With the advent of atomically thin and flat layers of conducting materials such as graphene, new designs for thin film energy storage devices with good performance have become possible. Here, we report an "in-plane" fabrication approach for ultrathin supercapacitors based on electrodes comprised of pristine graphene and multilayer reduced graphene oxide. The in-plane design is straightforward to implement and exploits efficiently the surface of each graphene layer for energy storage. The open architecture and the effect of graphene edges enable even the thinnest of devices, made from as grown 1-2 graphene layers, to reach specific capacities up to 80 μFcm(-2), while much higher (394 μFcm(-2)) specific capacities are observed multilayer reduced graphene oxide electrodes. The performances of devices with pristine as well as thicker graphene-based structures are examined using a combination of experiments and model calculations. The demonstrated all solid-state supercapacitors provide a prototype for a broad range of thin-film based energy storage devices.

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We report a high-performance redox flow capacitor by using redox-active hydroquinone-based pseudocapacitive slurry electrodes.

Capacitive deionization (CDI) using a flow-electrode primarily composed of porous materials and an aqueous electrolyte, exhibits continuous deionization and a high desalting efficiency. The development of flow-electrodes with high capacitance and low resistance is essential for achieving an efficient flow-electrode capacitive deionization (FCDI) system with low energy consumption. For this purpose, studies on conductive additives (CAs) that do not clog the flow-channel must be conducted. Here, we evaluated the desalting performance of flow-electrodes with spherical and plate-type conductive additives having sizes between 1 and 10 μm and possessing powder conductivities similar to or higher than nano-sized carbon black, which is often used as the CA in solid fixed electrodes in conventional CDI systems. We confirmed that plate-shaped CAs reduced resistance near the pores and enhanced the desalting performance of the flow-electrodes in FCDI systems. The positive effect of such plate-shaped CAs appears to originate from efficient charge percolation between the ACs via the electrical conductive direction of the graphite and the alignment of the exposed graphite edges to the pumping direction of the flow-electrode. Finally, we verified that the flow-electrode with the newly discovered micro-sized CA could be operated without clogging the flow-channel in FCDI and showed an improved desalting performance of around 1.5 times compared the flow-electrode without the micro-sized CA for extended periods of time.