Production of hydrogen with low COx-content for PEM fuel cells by cyclic water gas shift reactor

Hydrogen gas with low CO content was produced by cyclic water gas shift (CWGS) reactor based on the periodic reduction and re-oxidation of Fe₂O₃–CeO₂–ZrO₂. The process was operated with CO/H₂ mixtures produced by e.g. auto-thermal reforming of hydrocarbons. During the reduction phase of the cyclic process, the incoming CO/H₂ mixture converted Fe₂O₃–CeO₂–ZrO₂ into a reduced form. Subsequently, steam was fed into the reactor for re-oxidation of the reduced material. Thereby, H₂ was released which can be used for a proton exchange membrane fuel cell (PEMFC) without any further purification. As side product, some coke can be formed on the solid surface by Bouduard reaction. This coke is removed in the re-oxidation step with steam leading to the formation of carbon monoxide. The extent of coke formation is controllable by keeping the oxygen conversion of the material below a certain degree. The feasibility of the novel process was demonstrated by combining the CWGS reactor with a 5-cell PEMFC stack.