Membrane electrode assembly design to prevent CO2 crossover in CO2 reduction reaction electrolysis

Abstract

To reach a net-zero energy economy by 2050, it is critical to develop negative emission technologies, such as CO 2 reduction electrolyzers, but these devices still suffer from various issues including low utilization of CO 2 because of its cross-over from the cathode to the anode. This comment highlights the recent innovative design of membrane electrode assembly, utilizing a bipolar membrane and catholyte layer that blocks CO 2 cross-over and enables high CO 2 single-pass utilization.Low temperature (below 100 °C) CO 2 reduction reaction (CO 2 RR) electrolyzers are promising negative emission technologies that convert CO 2 to various value-added products 1,2 . These electrolyzers can be easily integrated with renewable power generation (solar and wind) to operate on renewable electricity. For CO 2 RR technologies to be commercially viable they must operate at high: (i) Faradaic efficiency (FE), (ii) conversion rate, (iii) selectivity and (iv) conversion efficiency 3 . It is challenging to achieve all of these four conditions in a single cell experiment, but it is even more difficult to translate the findings to a scaled-up electrolyzer stack system. Specific interest for low temperature electrolysis is its ability to generate multicarbon (C 2+ ) products, such as ethylene, ethanol, and propanol because of their commercial value. Recently, significant advances were made to reach competitive product selective current densities (>100 mA cm −2 ) in CO 2 RR to C 2+ products, with overall good stability. This was achieved with careful catalyst nanoparticles design, their integration within the gas diffusion layers to make gas diffusion electrodes, and with tailoring local environments by using ionomers or liquid electrolytes to achieve neutral or alkaline environments. This alkaline/neutral environment is essential for CO 2 RR cathodes because of the preferential formation of H 2 over C 2+ products in an acidic environment. Only very recently 4 researchers realized that basic chemistry is a big issue for CO 2 RR technology in alkaline environments: The rapid reaction of CO 2 with OHin alkaline media to form CO 3 2− is a thermodynamically favored reaction that results in a loss of CO 2 , consumption of OH − and non-steady-state operating conditions, where electrolyte is consumed:Interestingly, it requires much larger energy to regenerate CO 2 and OH − from aqueous CO 3 2− , and some studies suggest this value to be >230 kJ mol −1 5 . Overall, the energy stored in CO 2 RR electrolyzer is around 100-130 kJ/mol of electrons. Therefore, if one needs to regenerate electrolyte after the operation, it will be more energy intensive to do so than the energy stored in C 2+ products achieved through electrolysis. This is an inherent issue in alkaline/neutral media that many earlier studies have overlooked and only in the course of the last 2 years, or so, studies have started incorporating single-pass utilization (SPU) of CO 2 as one of the major metrics for the efficiency of the CO 2 RR electrolysis. This metric is defined as th...

Electrodeposited Porous Nickel–Copper as a Non-Noble Metal Catalyst for Urea-Assisted Anion Exchange Membrane Electrolysis for Hydrogen Production

“…No other byproducts were observed under these operating conditions (Figures S16 and S17). The intensity of CO 2 gas is comparatively lower than the N 2 gas signal, and this may be ascribed to losses arising from the immediate formation of CO 3 2– in the OH – environment, driven by thermodynamically favorable reaction energy (Δ G o = −56 kJ mol –1 ), in conjunction with losses via AEM crossover. , Moreover, step voltages were applied for over 2 h to monitor the intensity of MS signals. Figure a,b shows the MS signals for water electrolysis and urea electrolysis, respectively.…”

Tailoring hydrophilic and hydrophobic microenvironments for gas–liquid–solid triphase electrochemical reactions

“…For example, electrolyzers with GDEs and MEAs employ PTL to ensure the electrical connection between a current collector and catalyst layers, water supply and gas product removal/separation. Furthermore, the crossover of gaseous products (e.g., O 2 and H 2 for water electrolyzers) and reactants (e.g., CO 2 for CO 2 electrolyzers) across a membrane 172,173 is a practical issue that leads to efficiency, separation and safety problems in electrolyzers. Thus, these challenges present numerous opportunities for researchers.…”

“…, O 2 and H 2 for water electrolyzers) and reactants ( e.g. , CO 2 for CO 2 electrolyzers) across a membrane 172,173 is a practical issue that leads to efficiency, separation and safety problems in electrolyzers. Thus, these challenges present numerous opportunities for researchers.…”

The road to the electroreduction of CO2

“…Another important aspect of a CO 2 electrolyzer is ion management by membrane separation and the resulting cathode design. A commentary provided by Chang et al highlights recent advances in CO 2 electrolyzers with bipolar membranes (BPM) (10.1038/s42004-022-00806-0) 17 . By incorporating a non-buffer catholyte layer into a BPM electrolyzer, the CO 2 single-pass utilization (the ratio of carbon converted electrochemically to the total carbon input) can be enhanced due to the local chemical conversion of CO 3 2− and protons from the BPM.…”