(141e) Alkaline Hydrogen Evolution from Ni–Mo Intermetallics with High Mo Content
AIChE Annual Meeting
2017
2017 Annual Meeting
Catalysis and Reaction Engineering Division
Electrocatalysis and Photoelectrocatalysis II: HER/HOR
Monday, October 30, 2017 - 1:48pm to 2:06pm
Prior work on NiâMo electrocatalysts has suggested that the alloy phase exhibits monotonically increasing HER activity as the bulk Mo mole fraction is increased.3 However, the accessible composition range for binary NiâMo alloys is constrained by the solid solubility of Mo in the Ni fcc lattice, which is only ~25 mol% at 1000 °C. Surface-science experiments on bulk Ni0.8Mo0.2 alloys have indicated that the topmost atomic layer becomes considerably enriched in Mo, up to approximately equimolar Mo and Ni.4 Thus, the question remains as to how much Mo is present in the most active NiâMo binary HER electrocatalyst surface, let alone what is the mechanism for enhanced activity.
In this presentation, I will discuss recent and ongoing work aimed at understanding the influence of bulk composition on the activity of nanostructured NiâMo alkaline HER catalysts.5 We synthesized unsupported powders of Ni, Ni0.92Mo0.08 alloy, and the intermetallic compound Mo7Ni7. Mass-specific activity was found to be highest for the 8 mol% Mo alloy, but these data were clearly convoluted by catalyst morphologies, as the 50 mol% Mo intermetallic exhibited very low surface roughness. Attempts to account for electrochemically active surface area using a straightforward method based on electrochemical impedance spectroscopy (EIS) yielded unexpected results that conflicted with morphological analysis from electron microscopy. We have therefore postulated that Mo undergoes a pseudocapacitive redox transition near the onset potential for the HER, leading to erroneous results from EIS measurements. These results further implicate a plausible bifunctional catalytic mechanism that explicitly involves Mo redox transitions.
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(5) Csernica, P. M.; McKone, J. R.; Mulzer, C. R.; Dichtel, W. R.; Abruña, H. D.; DiSalvo, F. J. ACS Catal. 2017, 3375â3383.