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

Abstract

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.

Anion-Exchange Membrane Water Electrolyzers

“…Examples of intermetallics of Ni and Mo include Ni 7 Mo 7 , Ni 3 Mo, and Ni 4 Mo. In a recent study, polished samples of Ni 7 Mo 7 , Ni 3 Mo, and Ni 4 Mo were tested for the HER, and the metal dissolution was measured . Substantial dissolution of Mo occurred for Ni 7 Mo 7 , leading to an increase in the ECSA, while Ni 3 Mo and Ni 4 Mo did not show dissolution at potentials below 0 V versus the reversible hydrogen electrode.…”

“…However, the stability range of Ni 3 Mo appears to be relatively narrow (between −0.25 and −1 V versus the reversible hydrogen electrode), and dissolution was reported to take place at open-circuit potentials . In comparison to intermetallics, in disordered structures the Mo content only needs to be a few atom % to be effective for the HER. , For disordered structures, a Mo content of ∼10 atom % leads to the highest activity among Ni–Mo disordered catalysts …”

“…In 117 In comparison to intermetallics, in disordered structures the Mo content only needs to be a few atom % to be effective for the HER. 175,179 For disordered structures, a Mo content of ∼10 atom % leads to the highest activity among Ni−Mo disordered catalysts. 180 Many studies involve unsupported Ni−Mo catalysts of several hundred of nanometers in size.…”

Challenging the Durability of Intermetallic Mo–Ni Compounds in the Hydrogen Evolution Reaction

“…Supplying our society with the continuously increasing demand of energy while simultaneously replacing the limited resources of fossil fuels by suitable renewable energy carriers is one of the major challenges of our century. − Therefore, massive energy storage of generated electricity from renewable and sustainable resources on a scale of gigawatt-hours in North America, Europe, and Asia will be needed . In this context, hydrogen generation by water electrolysis is a feasible way to convert electrical energy into chemical energy .…”