Shape and Composition Effects on Photocatalytic Hydrogen Production for Pt–Pd Alloy Cocatalysts

The shape and composition effects of platinum-palladium (Pt-Pd) alloy nanoparticle cocatalysts on visible-light photocatalytic hydrogen evolution from an aqueous ammonium sulphite solution have been reported and discussed. The activity of Pt-Pd nanoparticles loaded Pt-Pd/CdS photocatalysts are affected based on both the Pt-Pd alloy nanoparticles' shape and their compositions. In this research, two shapes of Pt-Pd nanoparticles have been studied. One is Pt-Pd nanocubes enclosed by {100} crystal planes and the other is nano-octahedra covered with {111} crystal facets. Results show that the photocatalytic turnover frequency (TOF), defined as moles of hydrogen produced per surface mole of Pt-Pd metal atom per second, for Pt-Pd nanocubes/CdS (Pt-Pd NCs/CdS) photocatalyst can be 3.4 times more effective than Pt-Pd nano-octahedra/CdS (Pt-Pd NOTa/CdS) nanocomposite photocatalyst. Along with the shape effect, the atomic ratio of Pt to Pd can also impact the efficiency of Pt-Pd/CdS photocatalysts. When the Pt to Pd atomic ratio changes from 1:0 to about 2:1, the rate of hydrogen production increases from 900 μmol/h for Pt NCs/CdS catalyst to 1837 μmol/h for Pt-Pd (2:1) NCs/CdS photocatalyst-a 104% rate increase. This result suggests that the 33 mol % of more expensive Pt can be replaced with less costly Pd, resulting in a more than 100% hydrogen production rate increase. The finding of this research will lead to the research and development of highly effective catalysts for photocatalytic hydrogen production using solar photonic energy.