Thin Layer Sonoelectrochemistry: Electrocatalysis in Oxygen Reduction Reaction (ORR) and Methanol Electrolysis

Abstract

In electrochemical energy systems such as fuel cells, important reactions include the oxygen reduction reaction (ORR) and methanol oxidation. Even with platinum catalysts, oxygen reduction kinetics in water at acidic pH are slow. In H₂ proton exchange membrane fuel cells (PEM FCs), ORR is the rate determining kinetic process. In direct reformation fuel cells run on methanol with an oxygen or air cathode, methanol oxidation kinetics are rate limiting. Limitations include slow electron transfer processes coupled to generation of oxidation by-products that adsorb to the electrode and lead to passivation. Sonoelectrochemistry in thin layers of electrolyte enhances electrochemical rates without visible cavitation using low power oscillators [1]. Here, thin layer sonoelectrochemistry coupled with cyclic voltammetry is used to evaluate impacts of sonication in a thin layer on the electrochemical response of oxygen and methanol . For voltammetry at platinum electrodes for saturated oxygen in acidic aqueous electrolyte, the rate of the ORR is enhanced several orders of magnitude as shown by fit of the cyclic voltammetric data. For stoichiometric (50:50) methanol in water with acid electrolyte, oxidation and reduction currents at platinum electrodes are increased almost ten fold as shown in cyclic voltammetric responses. Sonication may increase the rates of electron transfer and remove deposited partial oxidation products. Improved kinetics of oxygen reduction and methanol electrolysis may provide a means to improved electrochemical energy technologies, including hydrogen and direct reformation fuel cells. The energy needed to drive the oscillator represents a low parasitic loss on fuel cell performance. Reference [1] Johna Leddy, Chester G. Duda, Jacob Lyon, and William J. Leddy III, "Thin Layer Sonoelectrochemistry and Sonoelectrochemistry Devices and Methods," published 28 May 2015 as US Patent Application 20150147594 A1.