ZnCl2 assisted in-situ synthesis of ZIF-8/wood to prepare nitrogen-doped porous self-supporting carbon for supercapacitors

Abstract

MOF-wood supercapacitor electrodes inherit the merits of wood and MOF that have self-supporting and hierarchical structure, and chemical tunability and tailor-made functionalities. However, the mass loading of MOFs is inferior and the distribution is non-uniform ascribing to lack of active sites and poor compatibility between wood and MOFs. Herein, a novel, economy and safety “dissolution-in situ synthesis-regeneration” method was developed to obtain a homogeneous, highly loaded (36.86 %) and size-controlled ZIF-8 nanoparticles for growth in delignified wood. High concentration of ZnCl2 (75 wt%) was used to dissolve cellulose in the cell wall of delignified wood while anchoring Zn2+ in it, which became the nucleation site of ZIF-8, and after regeneration, a membrane encapsulated the ZIF-8 nanoparticles to form a pomegranate-like ZIF-8-wood carbon precursor, named ZIF-8@RW2. Subsequently, ZIF-8 were employed as sacrificial templates to fabricate N-doping carbon electrode (CZIF-8@RW2). A proof-of-concept study is demonstrated wherein freestanding CZIF-8@RW2 performs well in applications of electrode (5.62F/cm2, 374.4F/g, 10 mA/cm2) and symmetric supercapacitors (1.24 mWh/cm2, 7.68mWh/cm3, 46.35 Wh/kg). Therefore, the present study provides a generalized approach for the synthesis of Zn-MOF-wood composites with homogeneity and high loading in energy storage fields and other potential areas.