rate of 89.26 % after 10,000 charge-discharge cycles.

Enhanced Capacitive Deionization of Hollow Mesoporous Carbon Spheres/MOFs Derived Nanocomposites by Interface-Coating and Space-Encapsulating Design.

Exploring new carbon-based electrode materials is quite necessary for enhancing capacitive deionization (CDI). Here, hollow mesoporous carbon spheres (HMCSs)/metal-organic frameworks (MOFs) derived carbon materials (NC(M)/HMCSs and NC(M)@HMCSs) are successfully prepared by interface-coating and space-encapsulating design, respectively. The obtained NC(M)/HMCSs and NC(M)@HMCSs possess a hierarchical hollow nanoarchitecture with abundant nitrogen doping, high specific surface area, and abundant meso-/microporous pores. These merits are conducive to rapid ion diffusion and charge transfer during the adsorption process. Compared to NC(M)/HMCSs, NC(M)@HMCSs exhibit superior electrochemical performance due to their better utilization of the internal space of hollow carbon, forming an interconnected 3D framework. In addition, the introduction of Ni ions is more conducive to the synergistic effect between ZIF(M)-derived carbon and N-doped carbon shell compared with other ions (Mn, Co, Cu ions). The resultant Ni-1-800-based CDI device exhibits excellent salt adsorption capacity (SAC, 37.82mg g-1) and good recyclability. This will provide a new direction for the MOF nanoparticle-driven assembly strategy and the application of hierarchical hollow carbon nanoarchitecture to CDI.

A Nanofibrous Polypyrrole Membrane with an Ultrahigh Areal Specific Capacitance and Improved Energy and Power Densities.

For conductive polymers to be competitive with carbon-based electrode materials, it is critical to increase their surface area and electroactivity. In this work, a thick nanofibrous polypyrrole (PPy) membrane with communicating interfiber spaces was prepared through one-pot interfacial polymerization for the first time. The electrochemical properties and conductivity of the membrane were studied with cyclic voltammetry, electrochemical impedance spectroscopy, and a four-point probe. Its morphology, chemistry, and thermostability were evaluated by scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The areal specific capacitances measured between 0.0 and 0.8 V at 1 mA/cm2 were 19179, 13264, 7238, and 4458 mF/cm2 for the membranes doped with docusate sodium (AOT), camphor-10-sulfonic acid (β) (CSA), Cl-, and poly(sodium 4-styrenesulfonate) (PSS), respectively. The capacity retentions after 1000 cycles were 83, 74, 67, and 61% for the AOT-, CSA-, PSS-, and Cl--doped membranes, respectively. The Coulombic efficiency was above 99% for all of the membranes. They showed energy densities of 1.7, 1.2, 0.7, and 0.4 mWh/cm2 and power densities of 0.61, 0.75, 0.66, and 0.62 mW/cm2 for the AOT-, CSA-, Cl--, and PSS-doped membranes, respectively. The ultrahigh areal specific capacitance of PPy-AOT is due to its nanofibrous structure. A mechanism has been proposed to explain how this structure is formed based on the role of AOT as the surfactant. This nanofibrous PPy membrane is easy to prepare and metal-free and offers a very high areal specific capacitance, making it an excellent candidate to construct electrodes in pseudosupercapacitors.

Mesoporous carbon particles by biomass waste based on sulfonation and copper oxide functionalization as efficient and stable electrode material for supercapacitor.

Here, the hierarchical mesoporous-activated carbon particles obtained by KOH activation from pistachio shell wastes are modified by both the sulfonation process and CuO doping by hydrothermal heating (CuO@S-doped PSAC) for use as a supercapacitor. It is predicted that the electrochemical performance of the porous carbon electrode material obtained by such CuO doping and sulfonation process will be significantly increased with increased Faradaic capacitance. The electrochemical performance of CuO@S doped PSAC composite is systematically investigated by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and galvanostatic charge/discharge (GCD) in the presence of 1M H2SO4, 1M Na2SO4, and 1M NaOH as electrolytes. The CuO@S doped PSAC-based electrode shows excellent stability with high specific capacitance up to 397.16 F/g at 0.1 A/g and 92.64% retention. Furthermore, FTIR, SEM, XRD, EDS, and nitrogen adsorption/desorption analyses are used for the characterisation of the obtained composites. Based on a significant supercapacitor performance, the synthesis strategy of carbon-based electrode material containing sulfonation and CuO modifications derived from agricultural biomass waste material is predicted to be a valuable example.

Template-induced synthesis of MnO2-g-C3N4/C three-phase composites and its performance for supercapacitors

Carbon based electrode materials have many advantages such as large specific surface area, good electrical conductivity, easy obtained, safety and non-toxicity. In this work, we have induced the synthesis of MnO2-g-C3N4/C composites using the apricot mushroom as a biological template. The rod-shaped MnO2 is uniformly anchored on the surface of g-C3N4/C. Structural design of MnO2-g-C3N4/C composites improves the poor electrical conductivity of single MnO2. The results show that biocarbon has good stability and conductivity, g-C3N4 provides more reactive sites, and MnO2 substantially enhances the pseudocapacitance of the material, thus realize the synergistic effect for higher supercapacitor property. Based on its excellent three-phase interface structure, the MnO2-g-C3N4/C’ capacitance was able to reach 276F·g−1 with a capacitance retention of 96 % after 1000 cycles. Therefore, this material has potential application in the energy storage industry.

Boron-manganese-nitrogen co-doped three-dimensional porous carbon realizes superior capacitive lithium-ion storage

Three-dimensional (3D) porous carbon has sufficient specific surface area and anchor positioning points. The pore structure facilitates uniform charge distribution, and buffers volume changes during stripping. However, single carbon materials have limited theoretical capacity and short cycle life. Here, 3D porous carbon material BCN/Mn-6 (B,N and Mn co-doped porous carbon with 6 mmol Mn content) co-doped with manganese, boron and nitrogen was synthesized by heat treatment. Affective modulation of the material structure and surface functional groups was achieved by adjusting the amount of manganese doping. The metal element doping can promote the diffusion of lithium ions, and the formed vacancies and defects can be used as lithium storage sites. Nitrogen doping can improve the dispersion and stability of metals and oxides, and regulate the redox capacity. Co-doping of metals and heteroatoms synergistically improves electrical conductivity. Thus, BCN/Mn-6 exhibits excellent cycling stability (99.60 % Coulombic efficiency after 300 cycles) and specific capacity (779.9 mAh/g), and shows capacity rise. This study provides a new direction for the preparation of carbon-based electrode materials doped with heteroatoms and the study of capacitive energy storage mechanisms.

Carbon-based electrode materials for sensor application: a review

Carbon-based electrode materials for sensor application: a review

Binder-free all-carbon composite supercapacitors

Carbon-based electrode materials have widely been used in supercapacitors. Unfortunately, the fabrication of the supercapacitors includes a polymeric binding material that leads to an undesirable addition of weight along with an increased charge transfer resistance. Herein, binder-free and lightweight electrodes were fabricated using powder processing of carbon nanofibers (CNFs) and graphene nanoplatelets (GNPs) resulting in a hybrid all-carbon composite material. The structural, morphological, and electrochemical properties of the composite electrodes were studied at different concentrations of GNPs. The specific capacitance (Cs) of the CNFs/GNPs composite was improved by increasing the concentration of GNPs. A maximum Cs of around 120 F g−1 was achieved at 90 wt% GNPs which is around 5-fold higher in value than the pristine CNFs in 1 M potassium hydroxides (KOH), which then further increased to 189 F g−1 in 6 M KOH electrolyte. The energy density of around 20 Wh kg−1 with the corresponding power density of 340 W kg−1 was achieved in the supercapacitor containing 90 wt% GNPs. The enhanced electrochemical performance of the composite is related to the presence of a synergistic effect and the CNFs establishing conductive/percolating networks. Such binder-free all-carbon electrodes can be a potential candidate for next-generation energy applications.

Effects of Intrinsic Defects in Pt-Based Carbon Supports on Alkaline Hydrogen Evolution Reaction.

Carbon material has widely been utilized in the synthesis of efficient carbon-supported Pt (Pt/C) catalysts, in which the structural properties greatly influence the electrocatalytic performances of Pt/C catalysts. However, the effects of intrinsic defects in carbon supports on the performance of the alkaline hydrogen evolution reaction (HER) have not been systematically investigated. Herein, porous carbon supports with different degrees of intrinsic defects were prepared by a simple template-assisted strategy, and the resulting samples were systematically studied by various analytical methods. The results suggested that the presence of abundant intrinsic defects (vacancy and topological defects) in the carbon support was advantageous in terms of favoring the dispersion and anchoring of Pt species, promoting electron transfer between Pt atoms and the carbon support, and tuning the electronic states of Pt species. These features improved the HER performance of Pt/C catalysts. Compared to the nontemplate-assisted carbon-supported Pt catalyst (Pt/NTC) with an overpotential of 178 mV, the optimized template-assisted carbon-supported Pt catalyst (Pt/TC) exhibited a lower overpotential of 58 mV at 10 mA cm-2. Besides, the Pt/TC catalyst displayed better HER durability than the Pt/NTC catalyst owing to its strong metal-support interaction. The DFT calculations confirmed the important role played by intrinsic defects (vacancy and topological defects) in stabilizing Pt atoms, with Pt-C3 coordination identified as the most favorable structure for improving the HER performance of Pt. Overall, novel insights on the significant contribution of intrinsic defects in porous carbon supports on the HER performances of Pt/C catalysts were provided, useful for future design and fabrication of advanced carbon-supported catalysts or other carbon-based electrode materials.

Research progress on lignin-based carbon electrode materials in rechargeable batteries

Lignin, with its carbon content of up to 60%, can be an ideal precursor for the preparation of carbon materials. Carbonaceous materials obtained from lignin can be transformed into porous and structural morphologies at different scales, providing a biomass approach to energy conversion and storage in batteries. Focusing on lignin-derived carbon materials, this paper summarizes the different morphologies and structures of lignin-based carbon obtained through different preparation methods, and the different electrochemical properties exhibited by these materials as electrode materials for rechargeable batteries (lithium-ion batteries, sodium-ion batteries, lithium-sulphur batteries, etc.). In addition, the development prospects and challenges of lignin-based carbon materials in the field of rechargeable batteries are summarized, providing ideas for the next step in the design and development of high-performance lignin-based carbon-based electrode materials.

Spinning of Carbon Nanofiber/Ni–Cu–S Composite Nanofibers for Supercapacitor Negative Electrodes

The preparation of composite carbon nanomaterials is one of the methods for improving the electrochemical performance of carbon-based electrode materials for supercapacitors. However, traditional preparation methods are complicated and time-consuming, and the binder also leads to an increase in impedance and a decrease in specific capacitance. Therefore, in this work, we reduced Ni-Cu nanoparticles on the surface of nitrogen-doped carbon nanofibers (CNFs) by employing an electrostatic spinning method combined with pre-oxidation and annealing treatments. At the same time, Ni-Cu nanoparticles were vulcanized to Ni–Cu–S nanoparticles without destroying the structure of the CNFs. The area-specific capacitance of the CNFs/Ni–Cu–S–300 electrode reaches 1208 mF cm−2 at a current density of 1 mA cm−2, and the electrode has a good cycling stability with a capacitance retention rate of 76.5% after 5000 cycles. As a self-supporting electrode, this electrode can avoid the problem of the poor adhesion of electrode materials and the low utilization of active materials due to the inactivity of the binder and conductive agent in conventional collector electrodes, so it has excellent potential for application.

A 3D-printed fully biocompatible supercapacitor

A fully biocompatible supercapacitor was fabricated utilizing a dopamine-grafted activated carbon-based (DPBAC) electrode material along with a choline chloride–urea-based eco-friendly Reline deep eutectic solvent electrolyte.

High-energy-density zinc ion capacitors based on 3D porous free-standing defect-reduced graphene oxide hydrogel cathodes.

Zinc ion capacitors (ZICs) have shown potential for breaking the energy density ceiling of traditional supercapacitors (SCs) via appropriate device design. Nevertheless, a significant challenge remains in advancing ZIC positive electrode materials with excellent conductivity, high specific capacitance, and reliable cycle stability. A highly attractive option for carbon-based electrode materials is reduced graphene oxide (RGO) due to its vast specific surface area, prominent porosity, and 3D cross-linked frame. However, the tight stacking of RGO sheets driven by van der Waals forces can restrict active sites, decrease specific capacitance, and elevate electrochemical impedance. To overcome these challenges, 3D defective RGO (DRGO) hydrogels were prepared by a metal Co cocatalytic gasification reaction. This method produced mesoporous defects on the surface of RGO hydrogels via a low-temperature hydrothermal self-assembly strategy. The surface of the layer has a wide and uniform distribution, which can offer abundant redox active sites, rich ion transfer channels, and fast reaction kinetics. In this work, 3D DRGO//Zn exhibited a wide operating window (0-1.8 V), high specific capacitance (189.39 F g-1 at 1 A g-1), outstanding energy density (85.23 W h kg-1 at 960.31 W kg-1; 52.36 W h kg-1 at 17454.87 W kg-1), and persistent cycling life (98.86% initial capacitance retention after 10 000 cycles at 10 A g-1). This study emphasizes the device design of ZIC and promising prospects of using 3D DRGO hydrogel as a feasible positive electrode for ZIC.

Bio-inspired carbon electrodes for metal-ion batteries.

Carbon has been widely used as an electrode material in commercial metal-ion batteries (MIBs) because of its desirable electrical, mechanical, and physical properties. Still, traditional carbon electrodes suffer from limited mechanical stability and electrochemical performance in MIBs. Drawing inspiration from biological species, the carbon allotropes, such as fullerenes, carbon nanotubes, and graphene, can be engineered into mechanically robust, highly conductive frameworks with enhanced ion storage and transport capabilities for MIBs. Here, we present an assortment of bio-inspired carbon electrodes that have enhanced the cycling stability, capacity retention, and overall performance of MIBs. In addition, mimicking the structure and functionality of biological systems has led to the development of flexible MIBs whose performance does not degrade even when stretched, bent, or twisted. Finite element analysis (FEA) is a useful guide in identifying such bio-inspired carbon frameworks because it can simulate and analyze potential failure scenarios, such as stress build-up or structural collapse in MIBs. This review highlights through several examples that there is much scope for improving carbon-based electrode materials through bio-inspired designs for practical high-performance MIBs.

Carbon-Based Electrode Materials for Electrocatalytic Transformations

Industrial processes for the synthesis of chemicals and fuels utilise selective hydrogenation reactions. The need for high temperatures and high pressure of H2 makes these reactions energy intensive and only viable on a large scale, requiring expensive transport of materials. Electrocatalytic hydrogenation (ECH) could potentially bypass these limitations, running at ambient conditions and generating the adsorbed hydrogen in-situ. The interest in new electrocatalyst materials increased in recent years, as ECH offers a synthetic route for fuels and value-added chemicals with a reduced carbon footprint. The development of new low-cost catalyst materials will be paramount for the integration of ECH into economic activities.In this work we focus on heteroatom-modified carbon based electrode materials for the ECH. Carbon materials possess a list of beneficial properties for electrochemical applications: they are widely available, environmentally benign, stable at cathodic potentials and can be tailored towards specific applications. One way of tailoring is to dope the carbon with heteroatoms like nitrogen.Nitrogen-doped carbon thin films have been synthesised using sputter deposition followed by an annealing process, to control graphitisation and nitrogen distribution of the carbon material. These model electrodes were investigated by themselves and as supports for thin nanoparticle films of MoS2 in the ECH and the hydrogen evolution reaction (HER), as the Volmer step of the HER is needed in the ECH. This allowed us to understand the influence of nitrogen moieties on reduction rates in the absence of morphological effects. The results suggest possible strategies for developing electrocatalysts for the ECH based on functional carbons.[1] Orella, M.J.; Román-Leshkov, Y.; Brushett, F.R., Emerging opportunities for electrochemical processing to enable sustainable chemical manufacturing. Current Opinion in Chemical Engineering 2018, 20, 159–167.[2] Behan, J. A.; Stamatin, S. N.; Hoque, M. K.; Ciapetti, G.; Zen, F.; Esteban-Tejeda, L.; Colavita, P. E., Combined Optoelectronic and Electrochemical Study of Nitrogenated Carbon Electrodes. The Journal of Physical Chemistry C 2017, 121 (12), 6596-6604.[3] Nolan, H.; Schröder, C.; Brunet-Cabré, M.; Pota, F.; McEvoy, N.; McKelvey, K.; Perova, T. S.; Colavita, P. E., MoS2/carbon heterostructured catalysts for the hydrogen evolution reaction: N-doping modulation of substrate effects in acid and alkaline electrolytes. Carbon 2023, 202, 70-80.

Fabrication of predesigned 3D carbon based microstructures via two-photon vat photopolymerization and susceptor-assisted microwave post-processing

This study presents a fabrication strategy for 3D carbon microstructures using via two-photon vat photopolymerization (2p-VPP) and susceptor-assisted microwave pyrolysis (SMWP). Fabricating carbon-based electrode materials with miniaturized functional structures is pivotal for developing high-performance electrochemical microdevices. However, efficiently producing these structures in the submicron regime with desired materials is still challenging. To address this, a hybrid microfabrication strategy was developed, and 3D carbon-based microstructures with submicron resolution were successfully produced. A carbon nanotube nanocomposite photoresist (SCNT-PR1) with improved dispersibility was first prepared. After a comprehensive printability assessment, 3D microstructures with a resolution of 833 ± 54 nm were produced using 2p-VPP. Through SMWP, the microstructures were transformed into pyrolytic carbon (PyC) nanocomposite microstructures with retained geometrical features. SMWP was shown to produce PyC with a less disordered carbon atomic structure, thanks to the accelerated pyrolysis reaction under MW irradiation, when compared to pyrolysis using a conventional furnace. The resistivity was reduced by over 75% from 0.69 ± 0.13 Ω cm to 0.16 ± 0.01 Ω cm, and enhanced electrochemical performance was confirmed. The fabricated PyC nanocomposite showed a further 12% reduction in electrical resistivity and a 20% lower charge transfer resistance for the redox reaction when using SCNT-PR1 as the precursor. Overall, this hybrid fabrication strategy demonstrates the advantages of producing 3D carbon microstructures with precise control over the geometric features and enhancing electrical and electrochemical properties compared to the conventional pyrolysis method. Its potential could be extended to the fabrication of miniaturized electrochemical devices, including microelectronics and point-of-care devices.