Even partially amorphous Pd2Ni2P metallic glass significantly promotes hydrogen evolution electrocatalysis

Abstract

Metallic glasses are expected to be endowed with higher electrocatalytic activity, with respect to their crystalline counterparts, due to the presence of a high density of under-coordinated sites. However, glasses made of metals, as opposed to metal oxide/sulfides are harder to synthesize, with the challenge increasing with amorphousness. In light of these issues, we calibrate the increase in hydrogen evolution reactivity using the Pd2Ni2P bulk metallic glass composition as a model system. This composition has a good glass-forming ability and is interesting from a catalytic point of view, as Ni and P lie on the opposite leg of the HER volcano plot with respect to Pd. Partially amorphous (PA) Pd2Ni2P alloy displayed a five-fold higher specific electrocatalytic activity on per unit electrochemical surface area (ECSA) basis compared to its crystalline (C) counterpart. This magnitude of specific electrocatalytic activity, which is on par with that for pure Pd, has been achieved with just 40% of the precious metal, leading to a considerable saving in cost. The homogeneous single-phase structure of the highly electro-active partially amorphous alloy leads to higher electrochemical stability than its polycrystalline counterpart. This finding implies that many compositions ignored traditionally due to their poor electrocatalytic activity or stability can now be reconsidered in amorphous forms, thus expanding the material space of valuable catalysts.