Electrocatalytic Mineralization of Urea in Aqueous Medium By Means of Ni(II)Cyclam-Modified Nanoparticulate TiO 2 Anodes and Simultaneous Electrogeneration of H 2 on Pt Cathodes

In this investigation we studied the electrocatalytic mineralization of urea contained in alkaline aqueous medium by means of Ni(II)cyclam-modified nanoparticulate TiO 2 films (OTE/TiO 2 /Ni(II)cyclam, where an optically transparent electrode OTE was utilized as electrons collector) and the simultaneous electrogeneration of H 2 through the H 2 O reduction on Pt cathodes which were inserted in the same cell. Our results showed that the standard potential for the H 2 evolution (E° H2O/ H2 = -0.83V vs. NHE) was achieved on the Pt cathode when a potential of 1.0V vs. NHE was applied to the OTE/TiO 2 /Ni(II)cyclam//electrolyte interface (where the urea mineralization was taking place). On the contrary, the standard potential for the H 2 evolution was achieved on the same Pt electrode when a potential of 1.2V vs. NHE was applied to the OTE/Ni(II)cyclam//electrolyte interface (in the absence of TiO 2 ). These interesting results demonstrated that the urea oxidation potential on Ni(II)cyclam-modified OTEs was 0.2V cathodically-shifted in the presence of nanoparticulate TiO 2 . Furthermore, H 2 was continuously evolved for 1h from Pt cathodes in three-electrodes cells where aqueous urea solutions were simultaneously electrolyzed on OTE/TiO 2 /Ni(II)cyclam or OTE/Ni(II)cyclam electrodes. Interestingly, measurements of total organic carbon (TOC) which were carried out in the urea solutions with and without electrolytic treatment, revealed that the H 2 evolution proceeds on a Pt cathode when the mineralization of urea achieves efficiencies of 20.8 and 10.4% on OTE/TiO 2 /Ni(II)cyclam and OTE/Ni(II)cyclam electrodes, respectively. These new results demonstrate that the OTE/TiO 2 /Ni(II)cyclam electrodes represents a novel pathway to carry out the electrochemical generation of H 2 from urea as energy carrier.