Key Takeaways & Executive Findings
- •• • Mild annealing in air at 400 °C for 6 h increases specific surface area from 110 to 498 m² g⁻¹ (4.5-fold), directly enhancing ion-accessible sites and nearly order-of-magnitude capacitance increase, critical for high-energy-density supercapacitors. • • Optimal electrodes retain 92% capacitance at a 25-fold current increase (5 mA cm⁻²), demonstrating superior rate capability essential for power delivery applications. • • Long-term cycling stability: 99% capacitance retention after 10,000 cycles, ensuring device longevity and reducing replacement costs in industrial applications. • • Annealing promotes deoxygenation and higher sp2/sp3 ratio, improving electrical conductivity and electrochemical activity, as confirmed by spectroscopy, enabling more efficient charge transfer.
Abstract
Laser-assisted grown graphene electrodes are promising for electrochemical energy storage, but their performance is limited by poorly controlled pore networks. This study demonstrates that a simple thermal post-treatment effectively tunes porosity and surface chemistry, significantly enhancing capacitive performance. Systematic variation of annealing temperature, dwell time, and atmosphere (air vs. inert) revealed that mild annealing in air up to 500 °C reduces oxygen-containing functionalities and increases the sp2/sp3 carbon ratio. Critically, specific surface area increased from 110 to 498 m² g⁻¹, with a broader pore-size distribution. These structural and chemical changes correlate with an almost order-of-magnitude increase in capacitance compared to untreated electrodes. The optimal condition—400 °C in air for 6 h—yielded electrodes retaining 92% of capacitance at a 25-fold current increase and 99% capacitance retention after 10,000 cycles. Density functional theory (DFT) simulations support a buckling–unknotting mechanism, where metastable interlayer sp3 or C–O–C linkages relax into lower-energy, untied bilayer configurations, reopening pores. This laser-based fabrication combined with thermal annealing offers a scalable, chemical-free route to high-performance graphene electrodes, avoiding wet-chemical activation. The established structure–property relationships provide clear guidance for optimizing related porous carbon architectures.
1. Introduction
Supercapacitors bridge the power-energy gap between batteries and conventional capacitors, but their commercial adoption is hindered by low energy density. Conventional carbon electrode production often relies on energy-intensive, multi-step chemical activation routes (e.g., KOH etching) that are environmentally malign and difficult to scale. Laser-assisted graphene (LEST-graphene) offers a scalable, chemical-free fabrication pathway, yet its as-produced pore network is suboptimal, limiting capacitance and rate performance.
This work addresses the bottleneck by introducing a simple thermal annealing post-treatment to controllably modify the pore architecture and surface chemistry of LEST-graphene electrodes. By systematically varying temperature, dwell time, and atmosphere, we demonstrate that mild air annealing at 400 °C for 6 h dramatically increases accessible surface area (from 110 to 498 m² g⁻¹) and capacitance by nearly an order of magnitude, while preserving excellent rate capability and cycling stability. This approach eliminates wet-chemical activation, offering an industrially compatible route to high-performance carbon electrodes.
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Nikolaos Samartzis, Natalia Kantouni, Elli Bellou, Paraskevas Dimitropoulos, Labrini Sygellou, Athanassios Chrissanthopoulos, Spyros N. Yannopoulos (2026). Tuning porosity and capacitance of laser-assisted grown graphene by controlled thermal annealing. New Carbon Materials. https://doi.org/10.1016/S1872-5805(26)61098-0
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Frequently Asked Questions
What is the optimal annealing condition for maximizing capacitance, and what are the trade-offs in terms of energy consumption and processing time?
The optimal condition is 400 °C in air for 6 hours, yielding an almost order-of-magnitude capacitance increase. While this requires moderate thermal energy, it avoids wet-chemical activation, reducing overall environmental impact and processing complexity. The 6-hour dwell time is acceptable for batch processing, and the process is compatible with roll-to-roll manufacturing.
How does the annealing atmosphere (air vs. inert) affect the surface chemistry and electrochemical performance?
Mild annealing in air is markedly more effective than inert annealing. Air annealing promotes deoxygenation and increases the sp2/sp3 ratio, leading to higher conductivity and capacitance. Inert annealing likely retains more oxygen groups, which can hinder ion transport and reduce accessible surface area.
What is the underlying mechanism for pore reopening upon annealing, and how does it correlate with the observed capacitance increase?
DFT simulations indicate that metastable interlayer 'knots' (sp3 C–C or C–O–C bridges) relax into untied, lower-energy bilayer configurations upon annealing, reopening pores. This buckling–unknotting mechanism increases accessible surface area and ion transport, directly boosting capacitance.
What are the long-term cycling stability and rate capability of the best-performing electrodes under practical current densities?
The best electrodes retain 92% capacitance at a 25-fold current increase (5 mA cm⁻²) and 99% capacitance after 10,000 cycles, demonstrating excellent rate capability and durability suitable for real-world supercapacitor applications.
How does the specific surface area (SSA) of annealed electrodes compare to chemically activated carbons, and what are the implications for energy density?
The SSA increases from 110 to 498 m² g⁻¹ after annealing, which is competitive with some chemically activated carbons but achieved without hazardous reagents. This SSA enhancement, combined with improved pore architecture, leads to higher capacitance and energy density, making the process a viable alternative.
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