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MXenes present unique features as materials for energy storage; however, limited interlayer distance, and structural stability with ongoing cycling limit their applications. Here, we have developed a unique method involving incorporating Nb atoms into MXene (Ti 3 C 2 ) to enhance its ability to achieve higher ionic storage and longer stability. Computational analysis using density functional theory was performed that explained the material structure, electronic structure, band structure, and density of states in atomistic detail. Nb-doped MXene showed a good charge storage capacity of 442.7 F/g, which makes it applicable in a supercapacitor. X-ray diffraction (XRD) indicated c-lattice parameter enhancement after Nb-doping in MXene (from 19.2A • to 23.4A • ), which showed the effect of the introduction of an element with a larger ionic radius (Nb). Also, the bandgap changes from 0.9 eV for pristine MXene to 0.1 eV for Nb-doped MXene, which indicates that the latter has the signature of increased conductivity due to more metallic nature, in support of the experimental results. This work presents not only the effect of doping in MXene but also helps to explain the phenomena involved in changes in physical parameters, advancing the field of energy storage based on 2D materials.

Summary Two‐dimensional material MXenes owing to their hydrophilic nature, surface termination, and high conductivity can be used in the energy storage device as an anode material. However, poor ion transfer and less available intercalating sites due to self‐stacking of MXene sheets prevent comprehensive utilization of their electrochemical properties. To resolve this problem, a facile method is introduced in this paper to disperse MXene sheets onto reduced graphene oxide sheets to form a porous structure by enhancing electrostatic interactions between two components, which can facilitate ion movement and provide access of ions to more intercalating sites. This hybrid material delivered a capacity of 357 mAh g−1 at 0.05 A g−1 as anode in case of lithium‐ion batteries. Furthermore, the hybrid material showed exceptional stability even after 1000 cycles at 1 A g−1. Current work offers an easy approach for the synthesis of high‐performance niobium carbide‐based hybrid energy storage materials.

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Li ion hybrid supercapacitors are summarized with an emphasis on the use of nitrogen doped graphene and activated carbons.

Conjugated polymers have been widely adopted as active materials in hydrogel‐based stretchable supercapacitors, but the relatively low conductivity and poor structural stability limit their applications. Herein, highly conductive graphene was incorporated as a substrate to anchor polyaniline (PANI) in a hydrogel‐based stretchable electrode. Graphene not only provided an effective conducting network in the electrode, but also stabilized PANI during repeating charge‐discharge processes due to strong π‐π interaction between graphene and PANI. The obtained electrode showed high capacitance of 500.13 mF cm−2 and 100 % capacitance retention after 10000 charge‐discharge cycles. The symmetrical supercapacitor using this novel stretchable electrode showed a high capacitance of 218.26 mF cm−2, high capacitance retention of 43 % even when stretched at 150 % strain, and no capacitance decay when stretched to 100 % and then released to 0 % repeatedly for 2000 cycles, all of which were much better than the device based on the electrode without adding graphene. Such outstanding electrochemical performance shows the great application potential of highly conductive graphene in conjugated polymer‐based stretchable energy storage devices.

Electrode imbalance" is one of the major issues that hinders the potential performance of asymmetric supercapacitors (ASCs), which arises mainly due to the huge dissimilarities of the electrodes microstructures. Herein, an "allgraphene" electrode system is designed by simple chemo-thermal modification of graphene oxide. Chemically functionalized graphene (FG) cathode and two anodes based on thermally reduced graphene oxide (TrGO) and iodine-doped graphene (IG) prepared via simple synthetic routes, followed by assembling into ASCs. The ASC comprising FG cathode-IG anode delivers phenomenally high energy-power (E-P) density (91 W h kg −1 and 424.95 W kg −1 ) and a good capacitance retention after 10 000 cycles. This outcome is accredited to the similar chemistry of electrodes resulting in a minimal electrode imbalance.The developed scheme has capacity to be employed as all-graphene hybrid energy storage system outputting enhanced performance and cyclic stability.asymmetric supercapacitor, all-graphene electrode system, functionalized graphene, iodinedoped graphene, ultra-high energy density

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