In Situ SERS Probing the Effect of Additional Metals on Pt-Based Ternary Alloys toward Improving ORR Performance

The surface/interface electronic structure of metal catalysts plays a decisive role in electrocatalytic reactions. Direct monitoring of intermediates during the oxygen reduction reaction (ORR) is an accessible method to elucidate the interaction between intermediates and electronic effects and to correlate this interaction with ORR activity. Herein, the reaction processes and intermediates of ORR on highly efficient PtCoSn ternary nanoalloys were explored by surface-enhanced Raman spectroscopy (SERS) via a “borrowing” strategy. Reactive *OOH intermediates were captured under ORR conditions to reveal the critical role of interfacial electronic effects in ORR at a molecular level. Direct SERS evidence demonstrated that alloying with Co and Sn can tailor the electronic structure of Pt, thus changing the configuration of *OOH on the surface to a weaker energy state. Combined with density functional theory (DFT) calculation and X-ray photoelectron spectroscopy (XPS), it was concluded that the electronic effects of the alloyed surface induced the *OOH configuration to converge toward the alloy surface. Especially when Sn was doped, the more stable PtCoSn structure enabled the *OOH adsorption configuration almost parallel to the surface, which greatly promoted the dissociation of the O–O bond, leading to the outstanding ORR performance of PtCoSn. These results showed that in situ SERS investigation delivered direct spectral evidence for the increase of ORR activity caused by the electronic effect, which is expected to provide practical theoretical guidance for the construction of highly active ORR electrocatalysts in the future.