472650 Activity and Stability of Pure and Modified Coooh for Oxygen Evolution Reaction in Alkaline Medium

Tuesday, November 15, 2016: 1:10 PM
Franciscan C (Hilton San Francisco Union Square)
Zhu Chen1, Coleman Kronawitter1, Yao-wen Yeh2, Xiaofang Yang1, Peng Zhao3, Yao Nan4 and Bruce Koel1, (1)Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ, (2)Department of Electrical Engineering, Princeton University, Princeton, NJ, (3)Department of Chemistry, Princeton University, Princeton, NJ, (4)Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, NJ

Improving the efficiency of the oxygen evolution reaction (OER) is critical for a number emerging energy conversion devices such as metal-air batteries, fuel cells and water-splitting cells. High overpotentials are required to increase the reaction kinetics of the OER in both alkaline and acidic conditions, which leads to significant efficiency lost. As a result, significant research efforts have been devoted to the development of active OER catalysts to improve device efficiency. To date, iridium and ruthenium oxides are considered the most active catalysts for OER, however their high cost and low abundance prevent large-scale application. Thus, active, stable, and affordable OER catalysts are highly sought after.

Transition metal oxides are very promising candidates for OER due to their high abundance, high OER activities, and availability in a wide range of structures and chemical compositions that allows optimization for OER activity. Recently, theoretical calculations as well as empirical evidence from Raman and X-ray absorption experiments have identified oxyhydroxides to be the OER active phase for a number of transition metal oxides in alkaline conditions under OER-relevant potentials. As a result, understanding the activity and stability of oxyhydroxides in alkaline conditions is critical and can aid in the design and optimization of OER catalysts. In this study, we wish to understand the correlation between OER activity and the structure and chemical composition of transition metal oxyhydroxides. To achieve this goal, we synthesized cobalt oxyhydroxide (CoOOH) with a well-controlled nanowire morphology and different dopant concentrations. The pure and modified CoOOH nanowires were synthesized directly onto a conductive substrate that offers excellent electrical contact between the nanowire catalysts and improves the area accessible to the electrolyte—both of which are important considerations for practical OER electrodes. Pure and modified CoOOH catalysts were characterized using electron microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy prior to and after electrochemical testing.

These electrodes showed improved OER activity in 0.1M KOH for CoOOH with nickel incorporation, whereas Mn incorporation did not affect the OER activity of CoOOH. Ni-modified CoOOH exhibited a lower Tafel slope compared to the pure and Mn-modified CoOOH. This suggests a difference in the reaction rate-determining step for Ni-modified CoOOH. Using electrochemical impedance spectroscopy, we determined that Ni modification of CoOOH lowers the charge transfer resistance and enhances the stability of surface species, whereas Mn modification did not alter the charger transfer resistance and decreases the stability of surface species. These results provide new insights regarding the effects of incorporating transition metals in CoOOH on OER activity and illustrate the stabilization of surface species as a strategy for optimization of CoOOH catalysts for the OER in alkaline conditions.

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