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Evidence for Oxygen Reduction Reaction Activity of a Ni(OH)2/Graphene Oxide Catalyst

Wednesday, May 14, 2014
Grand Foyer, Lobby Level (Hilton Orlando Bonnet Creek)
E. Farjami (NYC College of Technology, City University of New York), M. Rottmayer (Air Force Research Laboratory), and L. J. Deiner (NYC college of Technology, City University of New York)
Effective catalysis of the oxygen reduction reaction in alkaline solution is crucial to a variety of electrochemical energy storage and conversion devices like metal-air batteries and alkaline fuel cells.  While Pt-based catalysts exhibit excellent activity, their high cost and lack of stability motivates the search for alternative electrocatalysts.  Non-noble metal oxides like MnxOy have shown particular promise, especially when supported by carbon nanomaterials like graphene.  Most recently, the performance and stability of a MnxOy has shown additional improvement with the doping of Ni(OH)2.  The performance improvement is typically ascribed to stabilization of the Mn3+/Mn4+ couple, but it is also possible that Ni(OH)2 itself displays significant oxygen reduction reaction catalytic activity.  This work provides the first report of the oxygen reduction reaction activity of a Ni(OH)2nanoparticle catalyst supported by graphene oxide in basic media.

A Ni(OH)2/graphene oxide material was synthesized using a single step microwave reduction method. Cyclic voltammetry shows that the Ni(OH)2/graphene oxide material has a peak potential of -310 mV vs. Ag/AgCl, a shift of + 110 mV as compared to the unsupported Ni(OH)2 nanoparticles and + 90 mV as compared to the graphene oxide support alone.  Rotating disk electrode studies confirm that the activity of the Ni(OH)2/graphene oxide catalyst is greater than either the graphene oxide support or the Ni(OH)2 nanoparticles alone.  Significantly, the limiting current density of the oxygen reduction reaction on the Ni(OH)2/graphene oxide catalyst is 1.3 mA/cm2 (as normalized by electrochemically active surface area) and the electron transfer number is 3.5.  Chronoamperometry demonstrates that the Ni(OH)2/graphene oxide material is relatively stable, with the oxygen reduction current density sustaining a steady state value of 60 % of its initial value. Electrochemical impedance spectroscopy shows that the charge transfer resistance of the Ni(OH)2/graphene oxide catalyst is lower than either the Ni(OH)2 nanoparticles or the graphene oxide support.  Taken together, these data indicate that the Ni(OH)2/graphene oxide catalyst exhibits significant oxygen reduction reaction activity which may be related to the interaction of the support and the nanoparticles.