Cobalt Carbonate-Coated Nitrogen-Doped Carbon Nanotubes with a Sea-Cucumber Morphology for Electrocatalytic Water Splitting

Herein, we report CoCO₃-coated nitrogen-doped carbon nanotubes (NCNTs) with a sea cucumber-like morphology for water splitting. The sample with a CoCO₃ content of 26.8 wt % (CoCO₃/NCNT-1) exhibits excellent performance for the hydrogen evolution reaction in 1.0 M KOH electrolyte with an overpotential of 58 mV to reach 10 mA cm^–2, better than the most non-noble metal catalysts reported; meanwhile, it exhibits superior electrocatalytic activity for the oxygen evolution reaction. The excellent performance of the catalyst is attributed to the nanotip effect caused by the sea-cucumber-like morphology. Notably, CoCO₃/NCNT-1 can attain turnover frequencies of 2.7 s^–1 at an overpotential of 50 mV, higher than that of Pt/C (1.5 s^–1). A cell constructed using CoCO₃/NCNT-1 as the catalyst of the electrode pair needs a low cell voltage of 1.54 V at 10 mA cm^–2, superior to most reported cells. In addition, CoCO₃/NCNT-1 can maintain 10 mA cm^–2 for overall water splitting for 100 h without activity loss.