It is important to develop efficient catalysts for improving performance and reducing the cost of direct methanol fuel cells, very promising power sources for portable devices and vehicles. Composition optimization and shape control are two effective strategies to develop high-performance catalysts. Inspired by the excellent performance of PtBi-type catalysts in inhibiting CO-poisoning and the outstanding electrocatalytic performance of two-dimensional Pt-based alloy nanoplates, the synthesis of PtBiTe hexagonal nanoplates using Bi2Te3 hexagonal nanoplates as templates is proposed here. Both the Bi2Te3 nanoplates and the PtBiTe nanoplates have a hexagonal plate-like shape. The PtBiTe nanoplates catalyst displays outstanding specific activity and mass activity, and superior stability for the methanol oxidation reaction in alkaline electrolytes compared to the commercial Pt/C catalyst and the PtTe nanoplates catalyst. The results of the in-situ Fourier transform infrared spectroscopy measurement and the theoretical calculations based on the density functional theory support that methanol oxidation follows the CO-free pathway on the PtBiTe NPs, which effectively prevents the catalyst from being poisoned by CO.
A long-standing puzzle for methanol electrooxidation is the fundamental understanding of the origin of electrocatalytic selectivity. Herein, we unequivocally demonstrate that the Bi-modified Pt/C follows a CO-free dominated pathway during alkaline methanol electrooxidation and unveil the formaldehyde (HCHO) intermediate as a critical factor influencing pathway selectivity. These findings are substantiated by kinetic isotope effects, formate Faradaic efficiency, in situ spectroscopy, ab initio molecular dynamics simulations, and density functional theory calculations. Bi modification significantly increases the HCHO dehydrogenation barrier, which facilitates its desorption and subsequent conversion to the H2COOH– anion at the alkaline interface, intrinsically avoiding CO formation. More specifically, the formation of ensemble sites featuring a V-shaped Bi–Pt–Bi configuration inhibits the cleavage of the C–H bond, and the weak OH binding energy at Bi adatoms effectively prevents blockage of oxygenated species, allowing such ensemble sites to fulfill their functional role. This work provides in-depth insights into the origins of pathway selectivity and benefits the theory-guided design of advanced CO-free electrocatalysts.
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