Electrochemical continuous separation of oxygen from air (Ⅰ): Optimum of single cell performances

doi:10.11949/j.issn.0438-1157.20151502

Abstract

Abstract:

With rapid development of industrial processes, in particular more recently influenced by “Haze”, air quality draws more and more attentions. A refill of oxygen in air is one of crucial solutions to improve air quality. In contrast to conventional technologies for oxygen production (i.e. physical separation of air, chemical reactions, water electrolysis), the innovative technology of electrochemical continuous separation of oxygen from air features separation of pure oxygen from air, high efficiency, continuous operation, environment friendly, silent operation, ease of scale up and applicability to indoor or outdoor fields. This technology involves two crucial components of polymer electrolyte fuel cells and solid polymer electrolyte water electrolysis (abbreviated as fuel cell and electrolyzer). In this article, the effect of operation conditions on single cell performance such as operation temperature, reactant gases utilization ratios, relative humidity and pressure, etc. for fuel cell was investigated, as well as the ways of water supply (at anode and/or cathode), water flow rate and operation temperature, etc. for electrolyzer. In terms of fuel cell, the polarization curve was measured, the electrochemical impedance spectra were conducted and the ionic conductivity and activation energy of Nafion^® membrane were calculated. Polarization curve was fitted to obtain intrinsic parameters including Tafel slope, exchange current density of oxygen reduction reaction (i₀) and m, n, related to mass transfer etc. It showed that the optimum of fuel cell was under conditions of ambient pressure, 60℃ of operation temperature, 0.42 W·cm^-2 of peak power density, 77 mohm·cm² of cell areal resistance (membrane) and 41.4 mS·cm^-1 of ionic conductivity. The Tafel slope slightly varied with temperature, ca. 120 mV·dec^-1, but was influenced by the relative humidity. The relative humidity remarkably affected the fuel cell performances. In electrolyzer, the optimum was under conditions of 65℃ of operation temperature, 1.08 ohm·cm² of cell areal resistance and 11.7 mS·cm^-1 of ionic conductivity. The effect of water flow rate on performance was negligible. The ways of water supply follow an order of both anode and cathode≈anode>cathode. Under above conditions, activation energies of Nafion^®211 and Nafion^®115 membranes were calculated as 3.75 and 4.61 kJ·mol^-1, respectively. Based on the optimum of single cell performances of fuel cell and electrolyzer, in this article, the preliminary experimental data were provided for the subsequent implementation of scale up of cell stack system for oxygen production.

Key words: oxygen production, polymer electrolyte fuel cells, solid polymer electrolyte water electrolysis, electrochemistry, separation, optimization

摘要：

随着工业化进程高速发展,尤其受近期“雾霾”的影响,大气环境质量越来越受重视。空气中氧气补给是提高空气质量的关键方法之一。相对于传统制氧技术(如空气物理分离法、化学法以及水电解法等),空气源电化学连续分离制纯氧技术具有空气源分离制纯氧、能量效率高、连续运行、环境友好、安静、易规模放大等特点,可实现室内外场合应用。该技术的关键部件是质子交换膜燃料电池和固体聚合物电解质电解池(简称燃料电池和电解池)。分别考察了其单池操作条件对性能的影响,如燃料电池的操作温度、相对湿度、气体利用率和压强,以及电解池的供水方式、循环水流速、操作温度等。测试了燃料电池单池极化曲线、电化学交流阻抗谱,并计算了膜电导率和活化能。对极化曲线进行拟合得出塔菲尔(Tafel)斜率、氧还原反应交换电流密度i₀以及传质影响参数m、n等基本动力学参数。结果表明,氢空燃料电池单池最优化条件为:常压条件下,操作温度为60℃,峰值功率密度可达0.42 W·cm^-2,膜面电阻为77 mΩ·cm²,膜电导率为41.4 mS·cm^-1。Tafel斜率受温度影响较小,在120 mV·dec^-1左右,但受相对湿度影响较大。相对湿度对单池性能影响显著。电解池单池最优化操作条件为:操作温度对性能影响较大且最佳为65℃,膜面电阻为1.08 Ω·cm²,膜电导率为11.7 mS·cm^-1。循环水流速对性能影响较小。供水方式的优劣次序为两极供水≈阳极供水>阴极供水。在上述实验条件下,燃料电池中Nafion^®211膜和电解池中Nafion^®115膜的活化能计算值分别为3.75和4.61 kJ·mol^-1。基于燃料电池和电解池的单池电化学性能优化,研究结果可为后续的制氧机系统中电池堆的实施提供实验依据。

关键词: 制氧, 质子交换膜燃料电池, 固体聚合物电解质电解池, 电化学, 分离, 优化

CLC Number:

O646

ZHU Xiaobing, ZHANG Jianhui, LI Xiaosong, LIU Jinglin, LIU Jianhao, JIN Can. Electrochemical continuous separation of oxygen from air (Ⅰ): Optimum of single cell performances[J]. CIESC Journal, 2016, 67(5): 2022-2032.

朱晓兵, 张建辉, 李小松, 刘景林, 刘剑豪, 金灿. 空气源电化学连续分离制氧(Ⅰ):单池性能优化[J]. 化工学报, 2016, 67(5): 2022-2032.

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