Low-energy densification of carbon anodes for fluorine electrolysis applications via a multi-cycle impregnation–carbonization route

Abstract

Hard-to-control energy input and reliability trade-offs in conventional multi-high-temperature routes hinder densification of carbon anodes used in high-temperature electrochemical systems such as fluorine electrolysis, and the coupling between process parameters, pore evolution and properties remains insufficiently resolved. Here we report a scalable tri-impregnation semi-carbonization plus one final carbonization route that lowers peak carbonization stresses while maintaining densification efficiency. An infiltration framework that treats open/closed pores as vertical/horizontal capillaries and explicitly accounts for quinoline-insoluble (QI) filter-cake formation is established based on Darcy's law to quantify permeability evolution. A viscosity–temperature/thermogravimetric dual window delineates the wetting/filling regime while suppressing premature pyrolysis; in parallel, a bubble-escape-limited porogenesis mechanism rationalizes the role of heating ramps and isothermal holds on pore-size distribution and density gradients. Guided by these analyses, optimized parameters (impregnation at 210 °C, 1 MPa, 30 min; delayed heating in 300–500 °C) increase volume density, build a percolated conductive network, and mitigate swelling/cracking. The bulk resistivity decreases from 52.7 to 32.1 µΩ m, while compressive strength improves; density uniformity shows ΔD_max = 0.010–0.020 g cm⁻³ in early cycles, increasing to 0.042 g cm⁻³ later, indicating the need for staged pressure/temperature holds to enhance deep-zone densification. The resulting process-structure–property map defines transferable parameter windows and quality-control metrics, offering a low-energy, industry-ready route to high-reliability carbon anodes suitable for fluorine electrolysis and related high-temperature electrochemical processes.