Improved Charge Transfer in a Mn₂O₃@Co_1.2Ni_1.8O₄ Hybrid for Highly Stable Alkaline Direct Methanol Fuel Cells with Good Methanol Tolerance

A three-dimensional Mn₂O₃@Co_1.2Ni_1.8O₄ 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 Co_1.2Ni_1.8O₄ 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@Co_1.2Ni_1.8O₄, 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@Co_1.2Ni_1.8O₄ 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, Mn^III could be oxidized into Mn^IV more easily, simultaneously providing an electron to the absorbed oxygen.