Exploration of the crystal effects of hydrolytic dehydrogenation of ammonia borane over Pd/Cu model catalysts: A combined experimental and theoretical study

Abstract

During the evolution of supported catalysts toward highly efficient catalysts such as single atom catalysts, the influence of the crystal facets has become progressively more significant. The crystal facet effect remains underexplored in the hydrolysis of ammonia borane (AB). Understanding the catalytic mechanism of highly active crystal facets is crucial for high-performance catalysts, but detailed insights are scarce. In this study, we synthesized and compared the catalytic activities of Pd/Cu cubes, truncated octahedra, and octahedra for hydrogen evolution from ammonia borane in water via the galvanic replacement reaction method. Our findings showed that the Pd/Cu (111) crystal facet had better catalytic activity than Pd/Cu(100). DFT calculations indicated that the Pd/Cu(111) plane facilitated the B-H bond cleavage in AB but not the dissociation of H₂O. Further studies with an explicit solvent model and ab initio molecular dynamics method (AIMD) revealed that the conformations of H₂O molecules at different catalyst interfaces varied, mainly in hydrogen-bonding structures. The differences in hydrogen bond cooperative effects at different interfaces affected the free energy barrier of the H₂O dissociation process, which may constitute a critical source of the observed differences in catalytic activities among various catalyst crystal facets.