Iron-Doped Nickel Cobalt Oxide Based High Performance Oxygen Evolution Reaction Electrode in Alkaline Media

Reducing the overpotentials in the oxygen evolution reaction (OER) in alkaline medium is very important for realizing efficient performance in aqueous metal-air rechargeable batteries and in the electrolysis of water. Noble metal compounds especially based on iridium and ruthenium are good electrocatalysts for OER. Besides these noble-metal-based catalysts, transition metal oxides of the perovskite, spinel and pyrochlore family are also promising electrocatalysts.  Since noble metals based catalysts, are not suitable for large-scale application like grid-scale energy storage the research on low-cost OER catalysts based on transition metal oxides is an important area of research.  Among various non-noble metal based catalysts, nickel- and cobalt-based mixed oxides, especially the spinel oxide, NiCo2O4, has shown significant activity for OER. [1] The cost of this type of transition metal compounds is significantly lower than that of iridium and ruthenium for a large scale energy storage or electrolysis. [2,3] We present in this talk results on high performance catalysts for oxygen evolution reaction, based on iron-doped NiCo2O4oxides. We have also developed a single-step, low cost, synthetic approach for catalysts and also an electrode. The proposed method is scalable for mass scale production without any major modification.     The catalysts are synthesized right on the electrode bypassing separate synthesis of powder catalysts and followed by the construction of the electrode. The direct synthesis of the catalysts on electrode makes the process simple, energy efficient, scalable. The synthesis consists of coating of the precursor solution containing the relevant metals on to a nickel foam electrode of geometric area 25 cm2.  This process is now followed by two steps heat treatment to form the final oxide coated electrode. The first step of the heat treatment helps to dry out coating solution on nickel foam. The second step of the heat treatment forms the final catalyst layer.   All catalysts sample prepared by this method were investigated using electron microscopy, X-ray diffraction and other material characterization methods.  The OER activity was studied in a three electrode cell in 1 M potassium hydroxide solution The steady state polarization method was employed to investigate OER activity. After collection of steady polarization data, electrodes were investigated further for stability. Typically, stability was tested by polarizing the electrode for 100 hours using chrono-potentiometric method at a current density 10 mA/cm2.  Figure 1a shows the results of second stage heat treatment temperature on the OER activity, and 1b shows the long term stability test results at a current density 10 mA/cm2. We have found that the overpotential for OER was strongly dependent on second stage heat treatment temperature, and for the best performing catalysts the over potential at 10 mA/cm2current density is ~210mV. The overpotential remained stable over the period of 100 hours. The presentation will discuss these findings more elaborately and offer some insights for the high performance.   Acknowledgement  The work presented here was funded by the ARPA-E Grids Program, the University of Southern California and the Loker Hydrocarbon Research Institute.  References: P. Rasiyah, A.C.C Tesung, J. Electrochem. Soc.  130, 2384 (1983). S. Malkhandi, B. Yang, A. K. Manohar, A. Manivannan,  G. K. S. Prakash and S. R. Narayanan,  J. Phys. Chem. Lett., 3, 967 (2012). S. Malkhandi, P. Trinh, A. K. Manohar, A. Manivannan,   G. K. Surya Prakash and S. R. Narayanan, “Design Insights for Tuning the Electrocatalytic Activity of Perovskite Oxides For the Oxygen Evolution Reaction” J. Phys. Chem. C (2015) in press. Figure 1