No abstract

New 3D junction bipolar membrane made by polymer electrospinning allows for very high water splitting current densities.

No abstract

Bipolar membranes maintain a steady pH in electrolytic cells through water autodissociation at the interface between their cation- and anion-exchange layers. We analyze the balance of electric field and catalysis in accelerating this reaction.

that combine an anode reaction, typically oxygen evolution, with the CO 2 RR for the conversion of CO 2 to organic products has been gaining attention as well. [3] In order to be economically competitive, CO 2 electrolysis devices must achieve operating parameters that are similar to those of commercial water electrolyzers. That is, they should be able to operate continuously with high Faradaic and energy efficiency, and with current densities in the 1-2 A cm −2 range. At such high current densities, product crossover needs to be considered as a loss mechanism. In fuel cell technology, particularly in direct alcohol fuel cells, organic molecules can pass through polymer electrolyte membranes (PEMs) to be oxidized electrocatalytically, substantially lowering the overall efficiency of the device. [4] Because crossover is primarily driven by electrokinetic effects, its rate increases with increasing current density. For CO 2 electrolysis, even though there is no universal device design as yet, product crossover issues should be anticipated and indeed have already been identified in some studies of PEM-based CO 2 electrolyzers. [5] Thus, there is a need to identify membranes that can meet the operating requirements of CO 2 electrolysis cells while minimizing product crossover.Several groups have recently demonstrated the benefits of using bipolar membranes (BPMs) to maintain a steady electrolyte pH and prevent electrolyte crossover in electrolysis cells. With monopolar membranes, these performance parameters can be achieved only at extremes of pH. [6] Over the past few years, BPMs have been successfully incorporated into both electrochemical and photo-electrochemical devices for water and CO 2 electrolysis. [3c,7] In a BPM, anion-and cation-exchange layers are joined together at an interfacial layer that catalyzes the autodissociation of water. Under reverse bias conditions, H + and OH − ions are generated in the catalytic layer and are driven outward. The flux of protons in the BPM opposes the direction of product crossover from the cathode to the anode of an electrolytic cell. Thus, one should expect the electromigration of anionic products, as well as transport of neutral molecules by electroosmotic drag, to be minimized in BPM-based CO 2 electrolysis cells.We compare here crossover through anion-exchange membranes (AEMs) and BPMs in cells that simulate the conditions As electrocatalysts and electrolyzer designs for CO 2 reduction continue to improve in terms of current density and product selectivity, product crossover from the cathode to the anode is a loss mechanism that is relatively unexplored. The crossover rates of formate, methanol, and ethanol, which are desirable CO 2 reduction products, are compared in electrolyzers containing anion-exchange membranes and bipolar membranes. The crossover of formate, an anionic CO 2 reduction product, occurs by electromigration through anion-exchange membranes, and its rate increases linearly with current density. Crossover of electroneutral methanol or ethanol thr...