Phase diagrams guide synthesis of highly ordered intermetallic electrocatalysts: separating alloying and ordering stages

Supported platinum intermetallic compound catalysts have attracted considerable attention owing to their remarkable activities and durability for the oxygen reduction reaction in proton-exchange membrane fuel cells. However, the synthesis of highly ordered intermetallic compound catalysts remains a challenge owing to the limited understanding of their formation mechanism under high-temperature conditions. In this study, we perform in-situ high-temperature X-ray diffraction studies to investigate the structural evolution in the impregnation synthesis of carbon-supported intermetallic catalysts. We identify the phase-transition-temperature (T-PT)-dependent evolution process that involve concurrent (for alloys with high T-PT) or separate (for alloys with low T-PT) alloying/ordering stages. Accordingly, we realize the synthesis of highly ordered intermetallic catalysts by adopting a separate annealing protocol with a high-temperature alloying stage and a low-temperature ordering stage, which display a high mass activity of 0.96A mg(Pt)(-1) at 0.9V in H-2-O-2 fuel cells and a remarkable durability. The synthesis of highly ordered intermetallic compound catalysts remains a challenge owing to the limited understanding of their formation mechanism under high-temperature conditions. Here the authors identify phase-transition-temperature-dependent evolution process in the synthesis of intermetallic Pt catalysts and propose a separate alloying/ordering annealing synthetic protocol.