University of Maryland, College Park,
Keywords: cellulose nanofibers, flexible electronics, photonics, energy storage, green materials
Summary:I will discuss our recent results of novel cellulose based nanostructures with tailored optical and mechanical properties, and applications in flexible electronics, origami devices and solar cells. I will also discuss the fundamental advantages of using mesoporous, soft wood fibers for beyond-Li ion batteries. RESULTS AND DISCUSSION Fig. 1 shows the hierarchical structure of wood cellulose. The microsized primary cellulose fibers are made of many smaller elementary fibers with a diameter less than 10 nanometers and length up to 1 μm. The building blocks with different dimensions give us much flexibility in designing nanostructures. Transparent wood was realized for the first time which is directly fabricated from natural wood via a simple and scalable two-step process, namely lignin removal and polymer infiltration (Fig. 2). The complete removal of lignin results a low absorptivity of visible range light while the optical refractive index matching polymer infiltration further reduces light scattering at the interface at wood lumen walls. The resulting transparent wood yields a transmittance over 85% within visible range. We have also demonstrated a range of flexible and biodegradable electronics on smooth and optically transparent paper. A highly transparent transistors is shown in Fig. 3. We have recently demonstrated a novel construction strategy of an all-wood-structured asymmetric supercapacitor based on activated wood carbon anode, thin wood membrane separator and MnO2/wood carbon cathode (Fig 4). The unique structural merits of the carbonized wood include multi channels along the tree growth direction, low tortuosity, high ionic and electronic conductivities and high structure stability without the concern of electrode deformation. The all-wood-structured ASC device exhibits a high areal capacitance, high energy/power densities and long cycling life even using highly loaded electrodes. ACKNOWLEDGMENT We acknowledge the AFOSR YIP program, DOE EFRC, 3M non-tenured faculty awards and NSF-1362256. REFERENCES 1. Fang, Z. et al. Novel Nanostructured Paper with Ultrahigh Transparency and Ultrahigh Haze for Solar Cells, Nano Letters, 2014, 14, 765 2. Zhu, H. et al. Transparent Nanopaper with Tailored Optical Properties, Nanoscale, 2013, 5, 3787 3. Zhu, H. et al. Anomalous Scaling Law of Mechanical Properties of Cellulose, PNAS, Accepted. 4. Huang, J. et al. Highly Transparent and Flexible Nanopaper Transistors, ACS Nano 2013, 7, 2106. 5. Zhu, H. et al. Tin Anode for Sodium-Ion Batteries Using Natural Wood Fiber as a Mechanical Buffer and Electrolyte Reservoir, Nano Letters, 2013, 13, 3093. 6. Zhu, M, et al. “Highly Anisotropic, Highly Transparent Wood Composites.” Advanced Materials 28 (26): 5181–87. 2016. 7. Chen, Chaoji, et al. "All-wood, Low Tortuosity, Aqueous, Biodegradable Supercapacitors with Ultra-High Capacitance." Energy & Environmental Science (2017).