Development of Highly-Efficient CO 2 Electrolysis Cell Stacks

Low-temperature CO 2 electrolysis technology, which converts CO 2 into valuable products, has attracted attention for its potential to mitigate climate change caused by global warming. Various products, such as CO and ethylene glycol, can be obtained from electrochemical reactions [1,2]. CO, a useful raw material for hydrocarbons, is a particularly simple product. In order to implement an industrial-scale low-temperature CO 2 electrolysis system, we must further reinforce the properties of the CO 2 electrolysis cell: namely, energetic (energy conversion) efficiency, CO 2 conversion rate (current density and scaling) and durability. For realizing high energetic efficiency, decreasing ohmic resistance and overvoltage is required. Therefore, a zero-gap electrolysis cell, which has short electrodes distance leading to lower ohmic resistance, has been adopted. The zero-gap configuration contains a membrane electrode assembly (MEA) constructed from cathode and anode electrodes and a diaphragm. Anion exchange membranes (AEMs) have been mainly used in past research as the diaphragm, however, the AEMs have several shortcomings for practical use as the diaphragm, e.g., low thermal stability, weak mechanical strength and high cost. In this work, we have focused on porous membranes as a novel diaphragm which is more suitable for overcoming those instabilities and costs. We have achieved an increase in energetic efficiency of the zero-gap CO 2 electrolysis cell using the porous membrane when compared to that of AEMs. We have experimentally revealed higher ion permeability, lower ohmic resistance and lower overvoltage when using the porous membrane, resulting in improvement of the energetic efficiency. Regarding CO 2 conversion rate and durability, we have developed a large-scale cell stack constructed with ten layers of a 100 cm 2 size cell and demonstrated durable operation over one month. This work is partially supported by the Ministry of the Environment, Government of Japan. [1] Y. Kofuji, A. Ono, Y. Sugano, A. Motoshige, Y. Kudo, M. Yamagiwa, J. Tamura, S. Mikoshiba and R. Kitagawa, Chem. Lett. 50 , 482 (2021). [2] J. Tamura, A. Ono, Y. Sugano, C. Huang, N. Hideyuki, and S. Mikoshiba, Phys. Chem. Chem. Phys. 17 , 26072 (2015).