Synergy between Nickel Nanoparticles and N-Enriched Carbon Nanotubes Enhances Alkaline Hydrogen Oxidation and Evolution Activity

Electrocatalytic hydrogen oxidation (HOR) and evolution (HER) reactions under alkaline conditions are kinetically sluggish processes even when Pt catalysts are employed. Despite having markedly slower kinetics, nanostructured nickel catalysts represent a cheaper and more sustainable alternative to benchmark Pt-based systems. Accordingly, researchers seek to develop Ni nanoparticle-based materials with enhanced electrocatalytic performance through the exploitation of favorable and catalytically advantageous metal-support interactions. In this contribution, we report the study of various N-doped/decorated carbon nanotubes (N-CNTs) as carriers for nickel nanoparticles (Ni-NPs), prepared by the decomposition of Ni(COD)2 as a metal precursor, a synthetic method that does not require organic stabilizers. All materials are thoroughly characterized (XPS, HR-TEM, STEM, and XRD) and tested as electrocatalysts for HOR and HER under an alkaline environment. We demonstrate how an increase in the nanotube surface basicity dictated by the presence of N-basic functional groups tunes the NiOx content of the metallic Ni NP surface, conferring higher electrocatalytic performance to the composites. Ni-NPs supported on N-CNTs prepared by exohedral functionalization of multiwalled carbon nanotubes with NH-aziridine functional groups (Ni/CNT-NAz) exhibit the highest HOR activity (16 A gNi-1 at 150 mV vs RHE). In terms of their performance for H2 evolution, Ni/CNT-NAz exhibits better onset potential and activity compared to its Ni-based counterpart prepared from pure-carbon networks (Ni/CNT). Worthy of note, Ni/CNT-NAz exhibited an HER Tafel slope (66 mV dec-1) approaching that of benchmark Pt electrocatalysts.