Durability of Mo-Ni Intermetallic Compounds in the Hydrogen Evolution Reaction

Molybdenum-nickel materials are catalysts of industrial interest for the hydrogen evolution reaction (HER). This contribution investigates the potential influence of ordered crystal structures on the catalytic activity. Well-characterized surfaces of the single-phase intermetallic compounds Ni7Mo7, Ni3Mo and Ni4Mo were subjected to accelerated durability tests (ADTs) and thorough characterization to unravel, whether crystallographic ordering affects the activity. Due to their intrinsic instability, molybdenum is leached resulting in higher specific surface areas and nickel-rich surfaces. The gain in surface area scales with the applied potential and the molybdenum content of the pristine samples. The nickel-enriched surfaces are more prone to form Ni(OH)2 layers, which leads to deactivation of the Mo-Ni materials. The crystal structure of the intermetallic compounds has, due to the intrinsic instability of the materials in alkaline media, no effect on the activity. The earlier as durable identified Ni7Mo7 proves to be highly unstable in the applied ADTs. The results indicate that the enhanced activity of unsupported bulk Mo-Ni electrodes can solely be ascribed to increased specific surface areas.