Understanding adsorbate-induced surface segregation in PtCo/C electrocatalyst

The X-ray diffraction (XRD) was used to study the effect of treatment on particle size and catalyst structure of PtCo/C electrocatalysts. The XRD showed the grain sizes of N ₂-treated electrocatalysts increase with temperature treatment, while those treated with CO remain the same. The X-ray absorption spectroscopy (XAS) was used to study the changes in atomic distribution, extent of alloying as well as the surface population of PtCo/C nanoparticles. The XAS revealed that the time of CO treatments influence the surface population due to phase segregation. Catalysts treatment for 1, 3 and 5 h lead to higher population of Pt on the core and Co on the surface resulting in Pt rich in core-Co rich in shell. In contrast, CO treatments for 7, 10 and 15 h lead to higher population of Pt on the shell and Co on the core resulting in Pt rich in shell-Co rich in core. The electrochemical results showed that PtCo/C CO-treatment is more active than commercial PtCo/C for the oxygen reduction reaction and it is found that PtCo/C CO-treatment 3 h has the highest catalytic activity; because it has higher J _Pt and J _Co values, indicating a higher extent of Pt and Co alloying.