Synthesis of ethane-disulfonate pillared layered cobalt hydroxide towards the electrocatalytic oxygen evolution reaction

Abstract

We report the synthesis of a hybrid layered cobalt hydroxide sample and its redox behaviors in the electrochemical oxygen evolution reaction (OER). Compound Co₇(OH)₁₂(C₂H₄S₂O₆)·1.6H₂O was synthesized via a homogeneous alkalization reaction using Co(SO₃C₂H₄SO₃) and hexamethylenetetramine. This compound comprises cationic host layers of {[Co₇(OH)₁₂]²⁺}_∞, which comprise octahedrally (Co_Oh) and tetrahedrally (Co_Td) coordinated Co cations at a Co_Oh : Co_Td ratio of 5 : 2. The ethane-disulfonate ions are combined with the cationic host layers by electrostatic attractions and hydrogen bonding as a hybrid pillared layered framework. This hybrid sample can promote the OER in 1 M KOH with an overpotential as low as ∼410 mV (at a current density of 10 mA cm⁻²). In situ Raman spectroscopy showed that the sample first evolved into Co(III)-based phases comprising a mixture of layered CoOOH and spinel Co₃O₄, and the Co(III)-based compounds were converted into Co(IV)–O intermediates containing [CoO₆] units at the onsite of the OER. The structural evolution behaviors suggest that the catalyst prefers a topotactic phase transition and the Co_Oh and Co_Td units exhibit different activities in the electrochemical reaction. The electron transfer events involved in the electrochemical reaction were identified by Fourier-transformed alternating current voltammetry.