Measurement of Chemical Impedance for Interface of Electrocatalysis with Servo-analyzer Method and its Applications.

建立了用伺服分析仪测量化学阻抗的技术方法，并对燃料电池电极的电催化活性进行了估计。1. 频率响应分析仪（FRA）阻抗法的适用性：(1)利用FRA阻抗法获得了三维Cole-Cole图。(2)根据基本过程（如转移、扩散和成膜）的表达式，复平面形成一个半圆，其直径与转移反应和/或电极上的成膜阻力成正比。2. 用FRA阻抗法评价燃料电池阳极的电催化活性：(1)四氢硼酸盐在碱性溶液中具有良好的稳定性和阳极上的负电位，有望成为燃料电池良好的阳极活性物质。为了研究燃料阳极氧化过程中的电催化活性，在-0.7 V （vs，Hg/HgO在5M-NaOH中）条件下对Ni、Ni-Pd和Pd阳极进行了FRA阻抗法研究，其中Ni在碱性溶液中的钝化区域。(2) FRA分析结果表明，Ni-Pd阳极的复杂阻抗图（Cole-Cole图）中包含两个半圆。这种模式可以解释为燃料在阳极处的氧化（高频部分）和在图的低频部分表面上形成的氧化膜。随着合金中Pd含量的增加，氧化膜的形成受到抑制。而对于Ni- pd合金阳极，放电电流密度相对于Ni电极逐渐减小。(3)添加Pd的电催化效应表明，在含有2.5原子%-Pd的合金电极上，放电电流密度增加，比添加2.5原子%-Pd的合金电极的放电电流密度下降得更快。结果表明，放电后Ni和Ni-Pd阳极表面均存在氢氧化镍，导致电催化活性失活，而在-0.7V放电时，Ni-2.5原子%Pd合金则使电催化活性增强。FRA阻抗法有助于估计电催化活性。少

Technical method for chemical impedance measurement has been established with servo-analyzer and the electrocatalytic activity of fuel cell electrodes is estimated. 1. Applicability of a frequency response analyzer (FRA) impedance method: (1) Three dimensional Cole-Cole plots have been obtained by use of the FRA impedance method. (2) According to expression of rudimentary processes (such as transfer, diffusion, and film formation), the comples plane pictures a hemicircle, the diameter of which is proportional to the resitance of transfer reaction and/or film formation on the electrode. 2. Evaluation of electrocatalytic activity of the anode for a fuel cell with the FRA impedance method: (1) Tetrahydroborate is expected to be favorable anodic active mass for the fuel cell because of its good stability in alkaline solutions and negative potential on the anode. In order to study the electrocatalytic activity during the anodic oxidation of the fuel, the FRA impedance method has been carrie … More d out on Ni, Ni-Pd, and Pd anodes at -0.7 V (vs,Hg/HgO in 5M-NaOH) where the region of passivation of Ni in the alkaline solutions. (2) From results of the FRA analysis, two hemicircles were included in the complex-plane of impedance diagram (Cole-Cole plot) for the Ni-Pd anode. This pattern may be explained in terms of both the oxidation of the fuel at the anode in a high-frequency part and an oxide film formed on the surface in a low-frequency part of the diagram. The formation of the oxide film was inhibited with increasing the Pd content of the alloy. However, for the Ni-Pd alloy anode, the discharge current density decreased gradually in comparison with that of the Ni electrode. (3) The electrocatalytic effect of added Pd is shown that the discharge current density was increased on the alloy electrode containing 2.5atom%-Pd and it was decreased rapidly more than the addition of 2.5atom%-Pd. It is concluded that the nickel hydroxide, which was observed on the surfaces of both Ni and Ni-Pd anodes after discharge from ESCA spectra, contributes to the deactivation of the electrocatalytic activity, whereas the Ni-2.5atom%Pd alloy will increase it during discharge at -0.7V. The FRA impedance method facilitates to estimate the electrocatalytic activity. Less