  This report builds upon work introducing the concept of independent control
over current and potential in electrocatalytic systems, as a means of improving
control over their product selectivity. Previous work, describing an approach
investigating independent control over potentiostat bias and current flow,
implemented a biased PV-electrolyzer-type configuration. While permitting
separate modulation of current and potentiostat bias, that approach precludes
independent control over current flow and the applied cell potential. The
present study seeks to resolve that limitation, by exploiting the Schottky
diode behavior inherent to semiconductor-electrolyte interfaces. Light is
explored as a prospective second degree of freedom for controlling polarization
in a suitably-designed photoelectrochemical device, enabling the arbitrary
control of current with respect to an applied cell potential. In stark contrast
to metal electrodes, the unique property of light-dependent carrier
concentrations in semiconductor electrodes forms the operative means of
controlling charge fluxes at some arbitrary cell potential in PEC devices
featuring a genuine semiconductor-liquid junction. This functionality carries
prospects for exploring polarization states distinct from those of accessible
with a dark cell, with implications for improved control over electrochemical
reactions. Such opportunities are suggested by the experimental findings
reported here.
