Breaking trade-off between particle size and ordering degree of intermetallic catalysts for fuel cells

Atomically ordered intermetallic catalysts exhibit superior intrinsic activity over their disordered alloy counterparts for oxygen-reduction reaction in proton-exchange-membrane fuel cells. However, in traditional wet-impregnation method, the synthesis conditions for intermetallic catalysts such as high-temperature annealing inevitably accelerate metal sintering that leads to larger particles and thus lower mass-based activity. Herein, we quantitatively analyze the particle size, alloying degree, and ordering degree of a family of PtFe and PtCo catalysts with varied metal loading, annealing temperature, and carbon supports. We identify the trade-off between particle size and alloying/ordering degree is dependent on the inter-particle distance and annealing temperature. Accordingly, we achieve the optimal balance to prepare intermetallic PtFe catalysts with a small average particle size of 2.65 nm and a high ordering degree of 73 % simultaneously. The optimal PtFe catalyst exhibits a high mass activity of 2.1 and 0.78 A mgPt–1 at 0.9 ViR-corrected in half-cell and single-cell tests, respectively.