Hybrid Reactor by the Combination of Water Electolyzer with Methanation Reactor Targeting the Space and Terrestrial Applications

Abstract

Japan Aerospace Exploration Agency (JAXA) collaborates with Toyama University and Kyushu University to create the hybrid system where the water electrolyzer is directly combined with Sabatier reactor shown in Fig. 1.In order to generate oxygen, people use water electrolyzer. Under the micro-gravity condition, the specially designed gas-water separator is always needed to generate oxygen for breezing. The hydrogen which is the by-product from water electrolysis can also be used for the reduction reaction of carbon dioxide to generate methane and water. It is so called ‘Sabatier reaction’ which is very convenient for the water recovery in the closed environment.In general, the Sabatier reaction can be triggered with maintaining rather high temperature above 300 degrees C. However, the conversion of the reaction should become higher at lower temperature since the reaction is exothermic.We first focused our efforts to develop the catalysts which realizes the Sabatier reaction at around 200 degrees C.We then tried to transfer the heat generated from the Sabatier reaction to the water electolyzer.The novel internal structure of the water electolyzer was developed. Pressurized water without circulation is supplied to the water electrolyzer in which the interdigitated electrode locates. Water first contacts to the proton conducting electrolyte directly, and then diffuses to the electrode where the electrolysis reaction takes place. The electrode is covered with the hydrophobic materials so that only the gaseous material should pass through it without using any gas-water separation devices. The heat transferred from the Sabatier reaction enhances the efficiency of the water electrolysis reaction. By the combination, oxygen can be used for breezing, and hydrogen can be used for the reduction reaction of carbon dioxide to create water and methane as a unitized device.We successfully demonstrated the performance of the tandem device where the water electolyzer is combined with Sabatier reactor through both experiment and mathematical modeling.AcknowledgmentsThis work was partially supported by JST CREST and NEDO Green Innovation Fund Projects. Figure 1