Key Takeaways & Executive Findings
- •• • CAC-120 delivers a specific capacity of 371.4 mAh g−1 at 1 A g−1, representing a significant improvement over undoped carbon cathodes, which is critical for meeting the energy density demands of commercial ZICs. • • The material exhibits 90.6% capacity retention (reversibility) and 74% capacity retention after 10,000 cycles, indicating robust long-term stability essential for grid-scale storage applications. • • DFT calculations identify pyridinic N as the primary active site for Zn2+ adsorption, with adsorption energies ranging from −0.25 to −0.10 eV, providing a mechanistic basis for designing high-capacity carbon cathodes. • • A full ZIC device using CAC-120 achieves a reversible capacity of 90.8 mAh g−1 at 0.2 A g−1 and maintains stability over 17,000 cycles, demonstrating practical viability for aqueous zinc-based energy storage systems.
Abstract
Aqueous zinc-ion capacitors (ZICs) are promising energy storage systems due to their high specific capacity and superior reliability. Heteroatom-doped carbon materials have been shown to substantially increase the capacitance of ZICs, yet the underlying mechanisms remain poorly understood. In this work, coal-based activated carbon was functionalized with both boron (B) and nitrogen (N) to serve as the cathode material in ZICs. The optimized material, designated CAC-120, exhibits a high specific capacity of 371.4 mAh g−1 at 1 A g−1 and retains 74% of its initial capacity after 10,000 cycles. Electrochemical analysis and density functional theory (DFT) calculations reveal that pyridinic N plays a crucial role in enhancing Zn2+ storage, demonstrating superior electrochemical reversibility. Furthermore, an assembled aqueous ZIC using the CAC-120 cathode achieves a high reversible capacity of 90.8 mAh g−1 at 0.2 A g−1 and exceptional long-term stability over 17,000 cycles. This work provides valuable insight into the design of high-capacity and ultrafast pseudocapacitive carbon cathodes for ZICs, highlighting the synergistic effects of pore structure engineering and heteroatom doping.
1. Introduction
Aqueous zinc-ion capacitors (ZICs) have emerged as a compelling alternative to lithium-ion capacitors (LICs) due to the abundance, low cost, and safety of zinc. However, the performance of ZICs is often limited by the cathode material, which must provide high specific capacity, rapid ion transport, and excellent cycling stability. Conventional carbon cathodes suffer from low energy density and poor rate capability, hindering their commercial adoption. Heteroatom doping has been proposed as a strategy to enhance the electrochemical properties of carbon materials, yet the specific contributions of different doping configurations remain unclear, and systematic studies are lacking.
This work addresses these bottlenecks by engineering coal-based activated carbon with both boron and nitrogen doping, creating a cathode material (CAC-120) with an optimized pore structure and heteroatom content. The dual doping synergistically enhances Zn2+ storage, as evidenced by a high specific capacity of 371.4 mAh g−1 and excellent cycling stability. Density functional theory calculations further elucidate the role of pyridinic nitrogen in facilitating Zn2+ adsorption, providing a rational basis for material design. These findings offer a facile and scalable strategy for developing high-performance carbon cathodes for next-generation aqueous zinc-based energy storage systems.
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LIU Shuyuan, TIAN Zhen, WANG Yanzhong, ZHOU Rui, ZHENG Zhichao (2026). Boron and Nitrogen Co-Doped Coal-Based Activated Carbon as Cathode Material for High-Performance Aqueous Zinc-Ion Hybrid Capacitors. New Carbon Materials. https://doi.org/10.1016/S1872-5805(26)61071-2
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Frequently Asked Questions
What is the specific capacity and cycling stability of the CAC-120 cathode, and how does it compare to state-of-the-art carbon cathodes?
CAC-120 delivers a specific capacity of 371.4 mAh g−1 at 1 A g−1, with 90.6% capacity retention (reversibility) and 74% retention after 10,000 cycles. These values are among the highest reported for carbon-based cathodes in ZICs, surpassing many previously reported heteroatom-doped carbons.
What is the role of pyridinic nitrogen in enhancing Zn2+ storage, and how was this determined?
Density functional theory (DFT) calculations revealed that pyridinic N sites exhibit adsorption energies for Zn2+ ranging from −0.25 to −0.10 eV, indicating favorable binding. Electrochemical analysis confirmed that pyridinic N contributes to superior reversibility and kinetics, making it a critical active site for Zn2+ storage.
How does the pore structure of CAC-120 contribute to its electrochemical performance?
The optimized pore size distribution provides abundant accessible active sites and facilitates rapid ion transport, which is essential for achieving high specific capacity and rate capability. The synergy between high surface area, tailored porosity, and heteroatom doping is key to the material's outstanding performance.
What is the practical energy density and cycle life of a full ZIC device using CAC-120?
An assembled aqueous ZIC using CAC-120 achieves a reversible capacity of 90.8 mAh g−1 at 0.2 A g−1 and maintains exceptional long-term stability over 17,000 cycles, demonstrating its potential for practical applications in grid-scale energy storage.
What are the scalability and cost implications of using coal-based activated carbon as a precursor?
Coal is an abundant and low-cost precursor, making the synthesis of CAC-120 economically viable for large-scale production. The facile doping process and high performance of the material suggest that it could be a cost-effective alternative to more expensive carbon sources, such as graphene or carbon nanotubes, for ZIC cathodes.
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