Redox kinetics of pure and Zr+4 doped CeO2 used for thermochemical hydrogen production

Kinetics of pure and Zr+4 doped CeO2, synthesized via Pechini method, was investigated in view of their applicability as redox material for thermochemical hydrogen production. In pure CeO2 several reduced sub-oxide phases were formed after reduction, as evidenced by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). In Zr-doped CeO2 Zr-rich phases were formed at the pellet surface after treatment at high temperature under low partial pressure of oxygen (pO2) which is attributed to selective Ce evaporation. Reduction kinetics between 1543K and 1753K under various pO2 was monitored by Thermogravimetric analyses (TG) using pure and Zr+4 doped CeO2 pellets sintered at different temperatures. TG data show that Zr doping of CeO2 is beneficial in view of reduction but may be thermodynamically detrimental for re-oxidation by water vapor. Evidence suggests that the sintering temperature of Zr-doped CeO2 pellets affects the water-splitting efficiency.