Isolation and Characterization of Cellulose Nanofibers from Wheat Straw and Their Application for the Supercapacitor

As a by-product of wheat planting, wheat straw is an abundant agricultural residue with the highest cellulose content of all agricultural fibers. Its resourceful utilization contributes to alleviating the environmental problems it caused. In this study, cellulose from wheat straw (WS) is used as a dispersing agent to prepare a novel multi-walled carbon nanotube-modified nickel foam (NF) electrode. The new electrode is investigated for electrochemical properties relevant to supercapacitors. The 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidation is chosen to produce cellulose nanofibers (CNF) from wheat straw. The prepared CNF is used to facilitate the uniform dispersion of multi-walled carbon nanotubes (MWCNT) and favor the formation of a stable CNF-CNTs membrane on the nickel foam skeleton. The influence of dispersing materials and content of CNF on the electrochemical performance of electrodes is investigated. It is revealed that the incorporation of CNF can improve the electrochemical stability of electrodes. Moreover, it also exhibits optimum capabilities (70.2% capacitance retention from 1 to 40 mA cm−2) when CNF:MWCNT = 1:0.7. The areal capacity of the CNF-MWCNT/NF electrode for a scanning rate of 5 mV s−1 is twice that of the MWCNT/NF electrode and 30 times that of the NF electrode, indicating it is a promising candidate to ensure the synchronization of a green environment and energy development.