No abstract

Electrochemical double-layer (EDL) capacitors operating at high charge/ discharge rates are an important class of electrochemical energy storage devices. Aqueous EDL capacitors show great potential for use as inexpensive devices with much higher power; however, their energy density is severely limited by the narrow electrochemical window of water (1.23 V) and the small specific capacity of the electrodes. Here, we develop a highvoltage aqueous supercapacitor based on a highly concentrated Li + aqueous electrolyte (hydrate melt) and a two-dimensional titanium carbide MXene electrode. Experimental and theoretical analyses reveal the existence of dense hydrated Li + in the interlayer space of the deeply charged MXene, which is realized by the wide electrochemical window of a hydrate-melt electrolyte. The hydrate-melt electrolyte together with the largecapacitance MXene Ti 2 CT x improves the performance of an aqueous lithium-ion supercapacitor, offering a promising strategy for advanced aqueous capacitors.

Phase-pure Mo2AlB2 with a single Al layer, a possible precursor for MBenes, was synthesized topochemically by the removal of an Al layer from MoAlB.

An aqueous supercapacitor is a prospective energy storage device that achieves affordable clean-energy supply. Although recent intensive research on concentrated electrolytes paved the way to improve its low energy density by expanding the narrow electrochemical potential window of water, it was compromised by slow rate capability with respect to the capacitor standard. In this work, to reveal the rate-determining ion-transport mechanism that limits the reaction kinetics of aqueous capacitor electrodes, electrochemical impedance spectroscopy was conducted on layered titanium carbide (MXene) electrodes with concentrated aqueous electrolytes (water-in-salt and hydrate melt). With increasing salt concentration, the dissociation of contact-ion-pair becomes dominant to ion transport both in the bulk electrolyte and at the electrode-electrolyte interface.

A Ni-W thin-film was synthesized by electrodeposition, and its corrosion resistance and electrical surface conductivity were investigated. Amount of tungsten in the Ni-W thin-film increased linearly with current density during the electrodeposition, and crack-free and low-crystalline Ni-21 at.%W coating layer was obtained. Corrosion resistances of the Ni-W thin-films were examined with an anodic polarization method and a storage test in a strong sulfuric acid solution. As a result, the Ni-21 at.%W thin-film exhibited the greatest corrosion resistance, and maintained the electrical surface conductivity even after the severe corrosion test, which could be applicable as a surface treatment for advanced metallic bipolar plates in fuel cell or redox flow battery systems.