Electrochemical Impedance Spectroscopy (EIS) Study of Ru-La Oxide Coatings in NaCl Solution

Abstract

Electrochemical surface structure and electrochemical performance of Ti based Ru-La oxide coatings in 3.5% NaCl solution have been investigated by electrochemical impedance spectroscopy (EIS), together with cyclic voltammetry (CV) and scanning electron microscopy (SEM). The best-fit circuit to EIS data of the coatings in the absence of the chlorine evolution reaction is R s (R ct Q dl), and that in the potential range of chlorine evolution reaction is R s (R f Q f)(R ct WQ dl). The high-frequency region corresponds to the impedance behavior of the coating, and the low-frequency region to that of the interface between outer surface and electrolyte. Results show that the pseudo-capacitances of the oxide film and the double layer increase with increasing La content, reaching a maximum at the nominal La content of 30 mol%. This finding agrees with the CV result, suggesting that the La additive in suitable amount can improve the electrochemical activity of the RuO 2 coating. The electric conductivity of the coatings, however, significantly decreases when nominal La content is larger than 30 mol% in the region of the chlorine evolution potential. A character with a Warburg impedance at low-frequency region suggests the relationship to passivation of the coating surface and specific adsorption, resulting in a dramatic decrease of electrocatalytic activity of the coatings at norminal La content of 70 mol%.

Near-Field Noise Prediction for Landing Gear Based on Detached Eddy Simulations

“…Due to the complex configuration and strong interactions with surrounding fluid, the landing gear noise possesses wide frequency range [1]. The computational resources needed by directly solving the far-field noise are prohibitively high since it is necessary to use low-dispersion and low-dissipation numerical schemes and also very fine grid that can resolve the wavelength of high frequency sound wave.…”

Comparative Study on Kinetics of Chlorine Evolution Reaction for Ru-La-O Oxide Coatings

“…无 机 材 料 学 报 第 30 卷 钌基氧化物涂层具有很高的电化学活性, 多年 来在氯碱工业、硫酸盐工业以及水电解、超电容、 燃料电池等领域都受到极大关注。 尽管人们对 RuO 2 涂层的析氯反应机理做了大量工作 [1][2] , 但所得到 的数据却存在较大的分歧, 例如 Tafel 斜率就有 120 [3] 、108 [4] 、 40~50 [5] 、40 [6][7] 、31~32 [8] 、38 [8] 和 30 mV [9] 等多种结果, 这种差异可能与阳极的制备 工艺、 表面吸附及氧化物表面状态等因素有关 [10][11] 。 由于反应机理的确证主要以动力学参数 Tafel 斜率 和氯离子反应级数为依据, 因此到目前为止, 对钌 基氧化物涂层析氯反应机理还没有获得一致认识。 已提出的析氯反应机理, 有 Volmer-Tafel(再结 合)机理 [12] 、Volmer-Heyrovsky(放电解析)机理 [5] 、 Kristalik 机理 [13] 以及阳极催化活性物参加反应的机 理 [14][15] [16] 。 在 RuO 2 氧化物电极中添加其他元素, 可以提 高其催化活性, 降低成本 [17][18][19] 。 有研究表明, 稀土元 素能够有效提高钌基氧化物涂层的催化活性 [20][21] , 其中 La 对电化学活性的影响最为明显 [22] 。但到目 前为止, 关于镧对钌基氧化物涂层析氯过程的动力 学影响还未见报道。 在前期对钌镧氧化物涂层成分、 表面结构、双电层界面及电化学活性等研究的基础 上 [23][24][25] , 本工作利用极化曲线、微分电容等实验技术 对该体系涂层的析氯反应机理作了进一步研究, 为钌 镧基系列氧化物涂层的研究提供实验和理论依据。 1 实验方法 Frumkin 吸附条件下, 其动力学方程为 [16] : [27][28][29] 。 此外, 我们还注意到随着电位不同, 在最小值两端 吸附/解析的电位也不同, 这是由于在电解质表面存 在 Cl¯和 OH¯的竞争性吸附所致 [30] 。根据文献 [28] 表面 OH 可能经历如下反应:…”