Li Mengran, Lees Eric W, Ju Wen, Subramanian Siddhartha, Yang Kailun, Bui Justin C, Iglesias van Montfort Hugo-Pieter, Abdinejad Maryam, Middelkoop Joost, Strasser Peter, Weber Adam Z, Bell Alexis T, Burdyny Thomas
Department of Chemical Engineering, Delft University of Technology; 9 van der Maasweg, Delft, 2629HZ, the Netherlands.
Department of Chemical Engineering, The University of Melbourne, Melbourne, VIC, 3010, Australia.
Nat Commun. 2024 Sep 19;15(1):8222. doi: 10.1038/s41467-024-52409-z.
Bipolar membranes in electrochemical CO conversion cells enable different reaction environments in the CO-reduction and O-evolution compartments. Under ideal conditions, water-splitting in the bipolar membrane allows for platinum-group-metal-free anode materials and high CO utilizations. In practice, however, even minor unwanted ion crossover limits stability to short time periods. Here we report the vital role of managing ionic species to improve CO conversion efficiency while preventing acidification of the anodic compartment. Through transport modelling, we identify that an anion-exchange ionomer in the catalyst layer improves local bicarbonate availability and increasing the proton transference number in the bipolar membranes increases CO regeneration and limits K concentration in the cathode region. Through experiments, we show that a uniform local distribution of bicarbonate ions increases the accessibility of reverted CO to the catalyst surface, improving Faradaic efficiency and limiting current densities by twofold. Using these insights, we demonstrate a fully platinum-group-metal-free bipolar membrane electrode assembly CO conversion system exhibiting <1% CO/cation crossover rates and 80-90% CO-to-CO utilization efficiency over 150 h operation at 100 mA cm without anolyte replenishment.
电化学CO转化电池中的双极膜能够在CO还原和析氧区室实现不同的反应环境。在理想条件下，双极膜中的水分解使得阳极材料无需铂族金属且CO利用率高。然而在实际中，即使是少量不必要的离子交叉也会将稳定性限制在短时间内。在此，我们报告了管理离子种类对于提高CO转化效率同时防止阳极区室酸化的关键作用。通过传输建模，我们发现催化剂层中的阴离子交换离聚物可提高局部碳酸氢根的可用性，并且增加双极膜中的质子迁移数可提高CO再生并限制阴极区域中的K浓度。通过实验，我们表明碳酸氢根离子的均匀局部分布增加了还原态CO与催化剂表面的接触，提高了法拉第效率并将电流密度限制了两倍。利用这些见解，我们展示了一种完全不含铂族金属的双极膜电极组件CO转化系统，在无阳极电解液补充的情况下，在100 mA cm下运行150小时，CO/阳离子交叉率<1%，CO到CO的利用率为80-90%。
