High energy density, durability, and flexibility of supercapacitors are required urgently for the next generation of wearable and portable electronic devices. Herein, a novel strategy is introduced to boost the energy density of flexible soild-state supercapacitors via rational design of hierarchically graphene nanocomposite (GNC) electrode material and employing an ionic liquid gel polymer electrolyte. The hierarchical graphene nanocomposite consisting of graphene and polyaniline-derived carbon is synthesized as an electrode material via a scalable process. The meso/microporous graphene nanocomposites exhibit a high specific capacitance of 176 F g −1 at 0.5 A g −1 in the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF 4 ) with a wide voltage window of 3.5 V, good rate capability of 80.7% in the range of 0.5-10 A g −1 and excellent stability over 10 000 cycles, which is attributed to the superior conductivity (7246 S m −1 ), and quite large specific surface area (2416 m 2 g −1 ) as well as hierarchical meso/micropores distribution of the electrode materials. Furthermore, flexible solid-state supercapacitor devices based on the GNC electrodes and gel polymer electrolyte film are assembled, which offer high specific capacitance of 180 F g −1 at 1 A g −1 , large energy density of 75 Wh Kg −1 , and remarkable flexible performance under consecutive bending conditions.

Highly active, cost‐effective, and durable catalysts for oxygen evolution reaction (OER) are required in energy conversion and storage processes. A facile synthesis of CoFe layered double hydroxide (CoFe LDH) is reported as a highly active and stable oxygen evolution catalyst. By varying the concentration of the metal ion precursor, the Co/Fe ratios of LDH products can be tuned from 0.5 to 7.4. The structure and electrocatalytic activity of the obtained catalysts were found to show a strong dependence on the Co/Fe ratios. The Co2Fe1 LDH sample exhibited the best electrocatalytic performance for OER with an onset potential of 1.52 V (vs. the reversible hydrogen electrode, RHE) and a Tafel slope of 83 mV dec−1. The Co2Fe1 LDH was further loaded onto a Ni foam (NF) substrate to form a 3D porous architecture electrode, offering a long‐term current density of 100 mA cm−2 at 1.65 V (vs. RHE) towards the OER.

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