Bilateral growth of monoclinic WO3 and 2D Ti3C2Tx on 3D free-standing hollow graphene foam for all-solid-state supercapacitor

The free-standing three dimensional (3D) hollow graphene foam (HGF) decorated nanostructured pseudocapacitive materials could offer a large active surface area and a extreme conductive porous 3D network for fast reversible charge transfer reactions in the supercapacitor. Herein, the 3D HGF was prepared by a template assisted-chemical vapor deposition (TA-CVD) method and the monoclinic WO3 (m-WO3) interconnected nanoparticles as well as 2D Ti3C2Tx sheets were bilaterally loaded on the inner and outer sides of HGF by a simple unipolar electrodeposition (UPED) method and a drop casting method, respectively. The obtained 3D freestanding m-WO3/Ti3C2Tx/HGF electrode exhibited an excellent specific capacitance of 573F g(-1) at 5 mV s(-1) with outstanding rate performance and 93.3% cycling stability over 5000 cycles, which can be attributed to the metal-like conductivity and reversible redox reactions of hydrophilic 2D Ti3C2Tx. The asymmetric solid-state supercapacitor (ASC) illustrated a 2-fold wider potential of 1.4 V in an acidic electrolyte when compared with the MXene-based symmetric supercapacitor. It displayed an excellent specific capacitance of 145.2F g(-1) (111.3 mF cm(-2)) at 5 mV s(-1), an ultra-high energy density of 27.2 Wh kg(-1) (20.83 mu Wh cm(-2)) at a power density of 752 W kg(-1) along with 93% cycling stability over 10,000 cycles. Therefore, such a m-WO3/Ti-3 C2Tx/HGF electrode should be promising for the fabrication of advanced supercapacitors.