Trends in High-Temperature H₂ Production on CeO₂ Co-Doped with Trivalent Cations in Solid Oxide Electrolysis Cells

CeO₂-based catalysts incorporated with cooperative dopants show excellent potential for promoting H₂ production via the water-splitting reaction (WSR) in solid oxide electrolysis cells (SOECs). Here, we report that CeO₂ co-doped with Gd+Sb, Pr+Sb, and Bi+Sb trivalent cations have superior performance for WSR with the reaction rate 2-5 orders of magnitude larger than that of individual trivalent dopants including Ga, Sb, Lu, Gd, Sm, Pr, Bi, and La, owing to improved stability of hydridic H-species and accordingly decreased barrier for their decompositions into H₂ by co-doping. The energy of hydridic H-species and the turn-over frequency (TOF) toward H2 production is shown to correlate well with the average ionic radius of trivalent cations, where the TOF increases with decreasing ionic radius and Gd+Sb, Pr+Sb, and Bi+Sb with smaller ionic radius show better WSR activity than other dopants. Our studies suggest incorporating ceria with proper co-dopants with an average radius close to Gd+Sb, Pr+Sb, or Bi+Sb pairs as an effective strategy for enhancing WSR performance on CeO₂ in SOECs.