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

Abstract

Molybdenum–nickel materials are catalysts of industrial interest for the hydrogen evolution reaction (HER). 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. Their intrinsic instability leads to molybdenum leaching, resulting in higher specific surface areas and nickel-enriched surfaces. These 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. Ni7Mo7, identified earlier as durable, proves to be highly unstable in the applied ADTs. The results show that the enhanced activity of unsupported bulk Mo–Ni electrodes can solely be ascribed to increased specific surface areas.

Inverse ‘intra-lattice’ charge transfer in nickel–molybdenum dual electrocatalysts regulated by under-coordinating the molybdenum center

“…Computational studies by Bader charge analysis, 58–62 give us the reasoning of the experimentally observed inverse charge transfer in the Ni 73 Mo alloy. 63 A 4 × 4 Ni (111) surface was constructed with 6 layers consisting of 80 atoms.…”

“…55,56 The E  of NMH-24 is closer to 1.53 V versus the reversible hydrogen electrode (RHE), which is suitable for creating a hole accumulation layer at the anode-electrolyte interface for triggering the water oxidation process. Computational studies by Bader charge analysis, [58][59][60][61][62] give us the reasoning of the experimentally observed inverse charge transfer in the Ni 73 Mo alloy. 63 A 4 × 4 Ni (111) surface was constructed with 6 layers consisting of 80 atoms.…”

Synthesis of Isostructural Intermetallic Sn–Pb–Bi–Pt Platform Materials for Catalytic Investigations

“…The developed protocol allows for the synthesis of stable (Sn,Pb,Bi)Pt bulk materials, on which not only a broad range of analytical investigations are possible but also the return to a well investigated initial state is possible by polishing of the surface. This has proven especially useful in the field of electrocatalysis as all investigations can be conducted on an identical sample. ,,,− , The use of unsupported bulk materials reduces complexity and allows for the determination of intrinsic materials properties, resulting in a great benefit to understand material changes also in heterogeneous gas-phase catalysis, such as steam reforming , or hydrogenation reactions by using powdered materials.…”

“…For this purpose, the investigation of bulk samples has proven to be beneficial as simple polishing can revert any changes to the thermodynamically equilibrated material. This allows for investigations with identical starting points by multiple techniques in different reactions. ,,− …”

Probing the activity and stability of MoO2 surface nanorod arrays for hydrogen evolution in an anion exchange membrane multi-cell water electrolysis stack

“…As reported previously, the dissolution of Mo has been shown to occur from surface Ni-Mo alloys under HER relevant conditions. 22,41 An activity decrease at a positive potential due to the dissolution of Mo oxides is a cause of performance loss. This will present stability issues, especially during the intermittent operation of industrial electrolyzers (the cathode potential changes in the anodic direction immediately aer the electrolyzer is disconnected from the power source).…”