Novel anion exchange membranes with superior alkaline stability are proposed for an alkaline water electrolysis cell.
Future energy carriers are needed in order to lower the CO2 emissions resulting from the burning of fossil fuels. One possible energy carrier is ammonia, which can be stored safely and reversibly in metal halide ammines; however, the release often occurs in multiple steps at too high temperatures. Therefore, there is a need for new materials, releasing the ammonia in a narrow temperature interval. To search for new mixed metal halide chlorides, we use DFT calculations guided by a genetic algorithm (GA) to expedite the search, as the defined search space allowing up to three different metals contains more than 100,000 different structures. Here, we search for materials releasing the ammonia between 0 and 100 °C, a temperature range suitable for system integration with low-temperature polymer electrolyte membrane fuel cells (PEMFC). The efficiency of the implemented algorithm is verified by three trial runs capable of finding the same optimal mixtures starting from different random populations, testing < 5% of the candidates. Some of the best candidates are already confirmed experimentally and others offer a record high, accessible hydrogen capacity exceeding 9 wt%. Among the identified materials is the first known high-capacity ternary metal halide ammine, which we have subsequently synthesized and confirmed the ammonia storage properties using temperature programmed desorption (TPD). IntroductionAmmonia is a widely used chemical with many different applications; most importantly as the main component in fertilizers, sustaining the growth of the world's population. 1 A major drawback of ammonia is, however, its toxicity, requiring careful handling and storage. 2 It is well-known that pure metal halide ammines have the ability to store ammonia, and release it when heat is supplied. 3,4 These solid storage materials have been proposed as energy carriers for transportation usage 5-12 and for on-board reduction of NOX gases from combustion processes. 13 The metal halide ammines often display good kinetics 14,15 , but most of the pure metal halides release the ammonia at high temperatures and in multiple steps spread over broad temperature ranges. 8,16 Therefore, new materials with optimized release patterns are needed if ammonia should be used as a future energy carrier for transportation. A number of mixed metal halide ammines have already been investigated, both mixing the cations and the anions 17-19 , resulting in materials performing better than their individual components, encouraging the search for other mixed materials.
Dimethyl ether (DME) combines high energy density with easy handling and low toxicity and is therefore an attractive fuel. The absence of carbon-carbon bonds allows for electro-oxidation with good kinetics and it is therefore particularly interesting for use in fuel cells. This work presents the first durability studies of vapor-fed direct dimethyl ether fuel cells with phosphoric acid doped polybenzimidazole membranes as electrolytes. Fuel cells are operated in direct DME mode at 160 and 200 °C and the cell voltage at a constant current load of 100 mA cm -2 is recorded over more than 200 h. Regular electrochemical impedance spectroscopy and polarization data are used as diagnostic measures to monitor the cell characteristics. It is shown that the cell performance deteriorates severely within 200 h of operation at 160 or 200 °C. The degradation is connected to different modes that ultimately result in both increasing polarization resistance and increasing area specific resistance, which may be connected to the chemical incompatibility between the fuel and the electrolyte.
Anthropogenic climate change has brought on a global climate crisis and emergency. Increased levels of atmospheric carbon dioxide levels has brought with it undesirable changes to the world’s climate. To halt and eventually stop this trend the world needs to move to zero-carbon sources of electricity, transport and chemical production. To offset the variability in zero-carbon electricity sources storage or usage of the excess energy is necessary. One of several technologies to achieve this is water electrolysis. A promising candidate of this field of study is Alkaline Water Electrolysis The field of alkaline electrolysis have recently moved from a gap-based macro-material approach to a nanomaterials based membrane cell architecture. Due to recent advances in membrane technology both ion-conduction and electrolyte solvating membranes allow for a zero-gap architecture. With this approach comes new engineering challenges. Bubble formation, -diffusion, -suppresion, and –transport are all phenomena that are recently unexplored in the context of nanopowder-based electrode in flooded KOH systems. One of the ways of exploring this is the use of Galvanostactic Electrochemical Impedance Spectroscopy (GEIS).. Through GEIS investigations and Distribution of Relaxation Times of the electrochemical response of nano-powder based cathodes a Gerischer-like response indicating transport issues and a way of quantifying this.
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