Mimicking tetravalent dopant behavior using paired charge compensating dopants to improve the redox performance of ceria for thermochemically splitting H₂O and CO₂

A novel doping strategy based on paired charge compensating dopants is proposed to improve the solar thermochemical H₂O and CO₂ splitting performance of ceria. Density functional theory based ab initio calculations show that by co-doping trivalent and pentavalent cations into ceria the behavior of the trivalent dopant resembles that of tetravalent dopants. In this study, which investigated combinations of group IIIA and VA elements, it was found that the trivalent dopant identity has the largest effect on the reduction energy, while the pentavalent dopant only slightly modifies it. The trivalent dopant in these materials suppresses the reduction energy due to decreased ionic attraction of the trivalent cation and O²⁻ as compared to Ce⁴⁺ and O²⁻. We predict relative reducing capabilities in the following decreasing order: Hf-CeO₂ > ScX-CeO₂ > Zr-CeO₂ > YX-CeO₂ > LaX-CeO₂ > undoped CeO₂ (where X = V, Nb or Ta). Experimental thermogravimetric analysis confirms the computational predictions.