The study, published in the journal Ionics, was led by Ting Xiao and Xinyu Tan of China Three Gorges University, together with colleagues at Three Gorges University’s College of Electrical Engineering & New Energy and Jingchu University of Technology. Rather than treating the conductivity and stability problems separately, the team designed a synergistic optimization scheme built on two complementary interventions: molybdenum doping inside the MnO2 layers, and ammonium ion pre-intercalation between them, achieved through a process of in-situ electrochemical activation.

The first half of the strategy addresses the electronic limitations of the material. Molybdenum atoms were introduced into the intralayer sites of the MnO2 crystal structure, where they substitute for manganese and fundamentally alter the material’s microstructure and crystal chemistry. This substitution does more than simply dilute the host lattice. According to the researchers, Mo-doping modulates the crystal structure in ways that increase the number of electrochemically active sites available for charge storage, while simultaneously enhancing electrical conductivity through the introduction of oxygen vacancies. These vacancies, which form as the lattice accommodates the foreign cation, act as defects that improve charge transport and provide additional pathways for ion movement. The approach draws on a growing body of evidence that doping engineering can dramatically reshape the electrochemical behavior of manganese oxides, which have been studied extensively in contexts ranging from zinc-ion and lithium-ion batteries to electrocatalysis.

The second half of the strategy addresses the structural fragility that has plagued MnO2 electrodes during cycling. The team employed in-situ electrochemical activation to pre-intercalate ammonium ions into the interlayer and tunnel sites of the doped material. This electrochemical activation serves a dual purpose. First, the process elevates the concentration of oxygen vacancies even further, compounding the conductive benefits introduced by molybdenum doping. Second, and perhaps more importantly, the resident ammonium ions act as structural pillars within the host lattice. By occupying interlayer sites before the electrode ever sees service, the NH4+ ions cushion the mechanical stress of repeated ion insertion and extraction, significantly improving the structural stability of the material over thousands of cycles. Ammonium ion storage chemistry has attracted growing interest in recent years precisely because NH4+ is a lightweight, earth-abundant charge carrier whose tetrahedral geometry allows it to engage in hydrogen-bonding interactions with host lattices, and the new work leverages these properties to stabilize an otherwise fragile oxide.

The electrochemical results reported for the optimized electrode are striking. The Mo-MnO2/AC electrode delivered a high specific capacitance of 668.5 F g⁻¹ at a current density of 2 mA cm⁻², a figure that places it among the better-performing manganese dioxide electrodes reported for aqueous systems. More remarkably, the electrode retained 97.92 percent of its initial capacity after 10,000 charge–discharge cycles at 25 mA cm⁻². Capacity retention approaching 98 percent over ten thousand cycles represents the kind of cycling durability that has historically been elusive for MnO2-based electrodes, which often suffer from dissolution, phase transformations, and mechanical failure as ions shuttle in and out of the lattice.

To demonstrate the practical potential of the material, the researchers assembled an asymmetric supercapacitor pairing the optimized Mo-MnO2/AC positive electrode with activated carbon cloth as the negative electrode. This full-cell device achieved an areal energy density of 1.52 mWh cm⁻² at a power density of 2 mW cm⁻², performance metrics that underscore the viability of the dual-pre-intercalation strategy beyond simple three-electrode measurements. Asymmetric configurations of this kind are a standard route to widening the operating voltage window of aqueous supercapacitors, since the two electrodes operate in complementary potential ranges, and the reported energy density suggests the approach could translate into devices relevant for energy harvesting and storage applications where safety and cost matter more than ultimate energy density.

The significance of the work lies in its dual-front design philosophy. Pre-intercalation strategies have been explored before in the battery and supercapacitor literature, with ions such as Zn2+, Na+, and various metal cations inserted into host structures to pre-expand tunnels, stabilize phases, or boost conductivity. Similarly, molybdenum doping of manganese oxides has been studied for applications including lithium-ion batteries, zinc batteries, and electrocatalytic nitrogen fixation. What distinguishes the new study is the deliberate combination of an intralayer dopant with an interlayer guest ion, orchestrated so that each modification amplifies the benefits of the other. The Mo-doping prepares a more conductive, defect-rich framework; the electrochemically driven ammonium insertion then exploits and reinforces that framework, raising the oxygen vacancy concentration further while locking the structure into a configuration that resists degradation.

The choice of ammonium as the intercalating species is also notable in the broader context of energy storage research. Aqueous ammonium-ion batteries and supercapacitors have emerged as a family of technologies that avoid lithium, cobalt, and other supply-constrained elements, relying instead on nitrogen and hydrogen, two of the most abundant elements available. Because NH4+ is small, mobile in aqueous electrolytes, and capable of forming hydrogen bonds with lattice oxygen, it can navigate host structures with unusual facility, and several recent studies have documented exceptionally long cycling lives for ammonium-ion cells based on Prussian blue analogs, covalent organic frameworks, and molybdenum oxides. The present work extends that toolkit to manganese dioxide, arguably the most commercially accessible oxide electrode material available, and demonstrates that ammonium pre-intercalation can serve as a stabilization mechanism rather than merely a charge carrier role.

The experimental program behind the results combined structural characterization with electrochemical testing. The team, which included Yiwen Zhang, Can Tang, Yuting Mei, Xiuru Li, Yulong Qiao, Lihua Jiang, Shibing Ni, and Yequan Xiao, examined how Mo-doping altered the crystal structure and microstructure of the MnO2, and tracked the changes in oxygen vacancy concentration that accompanied both the doping step and the subsequent electrochemical activation. The authors acknowledge support from the National Natural Science Foundation of China and the 111 Project, and note that the work builds on their earlier investigations of NH4+ pre-intercalation and surface coordination effects on MnO2, as well as interface engineering strategies for co-intercalation of protons and ammonium ions in molybdenum oxides.

For the field of aqueous energy storage, the study offers a template that could be adapted to other host materials. The central insight, that intralayer doping and interlayer ion pre-intercalation can be choreographed to act synergistically rather than independently, suggests a path forward for electrode materials whose theoretical promise has been undermined by practical limitations. As demand grows for safe, inexpensive, and sustainable storage technologies to complement lithium-ion batteries in grid buffering, wearable electronics, and transient power applications, strategies of this kind that extract maximum performance from abundant materials are likely to attract increasing attention. The demonstration that a simple electrochemical activation step can simultaneously load a host lattice with stabilizing ions and generate beneficial defects is particularly appealing from a manufacturing standpoint, since it requires no exotic reagents or high-temperature post-treatments.

The researchers suggest that the synergistic pre-intercalation strategy provides a general framework for developing high-performance electrode materials for ammonium-ion energy storage, and the numbers reported in the study lend considerable weight to that claim. With a specific capacitance approaching 670 F g⁻¹, near-perfect retention over ten thousand cycles, and a working asymmetric device achieving over 1.5 mWh cm⁻² of areal energy, the Mo-MnO2/AC electrode stands as one of the more compelling demonstrations yet that manganese dioxide, properly engineered, can finally begin to deliver on the theoretical potential that has made it such an enduring object of study.

The researchers behind this breakthrough, G. Sivasankari, D. Prabha, and P. Atheek, employed an in-situ synthesis method to produce the g-C₃N₄/NiMn nanocomposite. This technique not only ensures that the structural integrity of the composite is maintained but also optimizes the distribution of the nanomaterials, enhancing electrochemical performance. The in-situ approach allows for uniform interaction between the components, leading to improved conductivity and overall energy storage capabilities.

Layered double hydroxides (LDHs) have garnered attention due to their tunable properties and high surface area. By integrating g-C₃N₄ with NiMn, the researchers have engineered a composite that leverages the strengths of both materials. The g-C₃N₄ acts as a support scaffold, promoting the stability of the nickel-manganese hydroxide, which is a well-known supercapacitor material. This synergy between the two components results in a composite that exhibits enhanced capacitance and cycle stability, making it a formidable candidate for next-generation energy storage devices.

Electrochemical characterization of the g-C₃N₄/NiMn layered double hydroxide nanocomposite reveals remarkable performance metrics. The composite demonstrates a high specific capacitance, far exceeding that of traditional capacitance materials. This remarkable performance can be attributed to the unique layered structure of the composite, which facilitates ion transport and enhances charge storage mechanisms. Additionally, the researchers report impressive cycle stability, a crucial factor for practical applications, as it indicates the material’s ability to maintain performance over repeated charge and discharge cycles.

One of the standout features of this nanocomposite is its exceptional energy density, a critical parameter that determines the efficiency of supercapacitors. The combination of g-C₃N₄ and NiMn enhances the energy storage capabilities of the device, ensuring higher performance outputs. This is particularly significant for high-demand applications, such as electric vehicles and large-scale energy storage systems, where efficiency and longevity are paramount to success.

The research further delves into the morphological and structural properties of the synthesized nanocomposite. Through advanced characterization techniques, including X-ray diffraction and scanning electron microscopy, the authors confirm the successful synthesis of the g-C₃N₄/NiMn composite. These analyses provide insights into the crystalline structure, surface morphology, and particle size distribution, all of which are essential for understanding how these factors influence the electrochemical performance.

Moreover, the study’s findings hold promise for integration into existing energy storage technologies. The versatility of the g-C₃N₄/NiMn nanocomposite lends itself well to various configurations, whether as standalone supercapacitors or in hybrid systems alongside batteries. This flexibility positions the composite as a valuable asset in the ongoing evolution of efficient energy storage architectures that bridge the gap between rapid power delivery and sustainable energy management.

The growing demand for sustainable energy solutions underpins the urgency of this research. With rising environmental concerns, the need for renewable energy technologies is greater than ever. Supercapacitors, with their rapid charge and discharge capabilities, are increasingly being identified as pivotal components for energy management in renewable systems such as solar and wind energy. The introduction of the g-C₃N₄/NiMn nanocomposite may serve to align supercapacitor technology with broader energy sustainability goals, providing a pathway towards greener energy solutions.

Furthermore, researchers highlighted the potential for scalable production of the nanocomposite. The synthesis methodology described in the study is not only efficient but also has the potential for easy scale-up, which is vital for commercial viability. This aspect of the research could lead to widespread adoption of the material in various industries, thereby impacting energy storage technology on a global scale.

In conclusion, the advent of the g-C₃N₄/NiMn layered double hydroxide nanocomposite marks a significant milestone in supercapacitor research. By synthesizing this innovative material with in-situ methods, the researchers have developed a composite that excels in performance, stability, and potential for scalability. This research not only contributes to the academic understanding of nanocomposites but also to the practical advancements in energy storage solutions, positioning it as a vital development in the ongoing narrative of energy technology evolution.

As we move forward into an era defined by energy efficiency and sustainability, the innovations reflected in this research will undoubtedly play a crucial role. The synergy between materials science and energy technology is paramount in addressing the challenges of the modern age. With studies like this illuminating the path ahead, the future of energy storage appears bright, promising new solutions that are not only efficient but also environmentally conscious.

These advancements invite further exploration, collating insights from various fields towards the common goal of delivering innovative energy solutions. As the scientific community continues to innovate, the implications of such research extend far beyond the laboratory, shaping the strategies we adopt in the quest for sustainable energy.

Subject of Research: Development and performance evaluation of g-C₃N₄/NiMn layered double hydroxide nanocomposite for supercapacitor applications.

Article Title: In-situ g-C₃N₄/NiMn layered double hydroxide nanocomposite for supercapacitor application.

Article References:

Sivasankari, G., Prabha, D., Atheek, P. et al. In-situ g-C₃N₄/NiMn layered double hydroxide nanocomposite for supercapacitor application. Ionics (2025). https://doi.org/10.1007/s11581-025-06728-w

Image Credits: AI Generated

DOI: https://doi.org/10.1007/s11581-025-06728-w

Keywords: Supercapacitor, g-C₃N₄, NiMn, layered double hydroxide, nanocomposite, energy storage, electrochemical performance, sustainability.