A pyrene-modified cobalt salophen complex immobilized on multiwalled carbon nanotubes acting as a precursor for efficient electrocatalytic water oxidation

Abstract

Immobilization of earth-abundant water oxidation catalysts (WOCs) on carbon supports to produce functional electrodes for electrochemical water splitting is a crucial approach for future clean energy production. Herein we report the non-covalent immobilization of a pyrene-bearing cobalt(II) Schiff base complex (2) on the surface of multiwalled carbon nanotubes (MWCNTs) to form a hybrid anode for electrocatalytic water oxidation. The 2/MWCNT anode displayed excellent catalytic activity and durability in neutral aqueous solution, and a catalytic current density of 1.0 mA cm⁻² was achieved at 1.15 V vs. the normal hydrogen electrode (NHE), corresponding to a low overpotential of 330 mV. A Tafel slope of 96 mV per decade was obtained. The Faradaic efficiency of oxygen evolution was more than 90% by bulk electrolysis measurement. After bulk electrolysis, the hybrid anode characterization using X-ray photoelectron spectroscopy (XPS) confirmed that complex 2 decomposed to form heterogeneous cobalt hydroxides and the cobalt hydroxides should be true catalytic active species, which are responsible for electrocatalytic oxygen evolution.