Influence of the Size and Shape of Palladium Nanoparticles on Their Electrochemical Hydrogen Sorption Capacity

Palladium hydrides (PdH x ) represent a prototypal platform for investigating metal-H interactions, owing to their well-defined phase transition, and are also relevant to molecular hydrogen storage, sensing and (electro)catalysis. It is well-known that the H sorption capacity of Pd nanoparticles (NPs) depends on their size and that H atoms become progressively trapped in Pd after repeated H sorption/desorption cycles. However, the influence of the NP shape on these properties has been much less explored. Herein, by synthesizing carbon-supported Pd nanocubes (NCs) enclosed by {100} facets, we reveal a pronounced size-dependent H sorption capacity, with the H:Pd ratio increasing from 0.55 to 0.68 as the Pd NC size increased from 5.4 to 20.2 nm in 0.1 M H 2 SO 4 at 20 °C. In parallel, a size-dependent H trapping is evidenced, with the fraction of trapped H decreasing from 13.9% to 5.1% as the Pd NC size increases over the same size range. Combining electrochemical measurements on both cubic and spherical Pd NPs with molecular dynamics simulations, we disentangle size and shape effects and demonstrate that both H sorption capacity and H trapping amplitude are primarily governed by the surface-to-volume ratio of the Pd NPs, rather than by their shape.