(23a) Control of Fe-Ni Nanoparticle Activity for the Oxygen Evolution Reaction (OER) and Methanol Electrooxidation

Authors: 
Greenlee, L. F., University of Arkansas
Rentz, N. S., National Institute of Standards & Technology
Candelaria, S., National Institute of Standards and Technology
The electrolysis of water for hydrogen generation and the electrochemical oxidation of alternative fuels such as methanol for alkaline fuel cells currently relies on the use of precious metal catalysts. However, the scarcity and high cost of these precious metals lead to the search for earth-abundant alternatives with similar electrocatalytic properties. Key challenges in the development of catalysts for the oxygen evolution half reaction (OER) of water electrolysis remain; these challenges include reducing the overpotential of the reaction and developing non-precious metal catalysts that are stable and active with minimal mass transport limitations. For direct electrooxidation of alternative fuels such as methanol, non-precious metal alternatives to precious metals such as platinum and palladium are often much less active. Among the non-precious metals, multimetallic nickel-based catalysts show particular promise for their high stability and high activity for the oxygen evolution reaction (OER) half-reaction of water electrolysis. In particular, it has recently been demonstrated by Trotochaud, Burke, Boettcher, and co-authors that iron incorporation into nickel hydroxide and cobalt hydroxide catalysts causes a significant increase in the OER activity of the catalyst [1-3]. It is now understood that the iron is in fact the active site of such bimetallic catalysts [2]. Additionally, nickel has exhibited high activity for methanol oxidation, particularly when in the form of a bimetallic catalyst such as NiPd [4]. However, promising active catalysts that are comprised entirely of non-precious metals such as nickel and iron have not been often reported for alternative fuel electrooxidation. Furthermore, there is a need for the development of nanostructured catalysts that can address mass transport limitations inherent in bulk or film-based catalyst materials [2]. As such, there continues to be an opportunity in alkaline electrocatalyst development to discover and understand nanostructured catalyst materials for both OER and alternative fuel electrooxidation.

In this presentation, our results on the development and optimization of an FeNi hydroxide core-shell nanoparticle catalyst will be discussed for both OER and methanol electrooxidation. Through control of critical synthesis parameters, such as the addition rate of reducing agent, ratio of reducing agent to iron, and reaction time for nanoparticle synthesis, we have demonstrated the ability to tune nanoparticle catalyst activity for either OER or methanol electrooxidation. Results for maximum OER current as a function of the rate of addition of reducing agent sodium borohydride illustrate the sensitivity of catalyst performance to changes in synthesis parameters. Characterization of nanoparticle structure and phase will be discussed and correlated to electrochemical performance. Results suggest that tuning of the crystalline structure and order are critical to electrocatalyst performance optimization, as well as the presence of oxide and hydroxide.

References

[1] L. Trotochaud, S.L. Young, J.K. Ranney, S.W. Boettcher, Nickel-iron oxyhydroxide oxygen-evolution electrocatalysts: The role of intentional and incidental iron incorporation, J. Am. Chem. Soc., 136 (2014) 6744-6753.

[2] M.S. Burke, L.J. Enman, A.S. Batchellor, S.H. Zou, S.W. Boettcher, Oxygen evolution reaction electrocatalysis on transition metal oxides and (oxy)hydroxides: Activity trends and design principles, Chemistry of Materials, 27 (2015) 7549-7558.

[3] M.S. Burke, M.G. Kast, L. Trotochaud, A.M. Smith, S.W. Boettcher, Cobalt-iron (oxy)hydroxide oxygen evolution electrocatalysts: The role of structure and composition on activity, stability, and mechanism, J. Am. Chem. Soc., 137 (2015) 3638-3648.

[4] A. Dutta, J. Datta, Energy efficient role of Ni/NiO in PdNi nano catalyst used in alkaline DEFC, J. Mater. Chem. A, 2 (2014) 3237-3250.