Self-assembly of cobalt hexacyanoferrate crystals in 1-D array using ion exchange transformation route for enhanced electrocatalytic oxidation of alkaline and neutral water

The present study reports a facile synthetic route for thin film formation of a self-standing 1-D structured array of cobalt hexacyanoferrate crystals using an aqueous solution based ion exchange transformation approach. For this, the cobalt hydroxycarbonate 1-D structured array film was used as a sacrificial precursor template for the ion exchange reaction in aqueous K₃[Fe(CN)₆] solution. By controlling the reaction, 1-D structured array film, or particulate structured film of the cobalt hexacyanoferrate crystals could be obtained, which thus offered possibilities on morphology-dependent property engineering. The films before and after the ion exchange reaction were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometry, energy dispersive X-ray analysis (EDX) and X-ray photoelectron spectroscopy (XPS). Further, electrochemical study of the films was performed using voltammetry, and electrochemical impedance spectroscopy. The study reveals the morphology-dependent electrocatalytic property of the cobalt hexacyanoferrate crystal film on water-oxidation. The 1-D structured array film of the cobalt hexacyanoferrate crystals has demonstrated superior electrocatalytic performance on water-oxidation from alkaline and neutral electrolytes, which is competitive to the catalytic performance demonstrated by many outstanding water-oxidation catalysts.