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A quasi-solid-state photothermal supercapacitor via enhanced solar energy harvest

The development of flexible supercapacitors with high volumetric capacitance and energy density for outdoor wearable electronics, especially for applications in low-temperature environments, remains an urgent challenge. Here, compressible film electrodes architected by an N-doped mesoporous carbon nanosphere-intercalated 3D graphene hydrogel (N-MCN@GH) composite were developed for energy storage applications. This N-MCN@GH electrode exhibited a hierarchical porous network with a large accessible surface area for rapid electron transportation and massive ion migration via uniform N-MCN bracing in conductive graphene; therefore, it could serve as a flexible supercapacitor and deliver a total volumetric (vs. the whole device) capacitance of 8.1 F cm−3 with a stable energy density of 1.12 mW h cm−3 at a power density of 13.30 mW cm−3. Very interestingly, this flexible N-MCN@GH electrode showed enhanced solar absorption and could achieve efficient solar-thermal conversion for the prevention of capacitance decay under low temperature environmental conditions. Additionally, the packaging of the photothermal supercapacitor in a transparent PET membrane preserved its enhanced photothermal capacitance performance. This work provides an innovative strategy to obtain flexible supercapacitors for practical applications and also initiates a new concept for optical/temperature sensing devices.