Transition metal oxy/hydroxides functionalized flexible halloysite nanotubes for hydrogen evolution reaction

The hierarchical halloysite nanotubes (HNT) have alumina containing positive Al-OH groups on its inner surface and silica-containing negative siloxane groups of Si-O-Si on its outer surface. The silicate laminate consists of silicon-oxygen at tetrahedral sites and aluminum-oxygen at octahedral sites. Since HNT has an abundant hydroxyl group on the surface with exceptional cation/anion exchange capacity, the surface-functionalized HNT could boost electrocatalytic activity. Hence, we have synthesized Ni, Co, and Cu metal oxy/hydroxides functionalized HNT by a facile hydrothermal method for HER. Among them, Co(OH)₂@HNT on flexible carbon cloth displays an ultra-low overpotential of 65 mV at 10 mA cm^-2 current density and Tafel slope of 181 mV dec^-1 and also exhibited a larger exchange current density of 3.98 mA cm^-2 in alkaline 1 M KOH electrolyte due to superior electrostatic affinity between OH^- and Co²⁺. The electrolyzers with anion exchange membrane consisting of RuO₂||Co(OH)₂@HNT show remarkable stability of over 50 h at 10 mA cm^-2 in alkaline electrolyte. The post stability sample retains the same surface oxidation state which confirms the robustness of the electrocatalyst. The reported results are far better than many of the transition metal oxides/chalcogenides electrocatalysts and hence it is expected that HNT could act as a potential alternative candidate to replace the benchmark platinum catalyst.