RuO2 has been established as the benchmark
catalyst
for the oxygen evolution reaction (OER). However, the low precious
metal content compared to other OER industrial catalysts like RuO2, Pt/C, and IrO2 makes a hybrid heterosurface of
RuO2 and F-doped graphene (RuO2@FGr) an excellent
catalyst with a high current density. Moreover, the advantage of graphene
support increases stability. We investigated the mechanism of the
OER on RuO2@FGr using density functional theory (DFT) and
the computational hydrogen electrode model (CHEM). In CHEM, the adsorption
energy of the reactive intermediates is considered for the reduction
potential calculation. This is followed by free energy calculation
and, eventually, overpotential calculation using standard or reversible
hydrogen electrodes (SHE/RHE). Computational OER activity calculated
in the gas phase using density functional theory (DFT) cannot explain
the contribution of the condensed phase, water organization energy,
the kinetics of the elementary steps, and electrochemical contribution.
The current study will address the issue by implementing an implicit
solvation model and the electrostatic contribution by considering
the charge extrapolation model. We used molecular RuO2 to
mimic the exact experimental weight percentage. Fluorine intercalation
doping improves the binding of oxygen-based intermediate species to
the reactive surface due to a shift in the d-band center toward the
Fermi level. The graphene sheet behaves as a conductor after fluorine
doping, and the electron density contribution near the Fermi level
is clearly distinguished from the projected density of states (PDOS).
Using the implicit solvation model with altered parameters, we find
improvements in the reaction barrier for hydroperoxo formation. An
overpotential of 0.40 V vs RHE is obtained for the cavity shape parameter
and charge density cutoff parameter of 0.8 and 0.0035 Å–3. For completion, we implement the constant potential model (CPM)
to extrapolate our results calculated at the nonzero potential environment
to 0.0 V potential. The mean energy path computed using the climbing
image nudged elastic band provides the activation and reaction energy,
and the values are extrapolated to 0.0 V RHE using the CPM correction.
Implementing both thermochemical and electrochemical corrections simultaneously,
we can find a reasonable overpotential of the studied catalytic reaction.