Pseudocapacitive Electrodes Produced by Oxidant-Free Polymerization of Pyrrole between the Layers of 2D Titanium Carbide (MXene).

The hard-template method belongs to an effective route for preparing porous carbon materials with ideal hierarchical pores. In this work, a kind of hierarchical porous carbon (HPC) with high gravimetric and volumetric capacitance is fabricated by the use of Al–Cu double hydroxides (Al–Cu DHs) as hard templates and polyethylene glycol-200 as carbon precursors. It is found that the Al/Cu molar ratio has a profound influence on the morphology and composition of Al–Cu DHs and the obtained hierarchical porous architecture of HPCs owing to the template and catalyst functions of both Cu and Al2O3. For Al/Cu molar ratios of 5:1 and 7:1, the prepared HPC-05 and HPC-07 display a large specific surface area and appropriate hierarchical porous architecture. They can be used as the electrode materials of supercapacitors without any activation. The HPC-05 exhibits gravimetric capacitance (296.9 F g−1) and high volumetric capacitance (183.3 F cm−3). Moreover, the capacitance retention is 105% in 1 M Na2SO4 electrolyte with an ultrahigh gravimetric energy density of 16.32 W h kg−1 and a volumetric energy density of 10.09 W h l−1. This paper provides a tunable double-hydroxide-template way to construct HPC materials with high gravimetric and volume capacitance.

To increase the volumetric and gravimetric capacitances of supercapacitors, a new class of electrode materials with high electrochemical activity and favorable structures is extremely desired. In this work, a hollow novel nitrogen-doped 3D elastic single-walled carbon nanotube sponge (NSCS) which is ultra lightweight with the lowest density of 0.8 mg cm-3, and has a high open surface structure for electrolyte accessibility and excellent compressible properties as the electrode scaffold has been successfully fabricated by the pyrolysis method which could produce the carbon nanotube sponge easily on a large scale without high-cost and time-consuming processes. Moreover, a NiCo2O4 nanosheet supported on the NSCS has been successfully fabricated. The highest volumetric and gravimetric capacitance of this electrode is 790 F cm-3 at 1.43 g cm-3 and 1618 F g-1 at 0.54 g cm-3 with excellent cycling stability. The density of NiCo2O4/NSCS electrode was adjusted by mechanical compression and the most favorable density of the film for both high volumetric and gravimetric capacitances obtained was 1.21 g cm-3. The thick NiCo2O4/NSCS film of 72 μm has been fabricated at this favorable density, presenting both high volumetric and gravimetric capacitances of 597 F cm-3 and 1074 F g-1 at 1 A g-1, respectively, indicating that the structure of the NSCS is extremely feasible for obtaining a thick film electrode with excellent volumetric and gravimetric capacitances. Furthermore, an asymmetric supercapacitor of NiCo2O4/NSCS//NGN/CNTs was fabricated, exhibiting a high gravimetric energy density of 47.65 W h kg-1 at 536 W kg-1 and a volumetric energy density of 33.44 W h L-1 at 376.16 W L-1.

Biomass waste derived functionalized hierarchical porous carbon with high gravimetric and volumetric capacitances for supercapacitors

Activated carbons (ACs) are derived from cornhusk via a simple technique consisting of hydrothermal carbonization and following KOH activation, with porous structures and morphology of the ACs controlled by adjusting the amount of KOH for the activation. As the main active materials of the electrode for supercapacitors (SCs), both the porosity and morphology exhibit significant influence in the compaction density of the electrode. The ACs activated with a KOH/biochar ratio of 3:1 not only provide a high surface area of 3024 m2 g−1 but also guarantee a high compaction density of 11.6 mg cm−2 for a 200 μm‐thick electrode, leading to high performances for both gravimetric and volumetric capacitance. Moreover, the morphology of a thin sheet‐like interconnected network benefits the densely compact nature of the ACs in the electrode. Concerning the practical application, the effect of electrode thickness on the electrochemical performance is examined to optimize the electrode with commercial‐level mass loading with organic electrolyte, which is of ≈344 F g−1 in gravimetric capacitance and 210 F cm−3 in volumetric capacitance as well as excellent capacitance retention over 90% after 5000 galvanostatic charge–discharge cycles. In addition, good electrochemical performances of the optimized electrode with commercial‐level mass loading are over a broad range of work temperature.

2D transition-metal carbides and nitrides, known as MXenes, have displayed promising properties in numerous applications, such as energy storage, electromagnetic interference shielding, and catalysis. Titanium carbide MXene (Ti3 C2 Tx ), in particular, has shown significant energy-storage capability. However, previously, only micrometer-thick, nontransparent films were studied. Here, highly transparent and conductive Ti3 C2 Tx films and their application as transparent, solid-state supercapacitors are reported. Transparent films are fabricated via spin-casting of Ti3 C2 Tx nanosheet colloidal solutions, followed by vacuum annealing at 200 °C. Films with transmittance of 93% (≈4 nm) and 29% (≈88 nm) demonstrate DC conductivity of ≈5736 and ≈9880 S cm-1 , respectively. Such highly transparent, conductive Ti3 C2 Tx films display impressive volumetric capacitance (676 F cm-3 ) combined with fast response. Transparent solid-state, asymmetric supercapacitors (72% transmittance) based on Ti3 C2 Tx and single-walled carbon nanotube (SWCNT) films are also fabricated. These electrodes exhibit high capacitance (1.6 mF cm-2 ) and energy density (0.05 µW h cm-2 ), and long lifetime (no capacitance decay over 20 000 cycles), exceeding that of graphene or SWCNT-based transparent supercapacitor devices. Collectively, the Ti3 C2 Tx films are among the state-of-the-art for future transparent, conductive, capacitive electrodes, and translate into technologically viable devices for next-generation wearable, portable electronics.

Competing effects of potassium hydroxide activation of graphene on gravimetric and volumetric capacitances

Rational design of MXene/activated carbon/polyoxometalate triple hybrid electrodes with enhanced capacitance for organic-electrolyte supercapacitors

3D MXene-holey graphene hydrogel for supercapacitor with superior energy storage

Rational design of sandwiched polyaniline nanotube/layered graphene/polyaniline nanotube papers for high-volumetric supercapacitors

Carbon-encapsulated niobium carbonitride with high volumetric capacitance and wide potential windows in aqueous pseudocapacitors

Free-standing boron and oxygen co-doped carbon nanofiber films for large volumetric capacitance and high rate capability supercapacitors

Activated carbon with high capacitance prepared by NaOH activation for supercapacitors

KMnO4-assisted synthesis of oxygen-containing porous graphene with high gravimetric and volumetric performances for supercapacitor

B/P/N/O co-doped hierarchical porous carbon nanofiber self-standing film with high volumetric and gravimetric capacitance performances for aqueous supercapacitors

Flexible graphene/carbon nanotube hybrid papers chemical-reduction-tailored by gallic acid for high-performance electrochemical capacitive energy storages