  Efficient artificial photosynthesis systems are currently realized as
catalyst- and surfacefunctionalized photovoltaic tandem- and triple-junction
devices, enabling photoelectrochemical (PEC) water oxidation while
simultaneously recycling CO2 and generating hydrogen as a solar fuel for
storable renewable energy. Although PEC systems also bear advantages for the
activation of dinitrogen - such as a high system tunability with respect to the
electrocatalyst integration and a directly controllable electron flux to the
anchoring catalyst through the adjustability of incoming irradiation - only a
few PEC devices have been developed and investigated for this purpose. We have
developed a series of photoelectrodeposition procedures to deposit mixed-metal
electrocatalyst nanostructures directly on the semiconductor surface for
light-assisted dinitrogen activation. These electrocatalyst compositions
containing Co, Mo and Ru in different atomic ratios follow previously made
recommendations of metal compositions for dinitrogen reduction and exhibit
different physical properties. XPS studies of the photoelectrode surfaces
reveal that our electrocatalyst films are to a large degree nitrogen-free after
their fabrication, which is generally difficult to achieve with traditional
magnetron sputtering or e-beam evaporation techniques. Initial
chronoamperometric measurements of the p-InP photoelectrode coated with the
Co-Mo alloy electrocatalyst show higher photocurrent densities in the presence
of N2(g) than in the presence of Ar at -0.09 V vs RHE. Indications of
successful dinitrogen activation have also been found in consecutive XPS
studies, where both, N 1s and Mo 3d spectra, reveal evidence of nitrogen-metal
interactions.
