Freeze-assisted Tape Casting of Vertically Aligned MXene Films for High Rate Performance Supercapacitors

Conventional electrode preparation techniques of supercapacitors such as tape casting or vacuum filtration often lead to the restacking or agglomeration of twodimensional(2 D)materials.As a result,tortuous paths are created for the electrolyte ions and their adsorption onto the surfaces of the active materials can be prevented.Consequently,maintaining high rate performance while increasing the thickness of electrodes has been a challenge.Herein,a facile freeze-assisted tape-casting(Fa TC)method is reported for the scalable fabrication of flexible MXene(Ti3C2Tx)supercapacitor electrode films of up to 700μm thickness,exhibiting homogeneous ice-template microstructure composed of vertically aligned MXene walls within lamellar pores.The efficient ion transport created by the internal morphology allows for fast electrochemical charge–discharge cycles and near thickness-independent performance at up to 3000 m V s-1 for films of up to 300μm in thickness.By increasing the scan rate from 20 to 10,000 m V s-1,Ti3C2Tx films of 150μm in thickness sustain 50%of its specific capacitance(222.9 F g-1).When the film thickness is doubled to 300μm,its capacitance is still retained by 60%(at 213.3 F g-1)when the scan rate is increased from 20 to3000 m V s-1,with a capacitance retention above 97.7%for over 14,000 cycles at10 A g-1.They also showed a remarkably high gravimetric and areal power density of 150 k W kg-1 at 1000 A g-1 and 667 m W cm-2 at 4444 m A cm-2,respectively.Fa TC has the potential to provide industry with a viable way to fabricate electrodes formed from 2 D materials on a large scale,while providing promising performance for use in a wide range of applications,such as flexible electronics and wearable energy storage devices.

Laser solid-phase synthesis of single-atom catalysts

Single-atom catalysts(SACs)with atomically dispersed catalytic sites have shown outstanding catalytic performance in a variety of reactions.However,the development of facile and high-yield techniques for the fabrication of SACs remains challenging.In this paper,we report a laser-induced solid-phase strategy for the synthesis of Pt SACs on graphene support.Simply by rapid laser scanning/irradiation of a freeze-dried electrochemical graphene oxide(EGO)film loaded with chloroplatinic acid(H2PtCl6),we enabled simultaneous pyrolysis of H2PtCl6 into SACs and reduction/graphitization of EGO into graphene.The rapid freezing of EGO hydrogel film infused with H2PtCl6 solution in liquid nitrogen and the subsequent ice sublimation by freeze-drying were essential to achieve the atomically dispersed Pt.Nanosecond pulsed infrared(IR;1064 nm)and picosecond pulsed ultraviolet(UV;355 nm)lasers were used to investigate the effects of laser wavelength and pulse duration on the SACs formation mechanism.The atomically dispersed Pt on graphene support exhibited a small overpotential of−42.3 mV at−10 mA cm−2 for hydrogen evolution reaction and a mass activity tenfold higher than that of the commercial Pt/C catalyst.This method is simple,fast and potentially versatile,and scalable for the mass production of SACs.