Two-dimensional Ti3C2T x MXenes have been extensively studied as pseudocapacitive electrode materials. This Letter aims at providing further insights into the charge storage mechanism of the Ti3C2T x MXene electrode in the acidic electrolyte by combining experimental and simulation approaches. Our results show that the presence of H2O molecules between the MXene layers plays a critical role in the pseudocapacitive behavior, providing a pathway for proton transport to activate the redox reaction of the Ti atoms. Also, thermal annealing of the samples at different temperatures suggests that the presence of the confined H2O molecules is mainly controlled by the surface termination groups. These findings pave the way for alternative strategies to enhance the high-rate performance of MXenes electrodes by optimizing their surface termination groups.

A metal-free supercapacitor electrode material is prepared by the hybridization of graphene and polyaniline in a very compact way without sacrificing their gravimetric capacitance. It exhibits a record high volumetric capacitance over 800 F cm(-3).

Natural vascular plants leaves rely on differences in osmotic pressure, transpiration and guttation to produce tons of clean water, powered by sunlight. Inspired by this, we report a sunlight-driven purifier for high-efficiency water purification and production. This sunlight-driven purifier is characterized by a negative temperature response poly(N-isopropylacrylamide) hydrogel (PN) anchored onto a superhydrophilic melamine foam skeleton, and a layer of PNIPAm modified graphene (PG) filter membrane coated outside. Molecular dynamics simulation and experimental results show that the superhydrophilicity of the relatively rigid melamine skeleton significantly accelerates the swelling/deswelling rate of the PNPG-F purifier. Under one sun, this rational engineered structure offers a collection of 4.2 kg m −2 h −1 and an ionic rejection of > 99% for a single PNPG-F from brine feed via the cooperation of transpiration and guttation. We envision that such a high-efficiency sunlight driven system could have great potential applications in diverse water treatments.

Filtering capacitor is a necessary component in the modern electronic circuit. Traditional filtering capacitor is often limited by its bulky and rigid configuration and narrow workable scope of applications. Here, an aqueous hybrid electrochemical capacitor is developed for alternating current line filtering with an applicable wide frequency range from 1 to 10,000 Hz. This capacitor possesses an areal specific energy density of 438 μF V 2 cm −2 at 120 Hz, which to the best of our knowledge is record high among aqueous electrochemical capacitors reported so far. It can convert arbitrary alternating current waveforms and even noises to straight signals. After integration of capacitor units, a workable voltage up to hundreds of volts (e.g., 200 V) could be achieved without sacrificing its filtering capability. The integrated features of wide frequency range and high workable voltage for this capacitor present promise for multi-scenario and applicable filtering capacitors of practical importance.