Journal of Organic & Inorganic Chemistry

Electrocatalytic water oxidation by cobaltcarbonate

2^nd Edition of EuroSciCon Conference on Chemistry
February 19-20, 2019 | Prague, Czech Republic

Shanti Gopal Patra, Erzsebet Illes C, Amir Mizrahi and Dan Meyerstein

Ariel University, Israel Shimon Peres Negev Nuclear Research Centre, Israel Ben-Gurion University, Israel

Posters & Accepted Abstracts: J Org Inorg Chem

DOI: 10.21767/2472-1123-C1-021

Abstract

Water oxidation (2H₂OâÂ?Â?>O₂+4H++4e−) is a key step in artificial photosynthesis. It has significant importance in biological processes, solar energy conversion and water electrolysis. Herein we present the homogeneous electro-catalytic water oxidation by cobalt-carbonate (Co-C) system. It is shown that cobalt-carbonate acts as an efficient water oxidation catalyst with onset potential of 1.22 V and peak/plateau of 1.36 V vs. Ag/AgCl with a current density of 10.5 mA cm^-2 at an overpotential of 680 mV. Before catalysis, there appears a CoIII/II peak with Epa at around 0.72 V. This peak is electrochemically irreversible and dependent on bicarbonate, carbonate, and metal salt concentrations as well as pH. It follows a proton-coupled electron transfer (PCET) where the CoII is stabilized by mono-dentate bicarbonate and water whereas the CoIII is coordinated to bidentate carbonate ligands. The peak shifts cathodically with increasing metal salt concentration, which means that a dimer is formed after oxidation. The catalyst further undergoes oxidation to form a CoIV=O species which then forms peroxo/percarbonate intermediates followed by the release of oxygen and goes back to its initial state. The catalytic current depends linearly with the metal salt concentration. The Tafel slope is calculated to be 195 mV dec^-1. After chronoamperometry at 1.3 V for 3.5 hours, a green solution is formed with a green deposit on the electrode surface. From the absorption spectra (peak at 258 nm), the green compound is found to be Na3[CoIII(CO₃)₃]. The same peak is also observed after pulse radiolysis of CoSO₄ in NaHCO₃. The anodic peak current (id) of Co^III/II peak follows the Randles-Sevcik equation and thus the process is homogeneous and the rate constant (kcat) of catalysis is 100.5 s^-1. The rate constant (k0) of the electron transfer for the CoIII/II peak is 0.85 x 10^-3 cm s^-1.

Biography

E-mail:

patrashantigopal@gmail.com