The European Hydrogen Strategy has strengthened the positioning of H2 among the alternative energy sources, making it the key element for achieving the 2050 decarbonisation objectives. Proton exchange membrane fuel cells (PEMFCs) allows to use H2 as alternative fuel, especially in the automotive sector. However, for their correct functioning a very pure H2 stream is required, with a strict limit on CO concentration (CO
Steam iron process is one of the oldest method for hydrogen production by water splitting based on iron redox properties. It was developed in the late 19th/early 20th century to produce hydrogen from gasified coal, mainly in the aviation sector. In the last decade, the process has received renewed attention as it can link together the production of renewable hydrogen and fuel cells technology. The produced H2 can be directly used to power PEMFC. If a renewable source is used to reduce the iron oxides, hydrogen becomes green. Syngas produced from biomass by different technology (pyrolysis, gasification, anaerobic digestion) has been widely explored. However, the use of bioethanol as a source of reducing agent by its thermal decomposition it is not thoroughly explored.
Bioethanol is already widely used as renewable fuel thanks its high calorific value and its good stability at ambient condition. At high temperature it can be thermally decomposed into mainly H2 and CO with traces of CH4, with high reducing power. One of the main issue related to the use of bioethanol in the steam iron process is related to the carbon formation by methane cracking, which can affect the H2 purity reacting with steam and producing CO. However, the production of highly pure H2, can be achieved tuning the reduction degree of iron oxides by feeding different amount of ethanol in reduction. The goal is to avoid the formation of deposited carbon during reduction, in order to prevent the presence of CO in oxidation at each cycles.
However, using pure Fe2O3 the system showed low thermal stability after repeated redox cycles affecting the amount of hydrogen produced in oxidation. Specifically, pure iron oxides undergo rapidly to deactivation due to particles agglomeration and sintering phenomena. Considering that, the stability of the redox element is a key factor of the process for the application at industrial scale, the addition of a structural promoter to inhibit particles deactivation is fundamental.
The novelty of the research is therefore to guarantee a stable and high H2 yield using bioethanol in the system. Furthermore, with respect to the steam reforming process the absence of the purification units and the use of liquid and renewable feedstocks (ethanol and water) makes steam iron process more suitable to produce H2 in localized site or directly on board of the vehicles. In this way the high cost related to the H2 storage and distribution can be significantly reduced.