Clarifying the Origin of Ordering Effect of PtCo Intermetallic Catalysts in Catalyzing Oxygen Reduction

Pt intermetallic catalysts exhibit higher activity for oxygen reduction reaction (ORR) than the disordered counterparts, but the origin of exact effect of structural ordering has not been fully clarified yet. Herein, by comparing the PtCo catalysts with changed ordering degree but the exactly same alloying degree, we distinguish the ordering effect from alloying effect of intermetallic catalysts in catalyzing ORR; the ordering effect is identified to increase the ORR activity by ∼1.5 times. The highly ordered PtCo intermetallic catalyst is first prepared by separating the alloying and ordering stages, then the disordered counterpart with the same alloying degree is obtained by quenching the ordered catalyst at high temperatures to freeze the random atomic arrangement. Experimental and theoretical studies reveal that both alloying effect and ordering effect of intermetallic alloy catalysts intrinsically originate from the compressive strain effect, which leads to the weakened adsorbate bonding towards oxygen-containing adsorbate and thus the promoted ORR kinetics.