Abstract:

The electrodeposited PbO₂ coating on stainless steel is feasible to apply on the cathode plate of proton exchange membrane fuel cell, but the PbO₂ coating prepared by the direct current (DC) process has poor compactness and insufficient corrosion resistance. In this paper, the pulse-controlled process of electrodepositing PbO₂ coating on 316 stainless steel was studied, the effects of parameters such as current density, frequency and duty cycle on the growth rate and microstructure were investigated, and the performance of the coating in the fuel cell environment was further investigated. Focusing on the electrochemical performance of PbO₂ coating at high potentials. the microstructure and XRD results showed that the PbO₂ coating by pulse electrodeposition had finer grains and denser structure than the coating by DC. The potentiodynamic polarization results indicated that the corrosion potential of the pulsed coating was slightly higher than that of the DC, and the corrosion current density was reduced by an order of magnitude. In the high potential polarization test, compared with the DC coating, the current density of the pulse process coating was significantly lower, the stability of the coating was significantly improved, the damage degree under high potential was less, and the substrate could be better protected. The polarization test at working potential showed that the reduction of PbO₂ was more serious in the anodic environment, but only a slight reduction occured in the cathodic environment. In a word, compared with the DC coating, the microstructure of the pulse coating was denser and finer, and had good corrosion resistance, especially the better stability at high potential, and it had a better application on the PEMFC cathode plate.

Key words: fuel cell, bipolar plates, film, pulse electrodeposition, high potential

摘要：

不锈钢表面电沉积PbO₂涂层在质子交换膜燃料电池（PEMFC）阴极板上具有应用可行性，但是传统直流工艺制备的PbO₂涂层存在致密性不佳、耐腐蚀性差的问题。本文研究了在316不锈钢上电沉积PbO₂涂层的脉冲控制工艺，考察了电流密度、频率和占空比等参数对生长速率和微观形貌的影响，进一步在燃料电池环境下对涂层的性能进行系统地测试，着重探究了PbO₂涂层在高电位下的电化学性能。微观形貌和XRD结果表明，脉冲电沉积PbO₂涂层比直流工艺的涂层晶粒更细小、组织更致密。动电位极化结果显示，脉冲工艺涂层的自腐蚀电位比直流工艺略有提升，腐蚀电流密度降低了一个数量级；在高电位的极化测试中，相比于直流工艺，脉冲电沉积涂层的电流密度显著减小，镀层的稳定性明显提升，在高电位下的破坏程度较小，能够更好地保护基体。正常工作电位下的极化测试表明，PbO₂在阳极环境下还原较严重，但在阴极环境下只有轻微的还原现象发生。总之，相比直流电沉积PbO₂涂层，脉冲电沉积涂层的微观组织结构更致密、细腻，耐蚀性能也更佳，尤其是在高电位下具有较好的稳定性能，在PEMFC阴极板上具有更好的适用性。

关键词: 燃料电池, 双极板, 膜, 脉冲电沉积, 高电位