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Support-catalyst interface plays a critical role in electrocatalytic processes as the rates of involved reactions are directly linked with the interfacial charge transfer efficiency. Here, we are presenting nitrogen doped exfoliated graphite foil (NGF) as the 3D support which offers electronically coupled interface to catalytic heterostructure comprises of nickel-iron based oxide and its borate. As developed hybrid (NGF/NiFe/Borate) show excellent oxygen evolution reaction (OER) under alkaline condition with low overpotential of 281 mV at current density of 10 mA cm−2 and Tafel slope 62 mv dec−1. The results beat most nonprecious metal catalysts and noble commercial IrO2 deposited over same NGF substrate with outstanding long-term durability over 10 h at high current density 300 mA cm−2. Efficient electron injection from NGF support and its low resistance leads to enhancement in current density by more than 136 % at operative potential of 1.55 V, in comparison to un-doped exfoliated graphite foil support. Beside electronically tuned support, high catalytic efficiency is also linked with planner growth of borate nanosheets that helps in fast interfacial charge transfer in its transverse direction to the catalytic site. Our work highlights the importance of electronic tuning of catalyst support to enhance the performance of supported borate catalyst and to rationally design low cost, highly active OER catalyst.

Exposing the surface states of metal–organic frameworks (MOFs) by tuning the shape and size of their nanostructures is expected to enhance their functionalities in practical applications. Herein, a highly scalable ‘hydrogel–organic interfacial diffusion’ driven approach is utilized for direct growth of metal–organic framework (MOF) nanocrystals over a porous graphene hydrogel framework with fine structural control. Molecular dynamics (MD) simulation of this heterostructure reveals that, two-stage diffusion (hydrogel–organic interfacial and intra-hydrogel) control of organic ligand molecules and their interaction with the graphene surface play key roles in tunable MOF–hydrogel formation. The resulting tri-metallic MOF–hydrogel-hybrid derived porous aerogel exhibits state-of-the-art oxygen evolution reaction (OER) performance metrics with excellent operational stability in alkaline medium. The overpotential required to achieve a current density of 10 mA cm−2 is as low as 255 mV and a small Tafel slope of 44.3 mV dec−1 signifies a very high rate of oxygen evolution reaction. The hydrogel–organic interfacial principle of this material could be applied to produce versatile graphene–MOF heterostructures as well as other diverse functional graphene-gel-nanohybrids (e.g. metal nanoparticles, conducting polymers) with intriguing application prospects.

A solvated network of two-dimensional materials in the form of hydrogel offers a unique platform for the full utilization of surface-dominated properties on a macroscopic scale. However, the development of such hydrogels with ceramic sheets of MXenes is highly challenging, and hence, they are often critically dried to aerogel form to make them self-standing. Herein, we report the preparation of a freestanding thin MXene hydrogel via spontaneous, quasi-ordered assembly over a metal plate and concurrent partial surface de-functionalization. We established that self-standing hydrogels can only be assembled from MXene solutions above a critical dispersion concentration (Cct) depending on the size of the sheets. On behalf of ordered porous structures with intrinsic hydrated ion-permeable channels, MXene hydrogels display very high surface capacitive contribution (>94%) in their pseudocapacitive energy storage performance. Consequently, the as-developed hydrogels display an excellent gravimetric capacitance of 391 F g−1 and rate performance, and continue to display an outstanding performance >337 F g−1 at a high enough mass loading up to ∼15 mg cm−2. As a versatility of hydrogel structures, an electrolyte-protected mechanical compression method was employed to obtain a compact yet ion channel–decorated electrode. As a result, compact MXene hydrogels achieved an excellent volumetric capacitance of 1120 F cm−3 and a rate capability of 73% at 1000 mV s−1.

The intricate design of nanomaterials through the controlled diffusion process is natural for biological bodies; however, understanding this mechanism for the development of morphology tuned nanoma...

Gravimetric and volumetric capacitance are the two important matrices for any supercapacitor device, but only moderate achievement has been realized till date on the first figure-of-merit for MXene based electrodes. In this study, aided by a small quantity (5 wt%) of graphene, an interfacial layer-by-layer self-assembly of MXene has been employed to develop hydrogel based supercapacitor electrodes that display excellent gravimetric capacitance of 653.7 F g−1 at 2 mV s−1 in three electrode setup. Very high areal (1442 mF cm−2) and volumetric capacitance (∼1522 F cm−3) were also achieved by simple tuning of respective conditions like gelation time and electrolyte protected mechanical compression. Considering the fact that MXene is prone to oxidation at elevated gelation temperatures, this purely ambient gelation protocol is established to protect its redox active titanium sites. MXene-graphene hybrid hydrogel structures consisting of network of 2D-sheets can allow full utilization of metallic surfaces and redox active sites on MXene basal plane, and thereby display outstanding performance metrics. These hybrid hydrogels also show excellent cyclic stability even with commercial scale mass loading which can pave the way to their application in practical devices.

High overpotentials required to cross the energy barriers of both hydrogen and oxygen evolution reactions (HER and OER) limit the overall efficiency of hydrogen production by electrolysis of water. The rational design of heterostructures and anchoring single-atom catalysts (SAC) are the two successful strategies to lower these overpotentials, but realization of such advanced nanostructures with adequate electronic control is challenging. Here, the heterostructure of edge-oriented molybdenum selenide (MoSe

Integration of pseudocapacitive nanomaterials within graphene based 3D-hydrogel network has shown suitable synergist in rate performance energy storage, but implementing the same with MXene through conventional heat involved processing is challenging due to its oxidation prone surface. Herein, we present a purely room temperature casting based approach to develop 3D-hydrogel hybrids of MXene and graphene (MGH) via metallic zinc particles induced spontaneous gelation, avoiding oxidation possibility. MGH was used as supercapacitor electrode that exhibits high mass specific capacitance of 357 F g–1 at 10 mV s–1, and excellent capacity retention of 95.6% after 10000 charge-discharge cycles. MGH was used as negative electrode to develop asymmetric supercapacitor, in combination with polyaniline (PANI)-graphene hybrid hydrogel (PGH) as positive electrode, that delivers a maximum energy density of 30.3 Wh kg–1 and a power density of 1.13 kW kg–1 with excellent capacity retention over 10000 cycles. In comparison to compact electrodes where pseudocapacitive materials cannot display their faradic activity with full potential, the hydrated porous network of MXene-graphene hydrogels with continuous channels permit the electrolyte ions to efficiently access MXene and PANI, thereby displaying high gravimetric and rate performance. MXene-graphene hydrogels, developed via this facile and cost effective protocol, are also attractive candidate for wide application areas that requires 3D porous structure.

Volumetric and areal energy densities are the key performance metrics for electrochemical supercapacitors (EC) used in portable storage devices, whereas mechanical flexibility and potential for direct integration with conventional cloths are the primary requirements for wearable usage. Herein, highly scalable, versatile EC electrodes are presented based on the spontaneously assembled hydrogel-hybrids of graphene and polyaniline (PANI). Our hydrogel-hybrids exhibit areal capacitance of 853 mF cm−2 (at 1 mA cm−2) with superb cycling stability (95.2% retention after 5000 cycles), which can be readily increased up to 2.2 F cm−2 by the multistacking of electrodes without sacrificing charging-discharging rate capability. Control of hydration level (water