Two-step solar thermochemical water splitting offers a viable solution for employing renewable energy pathways for production of high-purity hydrogen, which can be used in fuel cells or for the production of liquid fuels. One promising thermochemical cycle uses cerium dioxide (ceria) as the reactive material and splits water in two relatively simple steps. In the first step, an oxygen-deficient cerium oxide is generated by heating cerium dioxide to temperatures on the order of 1,500 °C until oxygen desorbs. Hydrogen is produced in the second step when steam is passed over the oxygen-deficient cerium oxide. The cerium dioxide formed during the hydrogen production step is then again heated to 1,500 °C until the oxygen-deficient cerium oxide is regenerated. Due to the high operating temperatures of this thermochemical cycle, stability over several water splitting cycles is often a limitation due to severe sintering of the materials. Our research has focused on adding a second oxide to ceria in an attempt to 1) increase the hydrogen production per unit mass of reactive material by increasing the oxygen mobility, and 2) improve the stability of the resulting mixed metal oxide over pure ceria. Using simple precipitation methods, selected metal oxides, such as oxides of zirconium, iron, praseodymium and terbium, were investigated in the thermochemical water splitting. The hydrogen production per unit mass of reactive material and the stability of the material were found to be dependent on both the amount and the identity of the second oxide.

Mixed cerium oxides as reactive materials for thermochemical water splitting

2019 Spring National Meeting

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