Facile synthesis of Zr- and Ta-based catalysts for the oxygen reduction reaction

Cathode catalysts for direct alcohol fuel cells (DAFCs) must have high catalytic activity for the oxygen reduction reaction (ORR), low cost, and high tolerance to the presence of methanol or ethanol. Pt is the benchmark catalyst for this application owing to its excellent electrocatalytic activity, but its high cost and low tolerance to the organic fuel permeating through the membrane have hindered the commercialization of DAFCs. Herein we present a facile synthesis route to obtain organic fuel-tolerant Zr- and Ta-based catalysts supported on carbon. This method consists of a simple precipitation of metal precursors followed by a heat treatment. X-ray diffraction analyses confirmed that the obtained samples were crystalline ZrO2-x and Na2Ta8O21-x having crystallite sizes of 26 and 32 nm, respectively. The thermal treatment effectively increased the activity of the catalysts towards the ORR, although further optimization is necessary. Both catalysts exhibited a high tolerance to the presence of methanol with only a moderate reduction in ORR activity even at high methanol concentration (0.5 mol/L).