Methyl Orange-Doped Polypyrrole Promoting Growth of ZIF-8 on Cellulose Fiber with Tunable Tribopolarity for Triboelectric Nanogenerator.

Cellulose fiber (CelF) is a biodegradable and renewable material with excellent performance but negligible triboelectric polarizability. Methods to enhance and rationally tune the triboelectric properties of CelF are needed to further its application for energy harvesting. In this work, methyl-orange-doped polypyrrole (MO-PPy) was in situ coated on CelF as a mediating layer to promote the growth of metal-organic framework ZIF-8 and to construct a cellulose-based triboelectric nanogenerator (TENG). The results showed that a small amount of MO-PPy generated in situ significantly promoted the growth of ZIF-8 on CelF, and the ZIF-8 deposition ratio was able to increase from 7.8% (ZIF-8/CelF) to 31.8% (ZIF-8/MO-PPy@CelF). ZIF-8/MO-PPy@CelF remained electrically conductive and became triboelectrically positive, and the triboelectricity's positivity was improved with the increase in the ZIF-8 deposition ratio. The cellulose-based TENG constructed with ZIF-8/MO-PPy@CelF (31.8% ZIF-8 deposition ratio) and polytetrafluoroethylene (PTFE) could generate a transfer charge of 47.4 nC, open-circuit voltage of 129 V and short-circuit current of 6.8 μA-about 4 times higher than those of ZIF-8/CelF (7.8% ZIF-8 deposition ratio)-and had excellent cycling stability (open-circuit voltage remained almost constant after 10,000 cycles). MO-PPy not only greatly facilitated the growth of ZIF-8 on CelF, but also acted as an electrode active phase for TENG. The novel TENG based on ZIF-8/MO-PPy@CelF composite has cheerful prospects in many applications, such as self-powered supercapacitors, sensors and monitors, smart pianos, ping-pong tables, floor mats, etc.