The food processing industry generates substantial quantities of (poly)saccharide-rich waste. However, they are often underutilized. This study deals with the potential of leveraging by-products from the sugar-producing industry as cellulose source and precursor for activated carbons, specifically for electrochemical applications. The change to an eco-friendlier energy system requires the development of renewable energy storage materials, making cellulose-rich side streams a crucial component of this transition.
In this work we focus on two supercapacitor components based on bioproducts: Porous cellulose separators and electrodes made from biobased activated carbons. Porosity induced separators were produced by two different approaches: (1) bacterial cellulose films grown on molasses and used as nanocellulose separator and (2) beet pulp was mixed in different ratios with prehydrolysed kraft pulp, dissolved in 1,5-diaza-bicyclo[4.3.0]non-5-enium acetate ([DBNH][OAc]) and regenerated in a water bath. The separators were characterized by their thermal and chemical stability. In addition, the porosity, pore size distribution and wettability were determined. Beet pulp was carbonized and KOH-activated at elevated temperatures to produce activated carbon. The carbons were characterized by SEM, TEM, Raman spectroscopy, gas sorption, elemental analysis, and XPS. All materials exhibit a pore size distribution which is advantageous for supercapacitors when used with aqueous electrolytes.
The performance of the supercapacitors was tested using 1 M H₂SO₄ as an electrolyte. Electrochemical characterization was carried out via cyclic voltammetry, galvanostatic charge-discharge experiments and electrochemical impedance spectroscopy. The results were compared to commercially available separators and activated carbon, with our material outperforming the commercial one by around 100%, with 193 F/g (at 20 mV/s).

By substituting petroleum-based materials, we were able to outperform the commercial reference by about 100%. This does not only lead to a potential new source of revenue in the high price segment for the food-based industry, but also supports the transition towards a more eco-friendly energy system.

Stefan Spirk

Graz University of Technology

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