Effectively refreshing deteriorated Ba0.5Sr0.5Co0.8Fe0.2O3-δ into an active and stable cathode for hydrogen-powered solid oxide fuel cells

Alkaline-earth-based perovskite cathodes like Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3−δ (BSCF) often suffer from CO 2 -induced degradation due to carbonates formation (e.g., SrCO 3 ), severely impairing oxygen reduction reaction (ORR) activity and long-term stability for solid oxide fuel cells. This study demonstrates that treating CO 2 -poisoned BSCF with the HfCl 4 solution not only restores ORR activity by chemically dissolving carbonates, but also enhances stability by introducing high-valence, reduction-inactive Hf 4+ cations. The modified BSCF exhibits superior electrochemical performance, with area-specific polarization resistance (ASR P ) decreasing from 0.077 to 0.038 Ω cm 2 and maximum power density increasing from 1.185 to 1.510 W cm −2  at 650 °C. Furthermore, under CO 2 exposure, the degradation rates of ASR P and cell voltage for the HfCl 4 solution-treated BSCF are significantly lower (0.007 Ω cm 2 min −1 and 4.08 × 10 −4  V h −1 ) compared to pristine BSCF (0.027 Ω cm 2 min −1 and 8.14 × 10 −4  V h −1 ). This facile acidic HfCl 4 solution treatment effectively regenerates degraded cathodes while simultaneously improving their CO 2 tolerance and operational stability.