Most transport fuels are derived from fossil fuels, generate greenhouse gases, and consume significant amounts of
water in the extraction, purification, and/or burning processes. The generation of hydrogen using solar energy to split
water, ideally from abundant water sources such as sea water or other non-potable sources, could potentially provide an
unlimited, clean fuel for the future. Solar, electrochemical water splitting typically combines a photoanode at which
water oxidation occurs, with a cathode for proton reduction to hydrogen. In recent work, we have found that a
bioinspired tetra-manganese cluster catalyzes water oxidation at relatively low overpotentials (0.38 V) when doped into
a Nafion proton conduction membrane deposited on a suitable electrode surface, and illuminated with visible light. We
report here that this assembly is active in aqueous and organic electrolyte solutions containing a range of different salts
in varying concentrations. Similar photocurrents were obtained using electrolytes containing 0.0 - 0.5 M sodium
sulfate, sodium perchlorate or sodium chloride. A slight decline in photocurrent was observed for sodium perchlorate
but only at and above 5.0 M concentration. In acetonitrile and acetone solutions containing 10% water, increasing the
electrolyte concentration was found to result in leaching of the catalytic species from the membrane and a decrease in
photocurrent. Leaching was not observed when the system was tested in an ionic liquid containing water, however, a
lower photocurrent was generated than observed in aqueous electrolyte. We conclude that immersion of the membrane
in an aqueous solution containing an electrolyte concentration of 0.05 - 0.5M represent good conditions for operation
for the cubium/Nafion catalytic system.
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