Citation: Sajjad, M.; Khan, A.J.; Eldin, S.M.; Alothman, A.A.; Ouladsmane, M.; Bocchetta, P.; Arifeen, W.U.; Javed, M.S.; Mao, Z. A New CuSe-TiO 2 -GO Ternary Nanocomposite: Realizing a High Capacitance and Voltage for an Advanced Hybrid Supercapacitor. Nanomaterials 2023, 13, 123. https:// doi.org/10.3390/nano13010123 Academic Editor: Pedro Gómez-Romero Received: 28 November 2022 Revised: 8 December 2022 Accepted: 21 December 2022 Published: 26 December 2022 Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). nanomaterials Article A New CuSe-TiO 2 -GO Ternary Nanocomposite: Realizing a High Capacitance and Voltage for an Advanced Hybrid Supercapacitor Muhammad Sajjad 1 , Abdul Jabbar Khan 2 , Sayed M. Eldin 3 , Asma A. Alothman 4 , Mohamed Ouladsmane 4 , Patrizia Bocchetta 5 , Waqas Ul Arifeen 6 , Muhammad Sufyan Javed 7, * and Zhiyu Mao 1, * 1 College of Chemistry and Life Sciences, Zhejiang Normal University, Jinhua 321004, China 2 College of Chemistry and Chemical Engineering, Huanggang Normal University, Huangggang 438000, China 3 Faculty of Engineering and Technology, Future University in Egypt, New Cairo 11835, Egypt 4 Department of Chemistry, College of Science, King Saud University, Riyadh 11451, Saudi Arabia 5 Dipartimento di Ingegneria dell’Innovazione, Università del Salento, Via Monteroni, 73100 Lecce, Italy 6 School of Mechanical Engineering, Yeungnam University, Daehak-ro, Gyeongsan-si 38541, Gyeongbuk-do, Republic of Korea 7 School of Physical Science and Technology, Lanzhou University, Lanzhou 730000, China * Correspondence: safisabri@gmail.com (M.S.J.); zhymao@zjnu.edu.cn (Z.M.) Abstract: A high capacitance and widened voltage frames for an aqueous supercapacitor system are challenging to realize simultaneously in an aqueous medium. The severe water splitting seriously restricts the narrow voltage of the aqueous electrolyte beyond 2 V. To overcome this limitation, herein, we proposed the facile wet-chemical synthesis of a new CuSe-TiO 2 -GO ternary nanocomposite for hybrid supercapacitors, thus boosting the specific energy up to some maximum extent. The capacitive charge storage mechanism of the CuSe-TiO 2 -GO ternary nanocomposite electrode was tested in an aqueous solution with 3 M KOH as the electrolyte in a three-cell mode assembly. The voltammogram analysis manifests good reversibility and a remarkable capacitive response at various currents and sweep rates, with a durable rate capability. At the same time, the discharge/charge platforms realize the most significant capacitance and a capacity of 920 F/g (153 mAh/g), supported by the impedance analysis with minimal resistances, ensuring the supply of electrolyte ion diffusion to the active host electrode interface. The built 2 V CuSe-TiO 2 -GO||AC-GO||KOH hybrid supercapacitor accomplished a significant capacitance of 175 F/g, high specific energy of 36 Wh/kg, superior specific power of 4781 W/kg, and extraordinary stability of 91.3% retention relative to the stable cycling performance. These merits pave a new way to build other ternary nanocomposites to achieve superior performance for energy storage devices. Keywords: CuSe; aqueous electrolyte; power density; energy density; impedance 1. Introduction With the development of modern civilization, massive industrialization gives birth to huge carbon dioxide emissions, which cause serious environmental problems, such as global warming, air pollution, and the emission of toxic chemicals into the environ- ment [1–3]. The poor energy density of supercapacitors can be optimized in two ways: either by increasing the capacitance or expanding the voltage frame of the symmet- ric/asymmetric/hybrid supercapacitors, as energy is related to the following expres- sion [4,5]: E = 1 2 C × V 2 . The schematic, as given in Figure 1, presents the illustration of the expansion of the voltage gap in this work by the theoretical model. The electrolysis process paves a pivotal role in an aqueous supercapacitor. The voltage frame is limited due to the severe water splitting at 1.23 V 2 [6–8], which can be boosted by optimizing the hydrogen evolution reaction (HER) that occurs on the positive electrode and the oxygen evolution reaction (OER) on the negative electrode in the KOH aqueous solution. This Nanomaterials 2023, 13, 123. https://doi.org/10.3390/nano13010123 https://www.mdpi.com/journal/nanomaterials