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.