Medium-entropy BaZr0.1Sn0.1Ce0.6Nd0.2O3-δ proton conducting electrolytes with exceptional chemical stability against CO2 and H2O for solid oxide fuel cells

Low-entropy BaZr 0 . 1 Ce 0 . 9 O 3-δ ( Δ S c o n f  = 0.33 R) was used as the matrix to design and construct a series of medium-entropy electrolyte systems - BaZr 0 . 1 Sn 0 . 1 Ce 0 . 6 X 0 . 2 O 3-δ ( Δ S c o n f  = 1.09 R)-via co-doping with Sn 4+ and rare-earth ions (X = Dy, Nd, Yb, Y). By combining experimental characterizations with first-principles calculations (DFT), the effects of different rare-earth dopants on the phase structure, chemical stability, and electrochemical performance of these electrolytes were systematically investigated. Among electrolytes, BaZr 0 . 1 Sn 0 . 1 Ce 0 . 6 Nd 0 . 2 O 3-δ (BZSCN) shows the most stable phase composition and microstructure after 3 h of boiling H 2 O treatment and 3 h of CO 2 treatment at 700 °C. It exhibits high conductivity (3.19 × 10 −2  S cm −1 ) in humid air at 700 °C, with relatively stable conductivities after H 2 O (1.80 × 10 −2  S cm −1 ) and CO 2 (2.49 × 10 −2  S cm −1 ) treatments under the same condition. According to the first-principles calculation, compared with other BaZr 0.1 Sn 0.1 Ce 0.6 X 0.2 O 3−δ (X = Dy, Yb, Y) electrolytes, BZSCN electrolyte exhibits elevated reaction energy barriers for H 2 O (5.12 eV) and CO 2 (0.28 eV), alongside reduced adsorption energies for H 2 O (−0.508 eV) and CO 2 (0.054 eV), collectively underpinning its enhanced chemical stability. BZSCN-based anode-supported cell demonstrates a maximum power output of 0.64 W cm −2 at 700 °C when operated with humidified H 2 .