Carbon-supported nickel-doped manganese oxides as electrocatalysts for the oxygen reduction reaction in the presence of sodium borohydride

The electrocatalytic activity for the oxygen reduction reaction of nickel-doped MnOx, nanoparticles, dispersed onto different carbon powders (M1000, MM225 and E350) is studied in alkaline media in the presence of borohydride ions. Differential electrochemical mass spectrometry (DEMS) is used to quantify the H-2 yields coming from the borohydride hydrolysis as a function of the electrode potential. The polarization results show that materials containing Ni segregate phases present significant Faradaic currents for the borohydride oxidation, while the on-line DEMS results clearly evidence the production of H-2. For these electrocatalysts, the presence of BH4- induces a decrease of the overall ORR activity, and this is assigned, into a large extent, to a superposition of the ORR reduction currents with the currents related to the direct borohydride oxidation. This effect is far more pronounced for the electrocatalyst dispersed onto the E350 carbon. On the contrary, materials dispersed onto M1000 carbon and without Ni segregated phases seem tolerant to the presence of BH4- ions. Therefore, these materials may be an alternative to be used as cathode electrocatalysts of direct borohydride fuel cells.(C) 2012 Elsevier B.V. All rights reserved.