ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Sustainable hydrothermal synthesis of NiMn₂O₄/ACWS nanocomposites derived from walnut shells for advanced supercapacitor applications

Muhammad Khan, B. M. Alotaibi, Albandari .W. Alrowaily, Haifa A. Alyousef, Abhinav Kumar, Hala M. Abo-Dief, and Rizwan Ul Hassan

Department of Physics, Government Graduate College, Taunsa Sharif, Pakistan

E-mail: Mkhanbaloch750@gmail.com

Received: 30 November 2025  Accepted: 9 June 2026

Abstract:

The synthesis of economical nanocomposites for energy preservation technologies, particularly supercapacitors, has drawn significant research interest. The use of biomass-derived carbon offers a more cost-effective and effective synthesis approach than expensive commercial carbon sources, making it suitable for extensive energy applications.In this study, active carbon obtained from walnut shells (ACWS) was synthesized through KOH activation, which was then combined with NiMn₂O₄, among the most beneficial spinel metal oxides, to evaluate electrode material’s effectiveness in energy conservation. NiMn₂O₄/ACWS showed specific capacitance (C_s) of 846.15 F g⁻¹, while investigation indicated energy density (E_d) of 18.42 Wh kg⁻¹ and high-power density (P_d) of 206 W kg⁻¹ at 1 A g⁻¹. A low solution resistance (R_s) value (0.74 Ω) seen in Nyquist diagram indicated remarkable conductivity of NiMn₂O₄/ACWS. Additionally, revealed remarkable stability in a KOH electrolyte (3.0 M KOH) throughout 3000^th cycles of cyclic voltammetry. An asymmetric two-electrode investigation was also carried out, and the results demonstrated an enhanced E_d of 57.51 Wh kg⁻¹ and P_d of 714 W kg⁻¹. Based on this study, NiMn₂O₄/ACWS is a viable and inexpensive electrode material for supercapacitor application in future.

Keywords: NiMn2O4/ACWS; Hydrothermal synthesis; Walnut shells; Activated carbon; Electrode materials

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-026-05196-4

Chemical Papers 80 (11) 13531–13544 (2026)