(581f) Hydrogen Evolution Electrocatalysis with Core-Shell Ni-Mo @ Oxides

Alkaline anion exchange membrane (AAEM) electrolyzers are promising for efficient and cost-effective hydrogen production because they offer a noncorrosive reaction environment that is conducive to the use of low-cost catalyst materials. As a result, active research is focused on developing robust membranes and on improving the sluggish kinetics of the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Ni-based catalysts, including Ni-Mo alloys, are known to be active non-precious catalysts for hydrogen evolution, but the mechanism for hydrogen evolution on these materials remains unclear. Moreover, the mixed-phase composition of the most active forms of Ni-Mo raise significant questions about the composition of the active site or sites. In this context, we are studying the composition, mechanism and practical performance of Ni-Mo nanoparticles with the final goal of designing even better catalysts for reversible alkaline hydrogen electrochemistry.

We recently showed that Ni-Mo alloy nanopowders consist of a Mo-rich oxide surrounding a Ni-rich alloy nanoparticle core, where the electrical resistivity of the oxide shell limits the practical activity of the catalyst.(Patil et al. 2019) We also found that these resistivity limitations can be mitigated by incorporating conductive carbon supports. The focus of this presentation will be on further studies of these Ni-Mo composites in terms of how synthesis and processing conditions influence their final composition and activity. We have found that the surface chemistry of the carbon support and the method used to incorporate the active catalyst each have a major effect on the dispersion and activity of Ni-Mo/C composites. The practical performance of the Ni-Mo/C catalysts was further characterized using accelerated degradation tests and by comparing proton and hydroxide ion exchange membrane ionomers in the catalyst films. We have also performed a series of in-situ TEM studies to directly monitor the nucleation and growth of Ni-Mo core-shell alloy@oxide nanoparticles from a crystalline NiMoO₄ precursor. The results suggest that at least two sequential reduction processes occur with corresponding changes in catalyst morphology. These morphological changes correlate with the catalytic performance of the composite toward hydrogen evolution, suggesting that thermal processing strategies can be optimized to obtain catalysts with still greater activity.

Reference:

Patil, Rituja B, Aayush Mantri, Stephen D House, Judith C Yang, and James R Mckone. 2019. “Enhancing the Performance of Ni-Mo Alkaline Hydrogen Evolution Electrocatalysts with Carbon Supports.” ACS Applied Energy Materials. doi:10.1021/acsaem.8b02087.