A Proton-Conductive Co(II)-Polyoxometalate Acts as a Precatalyst for Efficient Electrocatalytic Water Oxidation.

A cobalt(II)-containing polyoxometalate, [HO][{Co(HO)}{Na(HO)}WO]·3HO (), has been isolated in a one-step facile aqueous synthesis and characterized unambiguously using single-crystal X-ray crystallography along with routine spectral analysis. The paratungstate cluster anion [WO] coordinates with {Co(HO)} and {Na(HO)} complex cations resulting in the formation of the water-insoluble compound having three-dimensional (3-D) extended structure. Motivated by the protonated water molecules existing as the counter cations in , herein, we demonstrate the detailed proton conductivity studies of the , reaching a value of 1.04 × 10 S cm at 80 °C and 98% relative humidity (RH). The temperature- and humidity-dependent proton conductivity in is governed by Grotthus mechanism with = 0.25 eV. In addition, we examined the electrochemical behavior of , in an alkaline borate buffer where it is found to be electrochemically unstable and acts as a precatalyst (and not a true catalyst) for oxygen evolution reaction (OER). We also discuss the "post-mortem" analysis of the postelectrolysis sample to identify the active species which turns out to be a cobalt oxide material (CoO) incorporating small amounts of tungsten. Thus, in the present electrocatalysis work, the molecule transforms into an efficient water oxidation catalyst (WOC).