Analysis of Mass Flows and Membrane Cross-over in CO2 Reduction at High Current Densities in an MEA-Type Electrolyzer
Analysis of Mass Flows and Membrane Cross-over in CO2 Reduction at High Current Densities in an MEA-Type Electrolyzer
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DOI：
10.1021/acsami.9b13081
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发表时间：
2019-11-06
影响因子：
9.5
通讯作者：
Seger, Brian
中科院分区：
文献类型：
--
作者：
Larrazabal, Gaston O.;Strom-Hansen, Patrick;Seger, Brian
将膜电极组件（MEA）与高选择性催化剂集成的电池设计是在工业相关电流密度下减少欧姆损失并实现CO2还原的高能效的有前途的途径。在这项工作中，多孔银过滤膜被证明是简单而有效的气体扩散电极，用于在MEA型装置中在高电流密度下将CO2还原为CO。一氧化碳的分电流密度高达约。200 mA cm（-2）。3.3 V，与最小的H-2生产串联。然而，阴极和阳极出口流的分析表明，CO2跨越阴离子交换膜，主要是在CO 32的形式-但部分作为HCOO-在阴极上产生，实际上超过了CO2转化为目标产品的量，导致在一个不良的利用反应物和在早期开始的传质限制。此外，CO2交叉导致从阴极室的出口流速的非化学计量的减少。如果将CO2的入口流速用作计算部分电流密度和法拉第效率的参考，则这种效应可能导致催化性能的显著高估。这项工作的结果强调了进行碳平衡的重要性，除了传统的活性和选择性测量，以充分评估高电流密度下CO2还原装置的性能，并为未来旨在减轻MEA型电解槽中CO2还原膜交叉的努力提供信息。
Cell designs that integrate membrane-electrode assemblies (MEAs) with highly selective catalysts are a promising route to reduce ohmic losses and achieve high energy efficiency in CO2 reduction at industrially relevant current densities. In this work, porous silver filtration membranes are demonstrated as simple and efficient gas-diffusion electrodes for CO2 reduction to CO at high current densities in an MEA-type device. A partial current density for CO of up to ca. 200 mA cm(-2) was achieved at a cell voltage of ca. 3.3 V, in tandem with minimal H-2 production. However, the analysis of cathodic and anodic outlet streams revealed that CO2 cross-over across the anion-exchange membranes, mostly in the form of CO32- but partially as HCOO- generated over the cathode, actually exceeds the amount of CO2 converted to the target product, resulting in a poor utilization of the reactant and in the early onset of mass transfer limitations. In addition, CO2 cross-over leads to a nonstoichiometric decrease of the outlet flow rate from the cathodic compartment. This effect can lead to a substantial overestimation of catalytic performance if the inlet flow rate of CO2 is used as reference for calculating partial current densities and Faradaic efficiencies. The results of this work highlight the importance of carrying out a carbon balance, in addition to traditional measurements of activity and selectivity, to adequately assess the performance of CO2 reduction devices at high current densities, and inform future efforts aimed at mitigating membrane cross-over in MEA-type electrolyzers for CO2 reduction.