Anion exchange membrane fuel cells (AEMFCs) opens up the possibility of using non-platinum and/or non-platinum group metals (PGM) as electrocatalysts for both hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR). However, the slow kinetics of HOR along with the current lack of a durable and highly conducting OH^- ion membrane remain major bottlenecks limiting its practical application. HOR with PGM free catalysts are still in the early stages of research unlike ORR with non-PGM catalysts¹_. In order to overcome this limitation it is important to understand the mechanism of the HOR on the surface of the electro catalysts. It is considered that the two main descriptors, which enhance the electrocatalytic activity of the HOR, are the OH_ad or H_ad molecules on the surface of the catalytic materials.^2,3

Ni and its alloys with transition metals would be one of the alternative choices for the HOR as Raney Ni and some of the Ni based alloys have been found showing improved HOR activity.⁴ Morphology, size and surface of the metallic nanoparicles have significant role on the catalytic activity in their respective applications. In this work we have synthesized monodispersed NiCo, NiCu and NiFe based bimetallic alloy nanoparticles of less than 20 nm size by high temperature solvothermal process.⁵

The synthesized alloy nanoparticles have been evaluated for their electrocatalytic activity and stability towards the HOR in a conventional rotating disk electrode (RDE) configuration tehnique. The nanoparticles have also been characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) to understand their physicochemical properties.

The effect of surface state and alloying of the nanoparticles on the HOR kinetics is studied and analyzed in terms of mechanism and reaction steps involved. Our overall ambition in this work is to explore PGM free bi and trimetallic nanoparticles (NiM and NiMN) for the HOR and use them as anode catalysts in an operating AEM fuel cells.

References

1. Zhuang, Z. et al. Nickel supported on nitrogen-doped carbon nanotubes as hydrogen oxidation reaction catalyst in alkaline electrolyte. Nat.Commun.7, 10141(2016).
2. Strmcnik, D. et al. Improving the hydrogen oxidation reaction rate by promotion of hydroxyl adsorption. Nat.chem. 5,300-306 (2013).
3. Parsons, R.The rate of electrolytic hydrogen evolution and the heat of adsorption of hydrogen.Trans. Faraday Soc. 54, 1053–1063 (1958).
4. Kabir, S. et al. Platinum group metal-free NiMo hydrogen oxidation catalysts: high performance and durability in alkaline exchange membrane fuel cells. Jour.Mater.Chem. A, (2017).
5. Carenco,S. et al.Controlled design of size-tunable monodisperse nickel nanoparticles.Chem.Mater.22,1340-1349(2010).

Figure 1:Representative bright field scanning transmission electron microscopy (STEM) image of bimetallic NiCo nanoparticles