Cellulose Nanocrystals Based Flexible Substrates as Electrodes for Zn Batteries and Tribolayer in Triboelectric Nanogenerators (TENG) Devices

Nanocellulose is a promising polymer for applications in energy and electronic devices due to its biodegradable nature and properties. Among nanocelluloses, cellulose nanocrystals (CNC) are the most crystalline than bacterial cellulose and cellulose nanofibrils. Sulfate groups on CNC surfaces make them suitable for use as dispersants. In the presented work, a novel method of exfoliating MoS₂ in water using CNC and the use of exfoliated MoS₂ as an electrode in battery application is presented. In detail, electrodes are prepared from exfoliated MoS₂ (active material)-Cellulose Nano Crystals- (binder) with carbon nanotubes (electron-conducting support) and used in a Zinc battery half-cell that demonstrated a coulombic efficiency of 90%. Successful exfoliation of layered MoS₂into nanosheets is performed by sonicating Bulk MoS₂ with sulfated cellulose nanocrystals (CNC) for 4 hours. In addition to Raman and TEM confirmation, the Raman signals for exfoliated MoS₂ show a blue shift of both A¹_g and E¹_2g bands, suggesting CNC-induced lattice strain on nanosheets. The resulting stable water suspension shows no tendency for precipitation after two months of standing. The zeta potential, ζ, for sodium sulfated CNC (CNC-OSO₃Na)-MoS₂ in water suspension is observed as -45 mV, whereas sulfated CNC (CNC-OSO₃H)-MoS₂ in water suspension had a zeta potential of – 35 mV. CNC in the sodium form showed micelle characteristics like sodium dodecyl sulfate (SDS), with a critical aggregation concentration (CAC) of 1.1 wt%. Using CNCs at CAC efficiently exfoliated MoS₂ at a much lower concentration than has been reported for synthetic surfactants like SDS and CTAB (Cetyl trimethyl ammonium bromide). In addition to application in energy storage devices, flexible CNC films were also utilized to fabricate triboelectric nanogenerators (TENG). As CNCs are highly crystalline and to make them flexible, a plasticizer is optimized with a concentration of less than 13.5 wt% to maintain its recyclability. Flexible CNC films as a tribo-positive layer shows an output voltage of 120-200 V.<br/><br/><b>References </b><br/><br/>Sonker et al. Exfoliated MoS₂ Nanosheet/Cellulose Nanocrystal Flexible Composite Films as Electrodes for Zinc Batteries, ACS Applied Nano Materials 2023 6 (10), 8270-8278, DOI: 10.1021/acsanm.3c00543<br/>Sonker et al. Fabrication of flexible substrates from cellulose nanocrystal suspensions for application in Triboelectric nanogenerator (TENG) devices (unpublished work)