Improved Charge Transfer in a Mn2O3@Co1.2Ni1.8O4 Hybrid for Highly Stable Alkaline Direct Methanol Fuel Cells with Good Methanol Tolerance.

A three-dimensional Mn2O3@Co1.2Ni1.8O4 hybrid was synthesized via facile two-step processes and employed as a cathode catalyst in direct methanol fuel cells (DMFCs) for the first time. Because of the unique architecture with ultrathin and porous nanosheets of the Co1.2Ni1.8O4 shell, this composite exhibits better electrochemical performance than the pristine Mn2O3. Remarkably, it shows excellent methanol tolerance, even in a high concentration solution. The DMFC was assembled with Mn2O3@Co1.2Ni1.8O4, polymer fiber membranes, and PtRu/C as the cathode, membrane, and anode, respectively. The power densities of 57.5 and 70.5 mW cm-2 were recorded at 18 and 28 °C, respectively, especially the former is the best result reported in the literature at such a low temperature. The stability of the Mn2O3@Co1.2Ni1.8O4 catalyzed cathode was evaluated, and the results show that this compound possesses excellent stability in a high methanol concentration. The improved electrochemical activity could be attributed to the narrow band gap of the hybrid, which accelerates the electrons jumping from the valence band to the conduction band. Therefore, MnIII could be oxidized into MnIV more easily, simultaneously providing an electron to the absorbed oxygen.