(569dx) On the Oxidative Reactivity of Nickel—Molybdenum Composite and Its Effect Towards Hydrogen Evolution

Hydrogen is an essential industrial commodity with global consumption of ~95 million tons per year. The majority of hydrogen comes from fossil fuels through steam methane reforming which is unsustainable due to its tremendously high carbon footprint. Electrolytic hydrogen, produced from renewable or nuclear energy, can help attain carbon neutrality. It uses platinum group metals (PGMs), which despite their exceptional performance are also unsustainable due to large global warming impacts and enormous material and energy requirement.

In the quest for sustainable alternatives to PGMs, nanoparticulate alloys/composites of abundant transition metals are potential candidates for green hydrogen production. Our lab is focused on the development of nickel-molybdenum (Ni–Mo) composites supported on oxidized carbon, which are catalytically active towards hydrogen evolution and oxidation in alkaline media. Our most advanced catalysts exhibit core@shell morphology, where the shell is primarily molybdenum-rich oxide and the core is a metallic nickel-rich alloy.

This talk discusses about the catalyst stability, an another important aspect for electrolyzer performance, complimenting the catalytic activity. We have observed that extended storage of Ni–Mo composites in air leads to bulk oxidation of the nanoparticles. This further results in reduced catalytic activity by approximately 10-fold over a storage period of several weeks. The overall rate of oxidative degradation follows a first-order decay-like trend, over which we observed increased evidence for bulk Ni and Mo oxide phases by powder X-ray diffraction. These findings further suggest that the metallic alloy phase, and not the oxide component of the synthesized catalyst, is the primary active site for hydrogen chemistry.

We have undertaken additional efforts to reduce or reverse oxidative degradation in Ni–Mo catalysts. Ongoing work is focused on understanding the extent to which degradation processes associated with sample storage are similar or different under operating conditions in functional water electrolyzer assemblies.