Temperature-dependent carbon shell engineering for highly durable Pt@C catalysts in the oxygen reduction reaction

• A scalable all-dry synthesis for Pt@C/C catalysts via simple heat treatment. • Uniform Pt nanoparticles (2–4 nm) achieved through precise heat-treatment control. • Morphological evolution of carbon shells impacts catalytic activity and durability. • Pt@C/C synthesized at 200–400 ℃ achieved enhanced ORR activity and durability. • Carbon shell suppressed Pt growth over AST 30 k cycles, ensuring superior durability. In this study, we developed a straightforward and scalable all-dry synthetic process for carbon shell-encapsulated Pt catalysts (Pt@C/C) and analyzed the morphological evolution of the carbon shell at various heat-treatment temperatures. We investigated the impact of these morphological changes on the catalytic activity and durability for the oxygen reduction reaction (ORR). The synthesis process involved ball-milling Pt(acac) 2 and carbon black, followed by heat treatment under nitrogen at 200–800 °C. The resulting Pt@C/C samples exhibited an ultrathin carbon shell thickness of less than 1 nm and Pt nanoparticles (2–4 nm) uniformly dispersed on the carbon support. In-situ heating transmission electron microscopy revealed critical morphological transitions: thin amorphous carbon shells (<1 nm) at 200 °C, partial shell decomposition at 400 °C, and dense graphene layers (1–2 layers) at temperatures ≥ 600 °C. Pt@C/C samples prepared at 200 and 400 °C exhibited superior mass and specific ORR activities compared to Pt/C, attributed to the uniform size of Pt nanoparticles and the carbon shell mitigating ionomer poisoning. The carbon shells maintained integrity during 30,000 cycles of accelerated stress test, minimizing Pt particle growth and ensuring superior durability over Pt/C. This method eliminates the need for high temperatures (>600 °C) and additional etching, achieving outstanding catalytic activity and durability at temperatures ≤ 400 °C.