Structural Positive Electrodes Engineered for Multifunctionality

Multifunctional structural batteries are of high and emerging interest in a wide variety of high-strength and lightweight applications. Structural batteries typically use pristine carbon fiber as the negative electrode, functionalized carbon fiber as the positive electrode, and a mechanically robust lithium-ion transporting electrolyte. However, electrochemical cycling of carbon fibre-based positive electrodes is still limited to tests in liquid electrolytes, which does not allow for to introduction of multifunctionality in real terms. To overcome these limitations, structural batteries with a structural battery electrolyte (SBE) are developed. This approach offers massless energy storage. The electrodes are manufactured using economically friendly, abundant, cheap, and non-toxic iron-based materials like olivine LiFePO4. Reduced graphene oxide, renowned for its high surface area and electrical conductivity, is incorporated to enhance the ion transport mechanism. Furthermore, a vacuum-infused solid-liquid electrolyte is cured to bolster the mechanical strength of the carbon fibers and provide a medium for lithium-ion migration. Electrophoretic deposition is selected as a green process to manufacture the structural positive electrodes with homogeneous mass loading. A specific capacity of 112 mAh g-1 can be reached at C/20, allowing the smooth transport of Li-ion in the presence of SBE. The modulus of positive electrodes exceeded 80 GPa. Structural battery-positive half-cells are demonstrated across various mass-loadings, enabling them to be tailored for a diverse array of applications in consumer technology, electric vehicles, and aerospace sectors.

Epoxy-based multifunctional solid polymer electrolytes for structural batteries and supercapacitors. a short review

The potential applications of epoxy-based solid polymer electrolytes are continually expanding because of their versatile characteristics. These characteristics include mechanical rigidity, nonvolatility, nonflammability, and electrochemical stability. However, it is worth noting that pure epoxy-based solid polymer electrolytes inherently exhibit lower ion transport capabilities when compared to traditional liquid electrolytes. Striking a balance between high mechanical integrity and superior ionic conductivity at room temperature poses a significant challenge. In light of this challenge, this review is dedicated to elucidating the fundamental concepts of epoxy-based solid polymer electrolytes. It will explore various preparation techniques, the incorporation of different nanomaterials into epoxy-based solid polymer electrolytes, and an evaluation of their multifunctional properties. This comprehensive evaluation will cover both mechanical and electrical properties with a specific focus on their potential applications in batteries and structural supercapacitors.

Multifunctionality Analysis of Structural Supercapacitors- A Review

Structural supercapacitors (SSCs) are multifunctional energy storage composites (MESCs) that combine the mechanical properties of fiber-reinforced polymers and the electrochemical performance of supercapacitors to reduce the overall mass in lightweight applications with electrical energy consumption. These novel MESCs have huge potentials, and their properties have improved dramatically since their introduction in the early 2000's. However, the current properties of SSCs are not sufficient for complete energy supply of electrically driven devices. To overcome this drawback, the aim of the current study is to identify key areas for enhancement of the multifunctional performance of SSCs. Critical modification paths for the SSC constituents are systematically analyzed. Special focus is given to the improvement of carbon fiber-based electrodes, the selection of structural electrolytes and the implementation of separators for the development of more efficient SSCs. Finally, current SSCs are compared in terms of their multifunctionality including material combinations and modifications.

Stereolithography 3D Printed Carbon Microlattices with Hierarchical Porosity for Structural and Functional Applications

Hierarchically porous carbon microlattices (HPCMLs) fabricated by using a composite photoresin and stereolithography (SLA) 3D printing is reported. Containing magnesium oxide nanoparticles (MgO NPs) as porogens and multilayer graphene nanosheets as UV-scattering inhibitors, the composite photoresin is formed to simple cubic microlattices with digitally designed porosity of 50%. After carbonization in vacuum at 1000 °C and chemical removal of MgO NPs, it is realized that carbon microlattices possessing hierarchical porosity are composed of the lattice architecture (≈100 µm), macropores (≈5 µm), mesopores (≈50 nm), and micropores (≈1 nm). The linear shrinkage after pyrolysis is as small as 33%. Compressive strength of 7.45 to 10.45 MPa and Young's modulus of 375 to 736 MPa are achieved, proving HPCMLs a robust mechanical component among reported carbon materials with a random pore structure. Having a few millimeters in thickness, the HPCMLs can serve as thick supercapacitor electrodes that demonstrate gravimetric capacitances 105 and 13.8 F g-1 in aqueous and organic electrolyte, reaching footprint areal capacitances beyond 10 and 1 F cm-2 , respectively. The results present that the composite photoresin for SLA can yield carbon microarchitectures that integrate structural and functional properties for structural energy storages .

Electrochemical Comparison of 2D-Flexible Solid-State Supercapacitors Based on a Matrix of PVA/H3PO4

Different modifications of woven carbon fiber (WCF) based on carbon aerogel (CAG), copper oxide nanoparticles (CuO-NPs), and lignin (LIG) has been tested and used to study their effect on the fabrication and performance of a flexible supercapacitor. New symmetric flexible supercapacitors (SFSCs) were fabricated using different separators. According to the electrochemical results, the device fabricated using CAG and woven glass fiber (WGF) in a sandwich type configuration CAG/WGF/CAG embedded in H3PO4/PVA exhibited the best performance (1.4 F/g, 0.961 W/kg, 0.161 Wh/kg). A proof of concept based on a LED powered on and a bending test was done, and the capacitor demonstrated excellent electrochemical values even during and after bending. The new device was able to recover 96.12% of its capacitance when returned to its original unbent position. The manufacturing process was critical, as the fibers or layers must be completely embedded in the gel electrolyte to function effectively. A double flexible supercapacitor connected in parallel was fabricated and it showed higher stability, in the same voltage window, yielding 311 mF/cm2 of areal capacitance.

A geopolymer membrane for application in a structural mechanics and energy storage difunctional supercapacitor

A structural mechanics and energy storage difunctional supercapacitor based on a geopolymer membrane injected with a 0.5 M Na2SO4 electrolyte and a pseudocapacitive electrode Mn7O13 is designed and assembled. The geopolymer membrane is prepared as a structural electrolyte with metakaolin and alkaline activator solution. The wide channels in the geopolymer matrix provide paths for ion movement. The Mn7O13 electrode is prepared by different hydrothermal treatments at different temperatures and times, and assembled with activated carbon and a geopolymer with different moduli to form a difunctional supercapacitor. The results show that the electrode sample annealed at 300 °C for 45 min after hydrothermal treatment at 160 °C for 24 h exhibits the best comprehensive performance. The specific capacitance of the electrode is 175.5 F g-1 (2392.6 F m-2) at 1 A g-1, and the specific capacitance of the difunctional structure supercapacitor assembled with a geopolymer with a modulus of 1.2 and cured for 28 days is 144.12 F g-1 (1960.0F m-2) at 1 A g-1 under 15 MPa.

High-strength and machinable load-bearing integrated electrochemical capacitors based on polymeric solid electrolyte

Load bearing/energy storage integrated devices (LEIDs) allow using structural parts to store energy, and thus become a promising solution to boost the overall energy density of mobile energy storage systems, such as electric cars and drones. Herein, with a new high-strength solid electrolyte, we prepare a practical high-performance load-bearing/energy storage integrated electrochemical capacitors with excellent mechanical strength (flexural modulus: 18.1 GPa, flexural strength: 160.0 MPa) and high energy storage ability (specific capacitance: 32.4 mF cm^-2, energy density: 0.13 Wh m^-2, maximum power density: 1.3 W m^-2). We design and compare two basic types of multilayered structures for LEID, which significantly enhance the practical bearing ability and working flexibility of the device. Besides, we also demonstrate the excellent processability of the LEID, by forming them into curved shapes, and secondarily machining and assembling them into complex structures without affecting their energy storage ability.

Electrochemical Energy Storage Properties of High-Porosity Foamed Cement

Foamed porous cement materials were fabricated with H₂O₂ as foaming agent. The effect of H₂O₂ dosage on the multifunctional performance is analyzed. The result shows that the obtained specimen with 0.6% H₂O₂ of the ordinary Portland cement mass (PC0.6) has appropriate porosity, leading to outstanding multifunctional property. The ionic conductivity is 29.07 mS cm⁻¹ and the compressive strength is 19.6 MPa. Furthermore, the electrochemical energy storage performance is studied in novel ways. The PC0.6 also shows the highest areal capacitance of 178.28 mF cm⁻² and remarkable cycle stability with 90.67% of initial capacitance after 2000 cycles at a current density of 0.1 mA cm⁻². The superior electrochemical energy storage property may be attributed to the high porosity of foamed cement, which enlarges the contact area with the electrode and provides a rich ion transport channel. This report on cement–matrix materials is of great significance for large scale civil engineering application.

Designing Structural Electrochemical Energy Storage Systems: A Perspective on the Role of Device Chemistry

Structural energy storage devices (SESDs), designed to simultaneously store electrical energy and withstand mechanical loads, offer great potential to reduce the overall system weight in applications such as automotive, aircraft, spacecraft, marine and sports equipment. The greatest improvements will come from systems that implement true multifunctional materials as fully as possible. The realization of electrochemical SESDs therefore requires the identification and development of suitable multifunctional structural electrodes, separators, and electrolytes. Different strategies are available depending on the class of electrochemical energy storage device and the specific chemistries selected. Here, we review existing attempts to build SESDs around carbon fiber (CF) composite electrodes, including the use of both organic and inorganic compounds to increase electrochemical performance. We consider some of the key challenges and discuss the implications for the selection of device chemistries.

A three-dimensional electrode fabricated by electrophoretic deposition of graphene on nickel foam for structural supercapacitors

The synthesis of a 3D rGO@NF structural electrode was optimized by adjusting the electrophoretic deposition parameters and thermal reduction time.

Recent Developments in the Energy Harvesting Systems from Road Infrastructures

The rapid increase in energy demand has resulted in more dependence on fossil fuels, which leads to higher CO2 emissions every year. To overcome this problem, shifting from fossil fuel-based energy resources to renewable and sustainable ones is essential. One of the new research areas developed in this context is the harvesting of energy from urban infrastructures and, in particular, roads. A large amount of energy in the form of heat or kinetic energy is wasted annually on roads. Recovering these local forms of energy as electricity would improve the energy efficiency of cities. In this review paper, recent developments in the field of energy recovery from roads using solar panels, piezoelectric, thermoelectric and electromagnetic harvesters are discussed along with their efficiency, cost and field implementation. Moreover, new advancements in developing compatible energy storage systems are also discussed and summarised. Based on the review, although all of these systems have the potential of recovering at least a part of the wasted energy, only one of them (the electromagnetic converters) is capable of generating a considerable energy level. In addition, based on the evaluation of the maturity of the technologies, and their cost analyses, more studies are required in order to fill the gap between the current state of the technologies and their full operational form.

High Modulus, Thermally Stable, and Self-Extinguishing Aramid Nanofiber Separators

Mechanically and thermally robust separators offer an alternative approach for preventing battery failure under extreme conditions such as high loads and temperatures. However, the trade-off between electrochemical performance and mechanical and thermal stability remains an ongoing challenge. Here, we investigate aramid nanofiber (ANF) separators that possess high moduli and self-extinguishing characteristics. The ANF separators are formed from the dissolution of bulk Kevlar fibers and their subsequent vacuum-assisted self-assembly. Thermogravimetric analysis shows a high 5 wt % decomposition temperature of 447 °C, which is over ∼175 °C higher than commercial Celgard separators. The ANF separator also possesses a high Young's modulus of 8.8 GPa, which is ∼1000% higher than commercial separators. Even when dry or when soaked in battery electrolyte, the ANF separators self-extinguish upon exposure to flame, whereas commercial separators melt or drip. We show that these features, although adventitious, present a trade-off with electrochemical performance in which a lithium nickel manganse cobalt (NMC) oxide-based battery possessed a reduced capacity of 123.4 mA h g^-1. Considering the separator holistically, we propose that the ANF separator shows an excellent balance of the combined properties of high modulus, flame-resistance, thermal stability, and electrochemical stability and might be suitable for extreme environment applications with further testing.

Comparison of Nanoarchitecture to Porous Media Diffusion Models in Reduced Graphene Oxide/Aramid Nanofiber Electrodes for Supercapacitors

Structural electrodes made of reduced graphene oxide (rGO) and aramid nanofiber (ANF) are promising candidates for future structural supercapacitors. In this study, the influence of nanoarchitecture on the effective ionic diffusivity, porosity, and tortuosity in rGO/ANF structural electrodes is investigated through multiphysics computational modeling. Two specific nanoarchitectures, namely, "house of cards" and "layered" structures, are evaluated. The results obtained from nanoarchitecture computational modeling are compared to the porous media approach and show that the widely used porous electrode theories, such as Bruggeman or Millington-Quirk relations, overestimate the effective diffusion coefficient. Also, the results from nanoarchitecture modeling are validated with experimental measurements obtained from electrochemical impedance spectroscopy and cyclic voltammetry. The effective diffusion coefficients obtained from nanoarchitectural modeling show better agreement with experimental measurements. Evaluation of microscopic properties such as porosity, tortuosity, and effective diffusivity through both experiment and simulation is essential to understand the material behavior and to improve its performance.

Nacre-Inspired Composite Electrolytes for Load-Bearing Solid-State Lithium-Metal Batteries

Solid-state lithium-metal batteries with solid electrolytes are promising for next-generation energy-storage devices. However, it remains challenging to develop solid electrolytes that are both mechanically robust and strong against external mechanical load, due to the brittleness of ceramic electrolytes and the softness of polymer electrolytes. Herein, a nacre-inspired design of ceramic/polymer solid composite electrolytes with a "brick-and-mortar" microstructure is proposed. The nacre-like ceramic/polymer electrolyte (NCPE) simultaneously possesses a much higher fracture strain (1.1%) than pure ceramic electrolytes (0.13%) and a much larger ultimate flexural modulus (7.8 GPa) than pure polymer electrolytes (20 MPa). The electrochemical performance of NCPE is also much better than pure ceramic or polymer electrolytes, especially under mechanical load. A 5 × 5 cm² pouch cell with LAGP/poly(ether-acrylate) NCPE exhibits stable cycling with a capacity retention of 95.6% over 100 cycles at room temperature, even undergoes a large point load of 10 N. In contrast, cells based on pure ceramic and pure polymer electrolyte show poor cycle life. The NCPE provides a new design for solid composite electrolyte and opens up new possibilities for future solid-state lithium-metal batteries and structural energy storage.

Composite Electrodes of Activated Carbon and Multiwall Carbon Nanotubes Decorated with Silver Nanoparticles for High Power Energy Storage

Composite materials in electrodes for energy storage devices can combine different materials of high energy density, in terms of high specific surface area and pseudocapacitance, with materials of high power density, in terms of high electrical conductivity and features lowering the contact resistance between electrode and current collector. The present study investigates composite coatings as electrodes for supercapacitors with organic electrolyte 1.5 M TEABF4 in acetonitrile. The composite coatings contain high surface area activated carbon (AC) with only 0.15 wt% multiwall carbon nanotubes (MWCNTs) which, dispersed to their percolation limit, offer high conductivity. The focus of the investigations is on the decoration of MWCNTs with silver nanoparticles, where smaller Ag crystallites of 16.7 nm grew on carboxylic group-functionalized MWCNTs, MWCNT–COOH, against 27–32 nm Ag crystallites grown on unfunctionalized MWCNTs. All Ag-decorated MWCNTs eliminate the contact resistance between the composite electrode and the current collector that exists when undecorated MWCNTs are used in the composite electrodes. Ag-decorated MWCNT–COOH tripled the power density and Ag-decorated MWCNT additive doubled the power density and increased the maximum energy density by 6%, due to pseudocapacitance of Ag, compared to composite electrodes with undecorated MWCNTs.

Multifunctional Nanocomposites with High Strength and Capacitance Using 2D MXene and 1D Nanocellulose

The family of two-dimensional (2D) metal carbides and nitrides, known as MXenes, are among the most promising electrode materials for supercapacitors thanks to their high metal-like electrical conductivity and surface-functional-group-enabled pseudocapacitance. A major drawback of these materials is, however, the low mechanical strength, which prevents their applications in lightweight, flexible electronics. A strategy of assembling freestanding and mechanically robust MXene (Ti₃ C₂ T_x ) nanocomposites with one-dimensional (1D) cellulose nanofibrils (CNFs) from their stable colloidal dispersions is reported. The high aspect ratio of CNF (width of ≈3.5 nm and length reaching tens of micrometers) and their special interactions with MXene enable nanocomposites with high mechanical strength without sacrificing electrochemical performance. CNF loading up to 20%, for example, shows a remarkably high mechanical strength of 341 MPa (an order of magnitude higher than pristine MXene films of 29 MPa) while still maintaining a high capacitance of 298 F g^-1 and a high conductivity of 295 S cm^-1 . It is also demonstrated that MXene/CNF hybrid dispersions can be used as inks to print flexible micro-supercapacitors with precise dimensions. This work paves the way for fabrication of robust multifunctional MXene nanocomposites for printed and lightweight structural devices.

Multifunctional Structural Ultrabattery Composite

Here we demonstrate a composite material exhibiting dual multifunctional properties of a structural material and a redox-active battery. This incorporates three-dimensional aligned carbon nanotube interfaces that weave together a structural frame, redox-active battery materials, and a Kevlar-infiltrated solid electrolyte that facilitates ion transfer. Relative to the total measured composite material mass, we demonstrate energy density up to ∼1.4 Wh/kg, elastic modulus of 7 GPa, and tensile strength exceeding 0.27 GPa. Mechano-electrochemical analysis demonstrates stable battery operation under mechanical loading that validates multifunctional performance. These findings demonstrate how battery materials that are normally packaged under compression can be reorganized as elements in a structurally reinforced composite material.

Carbon Nanotube Reinforced Structural Composite Supercapacitor

Carbon nanotubes exhibit mechanical properties ideally suited for reinforced structural composites and surface area and conductivity attractive for electrochemical capacitors. Here we demonstrate the multifunctional synergy between these properties in a composite material exhibiting simultaneous mechanical and energy storage properties. This involves a reinforcing electrode developed using dense, aligned carbon nanotubes grown on stainless steel mesh that is layered in an ion conducting epoxy electrolyte matrix with Kevlar or fiberglass mats. The resulting energy storage composites exhibit elastic modulus over 5 GPa, mechanical strength greater than 85 MPa, and energy density up to 3 mWh/kg for the total combined system including electrodes, current collector, Kevlar or fiberglass, and electrolyte matrix. Furthermore, findings from in-situ mechano-electro-chemical tests indicate simultaneous mechanical and electrochemical functionality with invariant and stable supercapacitor performance maintained throughout the elastic regime.

Energy storage in structural composites by introducing CNT fiber/polymer electrolyte interleaves

This work presents a method to produce structural composites capable of energy storage. They are produced by integrating thin sandwich structures of CNT fiber veils and an ionic liquid-based polymer electrolyte between carbon fiber plies, followed by infusion and curing of an epoxy resin. The resulting structure behaves simultaneously as an electric double-layer capacitor and a structural composite, with flexural modulus of 60 GPa and flexural strength of 153 MPa, combined with 88 mF/g of specific capacitance and the highest power (30 W/kg) and energy (37.5 mWh/kg) densities reported so far for structural supercapacitors. In-situ electrochemical measurements during 4-point bending show that electrochemical performance is retained up to fracture, with minor changes in equivalent series resistance for interleaves under compressive stress. En route to improving interlaminar properties we produce grid-shaped interleaves that enable mechanical interconnection of plies by the stiff epoxy. Synchrotron 3D X-ray tomography analysis of the resulting hierarchical structure confirms the formation of interlaminar epoxy joints. The manuscript discusses encapsulation role of epoxy, demonstrated by charge-discharge measurements of composites immersed in water, a deleterious agent for ionic liquids. Finally, we show different architectures free of current collector and electrical insulators, in which both CNT fiber and CF act as active electrodes.

Mechanically Strong Graphene/Aramid Nanofiber Composite Electrodes for Structural Energy and Power

Structural energy and power systems offer both mechanical and electrochemical performance in a single multifunctional platform. These are of growing interest because they potentially offer reduction in mass and/or volume for aircraft, satellites, and ground transportation. To this end, flexible graphene-based supercapacitors have attracted much attention due to their extraordinary mechanical and electrical properties, yet they suffer from poor strength. This problem may be exacerbated with the inclusion of functional guest materials, often yielding strengths of <15 MPa. Here, we show that graphene paper supercapacitor electrodes containing aramid nanofibers as guest materials exhibit extraordinarily high tensile strength (100.6 MPa) and excellent electrochemical stability. This is achieved by extensive hydrogen bonding and π-π interactions between the graphene sheets and aramid nanofibers. The trade-off between capacitance and mechanical properties is evaluated as a function of aramid nanofiber loading, where it is shown that these electrodes exhibit multifunctionality superior to that of other graphene-based supercapacitors, nearly rivaling those of graphene-based pseudocapacitors. We anticipate these composite electrodes to be a starting point for structural energy and power systems that harness the mechanical properties of aramid nanofibers.

Macroscopic fibres of CNTs as electrodes for multifunctional electric double layer capacitors: from quantum capacitance to device performance

In this work we present a combined electrochemical and mechanical study of mesoporous electrodes based on CNT fibres in the context of electric double layer capacitors. We show that through control of the synthetic and assembly processes of the fibres, it is possible to obtain an active material that combines a surface area of 250 m(2) g(-1), high electrical conductivity (3.5 × 10(5) S m(-1)) and mechanical properties in the high-performance range including toughness (35 J g(-1)) comparable to that of aramid fibre (e.g. Kevlar). These properties are a consequence of the predominant orientation of the CNTs, observed by wide- and small-angle X-ray diffraction, and to the exceptionally long CNT length on the millimetre scale. Cyclic voltammetry measurements in a three-electrode configuration and using 1-butyl-3-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (PYR14TFSI) ionic liquid electrolyte, show that the CNT fibres have a large quantum capacitance, evidenced by the near linear dependence of geometric capacitance (and conductivity) on potential bias. This reflects the low dimensionality of the CNT building blocks, which were purposely synthesised to have 1-5 layers and a high degree of graphitization. From the charge-discharge measurements of supercapacitor devices with symmetric CNT fibre electrodes we obtain power and energy densities as high as 58 kW kg(-1) and 14 Wh kg(-1), respectively. These record-high values for CNT fibre-based supercapacitors, are a consequence of the low equivalent series resistance due to the high conductivity of the fibres, the large contribution from quantum capacitance, and the wide stability window of the ionic liquid (3.5 V). Cycle life experiments demonstrate stable capacitance and energy retention over 10,000 cycles of charge-discharge at 3.5 V.

Highly Flexible Self-Assembled V2O5 Cathodes Enabled by Conducting Diblock Copolymers

Mechanically robust battery electrodes are desired for applications in wearable devices, flexible displays, and structural energy and power. In this regard, the challenge is to balance mechanical and electrochemical properties in materials that are inherently brittle. Here, we demonstrate a unique water-based self-assembly approach that incorporates a diblock copolymer bearing electron- and ion-conducting blocks, poly(3-hexylthiophene)-block-poly(ethyleneoxide) (P3HT-b-PEO), with V₂O₅ to form a flexible, tough, carbon-free hybrid battery cathode. V₂O₅ is a promising lithium intercalation material, but it remains limited by its poor conductivity and mechanical properties. Our approach leads to a unique electrode structure consisting of interlocking V₂O₅ layers glued together with micellar aggregates of P3HT-b-PEO, which results in robust mechanical properties, far exceeding the those obtained from conventional fluoropolymer binders. Only 5 wt % polymer is required to triple the flexibility of V₂O₅, and electrodes comprised of 10 wt % polymer have unusually high toughness (293 kJ/m³) and specific energy (530 Wh/kg), both higher than reduced graphene oxide paper electrodes. Furthermore, addition of P3HT-b-PEO enhances lithium-ion diffusion, eliminates cracking during cycling, and boosts cyclability relative to V₂O₅ alone. These results highlight the importance of tradeoffs between mechanical and electrochemical performance, where polymer content can be used to tune both aspects.

Amorphous silicon honeycombs as a binder/carbon-free, thin-film Li-ion battery anode

Amorphous silicon thin films with honeycombed structures have been prepared using a self-assembled monolayer of polystyrene spheres as the template. The as-prepared thin films may serve as a good anode candidate for thin film Li-ion batteries. This approach can be extended to a wide range of coating materials and substrates with controlled periodic structures.

Highlights from Faraday Discussion 172: Carbon in Electrochemistry, Sheffield, UK, July 2014

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Concluding remarks: there's nowt so queer as carbon electrodes

This contribution provides a personal overview and summary of Faraday Discussion 172 on “Carbon in Electrochemistry”, covering some of the key points made at the meeting within the broader context of other recent developments on carbon materials for electrochemical applications. Although carbon electrodes have a long history of use in electrochemistry, methods and techniques are only just becoming available that can test long-established models and identify key features for further exploration. This Discussion has highlighted the need for a better understanding of the impact of surface structure, defects, local density of electronic states, and surface functionality and contamination, in order to advance fundamental knowledge of various electrochemical processes and phenomena at carbon electrodes. These developments cut across important materials such as graphene, carbon nanotubes, conducting diamond and high surface area carbon materials. With more detailed pictures of structural and electronic controls of electrochemistry at carbon electrodes (and electrodes generally), will come rational advances in various technological applications, from sensors to energy technology (particularly batteries, supercapacitors and fuel cells), that have been well-illustrated at this Discussion.