| Gaia: | The study of electrochemical reactions in seawater requires understanding of the
associated coupled chemistry with the components of seawater, especially the role of
the carbonate-bicarbonate buffer system in the case of proton coupled electron transfer
reactions. We report the comparative paradigmatic voltammetric response of the
reversible hydrogen oxidation reaction (HOR) in the absence or presence of dibasic
phosphate, formate or bicarbonate. Electrochemically and chemically reversible
voltammetry is seen in aqueous 0.7 M NaCl at platinum macro-electrodes in the absence
of a buffer whilst the presence of a chemically stable buffer systems, such as phosphate
or formate, leads either to a cathodic shift in the oxidation potential for high buffer
concentrations or to a split wave for concentrations approximately a factor of two less
than the dissolved H2. In the case of bicarbonate buffer the dehydration of carbonic acid
on the voltammetric timescale leads to chemically irreversible voltammetric behaviour,
with a similar response measured in authentic seawater. Numerical simulations based
on a simple Nernstian model with literature values for kinetic and thermodynamic
parameters are reported which display excellent agreement with experiment.
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