Corrosion Analysis of a High Entropy Alloy for Ammonia Production
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Date
2024
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Abstract
Global energy demand has increased significantly due to world population growth and the industrialization of developing economies. Energy production has been based mainly on fossil-fuel energy, which has increased global warming due to the rise of greenhouse gases in the atmosphere, such as carbon dioxide. According to the Energy Institute, renewable power generation through wind, solar, and other renewable sources, represent only 40,86% of energy sources in 2022 [1]. An alternative energy source for fossil fuels is hydrogen, which can be produced through renewable resources that increase energy efficiency. However, the storage and transportation of hydrogen present a series of technical challenges, resulting in high costs and motivating the development of intermediate technologies. Recently, ammonia generated by renewable energy sources has gained significant attention as an energy carrier, a medium to store and transport chemical energy, and directly as fuel [2]. Ammonia is also a primary raw material for making inorganic fertilizers, pharmaceuticals, synthetic fibers, resins, and other applications, benefiting nearly half the world's population. Ammonia can be transported more efficiently and safely than hydrogen in tanker vessels or pipelines due to its relative ease of being liquefied at room temperature and moderate pressure, increasing energy density. Currently, ammonia is produced mainly from hydrogen and nitrogen by the Haber-Bosch process, which utilizes fossil fuel, thus resulting in carbon dioxide emissions. Ammonia production can also involve the non-spontaneous nitrogen reduction reaction by electrochemical techniques, which uses hydrogen that can be provided from the water, reducing energy consumption and carbon dioxide emissions. However, the non-spontaneous nitrogen reduction reaction has low activity, and its voltage is close to that of the hydrogen evolution reaction. Plasma and electrothermal chemical cycle methods have been explored to improve the selectivity of non-spontaneous nitrogen reduction reactions. Several studies have proposed new catalysts to increase the active sites, modify the size and morphology of particles, and introduce defects, such as transition metal-based catalysts, carbon-based catalysts, phosphorus-based catalysts, etc. Nevertheless, traditional catalysts frequently degrade rapidly due to the harsh chemical environment and the inherent corrosiveness of the reactions involved. A highly active catalyst that degrades quickly due to corrosion offers limited practical value. Researchers are exploring novel materials like high-entropy alloys (HEAs) to address this challenge, which also have high corrosion resistance [3]. This study focuses on the potential of a HEA, FeCrMnNiCo, as a catalyst for the electrochemical conversion of nitrogen to ammonia via the electrochemical method, evaluating the influence of the microstructure on its mechanical properties, catalytic activity, and corrosion resistance. A ball burnishing deformation was applied to the HEA at different conditions. The X-ray diffraction revealed that the FeCrMnNiCo alloy presented a face-centered cubic crystalline structure, and scanning electron microscopy analysis showed that the alloying elements were segregated in the deformed samples. The mechanical deformation determined both catalytic activity and corrosion resistance of the HEA.