🤝 Collaborative Paper

Elucidating the synergistic behavior of plasma-surface interaction via air tornado-type atmospheric pressure plasma on graphite felt for vanadium redox flow batteries

Applied Surface Science, 695 (2025) 162874 | DOI: 10.1016/j.apsusc.2025.162874

Authors：Song-Yu Chen, Yu-Lin Kuo, Chen-Hao Wang, Tai-Chin Chiang

📄 Abstract

The electrochemical performance of graphite felt (GF) electrodes in vanadium redox flow batteries (VRFB) is often limited by poor wettability and low reaction activity. This study explores the feasibility of using compressed dry air in a tornado-type atmospheric pressure plasma jet (APPJ) for GF surface treatment. Wettability was assessed via water contact angle measurements, while plasma-surface interactions were analyzed using optical emission spectroscopy (OES) and gas detection. Structural and chemical modifications were characterized by Raman spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS), and electrochemical performance was evaluated through impedance measurements, cyclic voltammetry (CV), and single cell tests. At 550 W plasma power, GF's charge transfer resistance (Rct) is 3.94 Ω, while oxidation and reduction current densities reached 68.62 mA/cm² and −49.44 mA/cm², respectively. Single-cell test at 80 mA/cm² exhibited stable performance with no degradation, and the feasibility of scaling up this technology for commercial applications was demonstrated. These findings highlight the potential of air-based APPJ treatment as a scalable and effective method for enhancing GF electrode performance in VRFB.

🔬 Five Core Findings

Plasma surface modification significantly reduces charge transfer resistance: After 550 W air APPJ treatment, GF's Rct dramatically decreased from 217.4 Ω to 3.94 Ω, with oxidation and reduction peak current densities increasing to 68.62 mA/cm² and −49.44 mA/cm², respectively. Electrochemical reversibility (I_pa/I_pc ≈ 0.72) approaches ideal values.

Hydrophilicity transformation and increased oxygen-containing functional groups: XPS analysis shows oxygen content dramatically increased from 0.9% to 13.9%, with significant increases in C-O, C=O, and O-H functional groups, transforming graphite felt surface from hydrophobic to super-hydrophilic, indirectly confirming OH peak generation at 309 nm in OES spectrum.

Surface defects and microstructure regulation: SEM images show 500–550 W treatment can uniformly roughen GF surface, while 600 W causes excessive etching and fiber fracture; Raman ID/IG ratio increased from 0.44 (pristine) to 0.92 (550 W), indicating increased surface defect density and active sites.

Comprehensive single-cell performance improvement: At various current densities (40–100 mA/cm²), 550 W plasma-treated GF shows significantly higher voltage efficiency (VE) and energy efficiency (EE) than pristine GF; after 50 cycles, treated group maintains ~68–70% EE while pristine group drops to ~62%.

Large-scale application feasibility validated: Using 40 cm × 40 cm large-area GF (cut to 5 cm × 5 cm after 550 W APPJ treatment) for 100-cycle testing, treated group shows zero degradation while pristine group shows significant efficiency decline after 60 cycles, confirming commercial potential of air APPJ technology.

📊 Key Figures

Key Figure 1: Electrochemical performance analysis, caption embedded in image.

Key Figure 2: Material structure and surface analysis, caption embedded in image.