Micro-texturing by femtosecond laser ablation of a carbonaceous anode for production of fluorine by electrolysis

[Display omitted] •Enhancement of the fluorine gas production by electrolysis in a molten salt of KF-2 H F is achieved.•Femtosecond laser ablation results in a microstructure on the carbonaceous anode surface.•Microstructure changes the behavior of fluorine bubbles on the surface.•Changes of the gas dynamic improve the production performance. Micro-texturing of the carbon surface of the anode used for the production of fluorine gas by electrolysis is achieved by ablation using a pulsed laser in the femtosecond range; this avoids oxidation of the carbon during ablation. Samples microstructured on the surface via a grid of parallel and perpendicular grooves were prepared and then studied from an electrochemical point of view coupled with ultra-fast image acquisition to visualize the effect of micro-texturing on the dynamics of the fluorine bubbles. In addition, the quantity of gas formed was measured using an incremental flowmeter on an electrolysis cell. Surface micro-texturing controls both the dynamics and shape of the fluorine bubbles, as well as the electroactive zone. The bubbles, then spherical due to the controlled roughness, have a short residence time (about 1 s) and small sizes (a few mm). These observed changes suggest a different wettability of the carbonaceous anode surface by the fluorine gas or the KF-2 H F electrolyte with a beneficial effect on the electrode performance in terms of Faraday efficiency as opposed to the anode voltage which changes slightly. In addition, thanks to the particular dynamics of the fluorine bubbles, very high current densities of up to 75 A dm−² can be applied.