Application of LaGaO3 based electrolyte for steam electrolysis was studied for the useful utilization of unused heat energy from steelmaking process. It was found that the H2 formation rate almost obeys the Faraday's law suggesting unity of oxide ion transport number in LaGaO 3 perovskite under an electrolysis condition up to 2.0 V applied potential. Among the examined cathode catalyst, nickel shows the smallest cathodic overpotential and the addition of Fe to Ni is highly effective for increasing the H2 formation rate in the steam electrolysis at 873 K. The highest H2 formation rate is obtained at the composition of Ni : Fe=9 :1. Short stack of the steam electrolysis cell consisting of 25 cells in series connection was also studied and the formation rate of H2 was achieved as large as 70L/min at 1.8 V applied potential. Heat balance was calculated based on the developed stack level. It became clear that the heat source of 223 K level is enough for sustaining cell temperature because of large Joule heat.
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