The use of rice husk ash, an agricultural-waste-derived feedstock, a potentially greener route to ZnO and activated carbon from unripe plantain peel was considered in the synthesis of ZnO-AC nanocomposite material for electrodes. The ZnO-AC (activated carbon) nanocomposite was prepared in different ratios of as-synthesized ZnO and AC to ascertain the optimum electrode material. The nanocomposites were characterized by scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), and Brunauer-Emmett-Teller analysis (BET) (Micromeritics Instrument Corporation, Norcross, GA, USA). In addition, the electrochemical properties of the prepared nanocomposite electrodes were investigated using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) in 6 M KOH as the electrolyte in a three-electrode setup with nickel foam current collector. The as-prepared ZnO–AC nanocomposite electrodes with ratios of (1:1, 2:1, 3:1, and 4:1) had specific capacitance of 322 F g−1, 113 F g−1, 46.7 F g−1, and 40.7 F g−1 at 5 mV s−1, respectively. The electrochemical performance of the ZnO/activated carbon composites is strongly influenced by the ZnO-to-activated carbon ratio. The comparative kinetic investigation proves that electrode performance of the composite material was not governed solely by the quantity of pseudocapacitive zinc oxide added, but rather by the preservation of continuous electronic and ionic percolation pathways. Among the investigated compositions (1:1, 2:1, 3:1 and 4:1), the 1:1 ZnO-AC composite exhibited the optimal structural threshold as it maintains an unblocked porous carbon network for fast ion diffusion (Rd2 (finite-length diffusion resistance) = 0.5597 Ω), maximizes pseudocapacitive site utilization without inducing interfacial polarization (R2 (charge-transfer resistance) = 4.824 Ω), it synergizes EDLC and pseudocapacitive kinetics (b = 0.58) and delivered the highest specific capacitance from both CV (322 F g−1) at scan rate of 5 mV/s and GCD (227.56 F g−1) at current density of 1 A g−1 All the composites maintained good coulombic efficiency around unity and reasonable stability after 3000 cycles.
- Open Access
- Article
Optimization of ZnO-AC Nanocomposite Electrodes for Supercapacitor Applications
- Prosper Ifeanyichukwu Oghome 1,
- Innocent Sunday Ike 1,2,*,
- Eric Egwu Kalu 3,
- Felicia Lebechukwu Kamen 1,
- Samson Olufisayo Olubiyi 1,
- Mesfin Abayneh Kebede 4 and
- Abdulhakeem Bello 5
Author Information
Received: 11 September 2026 | Revised: 14 October 2026 | Accepted: 28 October 2026 | Published: 12 November 2026
Abstract
Keywords
rice husk | zinc oxide | activated carbon | specific capacitance | stability and coulombic efficiency
References
- 1.
Miller, J.R.; Simon, P. The Chalkboard: Fundamentals of Electrochemical Capacitor Design and Operation. Electrochem. Soc. Interface 2008, 17, 31–32. https://doi.org/10.1149/2.f02081if.
- 2.
Mensah-Darkwa, K.; Zequine, C.; Kahol, P.K.; et al. Supercapacitor Energy Storage Device Using Biowastes: A Sustainable Approach to Green Energy. Sustainability 2019, 11, 414. https://doi.org/10.3390/su11020414.
- 3.
Poonam; Sharma, K.; Arora, A.; et al. Review of supercapacitors: Materials and devices. J. Energy Storage 2019, 21, 801–825. https://doi.org/10.1016/j.est.2019.01.010.
- 4.
Simon, P.; Gogotsi, Y. Materials for electrochemical capacitors. Nat. Mater. 2008, 7, 845–854. https://doi.org/10.1038/nmat2297.
- 5.
Frackowiak, E.; Khomenko, V.; Jurewicz, K.; et al. Supercapacitors based on conducting polymers/nanotubes composites. J. Power Sources 2006, 153, 413–418. https://doi.org/10.1016/j.jpowsour.2005.05.030.
- 6.
Dissanayake, K.; Kularatna-Abeywardana, D. A review of supercapacitors: Materials, technology, challenges, and renewable energy applications. J. Energy Storage 2024, 96, 112563. https://doi.org/10.1016/j.est.2024.112563.
- 7.
Miller, E.E.; Hua, Y.; Tezel, F.H. Materials for energy storage: Review of electrode materials and methods of increasing capacitance for supercapacitors. J. Energy Storage 2018, 20, 30–40. https://doi.org/10.1016/j.est.2018.08.009.
- 8.
Gorgulu, S.C.; Yazar, I.; Karakoc, T.H. Review of supercapacitor technology and applications. J. Mechatron. Artif. Intell. Eng. 2024, 5, 131–143. https://doi.org/10.21595/jmai.2024.24103.
- 9.
Tshiani, C.T.; Umenne, P. The Impact of the Electric Double-Layer Capacitor (EDLC) in Reducing Stress and Improving Battery Lifespan in a Hybrid Energy Storage System (HESS) System. Energies 2022, 15, 8680. https://doi.org/10.3390/en15228680.
- 10.
Kumar, Y.; Sharma, S.; Pullabhotla, V.R. Electrochemical Characterizations of Electrode Materials for Supercapacitors. Mater. Int. 2025, 7, 10. https://doi.org/10.33263/materials71.010.
- 11.
Liu, H.; Zhang, L. Pore-structure control of porous carbon electrode materials and energy-storage performance in water-in-salt electrolytes. J. Electroanal. Chem. 2024, 961, 118233. https://doi.org/10.1016/j.jelechem.2024.118233.
- 12.
Noukelag, S.K.; Mohamed, H.E.A.; Moussa, B.; et al. Investigation of structural and optical properties of biosynthesized Zincite (ZnO) nanoparticles (NPs) via an aqueous extract of Rosmarinus officinalis (rosemary) leaves. MRS Adv. 2020, 5, 2349–2358. https://doi.org/10.1557/adv.2020.220.
- 13.
Forouzandeh, P.; Kumaravel, V.; Pillai, S.C. Electrode Materials for Supercapacitors: A Review of Recent Advances. Catalysts 2020, 10, 969. https://doi.org/10.3390/catal10090969.
- 14.
Sharma, R.K.; Rastogi, A.C.; Desu, S.B. Manganese oxide embedded polypyrrole nanocomposites for electrochemical supercapacitor. Electrochim. Acta 2008, 53, 7690–7695. https://doi.org/10.1016/j.electacta.2008.04.028.
- 15.
Selvakumar, M.; Krishna Bhat, D.; Aggarwal, A.M.; et al. Nano ZnO-activated carbon composite electrodes for supercapacitors. Phys. B Condens. Matter 2010, 405, 2286–2289. https://doi.org/10.1016/j.physb.2010.02.028.
- 16.
Pradeep, M.; Panwar, N.L.; Divyangkumar, N. Torrefaction of agricultural biomass: A state-of-the-art review on transforming waste into clean energy. Energy 360 2025, 3, 100023. https://doi.org/10.1016/j.energ.2025.100023.
- 17.
Samage, A.; Halakarni, M.; Yoon, H.; et al. Sustainable conversion of agricultural biomass waste into electrode materials with enhanced energy density for aqueous zinc-ion hybrid capacitors. Carbon 2024, 219, 118774. https://doi.org/10.1016/j.carbon.2023.118774.
- 18.
Ngom, I.; Ndiaye, N.M.; Fall, A.; et al. On the Use of Moringa Oleifera Leaves Extract for the Biosynthesis of NiO and ZnO Nanoparticles. MRS Adv. 2020, 5, 1145–1155. https://doi.org/10.1557/adv.2020.212.
- 19.
Yadav, M.S.; Singh, N.; Bobade, S.M. Zinc oxide nanoparticles and activated charcoal-based nanocomposite electrode for supercapacitor application. Ionics 2018, 24, 3611–3630. https://doi.org/10.1007/s11581-018-2527-1.
- 20.
Raja, V.; Selvan, G.; Anbarasu, R.; et al. Green synthesis of zinc oxide nanoparticles using Hyptis leaf extract and Activated carbon based Zinc oxide composite of Supercapacitor Applications. Indian J. Sci. Technol. 2019, 12, 107–108. https://doi.org/10.17485/ijst/2019/v12i40/148040.
- 21.
Mohamed, I.M.A.; Yasin, A.S.; Liu, C. Synthesis, surface characterization and electrochemical performance of ZnO @ activated carbon as a supercapacitor electrode material in acidic and alkaline electrolytes. Ceram. Int. 2020, 46, 3912–3920. https://doi.org/10.1016/j.ceramint.2019.10.119.
- 22.
Gorgulu, S.C.; Yazar, I.; Karakoc, T.H. Energy storage technologies and their combinational usage in micro/mini unmanned aerial vehicles: A review. J. Mechatron. Artif. Intell. Eng. 2024, 5, 72–88. https://doi.org/10.21595/jmai.2024.24104.
- 23.
Taer, E.; Taslim, R.; Aini, Z.; et al. Activated carbon electrode from banana-peel waste for supercapacitor applications. In Proceedings of the 6th International Conference on Theoretical and Applied Physics (The 6th ICTAP), Makassar, Indonesia, 19–21 September 2016; Vol. 1801, p. 040004. https://doi.org/10.1063/1.4973093.
- 24.
Wang, Y.; Wu, X.; Han, Y.; et al. Flexible supercapacitor: Overview and outlooks. J. Energy Storage 2021, 42, 103053. https://doi.org/10.1016/j.est.2021.103053.
- 25.
Saka, C.; Levent, A. Fabrication of nitrogen and ZnO doped on carbon particles obtained from waste biomass and their use as supercapacitor electrodes for energy storage. Int. J. Hydrogen Energy 2024, 90, 1070–1083. https://doi.org/10.1016/j.ijhydene.2024.10.061.
- 26.
Madhu, R.; Veeramani, V.; Chen, S.M.; et al. Functional porous carbon–ZnO nanocomposites for high-performance biosensors and energy storage applications. Phys. Chem. Chem. Phys. 2016, 18, 16466–16475. https://doi.org/10.1039/c6cp01285j.
- 27.
Öziç, C.; Baran, M.F.; Levent, A.; et al. Green synthesis and electroanalytical characterization of Ocimum basilicum-functionalized ZnO nanoparticles for supercapacitor electrode applications. Microchem. J. 2026, 227, 118675. https://doi.org/10.1016/j.microc.2026.118675.
- 28.
Aslan, K.S.; Ertaş, E.; Baran, M.F.; et al. Enhanced Electrochemical Performance of Supercapacitors Using Fe3O4-Doped Biomass-Derived Activated Carbon Electrodes. Electrochem. Sci. Adv. 2026, 6, e70014. https://doi.org/10.1002/elsa.70014.
- 29.
Aruchamy, K.; Nagaraj, R.; Manohara, H.M.; et al. One-step green route synthesis of spinel ZnMn2O4 nanoparticles decorated on MWCNTs as a novel electrode material for supercapacitor. Mater. Sci. Eng. B 2020, 252, 114481. https://doi.org/10.1016/j.mseb.2019.114481.
- 30.
Ma, Y.; Yin, J.; Liang, H.; et al. A two step approach for making super capacitors from waste wood. J. Clean. Prod. 2021, 279, 123786. https://doi.org/10.1016/j.jclepro.2020.123786.
- 31.
Palavai, S.S.; Awasthi, H.; Goel, S. Scalable hematite based symmetric supercapacitor with high capacitance for energy storage applications. Front. Batter. Electrochem. 2026, 5, 1795529. https://doi.org/10.3389/fbael.2026.1795529.
- 32.
Liu, Z.; Ye, D.; Zhu, X.; et al. ZIF-67-derived Co nanoparticles embedded in N-doped porous carbon composite interconnected by MWCNTs as highly efficient ORR electrocatalysts for a flexible direct formate fuel cell. Chem. Eng. J. 2022, 432, 134192. https://doi.org/10.1016/j.cej.2021.134192.
- 33.
Zhang, L.; Shi, D.; Liu, T.; et al. Nickel-based materials for supercapacitors. Mater. Today 2019, 25, 35–65. https://doi.org/10.1016/j.mattod.2018.11.002.
- 34.
An, C.; Zhang, Y.; Guo, H.; et al. Metal oxide-based supercapacitors: Progress and prospectives. Nanoscale Adv. 2019, 1, 4644–4658. https://doi.org/10.1039/c9na00543a.
- 35.
Xiao, S.; Huang, J.; Lin, C.; et al. Porous carbon derived from rice husks as sustainable bioresources: Insights into the role of micro/mesoporous hierarchy in Co3O4/C composite for asymmetric supercapacitors. Microporous Mesoporous Mater. 2020, 291, 109709. https://doi.org/10.1016/j.micromeso.2019.109709.
- 36.
Dong, Y.; Wang, Y.; Xu, Y.; et al. Facile synthesis of hierarchical nanocage MnCo2O4 for high performance supercapacitor. Electrochim. Acta 2017, 225, 39–46. https://doi.org/10.1016/j.electacta.2016.12.109.
- 37.
Salunkhe, R.R.; Kaneti, Y.V.; Yamauchi, Y. Metal–Organic Framework-Derived Nanoporous Metal Oxides toward Supercapacitor Applications: Progress and Prospects. ACS Nano 2017, 11, 5293–5308. https://doi.org/10.1021/acsnano.7b02796.
- 38.
Wang, F.; Wu, X.; Yuan, X.; et al. Latest advances in supercapacitors: From new electrode materials to novel device designs. Chem. Soc. Rev. 2017, 46, 6816–6854. https://doi.org/10.1039/c7cs00205j.
- 39.
Kuo, T.R.; Lin, L.Y.; Kubendhiran, S.; et al. Novel incorporation of redox active organic molecule with activated carbon as efficient active material of supercapacitors. J. Energy Storage 2022, 53, 105085. https://doi.org/10.1016/j.est.2022.105085.
- 40.
Zhang, W.; Pan, Y.; Wang, H.; et al. Preparation and Characterization of High-Performance Fe3O4/RGO Anode for Supercapacitors. J. Electron. Mater. 2023, 52, 6107–6120. https://doi.org/10.1007/s11664-023-10552-1.
- 41.
Potham, S.; Ramanujam, K. A novel hierarchical porous activated carbon-organic composite cathode material for high performance aqueous zinc-ion hybrid supercapacitors. J. Power Sources 2023, 557, 232551. https://doi.org/10.1016/j.jpowsour.2022.232551.
- 42.
Saka, C.; Levent, A. High-performance pseudo-capacitance supercapacitor with highly mesoporous fluorine doped polymeric carbon nitride nanosheets as electrode material. Diam. Relat. Mater. 2024, 148, 111504. https://doi.org/10.1016/j.diamond.2024.111504.
- 43.
Gouda, M.S.; Shehab, M.; Helmy, S.; et al. Nickel and cobalt oxides supported on activated carbon derived from willow catkin for efficient supercapacitor electrode. J. Energy Storage 2023, 61, 106806. https://doi.org/10.1016/j.est.2023.106806.
- 44.
Ozpinar, P.; Dogan, C.; Demiral, H.; et al. Activated carbons prepared from hazelnut shell waste by phosphoric acid activation for supercapacitor electrode applications and comprehensive electrochemical analysis. Renew. Energy 2022, 189, 535–548. https://doi.org/10.1016/j.renene.2022.02.126.
- 45.
Adan-Mas, A.; Alcaraz, L.; Arévalo-Cid, P.; et al. Coffee-derived activated carbon from second biowaste for supercapacitor applications. Waste Manag. 2021, 120, 280–289. https://doi.org/10.1016/j.wasman.2020.11.043.
- 46.
Raj, C.J.; Manikandan, R.; Rajesh, M.; et al. Cornhusk mesoporous activated carbon electrodes and seawater electrolyte: The sustainable sources for assembling retainable supercapacitor module. J. Power Sources 2021, 490, 229518. https://doi.org/10.1016/j.jpowsour.2021.229518.
- 47.
Xu, C.H.; Shen, P.Y.; Chiu, Y.F.; et al. Atmospheric pressure plasma jet processed nanoporous Fe2O3/CNT composites for supercapacitor application. J. Alloys Compd. 2016, 676, 469–473. https://doi.org/10.1016/j.jallcom.2016.03.185.
- 48.
Guan, D.; Gao, Z.; Yang, W.; et al. Hydrothermal synthesis of carbon nanotube/cubic Fe3O4 nanocomposite for enhanced performance supercapacitor electrode material. Mater. Sci. Eng. B 2013, 178, 736–743. https://doi.org/10.1016/j.mseb.2013.03.010.
This work is licensed under a Creative Commons Attribution 4.0 International License.
