Constant capacitance in nanopores of carbon monoliths

The results obtained for binder-free electrodes made of carbon monoliths with narrow micropore size distributions confirm that the specific capacitance in the electrolyte (C2H5)4NBF4/acetonitrile does not depend significantly on the micropore size and support the foregoing constant result of 0.094 ± 0.011 F m−2.We thank Dr Jose M. Rojo (ICMM-CSIC) for his useful assistance. Financial support from Spanish MICINN (project MAT 2011-25198) is gratefully acknowledged. G. Moreno-Fernandez thanks Spanish MINECO for a FPI fellowship. We also acknowledge institutional support from the Unit of Information Resources for Research at the “Consejo Superior de Investigaciones Científicas” (CSIC) for the article-processing charges contribution.Peer reviewe

Ion transport from water-in-salt electrolyte through porosity of hierarchical porous carbons unraveled by solid-state NMR

Electrical double-layer capacitors bring numerous strengths to the energy storage landscape but have limited use due to their high unit energy cost and low specific energy. Water-in-salt electrolytes have been recently purported as an option to provide more affordable energy storage, but high viscosity and limited conductivity hinder their direct use in high-power devices such as capacitors. By using solid-state NMR and electrolyte-tuned porosity carbons, we demonstrate, at the molecular level, a drastic impact of relative pore/ion size on proper electrolyte propagation deep down the pore volume. The NMR results also provide a rationale for the radical changes in low-and high-rate electrochemical response observed using carbons with differently nanosized pores and a water-in-salt electrolyte.We thank the financial support from MCIN/AEI/10.13039/501100011033/ and FEDER “Una manera de hacer Europa” through the project RTI2018–096199-B-I00.Peer reviewe

Ball-milling-enhanced capacitive charge storage of activated graphene in aqueous, organic and ionic liquid electrolytes

Ball-milling under either air or argon is explored as a facile way to adjust the textural properties, surface chemistry and morphology of activated reduced graphene oxide to the requirements for optimum electrode materials in electrical double layer capacitors operating in aqueous (KOH), organic (tetraethylammonium tetrafluoroborate in acetonitrile) and ionic liquid (1-Ethyl-3-methylimidazolium bis(trifluoromethyls​ulfonyl)​imide) electrolytes. Ball-milling is evidenced to specifically remove excessively large pores through the collapse of mesoporosity with no negative effect on in-pore resistance in any electrolyte, a concomitant improvement in volume-based storage and no loss of gravimetric performance. Ball-milling under air results in high oxygen content in the materials, which brings about performance deterioration in tetraethylammonium tetrafluoroborate in acetonitrile, but not significantly in aqueous and ionic liquid electrolytes. The best performance is achieved using activated graphene ball-milling under argon, with a volumetric capacitance of 90, 60, 70 F.cm−3 and a characteristic cell response time of 0.28, 1.3 and 8 s for aqueous, organic and ionic liquid electrolyte. While the highest energy density of 25 Wh.L−1 is reached in ionic liquid electrolyte at a cell potential of 3 V, the highest practical power density of 15 kW.L−1 is measured in tetraethylammonium tetrafluoroborate in acetonitrile at the energy density of 10 Wh.L−1. Our study underscores that simple ball-milling can provide the best trade-off among multiple performance parameters, resulting in sufficiently high volumetric capacitance with no detriment in high-rate response and cycle stability

Spray Deposition of Supercapacitor Electrodes using Environmentally Friendly Aqueous Activated Graphene and Activated Carbon Dispersions for Industrial Implementation

A spray gun machine was used to deposit high‐surface‐area supercapacitor electrodes using green non‐toxic aqueous dispersions based on different kinds of high specific surface area nanostructured carbon materials: activated graphene (a‐rGO) and activated carbon (AC). Tuning the spray conditions and dispersion formulation allowed us to achieve good adhesion to stainless‐steel current collectors in combination with high surface area and a satisfactory mechanical stability of the electrodes. The specific surface area of approximately 2000 m2/g was measured directly on a‐rGO and AC electrodes showing only around a 20 % decrease compared to the precursor powder materials. The performance of the electrodes deposited on stainless‐steel and aluminum current collectors was tested in supercapacitor devices using three electrolytes. The electrodes were tested in an “as‐deposited” state and after post‐deposition annealing at 200 °C. The spray deposition method and post‐deposition annealing are completely compatible with roll‐to‐roll industrial production methods. The a‐rGO demonstrated superior performance compared to AC in supercapacitor electrodes with gravimetric capacitance, energy, and power density parameters, which exceed commercially available analogues. The formulation of the dispersions used in this study is environmentally friendly, as it is based on only on water as a solvent and commercially available non‐toxic additives (graphene oxide, fumed silica, and carbon nanotubes)