1 research outputs found
Highly Active NiO Photocathodes for H<sub>2</sub>O<sub>2</sub> Production Enabled via Outer-Sphere Electron Transfer
Tandem dye-sensitized
photoelectrosynthesis cells are promising
architectures for the production of solar fuels and commodity chemicals.
A key bottleneck in the development of these architectures is the
low efficiency of the photocathodes, leading to small current densities.
Herein, we report a new design principle for highly active photocathodes
that relies on the outer-sphere reduction of a substrate from the
dye, generating an unstable radical that proceeds to the desired product.
We show that the direct reduction of dioxygen from dye-sensitized
nickel oxide (NiO) leads to the production of H<sub>2</sub>O<sub>2</sub>. In the presence of oxygen and visible light, NiO photocathodes
sensitized with commercially available porphyrin, coumarin, and ruthenium
dyes exhibit large photocurrents (up to 400 μA/cm<sup>2</sup>) near the thermodynamic potential for O<sub>2</sub>/H<sub>2</sub>O<sub>2</sub> in near-neutral water. Bulk photoelectrolysis of porphyrin-sensitized
NiO over 24 h results in millimolar concentrations of H<sub>2</sub>O<sub>2</sub> with essentially 100% faradaic efficiency. To our knowledge,
these are among the most active NiO photocathodes reported for multiproton/multielectron
transformations. The photoelectrosynthesis proceeds by initial formation
of superoxide, which disproportionates to H<sub>2</sub>O<sub>2</sub>. This disproportionation-driven charge separation circumvents the
inherent challenges in separating electron–hole pairs for photocathodes
tethered to inner sphere electrocatalysts and enables new applications
for photoelectrosynthesis cells