Solar energy, with tremendous potential as an environmentally sound and sustainable energy source, dwarfs all the derivative sources by a wide margin. The challenge, however, is to take full advantage of the abundant and infinite solar energy and to convert it into readily utilisable and storable forms.

Solar thermochemical CO₂ and H₂O splitting (STCDS, STWS), tapping sunlight directly and storing solar energy in renewable fuel, are emerging technologies towards meeting this goal. Successful adoption of solar-to-fuel technologies is predicated upon identifying advanced materials with higher efficiency.

Schematic of the proposed reaction mechanism for MDR-STCDS and MDR-STWS processes over 5Ni/CeO₂-TiO₂ redox catalyst. (Image by RUAN Chongyan) 

Recently, a research group led by Prof. WANG Xiaodong from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences developed a Ni promoted ceria-titanium oxide catalytic system for highly effective thermochemical CO₂ and H₂O splitting as well as partial oxidation of CH₄ at 900 °C.

The CO and H₂ production rates and productivities were 10-140 and 5-50 times higher than the current state-of-the-art STCDS and STWS processes, respectively. Close to complete CH₄ conversions with high selectivity towards syngas were achieved in the reduction step. Their findings were published online in Energy & Environmental Science.

By combining detailed experimental characterization with density functional theory (DFT) calculations, Prof. WANG Xiaodong and his collaborators from Xi’an Jiaotong University shed light upon the underlying mechanism for the exceptional reaction performance.

It was revealed that the metallic Ni and the Ni/oxide interface manifested the catalytic activity for both CH₄ activation and CO₂ or H₂O dissociation, whereas CeO₂-TiO₂ enhanced the lattice oxygen transport via the CeO₂-TiO₂ / Ce₂Ti₂O₇ stoichiometric redox cycle for CH₄ partial oxidation and the subsequent CO₂ or H₂O splitting promoted by catalytic active Ni.

"We anticipate the fundamental understanding on the crucial roles of the catalytic sites for reactants activation and the stoichiometric redox chemistry for enhanced lattice oxygen availability can provide important guidance for the rational design of advanced materials toward solar fuel production," said Prof. WANG.