Non-destructive purification of freestanding single-walled carbon nanotube networks for high-performance proton-exchange membrane electrolyzer cathodes

Freestanding single-walled carbon nanotube (SWCNT) networks offer a versatile platform for the fabrication of binder-free electrodes in proton-exchange membrane (PEM) devices, combining high electrical conductivity, mechanical durability, and large surface area. However, as-synthesized SWCNT networks typically contain residual Fe catalyst nanoparticles that compromise electrochemical stability and membrane compatibility. Here, we present a robust purification strategy that effectively removes residual Fe from freestanding SWCNT networks while preserving their structural integrity. Notably, the chemical purification not only eliminates metallic impurities but also functionalizes the SWCNT surface, enabling direct fabrication of catalyst-decorated electrodes without the need for polymer binders or catalyst inks. This streamlined approach transforms freestanding SWCNTs into ready-to-use electrodes, offering a scalable and solvent-efficient alternative to conventional membrane coating techniques. Multi-step treatment with mineral acids reduces the Fe content to ≤ 5 wt%, yielding networks that retain a high I G /I D ratio in Raman spectroscopy, indicative of minimal structural damage. The purified SWCNTs exhibit excellent electrical conductivity and are ideally suited as catalyst supports for PEM electrolyzers. As a demonstration, we fabricated membrane–electrode assemblies (MEAs) using Pt-decorated, purified freestanding SWCNT networks as the cathode. The resulting devices display remarkable electrochemical stability, with no detectable performance degradation over 120 h of continuous operation at 1.8 V under potentiostatic conditions.