  Experimentally determined thermodynamic parameters are rarely reported for
electrocatalytic reactions including the oxygen evolution reaction (OER). Yet,
they contain unique and valuable mechanistic insight and present a missing link
to theoretical investigations. Herein, a protocol for determining thermodynamic
properties of the rate determining steps (RDS) of the OER is presented. Cobalt
oxide is investigated at pH 7 as a case study. Two different approaches are
employed: steady state polarization (SSP) that uses chronopotentiometry at
different temperatures and current values, and potentiostatic electrochemical
impedance spectroscopy (PEIS) at different DC voltages and temperatures. The
data is used to fit a 3D plane from which entropy and enthalpy of the RDS are
obtained. The data analysis requires an appropriate filtering of the data.
Hence, we discuss suitable figures of merit for establishing appropriate
filtering criteria. The values obtained are 0.72 and -0.39 eV (at 298 K) for
enthalpic and entropic contributions, respectively. The obtained values are
reproducible for both approaches and consistent with literature. We further
highlight that the RDS entropy gives clue of the number of water molecules
adsorbed or protons released prior to RDS and thereby helps identifying
plausible OER mechanisms.
