Design of SnPt/C cathode electrocatalysts with optimized Sn/Pt surface composition for potential use in Polymer Electrolyte Membrane Fuel Cells

Reductive Treatment of Pt Supported on Ti0.8Sn0.2O2-C Composite: A Route for Modulating the Sn-Pt Interactions

The composites of transition metal-doped titania and carbon have emerged as promising supports for Pt electrocatalysts in PEM fuel cells. In these multifunctional supports, the oxide component stabilizes the Pt particles, while the dopant provides a co-catalytic function. Among other elements, Sn is a valuable additive. Stong metal-support interaction (SMSI), i.e., the migration of a partially reduced oxide species from the support to the surface of Pt during reductive treatment is a general feature of TiO2-supported Pt catalysts. In order to explore the influence of SMSI on the stability and performance of Pt/Ti0.8Sn0.2O2-C catalysts, the structural and catalytic properties of the as prepared samples measured using XRD, TEM, XPS and electrochemical investigations were compared to those obtained from catalysts reduced in hydrogen at elevated temperatures. According to the observations, the uniform oxide coverage of the carbon backbone facilitated the formation of Pt-oxide-C triple junctions at a high density. The electrocatalytic behavior of the as prepared catalysts was determined by the atomic closeness of Sn to Pt, while even a low temperature reductive treatment resulted in Sn-Pt alloying. The segregation of tin oxide on the surface of the alloy particles, a characteristic material transport process in Sn-Pt alloys after oxygen exposure, contributed to a better stability of the reduced catalysts.

Introduction of Surface Modifiers on the Pt-Based Electrocatalysts to Promote the Oxygen Reduction Reaction Process

The design of Pt-based electrocatalysts with high efficiency towards acid oxygen reduction reactions is the priority to promote the development and application of proton exchange membrane fuel cells. Considering that the Pt atoms on the surfaces of the electrocatalysts face the problems of interference of non-active species (such as OH_ad, OOH_ad, CO, etc.), high resistance of mass transfer at the liquid-solid interfaces, and easy corrosion when working in harsh acid. Researchers have modified the surfaces' local environment of the electrocatalysts by introducing surface modifiers such as silicon or carbon layers, amine molecules, and ionic liquids on the surfaces of electrocatalysts, which show significant performance improvement. In this review, we summarized the research progress of surface modified Pt-based electrocatalysts, focusing on the surface modification strategies and their mechanisms. In addition, the development prospects of surface modification strategies of Pt-based electrocatalysts and the limitations of current research are pointed out.

Low-Pt-Based Sn Alloy for the Dehydrogenation of Methylcyclohexane to Toluene: A Density Functional Theory Study

Spin-polarized van der Waals corrected density functional theory calculations were applied to Sn–Pt alloys with Pt content ≤ 50% (referred to as low Pt alloys) to evaluate their catalytic activity towards the dehydrogenation of methylcyclohexane (MCH), with the formation of toluene as product. The calculated adsorption energies of MCH, its intermediates and toluene showed that these molecules bind on the considered Sn–Pt alloys. Sn–Pt alloys had the lowest dehydrogenation energetics, indicating that the activity of this catalytic material is superior to that of a pristine Pt catalyst. Desorption of the intermediate species was feasible for all Sn–Pt alloy configurations considered. The catalytic dehydrogenation reaction energetics for the various Sn–Pt alloy configurations were more favourable than that achieved with pristine Pt surfaces. The current study should motivate experimental realization of Sn–Pt alloys for the catalytic dehydrogenation reaction of MCH.

Tuning d-Band Center of Pt by PtCo-PtSn Heterostructure for Enhanced Oxygen Reduction Reaction Performance

The development of efficient and stable Pt-based catalysts is significant but challenging for fuel cells. Herein, Sn and Co elements are introduced into Pt to form PtCo-PtSn/C heterostructure for enhancing the oxygen reduction reaction (ORR). Electrochemical results indicate that it has remarkable ORR intrinsic activity with a high mass activity (1,158 mA mg^-1 Pt) at 0.9 V in HClO₄ solution, which is 2.18-, 6.81-, and 9.98-fold higher than that of PtCo/C, PtSn/C, and Pt/C. More importantly, the catalytic activity attenuation for PtCo-PtSn/C is only 27.4% after 30 000 potential cycles, showing high stability. Furthermore, theoretical calculations reveal that the enhancement is attributed to charge transfer and the unique structure of PtCo-PtSn/C heterostructure, which regulate the d-band center of Pt and prevent non-noble metals from further dissolution. This work thus opens a way to design and prepare highly efficient Pt-based alloy catalysts for proton exchange membrane fuel cells.