The widespread commercialization of artificial photosynthesis technologies will require efficient photocathodes capable of catalyzing reactions such as H+/H2 and CO2/CO. Sensitized photocathodes operate in an analogous manner to DSSCs, where photoexcitation provides a driving force for electrocatalytic transformations. Geminate recombination is a major free energy loss in p-type photocathodes, which have a large thermodynamic driving force for electron-hole recombination that inhibit energy storing half reactions such as CO2 and H+ reductions. In this work, a series of iron-(III) porphyrin complexes were sensitized on p-type NiO to examine photoelectrochemical activity for O2 reduction. The thermodynamic potential alignment of the NiO valence band edge and the O2/H2O couple suggest improved opportunity for activity that could provide substantial insights on improving the efficiency of p-type photocathodes.
Light-driven oxygen reduction reaction was achieved by a sensitized NiO photocathode, constructed by covalent attachment of iron-(III) porphyrins on the surface of porous NiO deposited onto FTO. The iron-(III) porphyrin plays a dual role as both the chromophore and electrocatalyst. Electrochemical responses obtained from CV, OPE, and CPE experiments indicate at a current density of 1 mA/cm2, the oxygen reduction onset overpotential increases from -0.926 V to -0.906 V under the exposure to light. In this work, it is shown for the first time that NiO electrodes sensitized with iron-(III) porphyrins are able to photocatalytically drive the reduction of O2. The shift in the current density for O2 reduction under illumination confirms the possibility of utilizing photocatalysts that have better thermodynamic potential alignments.
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