Research On The Stability Of Direct Methanol Fuel Cell Anode

Direct methanol fuel cell (DMFC) is gaining more and more attention due to its advantages of relatively widely available resources of the fuel,convenience of fuel storage,system simplicity, operating easily and environment friendly.The anode is one of the key materials related to DMFC’s characteristic, life and costs. Evaluating he performance of the DMFC anode not only is benefical to select catalyst and prepare anode but also have great significance to accelerate the DMFC large-scale applications.The anode characteristic is often evaluated by conventional electrochemical method in simulated DMFC environment. These results gotten from off-line environment can’t reflect the real state of anode at operating mode and provide the micro-area information. Thus, it is difficult to reveal the process of anode change under operating environment. In order to investigate the performance of battery and explain the degradation mechanism of anode, In-situ test of DMFC anode is conducted under operating mode. The electrochemical properties of the DMFC anode are characterized in simulated conditions by Cyclic Voltammograms (CV), Potentiostatic Polarization, Electrochemical Impedance Spectroscopy (EIS), Scanning Electrochemical Microscopy (SECM) and Localized Electrochemical Impedance Spectroscopy (LEIS).The results show that the forward and the backward oxidation peak potential of CV shift to the negative, and the corresponding peak current density decrease when the potential is raised from0.2V to0.6V at the same loading time. But at0.8V, the peak potential significantly moves to the right. While, when loading time extends (at the same loading potential), the forward and the backward oxidation peak current density of CV is increases and peak potential moves to the right. At the same time, the forward and backward current ratio decreases, which means the poison tolerance of catalyst becomes lower. After loading16h and72h at0.6V, the average catalysts particle size changes from3.4nm to3.6nm and4.4nm, increased5.88%and29.41%respectively. After72h under0.8V, the ratio PtRu in catalyst changes from2:1to3.9:1. The SECM shows that the catalytic activity of the anode catalyst is uneven distribution. In SECM test, the jagged current peaks of anode have a sharp change from4h at the same loading potential. The quantity and the intensity of current peaks reduces guadually with the increase of loading time.The LEIS of anode is also uneven distributed. The Jagged peaks of LEIS decreased and impedance value increase when the loading potential is increased and the loading time is extended. The following reason such as impedance increase, electrochemical activity reduce, catalyst particle size enlarge, the loss of Ru, etc, make the charge transfer and the electrochemical reaction on the surface of catalyst become more difficulty, which result in reducing the catalytic activity of anode.