Polyoxothiometalate-Derivatized Silicon Photocathodes for Sunlight-Driven Hydrogen Evolution Reaction

Silicon
photocathodes coated with drop-casted {Mo3S4}-based polyoxothiometalate assemblies are demonstrated to
be effective for sunlight-driven hydrogen evolution reaction (HER)
in acid conditions. These photocathodes are catalytically more efficient
than that coated with the parent thiomolybdate incorporating an organic
ligand, as supported by a higher onset potential and a lower overvoltage
at 10 mA cm–2. At pH 7.3, the trend is inversed
and the beneficial effect of the polyoxometalate for the HER is not
observed. Moreover, the polyoxothiometalate-modified photocathode
is found to be also more stable under acid conditions and can be operated
at the light-limited catalytic current for more than 40 h. Furthermore,
X-ray photoelectron spectroscopy and atomic force microscopy measurements
indicate that the cathodic polarization of both photocathodes leads
to the release of a large amount of the deposited material into the
electrolyte solution concomitantly with the formation of mixed valence
species {Mo­(IV)3–xMo­(III)xO4–nSn}(4–x)+ resulting
from the replacement of S2– sulfido ligands in the
cluster by oxo O2– groups; these combined effects
are shown to be beneficial for the photoelectrocatalysis.