Pd/Pt-PW Keggin Systems for H2 Generation: A DFT Study

We present a comprehensive density functional theory (DFT) investigation into the potential of a hybrid system TM_nPW (where TM = Pd, Pt, n = 1-7, PW = the tungsten Keggin anion, PW₁₂O₄₀^3-) for hydrogen generation. The computed growth and nucleation energies of the metallic phase show that both palladium and platinum clusters exhibit a growth tendency on the Keggin anion, forming stable spatial structures. The frontier orbital energies and the band gap width in the mixed TM_nPW complexes indicate that they possess unique catalytic properties, therefore, their behaviour in the hydrogen adsorption process is studied. Density Functional Theory calculations reveal that while hydrogen atoms on palladium clusters form bridging bonds between two, sometimes three Pd atoms, in the case of platinum, on small platinum clusters, the formation of a single Pt-H bond is observed. The analysis of the H adsorption energies and the Gibbs free energies allows for the selection of the best composites for the hydrogen evolution reaction, while the performed literature survey confirms their possible activity.