Mixed-metal oxide (MMO) films consisting of Ni-Fe and Ni-Co-Fe were investigated as electrocatalysts for the oxygen evolution reaction (OER) under alkaline conditions.[1] High surface area Ni-Fe-Co films on a Raney nickel support were produced by using aniline as a capping agent to optimize the catalyst morphology. The Raney nickel support provides excellent catalyst dispersion which results in high-active site utilization. This catalyst shows enhanced mass activity when compared to other Ni-Fe OER electrocatalysts.[2-4] Cyclic voltammetry of binary MMO catalysts shows changes in the Ni^2+/3+ transitions in films containing Fe or Co. In-situ X-ray absorption spectroscopy (XAS) analysis verifies the hypothesis that Fe stabilizes Ni in the 2+ oxidation state while Co facilitates oxidation to the 3+ state. The enhancement of the OER from the Ni-Fe-Co catalyst is a result of two effects (1) the presence of Co effectively “shrinks” the Ni and Fe local geometry resulting in an optimized Fe-OH/OOH bond strength and (2) the formation of a conductive Ni^IIIOOH phase at a lower overpotential as a result of charge transfer effects from Co. This conductive phase activates Fe sites which are inaccessible to electron transfer in the nonconductive Ni^II(OH)₂ lattice. Heat treatment studies of films at 400 ^oC in the presence of air show an improvement the OER activity of the Ni-Fe-Co catalyst but deactivates the Ni-Fe. This presentation will entail detailed correlation of electrochemical data (RDE and single cell) with in situ spectroscopy obtained using Raman and Synchrotron x-ray absorption.

Acknowledgements:

The authors gratefully acknowledge the financial support of the Department of Energy (DOE) via Energy Efficiency and Renewable Energy (EERE), under the auspices of an incubator effort lead by Proton On-Site and a new grant (DE-EE0006958 ) under the HydroGen initiative. Authors also acknowledge the support from arpa.e under their open initiative via a grant lead by Pajarito Powders, Albuquerque (DE-AR0000688). The support from (DOE) office of science under contract no DE-SC0012704 for building and maintaining the National Synchrotron Light Source-II (NSLS-II) at Brookhaven National Laboratory (BNL), Upton, NY and Thermo Fisher for instrumental support is gratefully acknowledged.

References

1. Bates, M.K., et al., Charge-Transfer Effects in Ni–Fe and Ni–Fe–Co Mixed-Metal Oxides for the Alkaline Oxygen Evolution Reaction. ACS Catalysis, 2016. 6(1): p. 155-161.
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