<p>The development of an electrocatalyst with a rapid
turnover frequency, low overpotential and long-term stability is highly desired
for fuel-forming reactions, such as water splitting and CO<sub>2</sub>
reduction. The findings of the scaling relationships between the catalytic rate
and thermodynamic parameters over a wide range of electrocatalysts in
homogeneous and heterogeneous systems provide useful guidelines and predictions
for designing better catalysts for those redox reactions. However, such
relationships also suggest that a catalyst with a high catalytic rate is
typically associated with a high overpotential for a given reaction. Inspired
by enzymes, the introduction of additional interactions through the secondary
coordination sphere beyond the active site, such as hydrogen-bonding or
electrostatic interactions, have been shown to offer a promising avenue to
disrupt these unfavorable
relationships. Herein, we further investigate the influence of these
cooperative interactions on the faster chemical steps, in addition to the
rate-limiting step widely examined before, for molecular electrocatalysts with
the structural and electronic modifications designed to facilitate the dioxygen
reduction reaction, CO<sub>2</sub> reduction reaction and hydrogen evolving
reaction. Based on the electrocatalytic kinetic analysis, the rate constants
for faster chemical steps and their correlation with the corresponding
thermodynamic parameters are evaluated. The results suggest that the effects of
the secondary coordination sphere and beyond on these fuel-forming reactions
are not necessarily beneficial for promoting all chemical steps and no apparent
relation between rate constants and thermodynamic parameters are found in some cases
studied here, which may implicate the design of electrocatalysts in the future.
Finally, these analyses demonstrate that the characteristic features for
voltammograms and foot-of-the-wave-analysis plots are associated with the
specific kinetic phenomenon among these multi-electron electrocatalytic
reactions, which provides a useful framework to probe the insights of chemical
and electronic modifications on the catalytic steps quantitatively (i.e.
kinetic rate constants) and to optimize some of critical steps beyond the
rate-limiting step.</p>
Reaction of Woodward's reagent K with d-xylose isomerases. Modification of an active site carboxylate residue