DOI: 10.1002/celc.201402262
Benchmarking the Stability of Oxygen Evolution Reaction
Catalysts: The Importance of Monitoring Mass Losses
Rasmus Frydendal,a Elisa A. Paoli,a Brian P. Knudsen,a Bjçrn Wickman,a, b Paolo Malacrida,a
Ifan E. L. Stephens,*a and Ib Chorkendorff*a
Because of the rising need for energy storage, potentially facilitated
by electrolyzers, improvements to the catalysis of the
oxygen evolution reaction (OER) become increasingly relevant.
Standardized protocols have been developed for determining
critical figures of merit, such as the electrochemical surface
area, mass activity and specific activity. Even so, when new and
more active catalysts are reported, the catalyst stability tends
to play a minor role. In this work, we monitor corrosion on
RuO2 and MnOx by combining the electrochemical quartz crystal
1. Introduction
Water electrolysis is set to play a key role in the provision of
solar fuels, as a sustainable substitute for fossil fuels.1 Polymer
electrolyte membrane (PEM) electrolysers are particularly wellsuited
towards the localised storage of renewables such as
wind or solar, which are inherently intermittent. It turns out
that the majority of the efficiency losses on these devices can
be traced back to the oxygen evolution reaction (OER).2, 3 Consequently,
it is critical that the OER catalyst has a sufficiently
high activity, to minimise these losses, and that this activity is
stable over the whole lifetime of the catalyst. This is particularly
challenging, not only because the anode operates at inherently
oxidising potentials, but also as a result of the acidic electrolyte
of PEM electrolysers. At present, only IrOx and RuOx
based materials show reasonable activity and stability under
such conditions.4, 5 The best-performing catalysts in acidic
media are shown in the Tafel plot in Figure 1 a, which provides
an overview of the current state of the art, clearly dominated
by oxide catalysts based on the scarce elements Ru and Ir.
However, should PEM electrolysis make a true impact to the
global energy landscape, it will need to be scaled up to the
terawatt level;6 consequently, the loading of the precious
metals required to catalyse the OER should be decreased drastically
or eliminated altogether.7, 8 In principle, the proton-con-
microbalance (EQCM) with inductively coupled plasma mass
spectrometry (ICP–MS). We show that a meaningful estimation
of the stability cannot be achieved based on purely electrochemical
tests. On the catalysts tested, the anodic dissolution
current was four orders of magnitude lower than the total current.
We propose that even if long-term testing cannot be replaced,
a useful evaluation of the stability can be achieved
with short-term tests by using EQCM or ICP–MS.
Figure 1. Overview of the state of the art for the oxygen evolution reaction:
a) In acid media. Data adapted from: Present work for sputtered RuO2,16 for
Ru, Ir and Pt polycrystalline (pc) and nanoparticles (NP),17 for Ru0.7Ni0.3O2y
nanocrystals,18 for RuCo and RuIr NP,19 for IrO2 film and7 for RuO2 and IrO2
NP (# normalised to oxide area). b) In alkaline media. Data adapted from:
Present work for sputtered MnOx, from this group for sputtered RuOx,20 for
Ni0.9Fe0.1Ox,21 For Ni0.95Fe0.05(OH)2,22 for Fe0.3Co0.3Ni0.3Ox,9 for Ba0.5Sr0.5Co0.8Fe0.2
(# normalised to oxide area),10 for Pr0.5Ba0.5CoO3d (# normalised to oxide
area),11 for Ir/C and Mn2O3 E-dep,23 for Co3O4 NP,24 for RuO2-Ni and25 for
RuO2 (100) (normalised to oxide area).
a R. Frydendal, E. A. Paoli, B. P. Knudsen, Dr. B. Wickman, Dr. P. Malacrida,
Prof. I. E. L. Stephens, Prof. I. Chorkendorff
Center for Individual Nanoparticle Functionality
Department of Physics, Technical Univ. of Denmark
DK-2800 Kongens Lyngby (Denmark)
E-mail: ifan.stephens@fysik.dtu.dk
ibchork@fysik.dtu.dk
b Dr. B. Wickman
Department of Applied Physics
Chalmers University of Technology
SE-41296 Gçteborg (Sweden)
2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim ChemElectroChem 0000, 00, 1–8 &1&
These are not the final page numbers!
CHEMELECTROCHEM
ARTICLES