Sustainable high-purity graphite purification via pulsed electrolysis with reduced fluoride consumption

Abstract

Pulsed electrolysis is demonstrated as a sustainable and efficient strategy for purifying natural graphite, addressing the inherent limitations of conventional hydrofluoric acid leaching and anodic electrolysis. By integrating electrochemical regulation with optimized HF–H₂SO₄ electrolytes, this method achieves 99.9% purity of graphite while reducing hydrofluoric acid consumption by 60% (0.4 mL g⁻¹) compared to acid leaching (1.0 mL g⁻¹) and anodic electrolysis (0.7 mL g⁻¹). Systematic investigations reveal that alternating anodic/cathodic potentials in pulsed mode synergistically regulate H⁺ and F⁻ migration, enabling cyclic activation and dissolution of quartz impurities. Unlike anodic electrolysis, which induces structural expansion and oxidative degradation, pulsed electrolysis preserves graphite crystallinity with minimal layer spacing changes and minimizes oxidation while doping fluorine and sulfur onto the graphite surface. Quartz removal experiments and finite element analysis confirm an efficiency enhancement under pulsed operation, attributed to disrupted concentration polarization and enhanced ion accessibility at the electrode–electrolyte interface. Crucially, the substitution of HF with NH₄F in acidic media achieves comparable purity with reduced fluorine consumption, mitigating environmental and safety risks. This work establishes pulsed electrolysis as a scalable, eco-conscious purification platform, offering dual benefits of high-purity graphite production and functional surface modification for advanced energy applications.