  Despite numerous experimental and theoretical studies devoted to the oxygen
evolution reaction, the mechanism of the OER on transition metal oxides remains
controversial. This is in part owed to the ambiguity of electrochemical
parameters of the mechanism such as the Tafel slope and reaction orders. We
took the most commonly assumed adsorbate mechanism and calculated the Tafel
slopes and reaction orders with respect to pH based on microkinetic analysis.
We demonstrate that number of possible Tafel slopes strongly depends on a
number of preceding steps and surface coverage. Furthermore, the Tafel slope
becomes pH dependent when the coverage of intermediates changes with pH. These
insights complicate the identification of a rate-limiting step by a single
Tafel slope at a single pH. Yet, simulations of reaction orders complementary
to Tafel slopes can solve some ambiguities to distinguish between possible
rate-limiting steps. The most insightful information can be obtained from the
low overpotential region of the Tafel plot. The simulations in this work
provide clear guidelines to experimentalists for the identification of the
limiting steps in the adsorbate mechanism using the observed values of the
Tafel slope and reaction order in pH-dependent studies.
