Reversely trapping atoms from a perovskite surface for high-performance and durable fuel cell cathodes

Atom trapping of scarce precious metals onto a suitable support at high temperatures has emerged as an effective approach to build thermally stable single-atom catalysts. Here, following a similar mechanism based on atom trapping through support effects, we demonstrate a reverse atom-trapping strategy to controllably extract strontium atoms from a rigid lanthanum strontium cobalt ferrite ((La 0.6 Sr 0.4 ) 0.95 Co 0.2 Fe 0.8 O 3− δ , LSCF) surface with ease. The lattice oxygen redox activity of LSCF is accordingly fine-tuned, leading to enhanced cathode performance in a solid-oxide fuel cell. An over 30−70% increases in maximum power density of the single cells at intermediate temperatures is achieved by LSCF with surface strontium vacancies compared to the pristine surface. In addition, the strontium-deficient surface excludes strontium segregation and formation of electrochemically inert SrO islands, thus improving the longevity of the cathode. This development can be broadly applicable for modifying structurally stable oxide surfaces, and opens more possibilities of scalable single-atom extraction strategies. Atom trapping is a well-established route to prepare single-atom catalysts. Here the authors propose a reverse atom-trapping strategy in which surface strontium atoms of LSCF fuel cell cathodes are extracted by MoO 3 , forming single strontium vacancies on LSCF in a controllable manner and tuning its performance for the oxygen reduction reaction.