Expanding Opportunities for Urea Electro-oxidation for Both Hydrogen Energy Storage and Cleaner Water

Abstract

Oxidation of urea over nickel-catalysts is capable of such activity as to potentially disrupt several industrial and scientific fields, such as fuel cell power, and environmental pollution remediation. Though well suited for photoelectrochemical applications the reaction has commonly observed a loss in activity coinciding with the onset of oxygen evolution, leaving a narrow ~0.3 V electrochemical window. This narrow window limits many options for semiconductor substrates in a photoactive system. By adsorbing Ni-ions onto high surface area carbon black (CB) electrodes, instead of using metallic Ni catalysts, the loss in activity is avoided. The resulting oxidation window is expanded to over 1 V positive of urea’s oxidation onset potential. In addition to the expanded oxidation window, the use of a specially designed rotating-ring disc electrode is explored to electrochemically modify the local pH environment to limit the alkalinity of the bulk aqueous system. It is shown that with proper system parameters urea electro-oxidation is able to operate at 1 mA/cm2 despite the bulk solution’s neutral pH. This allows for a potentially additive-free use of this technology in environmental applications, or austere locations.