Double Confinement Design to Access Highly Stable Intermetallic Nanoparticles for Fuel Cells.

Maintaining the stability of low Pt catalysts during prolonged operation of proton exchange membrane fuel cells (PEMFCs) remains a substantial challenge. Here, a double confinement design is presented to significantly improve the stability of intermetallic nanoparticles while maintaining their high catalytic activity toward PEMFCs. First, a carbon shell is coated on the surface of nanoparticles to form carbon confinement. Second, O is introduced during the annealing process to selectively etch the carbon shell to expose the active surface, and to induce the segregation of surface transition metals to form Pt-skin confinement. Overall, the intermetallic nanoparticles are protected by carbon confinement and Pt-skin confinement to withstand the harsh environment of PEMFCs. Typically, the double confined PtCo catalyst exhibits an exceptional mass activity of 1.45 A mg at 0.9 V in PEMFCs tests, with only a 17.3% decay after 30 000 cycles and no observed structure changes, outperforming most reported PtCo catalysts and DOE 2025 targets. Furthermore, the carbon confinement proportion can be controlled by varying the thickness of the coated carbon shell, and this strategy is also applicable to the synthesis of double-confined PtFe and PtCu intermetallic nanoparticles.