Bipolar Membrane with Porous Anion Exchange Layer for Efficient and Long‐Term Stable Electrochemical Reduction of CO₂ to CO

Abstract

Bipolar membranes in forward bias have the potential to address several challenges of alkaline zero‐gap CO2 electrolyzers. However, the inevitable gas evolution of CO2 at the membrane junction typically leads to delamination and failure of the membrane after a few hours, limiting its applicability in electrolyzers so far. In this work, a bipolar membrane with a perforated anion exchange layer is presented that allows the CO2 gas to flow back to the cathode and thus preventing accumulation of gas at the junction. This configuration for the first time enables stable operation of a forward bias bipolar membrane showing a degradation rate of 0.5 mV h−1 in a 200 h constant current hold at 100 mA cm−2 and 3.1 V. Highest reported energy efficiency of EECO = 39% and Faradaic efficiency of FECO = 96% at 200 mA cm−2 among forward bipolar membranes prove that the perforated membrane does not compromise efficiency. A maximum CO2 single‐pass conversion of 52% at 0.75 mLCO2 min−1 cm−2 and a low specific energy consumption of 665 kJ mol−1 CO2 shows that this concept is superior not only to other bipolar membranes in the literature, but potentially also to conventional anion exchange membrane‐based electrolyzers.

Gas-Induced Structural Damages in Forward-Bias Bipolar Membrane CO2 Electrolysis Studied by Fast X-ray Tomography

“…There is still potential for BPM-CO2ELY, considering that currently available BPMs are not optimized for forward-bias CO2ELY. Modifying the BPM, e.g., the composition of the layers and the junction, as a way to enhance CO 2 back-diffusion toward the cathode should not only solve the degradation described in this study but also improve the CO 2 utilization for electrochemical reduction. Currently available BPMs also show higher Ohmic losses than that in purely anion or cation conducting membranes , and need to be improved for energy efficient application.…”

“…Empirical data suggest the need of an alkaline electrolyte for good performance and stability, e.g., KOH or KHCO 3 , at the anode . Recent studies could furthermore show that sufficient direct supply of alkali cations at the cathode improves performance and stability. − Effectively, cations not only have an apparent positive effect on the CO 2 reduction reaction but also lead to salt precipitation and fast performance degradation, calling for a delicate balance , or regularly regenerating the cathode . The effect of cations on the CO 2 reduction kinetics is currently a discussed topic in the field of CO2ELY, including the question whether modifying ionomers in the catalyst composition might potentially achieve the same functionality .…”

Advancements in Bipolar Membrane Electrodialysis Techniques for Carbon Capture

“…Disch et al conducted research aimed at overcoming challenges associated with alkaline zero-gap CO 2 electrolyzers using forward bias bipolar membranes. These membranes have shown promise, but their susceptibility to the accumulation of CO 2 gas at the membrane junction has limited their practical application, leading to delamination and eventual failure.…”

“…These anionic species migrate through the alkaline layer of the BPM to the interface, where they recombine with H + from the anode, ultimately forming CO 2 and H 2 O. 103 Disch et al 104 conducted research aimed at overcoming challenges associated with alkaline zero-gap CO 2 electrolyzers using forward bias bipolar membranes. These membranes have shown promise, but their susceptibility to the accumulation of CO 2 gas at the membrane junction has limited their practical application, leading to delamination and eventual failure.…”

Pure-Water-Fed Forward-Bias Bipolar Membrane CO2 Electrolyzer

“…In addition, using buffering electrolytes on the cathode side can lead to operation instabilities attributed to bubble formation and liquid breakthrough. , Other strategies such as oscillating voltage operation, CO 2 recovery, and novel reactor design have shown promises; however, most systems still cannot operate at industrially relevant conditions or address both of the two above-mentioned challenges. More recent works report water-fed bipolar-based CO 2 electrolyzers, which show a great promise in preventing CO 2 crossover. − However, these systems still face challenges in high cell voltages or periodic activation to sustain continuous and stable operation.…”