Future basic anion-exchange membrane in electrolytic cell where
2020 March 9, Washington State University Professor Lin Yue River and Alamos Laboratory Professor Yu Seung Kim common reported a highly quaternized polystyrene ionic polymer as an electrode binder , and paired with the low cost oxygen evolution catalyst is Ni-Fe, pure water system assembled in alkaline water electrolysers AEM having a voltage of 2.7 cm -2 of the high current density at 1.8 V. This not only greatly reduces the cost, and its hydrogen production performance comparable to a proton exchange membrane . The article to \”Highly quaternized polystyrenes for high performance anion exchange membrane water electrolysers\” was published in Nature Energy journals. 2020 April 28, Nature Energy published online US Department of Chemical Engineering University of South Carolina Prof. William E. Mustain and Atlanta, Georgia Institute of technology Prof. Paul A. Kohl wrote entitled \”Improving alkaline ionomers\” view article, and for the development of future cell AEM It provides direction. thousand readers have a thousand eyes of Hamlet, deep plowing in the field for many years, Daniel is how you see it? Let us follow the perspective of two large cattle to re-interpret this be called a major breakthrough in the field of water electrolysis hydrogen production.
Studies pain points
Hydrogen If you want to become a future energy carrier, must be the same as gasoline, allowing consumers around the world can use anytime, anywhere. Therefore, in order to avoid costly and inefficient practical application of collection and distribution networks, small and medium scaleThe hydrogen production also requires economizing. Water electrolysis hydrogen production technology is an important means to achieve sustainable hydrogen energy economy. Currently the most mature technology commercially alkaline water electrolysis, using a mass fraction of 20-30 wt% concentration of NaOH or KOH solution as electrolyte. However, since the reactive basic solution with CO2 in the air in the production K2CO3, to produce high-ohmic losses, which typically leads (200-400 mA cm -2 ) operating at a relatively low current density. Further, the alkaline water electrolysers difficult transient load response, this problem occurs when paired with renewable electricity. A solid proton exchange membrane (PEM) electrolyzer having high proton conductivity, it can operate at lower temperatures and higher current density, but requires expensive perfluorosulfonic acid proton exchange membrane and a platinum-based catalyst, resulting in PEM electrolyser operating costs are too high slot. basic anion exchange membrane (AEM) electrolytic process Because the collection of simple and easy operability of the solid electrolyte, and can be compatible with low-cost electrodes and alkaline hydrocarbon film, attracted much attention. Although AEM cell performance enables efficient production of hydrogen in an alkaline solution, there is still need for further development. To date, most of the work using the same catalyst and PEM electrolyzer expensive, and the cycle continues to use relatively high concentrations (0.1-1.0 M) of NaOH / KOH electrolyte, in order to avoid high operating voltage. Recently, Lin Yue, who made river in the required ion polymer cell AEM terms of significant progress, reports the AEM electrolytic cell can operate in the absence of an alkaline electrolyte That is water under the system, and using inexpensive non-platinum catalysts.
design ideas ionic polymer
major role in cell AEM ionic polymer is conducting hydroxide ions to the catalyst surface and the conducting hydroxide ions from the catalyst surface, and as a binder to mechanical anchoring of the catalyst particles in the electrode. Therefore, the ionomer must be able to run thousands of hours. However, due to the high potential, the oxygen evolution reaction occurs on the anode, whereby an ionic polymer oxidative degradation, reduction in catalytic efficiency. Studies have shown that on the one hand from the oligomer backbone ring structure adsorbed on the catalyst surface and interfere with the electron transfer, on the other hand are formed relatively acidic oxidizing phenolic compounds. These phenolic compounds may neutralize the basic charge carriers in the polymer, loweringLow ion exchange capacity, thereby affecting the performance of AEM cell. To solve this problem, Lin Yue and his colleagues realized river screening and compares several ionomer-situ by rotating disk electrode (RDE). Research team indicate that ionomer local high ionic conductivity and high pH can greatly improve the rate of hydrogen evolution and oxygen evolution, thereby efficiently driving AEM cell. Ion exchange capacity refers to the amount ion-conducting functional groups per polymer mass positively charged polymer. By increasing the ion exchange capacity of the ionomer can increase the conductivity and pH simultaneously. Thus, when designing an efficient AEM cell, the ionomer having a higher ion exchange capacity, the better. Based on this, researchers have designed a series of polystyrene polymers having a high content of hydroxide ion quaternary amine groups, wherein the polymer backbone does not contain a benzene group, excluding long alkyl chain, all side chains phenyl ring are substituted with quaternary amine or amino groups.
a bright spot: water system.
Researchers reported that, when using pure water as an electrolyte, AEM cell having 2.7 A cm -2 is a high current density at 1.8 V. Use pure water is very beneficial, because the main drawback is the need of today\’s cell AEM addition of a conductive salt in the water. Although salt content will not damage the cell, it needs to save water is recycled to the electrolysis of salt used, thereby increasing the cost and complexity of the system. Thus, if the implementation of the above-mentioned report performance in a practical system, it is possible to significantly reduce equipment and operating costs, and thus replace existing PEM electrolyzer and an alkaline electrolysis apparatus. However, it is worth noting that the performance is reported above in unsteady linear sweep voltammetry experiment, typically no need to consider the mass transfer in this experiment. In fact, according to the shape of the polarization curves it reported herein indicate that mass transfer effects on the cell performance is very important. When the cell always runs with a constant current, further confirms this. When one (0.2 A cm -2 ) the applied current density is less than the above-mentioned current density, the cell voltage steadily increased during the first 40 hours of operation, far more than 2.0 V, which It indicates that the battery mass transfer resistance is increasing, the need for further research in the future to overcome this.
Highlights II: low-temperature and low-cost electrolytic oxygen evolution catalystAgents.
Studies have shown that, by the advanced design of the structure and properties of the ionomer, can effectively reduce the operating voltage, can be achieved using a low temperature solid polymer electrolyte electrolysis. In addition, researchers at the anode using a low-cost catalyst, greatly reducing operating costs, although the need to further improve the performance.
In order to further improve the performance of AEM electrolyzer and to promote its large-scale commercial applications, there are many challenges to be addressed in the future: a challenge: to achieve steady-state performance at low and high voltage stability. This need to explore comprises an ionomer, catalyst and gas diffusion electrode assembly of each layer of the mass transfer, and mass transfer across the membrane. Challenge: ion-conductive polymer containing no development any aromatic group, in order to further enhance the transport of water and ions. Future structure of the electrode design also must be considered and its role in water, and the product gas ions promote transmission. Essentially, there is no real ideal electrode engineering, cell AEM enables high performance and high stability. three challenges: continue to develop a highly active catalyst non-noble metal (or precious metal content is low) is. I believe these challenges, AEM cell can really promote the efficient, low-cost, achieve sustainable hydrogen energy future.
Reference:.. 1 Mustain, WE, Kohl, PA Improving alkaline ionomers Nat Energy (2020) DOI:.. 10.1038 / s41560-020-0619-4.2 Li, D., Park, EJ, Zhu ,. W. et al Highly quaternized polystyrene ionomers for high performance anion exchange membrane water electrolysers Nat Energy (2020) DOI:.. 10.1038 / s41560-020-0577-x.