A comprehensive experimental design for optimizing zinc storage performance via nitrogen and sulfur co-doped porous carbon

Aqueous zinc-ion hybrid capacitors (ZICs) combine the energy storage mechanisms of aqueous zinc-ion batteries and supercapacitors to achieve high energy and power densities. However, a critical mismatch in capacity and reaction kinetics between the capacitive carbon cathode and battery-type zinc anode significantly limits the overall energy density of ZICs. To address this key problem, this research designs a comprehensive experiment to optimize the zinc storage performance of heteroatom-doped porous carbon cathode materials. This study aims to fabricate high-performance porous carbon cathode materials by precisely regulating activation processes and to establish the intrinsic correlation between material composition, structure, and electrochemical performance. This provides experimental guidance for enhancing ZIC electrochemical performance. In addition, this research, encompassing material synthesis, structural characterization, device assembly, and performance testing, can cultivate the innovative research thinking and experimental operation skills of students, fostering comprehensively innovative talent in materials and energy.

In this study, glucose powder was used as the carbon source, and ammonium persulfate and glacial acetic acid were used as the initiator and cross-linking agent, respectively. First, nitrogen and sulfur co-doped cross-linked carbon microspheres were prepared via a hydrothermal method. Subsequently, a honeycomb-like nitrogen and sulfur co-doped porous carbon material was synthesized by adjusting the ratio of KOH activator and activation temperature. The compositions, surface morphologies, specific surface areas, and pore size distribution of the resulting materials were characterized and analyzed. Then, coin-type ZICs were assembled using the prepared nitrogen and sulfur co-doped porous carbon as the cathode and zinc foil as the anode. Their specific capacity, rate performance, reaction kinetics, cycling stability, and energy density were evaluated through galvanostatic charge-discharge tests, cyclic voltammetry, and electrochemical impedance spectroscopy. The effects of the KOH activator ratio and activation temperature on the electrochemical performance of nitrogen and sulfur co-doped porous carbon materials were systematically investigated.

The nitrogen and sulfur co-doped porous carbon material features abundant and interconnected micropores, mesopores, and macropores, facilitating rapid ion transport. X-ray photoelectron spectroscopy analysis confirms the successful doping of nitrogen and sulfur into the carbon skeleton, providing ample electrochemical active sites. The electrochemical results demonstrate that the assembled ZIC exhibits excellent zinc storage performance. At a current density of 0.5 A·g⁻¹, the N, S-PC-2-700 electrode achieves a high specific capacity of 271.15 mAh·g⁻¹. At a power density of 444.4 W·kg⁻¹, it delivers an energy density as high as 241 Wh·kg⁻¹, significantly outperforming previously reported carbon-based ZICs, while also demonstrating good rate capability and cycling stability. Analysis of the electrochemical behavior of materials prepared under different process conditions enables a structure-activity relationship to be established between the nitrogen and sulfur co-doped porous carbon structure and its excellent zinc storage performance. The synergistic mechanism between the hierarchical porous structure and heteroatom doping is also revealed.

In this comprehensive experiment, a carbon cathode material with synergistically optimized hierarchical pore structure and heteroatom doping was successfully obtained through a hydrothermal method combined with KOH activation. This effectively addresses the capacity and kinetic mismatch between the carbon cathode and zinc anode, resulting in a device that achieves an excellent energy density of 241 Wh·kg⁻¹. This comprehensive experiment enables students to systematically master advanced carbon material preparation processes, material characterization methods, device assembly procedures, and electrochemical performance testing techniques, thereby deepening their understanding of the intrinsic correlation between material composition, structure, and performance. By independently investigating the effects of experimental conditions on material performance, students’ innovative thinking abilities are effectively enhanced, contributing to the cultivation of comprehensively innovative talent capable of material design and energy device development.