DOI: 10.1002/cssc.201902326
Communications
H2O2 Production at Low Overpotentials for
Electroenzymatic Halogenation Reactions
Sebastian Bormann+,[a] Morten M. C. H. van Schie+,[b] Tiago Pedroso De Almeida,[b]
Wuyuan Zhang,[b] Markus Stçckl,[c] Roland Ulber,[d] Frank Hollmann,*[b] and Dirk Holtmann*[a]
Dedicated to Professor Marko Mihovilovic on the occasion of his 50th birthday
Various enzymes utilize hydrogen peroxide as an oxidant. Such
“peroxizymes” are potentially very attractive catalysts for a
broad range of oxidation reactions. Most peroxizymes, howev-
er, are inactivated by an excess of H2O2. The electrochemical
reduction of oxygen can be used as an in situ generation
method for hydrogen peroxide to drive the peroxizymes at
high operational stabilities. Using conventional electrode mate-
rials, however, also necessitates significant overpotentials,
thereby reducing the energy efficiency of these systems. This
study concerns a method to coat a gas-diffusion electrode
with oxidized carbon nanotubes (oCNTs), thereby greatly re-
ducing the overpotential needed to perform an electroenzy-
matic halogenation reaction. In comparison to the unmodified
electrode, with the oCNTs-modified electrode the overpotential
can be reduced by approximately 100 mV at comparable prod-
uct formation rates.
halogenations.[1,2] A major issue for the technical application of
these “peroxizymes” is H2O2-mediated inactivation of the en-
zymes. Given that H2O2 is a strong oxidant, it is not surprising
that, in particular, labile amino acids can be oxidized by H2O2
or reactive oxygen species interact with the protein.[3] There-
fore, a major challenge en route to practical reaction systems
is to control the H2O2 concentration at levels that enable effi-
cient catalytic turnover of the enzyme while simultaneously
minimizing the undesired inactivation reaction. Several H2O2
dosing systems have been proposed to enable high productivi-
ties combined with high operational stabilities of the hydrogen
peroxide-dependent enzymes, for example, enzymatic,[4] pho-
tochemical[5] or electrochemical H2O2 production systems.[6] In
recent years the electrochemical reduction of oxygen to H2O2
at gas-diffusion electrodes (GDEs) has gained more and more
attention.[7] GDEs are typically being used in alkaline and
proton exchange membrane fuel cells.
The GDEs are installed in an electrochemical cell in a way
that one side is facing the liquid electrolyte and the other side
is facing the gas phase (e.g., air or pure oxygen). GDEs have a
porous structure into which the electrolyte can float from one
side and the desired gas can diffuse into the electrode from
the other side. This setting leads to a huge 3-phase boundary
between the solid catalyst, liquid electrolyte, and gas phase.
Scheme 1 shows the principle of the GDE for the reduction of
molecular oxygen to hydrogen peroxide. The GDEs were suc-
cessfully combined with different H2O2-dependent enzymes,
such as the unspecific peroxygenase from Agrocybe aegerita[8]
and a chloroperoxidase from Caldariomyces fumago.[9] To date,
process engineering parameters, such as electrochemical po-
tential, buffer composition, and flow rate, have been opti-
mized. However, a key parameter that has been neglected in
the investigations is the applied electrocatalyst. To date, most
applied catalyst have consisted of carbon and these have not
been investigated or optimized. Very recently, it was shown
that the oxidation of the surface of a carbon catalyst to
-CÀOÀC- groups inside the structure and -COOH groups at the
edges leads to a significant decrease in the overpotentials re-
quired for O2 reduction.[10] Therefore, the application of oxi-
dized carbon nanotubes (oCNT) resulted in more energy-effi-
cient H2O2 production. These results motivated us to investi-
gate the novel electrocatalyst in combination with a H2O2-de-
pendent enzyme. This approach combines the advantages of
GDEs (high atom efficiency in H2O2 synthesis, overcoming solu-
bility issues of O2) and enzyme catalysis (high selectivity and
specificity) with the reduced energy demand of the novel elec-
Hydrogen peroxide is increasingly considered as an oxidant for
biocatalytic reactions. The promise of H2O2-driven biocatalysis
is that the high oxidation power of H2O2 and its ecological
properties can be combined with the high selectivity and fur-
ther advantages of the enzymatic oxidation reactions.[1] This
point motivates many researchers to investigate H2O2-driven
biocatalysis for reactions such hydroxylations, epoxidations or
[a] S. Bormann,+ Dr. D. Holtmann
Industrial Biotechnology, DECHEMA Research Institute
Theodor-Heuss-Allee 25, 60486 Frankfurt am Main (Germany)
[b] M. M. C. H. van Schie,+ T. P. De Almeida, W. Zhang, Prof. Dr. F. Hollmann
Department of Biotechnology, Biocatalysis Group
Technical University Delft, Van der Maasweg 9
2629HZ Delft (The Netherlands)
[c] Dr. M. Stçckl
Electrochemistry, DECHEMA Research Institute
Theodor-Heuss-Allee 25, 60486 Frankfurt am Main (Germany)
[d] Prof. Dr. R. Ulber
Bioprocess Engineering, University of Kaiserslautern
Gottlieb-Daimler-Str. 49, 67663 Kaiserslautern (Germany)
[+] These authors contributed equally to this work.
Supporting information and the ORCID identification number(s) for the
author(s) of this article can be found under:
ꢀ 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
This is an open access article under the terms of the Creative Commons
Attribution License, which permits use, distribution and reproduction in
any medium, provided the original work is properly cited.
ChemSusChem 2019, 12, 1 – 6
1
ꢀ 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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