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Page 66
Journal of Organic & Inorganic Chemistry
ISSN 2472-1123
2
n d
E d i t i o n o f E u r o S c i C o n C o n f e r e n c e o n
Chemistry
F e b r u a r y 1 9 - 2 0 , 2 0 1 9
P r a g u e , C z e c h R e p u b l i c
Chemistry 2019
W
ater oxidation (2H
2
O―>O
2
+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 Co
III/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(CO
3
)
3
]. The same peak is also observed after pulse radiolysis of CoSO4 in NaHCO3. The
anodic peak current (id) of CoIII/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 Co
III/II
peak is 0.85 x 10-3 cm s
-1
.
patrashantigopal@gmail.comElectrocatalytic water oxidation by cobalt-
carbonate
Shanti Gopal Patra
1
, Erzsébet Illés
C
, Amir Mizrahi
2
and
Dan Meyerstein
1, 3
1
Ariel University, Israel
2
Shimon Peres Negev Nuclear Research Centre, Israel
3
Ben-Gurion University, Israel
J Org Inorg Chem 2019, Volume: 5
DOI: 10.21767/2472-1123-C1-021