Abstract
Biorefineries produce impure sugar waste streams that are being underutilized. By converting this waste to a profitable by-product, biorefineries could be safeguarded against low oil prices. We demonstrate controlled production of useful carbon materials from the waste concentrate via hydrothermal synthesis and carbonization. We devise a pathway to producing tunable, porous spherical carbon materials by modeling the gross structure formation and developing an understanding of the pore formation mechanism utilizing simple reaction principles. Compared to a simple hydrothermal synthesis from sugar concentrate, emulsion-based synthesis results in hollow spheres with abundant microporosity. In contrast, conventional hydrothermal synthesis produces solid beads with micro and mesoporosity. All the carbonaceous materials show promise in energy storage application. Using our reaction pathway, perfect hollow activated carbon spheres can be produced from waste sugar in liquid effluence of biomass steam pretreatment units. The renewable carbon product demonstrated a desirable surface area of 872 m2/g and capacitance of up to 109 F/g when made into an electric double layer supercapacitor. The capacitor exhibited nearly ideal capacitive behavior with 90.5% capacitance retention after 5000 cycles.
Highlights
Over the last decade, there has been growing interest in tailoring carbon sphere structures for different applications in renewable energy sectors
The aggregated chains, form spherical, micelle-like structures with a hydrophobic core and hydrophilic corona[28]. This evolution mechanism of the spherical carbonaceous aggregates was perfectly captured by scanning electron microscopy (SEM) [Fig. 1(b–d)] with our water-based hydrothermal carbonization (HTC) synthesis
thermogravimetric analysis (TGA) results show that carbon yield during high temperature carbonization increases as the HTC duration increases
Summary
There has been growing interest in tailoring carbon sphere structures for different applications in renewable energy sectors. Supercapacitors store energy based on two different principles: EDL capacitance from the pure electrostatic charge accumulation at the electrode interface, and (2) the pseudo-capacitance based on fast and reversible redox processes at characteristic potentials[17]. While previous studies have shown the possibility of producing carbon spheres from carbohydrates and even acid or alkaline pretreated biomass-derived hydrolyzed hemicellulose using HTC, detailed understanding on the structural evolution with respect to the hydrothermal reaction media is not fully understood[3,7,11,24]. After establishing that perfectly hollow carbon spheres can be made from pretreatment liquid effluence, we explored the potential application of our model material as supercapacitor electrodes. This study exhibits a pathway to design sustainable energy storage materials from the waste stream of a future biorefinery
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