Tuning atomic Pt site surface on PtAu alloy toward electro-oxidation of formic acid

Abstract

PtAu alloy is considered to be a promising catalyst for the formic acid (HCOOH) electro-oxidation reaction. Nevertheless, the mechanism of HCOOH electro-oxidation on various surface compositions of PtAu is still unclear. Here, a series of ∼5 nm PtAu catalysts from Pt50Au50 to atomically dispersed Pt surface is successfully prepared. We reveal that the electro-oxidation HCOOH mechanism depends on the surface Pt sites; i.e., when PtAu alloy surface tunes to surface atomic Pt site, their mechanisms will change from a dual pathway mechanism to a direct pathway. Therefore, PtAu alloy (Pt5Au95) with atomic Pt sites surface showed an excellent activity with 104.8 mA cm−2 at 0.24 V (normalized by the Pt active surface area), which is five times higher than that of Pt50Au50 (19.3 mA cm−2 at 0.24 V) toward HCOOH electro-oxidation. Significantly, external reflection in-situ Fourier transform infrared spectroscopy (FTIRS) results furtherly prove that the atomic Pt sites surface on PtAu alloy will prevent the formation of CO poisoning intermediate and undergo the direct pathway to form CO2. Moreover, attenuated total reflection (ATR) in-situ FTIRS results also demonstrate that the bridge formic acid anion on PtAu alloy is not a real intermediate for electro-oxidation HCOOH.