10.1021/acscatal.8b04757.s001
Soumalya Sinha
Soumalya
Sinha
Moumita Ghosh
Moumita
Ghosh
Jeffrey J. Warren
Jeffrey J.
Warren
Changing the Selectivity of O<sub>2</sub> Reduction
Catalysis with One Ligand Heteroatom
American Chemical Society
2019
cobalt
four-electron reduction
EPG
CoTPPy
O 2 Reduction Catalysis
O 2 reduction selectivity
O 2 reduction catalysts
Fe
2- pyridyl group
H 2 O
O 2
porphyrin
Co
O 2 reduction
fuel cell technologies
TOF
edge plane graphite
2019-02-11 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Changing_the_Selectivity_of_O_sub_2_sub_Reduction_Catalysis_with_One_Ligand_Heteroatom/7752395
The development of
catalytic systems that selectively reduce O<sub>2</sub> to water is
needed to continue the advancement of fuel cell
technologies. As an alternative to platinum catalysts, derivatives
of iron (Fe) and cobalt (Co) porphyrin molecular catalysts provide
one benchmark for catalyst design, but incorporation of these catalysts
into heterogeneous platforms remains a challenge. Co-porphyrins can
be heterogeneous O<sub>2</sub> reduction catalysts when immobilized
on to edge plane graphite (EPG) electrodes, but their selectivity
for the desired four-electron reduction of O<sub>2</sub> to H<sub>2</sub>O is often poor. Herein, we demonstrate substantial improvements
in the O<sub>2</sub> reduction selectivity using a Co-porphyrin that
incorporates a 2-pyridyl group at one of the <i>meso</i>-positions of a Co-tetraarylporphyrin (cobaltĀ(II) 5-(2-pyridyl)-10,15,20-triphenylporphyrin,
CoTPPy). The properties of CoTPPy immobilized on EPG were investigated
using cyclic voltammetry, rotating disk, and rotating ring-disk electrochemistry.
The presence of a single 2-pyridyl group in the CoTPPy gives rise
to the four-electron reduction of O<sub>2</sub>, as opposed to the
two-electron reduction commonly associated with cobalt porphyrins.
Detailed electrochemical studies of CoTPPy and related Co and Fe porphyrins
are described. Use of Co instead of Fe improves overpotentials by
over 200 mV with a factor of 2 increase in maximum turnover frequency
(TOF<sub>max</sub>). This work demonstrates that a simple change in
catalyst structure can dramatically change the selectivity for O<sub>2</sub> reduction.