Hydrophilic carbon nanotube-based electrodes for enhanced hydrogen evolution reaction by defect engineering control

Developing innovative methods to produce green hydrogen is essential for promoting sustainable energy solutions and decreasing dependence on fossil fuels. This study presents the fabrication and characterization of hydrophilic Carbon Nanotube (CNTs)-based electrodes designed to improve the Hydrogen Evolution Reaction (HER) through defect engineering and surface functionalization. Horizontally aligned, porous CNT sheets were fabricated via dry-spinning techniques and subsequently densified using ethanol to improve packing density and electrical conductivity. To further enhance electrocatalytic performance, the CNT electrodes were functionalized via an acid mixture composed of sulfuric and nitric acids, introducing oxygen-containing functional groups (−COOH, −OH) that increased hydrophilicity and active site density. Comprehensive characterization confirmed the preservation of structural integrity and successful functionalization of the CNTs. Electrochemical evaluation in 0.5 M H₂SO₄ demonstrated a substantial reduction in onset potential from 540 mV (bare CNTs) to 103 mV (acid-treated CNTs) and an overpotential of 696 mV to reach a current density of 10 mA cm⁻² for 10 min treated electrode. The optimized electrodes exhibited improved wettability and electron transfer kinetics, with a Tafel slope reduced from 618 mV dec⁻¹ to 439 mV dec⁻¹ . • Hydrophilic CNT electrodes fabricated via dry-spinning and acid functionalization. • Surface –OH/–COOH groups enhanced HER activity and wettability in acidic media. • Onset potential dropped from 540 mV to 103 mV after 10 min acid treatment. • Defect engineering preserved structure while improving electron transfer kinetics.