Researchers at the intersection of materials science and energy storage have developed a flexible, solid-state supercapacitor using a novel trimetallic oxide-hydroxide material grown directly onto carbon cloth. The work addresses the growing need for energy-storage systems that can withstand mechanical deformation while maintaining stable electrochemical output, a critical requirement for the next generation of wearable technology and portable electronics.
The central finding of the study is that a Ce-Mn-Co trimetallic oxide-hydroxide electrode, synthesized with a 1:1:1 molar ratio of the three metals, achieves the highest areal specific capacitance among the tested compositions. This specific formulation, denoted as Ce1−Mn1Co1, was grown hydrothermally on a carbon cloth substrate, creating a binder-free electrode that leverages the conductive network of the carbon fibers.
The motivation for this research stems from the limitations of traditional energy-storage devices in flexible applications. As electronic devices become slimmer and more portable, the energy-storage components must provide a reliable power supply under various mechanical deformations. Flexible supercapacitors are promising candidates for these applications due to their rapid charge-discharge capability, long cycling stability, and high power density. However, the mechanical and electrochemical responses of flexible electrodes differ significantly from those of flexible electrolytes, requiring careful design of the active electrode materials to maximize energy density and overall performance.
Supercapacitors are generally classified into two types based on their energy-storage mechanisms: electric double-layer capacitors and pseudocapacitors. Electric double-layer capacitors primarily use carbon-based materials, offering excellent cycling stability and high power density but relatively low specific capacitance. In contrast, pseudocapacitors provide significantly higher theoretical capacitance and energy density through fast and reversible surface redox reactions, although their cycling stability is often lower. The study focuses on transition-metal oxides and their hybrid structures, which have received considerable attention as promising pseudocapacitive electrode materials due to their multiple oxidation states and rich redox chemistry.
The researchers selected cerium dioxide, cobalt oxide, and manganese oxide as the constituent components for the trimetallic electrode. Cerium dioxide is an attractive component due to its low toxicity, biocompatibility, and reversible redox couple, but its practical application is restricted by poor electrical conductivity and limited mechanical robustness. Cobalt oxide exhibits high theoretical capacitance and favorable electrochemical characteristics, while manganese-based materials offer high theoretical capacitance and strong surface adsorption characteristics. The combination of these three redox-active components was hypothesized to provide complementary electrochemical properties and multiple faradaic reaction pathways, potentially overcoming the individual limitations of each metal oxide.
The synthesis process involved a simple hydrothermal method to directly grow the Ce-Mn-Co trimetallic oxide-hydroxides on the carbon cloth. Four different precursor solutions with varying Ce:Mn:Co molar ratios were prepared and reacted in stainless-steel autoclaves at 100 degrees Celsius for two hours. The carbon cloth served as both a flexible, conductive substrate for the conformal growth of the active material and an effective current collector. This direct integration facilitates electron transport, improves electrolyte accessibility, and enhances the utilization of electrochemically active sites, which is crucial for the performance of flexible supercapacitors.
Morphological characterization using scanning electron microscopy revealed that the carbon fibers were coated with a thin film of particles after hydrothermal treatment. The particles exhibited irregular shapes and meso- and microporosity. X-ray photoelectron spectroscopy confirmed the presence of cerium, manganese, and cobalt in their respective oxidation states, including Ce4+, Ce3+, Mn2+, Mn4+, Co2+, and Co3+. X-ray diffraction patterns displayed only broad, graphite-like reflections, indicating a highly dispersed or amorphous state for the metal elements.
Electrochemical testing in a 1 M sodium sulfate electrolyte showed that the Ce1−Mn1Co1@CC electrode delivered a specific capacitance of 220.5 millifarads per square centimeter at a current density of 1.5 milliamperes per square centimeter. This value significantly surpassed the performance of the other tested compositions, such as Ce2−Mn1Co1@CC, which delivered 52.6 millifarads per square centimeter under the same conditions. Cyclic voltammetry curves for the Ce1−Mn1Co1@CC sample displayed no distinct redox peaks, characteristic of electric double-layer capacitor behavior, but the absence of distinct peaks also suggests a pseudocapacitive intercalation/deintercalation mechanism. The electrode exhibited a markedly lower charge-transfer resistance compared to the other electrodes, indicating superior interfacial charge transfer properties.
The assembly of the flexible quasi-solid-state symmetric supercapacitor involved using two identical Ce1−Mn1Co1@CC electrodes separated by a cellulose membrane and a polyvinyl alcohol/sodium sulfate gel electrolyte. The gel electrolyte was selected to provide a leakage-resistant and mechanically stable medium suitable for flexible device operation, despite having lower ionic conductivity than liquid electrolytes. The device demonstrated good mechanical flexibility, with cyclic voltammetry profiles remaining consistent under bending angles of 0, 45, and 180 degrees. This consistency confirms the durability and reliability of the supercapacitor for flexible device applications, indicating that its supercapacitive properties are resilient to mechanical deformation.
Long-term cycling stability tests revealed that the device retained 86% of its original capacitance after 10,000 cycles at a current density of 4 milliamperes per square centimeter. The galvanostatic charge-discharge profiles remained nearly unchanged after this extensive cycling, further evidencing robust performance. In a practical demonstration, three of these flexible supercapacitor devices were connected in series to illuminate red light-emitting diodes for 10 minutes, showcasing their potential for powering small electronic components in wearable or portable systems. These results highlight the synergistic combination of the trimetallic oxide-hydroxide with the carbon cloth substrate, which enhances electrical conductivity, facilitates rapid ion transport, and ensures superior structural stability.
The study underscores the importance of compositional engineering in developing high-performance pseudocapacitive electrodes. By incorporating multiple transition-metal species into a single oxide-hydroxide framework, the researchers were able to provide multiple redox-active centers and promote synergistic interactions among the constituent metal ions. This approach can modify the electronic structure, electrical conductivity, and ion-diffusion pathways of the resulting electrode, leading to enhanced electrochemical performance compared to single-metal oxides. The findings suggest that Ce-Mn-Co trimetallic oxide-hydroxides directly supported on carbon cloth are promising electrode materials for flexible solid-state supercapacitors, contributing to the advancement of next-generation flexible and wearable energy storage technologies.
The electrochemical characterization of the individual Ce1−Mn1Co1@CC electrode revealed a specific capacitance of 94 mF/cm² when measured via cyclic voltammetry at a scan rate of 10 mV/s. The cyclic voltammetry profiles remained consistent across this range of scan rates, indicating improved electron and ion transfer at the electrode-electrolyte interface. When the potential window was widened during these measurements, an oxygen-related peak emerged. The galvanostatic charge-discharge curves for the individual electrode displayed symmetrical profiles, supporting the conclusion that intercalation and deintercalation processes dominate the charge storage mechanism in the 1 M Na2SO4 electrolyte system.
Electrochemical impedance spectroscopy provided further insight into the interfacial properties of the modified electrodes. The Ce1−Mn1Co1@CC electrode exhibited a markedly lower charge-transfer resistance in the high-frequency region compared to the other tested compositions. This reduction in resistance indicates superior interfacial charge transfer properties, which contribute to the enhanced electrical conductivity of the electrode.
The selection of the Na2SO4 electrolyte was based on previous comparative studies of different electrolytes for related transition-metal oxide and hydroxide electrodes. In those prior investigations, Na2SO4 provided a favorable electrochemical response and good compatibility with the electrode materials, leading the researchers to adopt it in the present work to maintain optimized experimental conditions. For the flexible quasi-solid-state device, a PVA/Na2SO4 gel electrolyte was prepared by dissolving polyvinyl alcohol in distilled water and adding Na2SO4. Although the ionic conductivity of this gel electrolyte is lower than that of the corresponding liquid electrolyte, it was chosen to provide a leakage-resistant and mechanically stable medium. This represents a practical trade-off between ionic transport efficiency and the mechanical integrity required for flexible supercapacitor operation, ensuring the device remains stable during bending and deformation.
The active-material loading on the carbon cloth was determined from the mass difference of the substrate before and after the hydrothermal growth process. This calculation resulted in an active-material loading of approximately 14.3 wt% relative to the initial mass of the carbon cloth. The carbon cloth itself, with dimensions of 20 by 25 mm², provides an interconnected macroporous carbon-fiber network that serves as a flexible and conductive substrate. The carbon fibers have an average diameter of approximately 7 micrometers and a uniform, smooth surface before treatment. After hydrothermal processing, the surfaces appear coated with a thin film, and particles are deposited non-uniformly.
The synthesis protocol involved preparing four aqueous precursor solutions with different Ce:Mn:Co molar ratios by dissolving Ce(NO3)2·6H2O, Co(NO3)2·6H2O, and KMnO4 in 35 mL of distilled water. For the Ce1−Mn1Co1 composition, 0.33 mmol of each precursor was used, while the amounts for other compositions were adjusted according to their specific molar ratios. In addition, 0.5 mL of 35 wt% HCl was added to each precursor solution to establish an acidic reaction environment. The pH of these solutions was not directly measured or adjusted to a specific numerical value. The prepared solutions were transferred into 100 mL stainless-steel autoclaves equipped with PTFE liners, where the cleaned carbon cloth substrates were completely immersed. The autoclaves were sealed and placed in a preheated oven maintained at 100 °C for 2 hours, with no specific heating ramp rate intentionally controlled or recorded.
Subject of Research: Hydrothermal growth of Ce-Mn-Co trimetallic oxide-hydroxides on carbon cloth toward flexible solid-state supercapacitors
Article Title: Hydrothermal growth of Ce-Mn-Co trimetallic oxide-hydroxides on carbon cloth toward flexible solid-state supercapacitors
Article References: Momeni, M. M., & Mohammadinejad, F. (2026). Hydrothermal growth of Ce-Mn-Co trimetallic oxide-hydroxides on carbon cloth toward flexible solid-state supercapacitors. Results in Engineering, 32, Article 113909. https://doi.org/10.1016/j.rineng.2026.113909
Image Credits: AI Generated
DOI: 10.1016/j.rineng.2026.113909
Keywords: Hydrothermal, growth, Ce-Mn-Co, trimetallic, oxide-hydroxides, carbon, cloth, toward, flexible, solid-state, supercapacitors, scientific research
News Source: Neil Sanderson. (November 10, 2026). Trimetallic Oxide Coating Yields Flexible Supercapacitor with 86% Retention. Scienmag.
