Being an essential component in proton echange membrane fuel cells, Pt catalyst suffers from sluggish oxygen reduction reaction (ORR) kinetics and undesirable stability issue. To address these issues, numerous efforts have been devoted to improving ORR catalysis of Pt by alloying it with first-row transional metals (M). Despite the impressive initial activity demonstrated, these alloys are often prepared in a solid solution A1 structure and M is difficult to be stabilized, resulting in extensive M leaching in fuel cells and compromising the benefits brought by alloys. Herein, using Fe and Co as examples, we demonstrate that M can be effeciently stabilized in an intermetallic L10 structure. Compared with A1 structure, the M and Pt in L10 structure have strong 3d-5d coupling along the crystallographic c-direction, stabilizing M against acid etching. Monodisperse L10-MPt nanoparticles (NPs) were synthesized via organic solution phase method and converted into core/shell structure via acid treatment followed by repair annealing. The Pt shell in 2~3 atomic layers are compressed in the same lattice to that of L10-core, further stabilizing M under fuel cell condition and improving ORR catalysis. The core/shell L10-FePt/Pt has a mass activity of 0.7 A/mgPt in the liquid half-cell and shows no obvious mass activity loss after 30,000 potential cycles between 0.6 V and 0.95 V at 80°C in the membrane electrode assembly (MEA), meeting the DOE 2020 durability target. Moreoer, the core/shell L10-CoPt/Pt shows a mass activity of 2.25 A/mgPt in the liquid half-cell and 0.56 A/mgPt in the MEA, respectively, with only ~19% loss in mass activity after 30,000 cycles in the MEA, meeting DOE 2020 target on both activity and durability (mass activity &gt;0.44 A/mgPt and mass activity loss &lt;40 %). We are extending the concept and preparing other binary and terneary L10-MPt/Pt NPs as a highly efficient ORR catalyst for fuel cells.

Stabilizing M (Fe, Co) by intermetallic L10-MPt and enhanced oxygen reduction reaction catalysis in core/shell L10-MPt/Pt for fuel cells

256th National Meeting (2018)

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