Browsing by Author "Mitterer, Christian"

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    Coffee Waste-Derived Nanoporous Carbons for Hydrogen Storage
    (AMERICAN CHEMICAL SOCIETY, 2022-09-26) Stock, Sebastian; Kostoglou, Nikolaos; Selinger, Julian; Spirk, Stefan; Tampaxis, Christos; Charalambopoulou, Georgia; Steriotis, Theodore; Rebholz, Claus; Mitterer, Christian; Paris, Oskar; Department of Bioproducts and Biosystems; Biorefineries; University of Leoben; Demokritos National Centre for Scientific Research; University of Cyprus; Graz University of Technology
    Biological waste such as residues from the food and beverage industry provides a valuable and abundant resource to be used as a precursor for the synthesis of activated carbons that can be subsequently employed as adsorbents for, e.g., hydrogen storage. Materials with a large specific surface area and pores of appropriate size are necessary to achieve reasonable hydrogen adsorption capacity. Here, we present the repeatable synthesis of activated carbons from coffee waste, i.e., spent coffee grounds and coffee silver skins, on the basis of two independently synthesized batches. The carbonization process under nitrogen gas flow followed by chemical activation with solid potassium hydroxide results in microporous carbons with bimodal pore size distribution and specific surface area up to 3300 and 2680 m2/g based on Brunauer-Emmett-Teller and density functional theory methods, respectively. The materials exhibit excellent hydrogen adsorption performance under cryogenic conditions (77 K), reaching high and fully reversible excess gravimetric hydrogen uptake values of up to 5.79 wt % at 37 bar, and total capacities exceeding 9 wt % at 100 bar.
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    Nanoporous Carbon Electrodes Derived from Coffee Side Streams for Supercapacitors in Aqueous Electrolytes
    (MDPI AG, 2022-08) Selinger, Julian; Stock, Sebastian; Schlemmer, Werner; Hobisch, Mathias; Kostoglou, Nikolaos; Abbas, Qamar; Paris, Oskar; Mitterer, Christian; Hummel, Michael; Spirk, Stefan; Department of Bioproducts and Biosystems; Biorefineries; Biopolymer Chemistry and Engineering; University of Leoben; Graz University of Technology
    Coffee, as one of the most traded resources, generates a vast amount of biogenic by-products. Coffee silver skins (CSS), a side stream from the roasting process, account for about 4 wt.%. Despite the abundancy of CSS, possible routes to generate added value for broad applications are limited. Herein, we present an approach to use CSS as a precursor material for supercapacitor electrodes. KOH activated carbon (AC) was produced from CSS. The resulting AC—CSS was characterized by X-ray diffraction, gas sorption analysis, scanning electron microscopy, and Raman spectroscopy. The highly porous AC—CSS exposes a specific surface area of more than 2500 m2 g−1. Electrodes formed with AC—CSS were electrochemically characterized by performing cyclic voltammetry and galvanostatic cycling. The electrodes were further assembled into a supercapacitor device and operated using 1 M sulfuric acid as electrolyte. In addition, various quinones were added to the electrolyte and their impact on the capacitance of AC—CSS electrodes was analyzed. In this work, we were able to show that CSS are a valuable source for supercapacitor applications and that coffee-waste-derived quinones can act as capacitance enhancers. Thus, the findings of this research show a valuable path towards sustainable and green energy storage solutions.