(Keynote) 2D+1D and 2D+0D Hybrid Nanostructures and Their Applications in Electrochemical Energy Storage

Flexible and binder-free hybrid materials can be prepared by combining nanosheets of graphene, graphene oxide, MXenes (two-dimensional transition metal carbides) and other 2D materials with carbon onions, carbon black, porous carbide-derived carbon nanoparticles, and nanotubes. This helps to overcome the tendency of 2D sheets to restack, which minimizes their surface area accessible to the electrolyte and hinders their overall performance in electrochemical applications. Nanospacers such as carbon nanotubes (CNTs) are often introduced between reduced graphene oxide (rGO) sheets to enhance the electrolyte accessibility and electronic conductivity of the film. However, there are opportunities to use other 2D nanosheet-nanoparticle combinations that provide the desired set of properties due to synergistic effects of the nanoparticles. A brief overview of the carbon-carbon and carbon-carbide hybrids will be provided in this talk. We have demonstrated fabrication of flexible, sandwich-like Ti3C2 MXene/CNT composite paper electrodes through alternating filtration of MXene and CNT dispersions. Spraying and other manufacturing methods can be used as well. Films containing onion- like carbon (OLC) and reduced graphene oxide (rGO) were also fabricated and compared with those with CNTs. The sandwich-like electrodes exhibited significantly improved electrochemical performance compared to those of pure MXene and randomly mixed MXene/CNT papers. Examples of Li-ion battery and electrochemical capacitor electrodes will be provided. We also used highly porous carbide derived carbon (CDC) nanoparticles as spacers between graphene sheets and prepared rGO-CDC hybrid electrodes. The electrodes were made by thermal reduction of GO-CDC paper produced by vacuum-assisted filtration of aqueous solutions of GO-CDC composite containing 10-20 wt.% of CDC. Taking advantage of the high surface area and conductivity of rGO and the accessible pores of the CDC, the hybrid electrodes showed specific capacitances as high as 200-210 F/g at a scan rate of 100 mV/s. The addition of CDC between the rGO layers enhances the accessibility of electrodes to the electrolyte ions and good performance of the electrodes with the thickness to 40-50 μm was observed.