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Quantification of water transport in a CO2 electrolyzer
Energy & Environmental Science ( IF 32.5 ) Pub Date : 2020-11-18 , DOI: 10.1039/d0ee02219e
Danika G. Wheeler 1, 2, 3, 4 , Benjamin A. W. Mowbray 2, 3, 4, 5 , Angelica Reyes 1, 2, 3, 4 , Faezeh Habibzadeh 2, 3, 4, 5 , Jingfu He 2, 3, 4, 5 , Curtis P. Berlinguette 1, 2, 3, 4, 5
Affiliation  

A sufficient supply of water at the catalyst layer is needed to mediate the CO2 reduction reaction (CO2RR), yet too much water favours the competing hydrogen evolution reaction (HER) and lowers the efficiency of CO2 electrolysis. It is therefore important to quantify water at the cathode, but CO2 electrolyzers are typically enclosed systems where only the inputs and outputs can be readily measured. We report herein an analytical CO2RR electrolyzer with sensors in the cathode chamber to directly measure the relative humidity (RH) and temperature during electrolysis. These measurements enable the flow of water to be tracked inside the flow cell, and provide the boundary conditions necessary for a 3D model of mass transport and fluid flow in the cathode chamber. We developed a 3D model which showed that the molar fraction of water at the cathodic GDE/membrane interface, xH2O,mem, is constant under a range of applied current densities (25–200 mA cm−2) and CO2 flow rates (25–200 sccm), and does not change as a function of humidification of the CO2 feed. The value of xH2O,mem is held at parity because more water is drawn across the membrane (from the liquid-fed anode) when insufficient water is supplied to the cathode from the CO2 feed. This result points to a higher flux of water across the membrane when using drier CO2 feedstocks at higher flow rates and higher current densities. Consequently, undesirable anolyte crossover (which causes salt precipitation at the cathode) can be suppressed by maintaining a humidified CO2 feed. This 3D model can be used for a range of operating conditions, materials, and flow fields to help with CO2RR electrolyzer design and optimization.

中文翻译:

量化CO2电解槽中水的输送

在催化剂层需要足够的水供应以介导CO 2还原反应(CO 2 RR),但是太多的水有利于竞争性氢释放反应(HER),并降低了CO 2电解的效率。因此,重要的是量化阴极处的水,但是CO 2电解槽通常是封闭的系统,在该系统中,只有输入和输出可以很容易地测量。我们在此报告分析性CO 2RR电解槽在阴极室中带有传感器,可直接测量电解过程中的相对湿度(RH)和温度。这些测量使得能够在流通池内部跟踪水的流动,​​并提供了3D模型的质量传输和阴极室内流体流动所需的边界条件。我们开发了3D模型,该模型显示出在阴极GDE /膜界面处的水摩尔分数x H 2 O,mem在施加的电流密度(25-200 mA cm -2)和CO 2流量范围内是恒定的速率(25–200 sccm),并且不会随CO 2进料的加湿而变化。的值X ħ 2 O,MEM保持平价是因为当从CO 2进料向阴极提供的水不足时,有更多的水(从液体进给的阳极)流过膜。该结果表明当在较高的流速和较高的电流密度下使用干燥的CO 2原料时,较高的水通过膜的通量。因此,可以通过保持加湿的CO 2进料来抑制不希望的阳极电解液穿越(其导致盐在阴极沉淀)。该3D模型可用于各种运行条件,材料和流场,以帮助进行CO 2 RR电解槽的设计和优化。
更新日期:2020-11-18
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