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Abstract The introduction of surface functional groups onto graphite can provide additional pseudocapacitance for supercapacitors. However, the compensation for the loss of electrical conductivity arising from the destruction of the π-π conjugation remains a big challenge. Here, the graphite paper is electrochemically oxidized first, followed by the mild reduction using hydroiodic acid to afford the largely exfoliated and moderately reduced sample (noted as MOGP-4). The as-prepared MOGP-4 not only has the abundant oxygenous groups, but also preserves the highly conductive network (sp2 carbon). Owing to the good conductivity (1.14 × 103 S m−1), MOGP-4 exhibits a high rate capability of 93% (from 18.3 mF cm−2 to 17 mF cm−2) as the current density increases from 0.5 to 10 mA cm−2 and predominant cycling performance. Furthermore, the flexible solid-state supercapacitors (SSCs) based on MOGP-4 with different sizes are assembled and deliver excellent durability, high flexibility and superior rate capability. The high electrochemical performances of the as-fabricated supercapacitors should envision promising applications for energy storage devices. Graphical abstract Image 1 highlights Graphite paper (GP) row material is low-cost, commercial, large-area and flexible. GP is electrochemically oxidized in mixed acids and then mildly reduced by HI. The strategy can introduce oxygenous groups and preserve high conductivity of GP. The fabricated SCs have high rate capability, stability and coulombic efficiency. [ABSTRACT FROM AUTHOR]

In this work, hierarchical MgCo 2 O 4 @CoFe layered double hydroxide (LDH) core-shell nanowire arrays on Ni foam (NF) are synthesized by facile hydrothermal and calcination methods. MgCo 2 O 4 /NF has been first synthesized via a hydrothermal reaction and annealing treatment and then utilized to prepare MgCo 2 O 4 @CoFe-LDH/NF core-shell nanocomposites via the second hydrothermal reaction. It is found that the MgCo 2 O 4 @CoFe-LDH/NF core-shell nanocomposite prepared from 3 h hydrothermal reaction (MC@CF-LDH-3) exhibits an excellent specific capacitance of 903.15 C g−1 (2007 F g−1) at the current density of 1 A g−1. Moreover, a high capacitance retention (80.2% maintained after 5000 cycles) and a low internal resistance (Rs) (0.75 Ω) can be acquired. Furthermore, an all-solid-state asymmetric supercapacitor (ASC) is assembled using MgCo 2 O 4 @CoFe-LDH/NF-3 as the positive electrode and activated carbon (AC) as the negative electrode. The as-fabricated MgCo 2 O 4 @CoFe-LDH/NF-3//AC ASC shows a high energy density of 60.82 Wh kg−1 at 725 W kg−1. Meanwhile, the MgCo 2 O 4 @CoFe-LDH/NF-3//AC ASC device possesses an excellent cycling stability of 93.6% retention of the initial capacitance after 5000 cycles and two ASC devices connected in series can light up a LED bulb for 8 min. Our results manifest that this hierarchical MgCo 2 O 4 @CoFe-LDH composite has huge potential application in energy storage devices. Image 1 • MgCo 2 O 4 @CoFe-LDH core-shell nanoarrays is fabricated on Ni foams. • The materials are obtained by a facile hydrothermal strategy. • MgCo 2 O 4 @CoFe-LDH electrode exhibits superb supercapacitive performance. [ABSTRACT FROM AUTHOR]

The hierarchical nanostructure hybrids of porous Co 3 O 4 nanowires coated NiMn layered double hydroxide nanosheets array on Ni foams (Co 3 O 4 @NiMn-LDH/Ni) are designed and prepared via the two-step hydrothermal reactions with a combination of annealing process. The Co 3 O 4 nanowires can be utilized as backbone to grow the NiMn-layered double hydroxide (NiMn-LDH) nanosheets, which provide a large surface area and leading to the enhanced capacitive performance owing to the effective ion/electron diffusion rates. The areal capacitance of the as-prepared Co 3 O 4 @NiMn-LDH/Ni electrode reaches 19.7 F cm−2 (5419.7 F g−1) at 2 mA cm−2 (0.56 A g−1). Moreover, a high capacitance retention (93.25% of capacitance maintained after 6000 cycles) and a low internal resistance R s (0.62 Ω) can be acquired. Additionally, an all-solid-state asymmetric supercapacitor (Co 3 O 4 @NiMn-LDH/Ni//AC ASC) based on the Co 3 O 4 @NiMn-LDH/Ni as positive electrode and activated carbon (AC) as negative electrode is successfully obtained. The Co 3 O 4 @NiMn-LDH/Ni//AC ASC shows a high energy density of 47.15 Wh kg−1 at 376 W kg−1. Additionally, a LED can be lit up for 12 min when three ASCs are connected in series. Therefore, this novel Co 3 O 4 @NiMn-LDH/Ni with outstanding electrochemical performance should envision potential practical applications in high energy storage appliances. Image 1 • The porous Co 3 O 4 nanowires provide more paths for ions diffusion. • NiMn layered double hydroxide nanosheets provide large surface areas. • Co 3 O 4 @NiMn-LDH/Ni electrode exhibits excellent supercapacitive properties. [ABSTRACT FROM AUTHOR]