Covalent Cobalt Porphyrin Framework on Multiwalled Carbon Nanotubes for Efficient Water Oxidation at Low Overpotential

A noble-metal-free, efficient, and robust catalyst made of Earth-abundant elements for water oxidation is vital to achieve practical water splitting for future clean energy production. Herein, we report the synthesis of multilayer covalent cobalt porphyrin framework on multiwalled carbon nanotubes ((CoP)(n)-M-WCNTs) to produce a highly active electrocatalyst for water oxidation. A linear sweep voltammetry curve showed that a catalytic current density of 1.0 mA/cm(2) can be achieved under a potential of only 1.52 V (vs RHE, corresponding to an overpotential of only 0.29 V) in alkaline solution at pH 13.6. Such an onset potential is much lower than that of cobalt porphyrin monomer (CoP-TIPS) and pure MWCNTs. In addition, the chronopotentiometry data confirmed its excellent catalytic activity and suggested that the (CoP)(n)-MWCNTs catalyst has good durability for water oxidation catalysis. A Tafel slope of 60.8 mV per decade was obtained by bulk electrolysis measurement, and the Faradaic efficiency of oxygen production was >86%.