Effect of ball milling on electrochemical characteristics of walnut shell-based carbon electrodes for EDLCs

Walnut shell-based activated carbons (WS-ACs) were prepared by chemical activation with KOH and used as an electrode material for electrical double layer capacitors (EDLCs). The WS-AC samples were characterized before and after ball milling for 8 h to assess their electrochemical characteristics as carbon electrodes for EDLCs. Nitrogen adsorption analyses showed that the Brunauer–Emmett–Teller (BET) surface areas of the WS-ACs were decreased to approximately 10% of their original value after ball milling. However, their capacitances were slightly increased and their other electrochemical properties such as impedance and charge/discharge stability were improved. Pore size distribution analysis revealed that whereas most of the micropores were destroyed, a considerable number of mesopores in the size range of 2–10 nm were formed by ball milling. Furthermore, X-ray photoelectron spectroscopy (XPS) analysis confirmed a 10% increase in the graphite content after ball milling.

Pore size distribution and specific capacitances of WS-1/4 before and after ball milling.Figure optionsDownload as PowerPoint slideHighlights
► Walnut shell-based activated carbons (ACs) are prepared by KOH activation.
► The prepared ACs are ball milled to fabricate EDLC electrodes.
► The electrochemical properties of ball milled ACs are considerably improved.
► Nitrogen adsorption and XPS analyses clarify properties of activated carbons.
► The formation of mesopores and graphitic sites are main reasons for improvement.