Improved Alkaline Hydrogen Oxidation on Strained-Modulated Pt Overlayers on Ordered Intermetallic PtSb Cores

Alkaline exchange membrane fuel cells (AEMFCs) have emerged as an inexpensive and robust renewable energy conversion device. However, the kinetics Hydrogen Oxidation Reaction (HOR) in alkaline conditions (the anode reaction of AEMFCs) is ~100x slower in than in acidic electrolytes. Significant progress has been made developing improved catalyst materials for alkaline HOR, yet due to the complexity of alloy surfaces, it is difficult to determine the true source of such enhancement.<br/>To address this issue, here we report the use of Ordered Intermetallic Compounds (OICs) as a well-defined platform to produce strain modulated Pt overlayers. Two OICs phases of the Pt-Sb system, PtSb and PtSb₂, with different crystal structures were prepared. Electrochemical dealloying of the Pt-Sb alloys resulted in the formation of core shell Pt-Sb@Pt particles. By judicious choice of the OIC precursor material, we were able to produce PtSb@Pt and PtSb₂@Pt with compressive and tensile strain, respectively, relative to elemental Pt. It is worth noting that this approach cannot be accomplished with solid solution alloys (with an alloy core composed of the same two elements) since the d-spacing of the lattice follows Vegard’s law. This enabled us to interrogate the role of how strain controls HOR performance without the possible influence of atoms with different identities on the surface of the Pt. PtSb@Pt exhibited a weaker HBE than Pt, enabling to achieve an exchange current density (j_o) 1.5x larger than benchmark Pt catalyst for alkaline HOR; whereas PtSb₂ exhibited tensile strain which increased the HBE, reducing the j_o by 1.5x to Pt catalyst. Interestingly we found no correlation with the OH_ads coverage as estimated by CO stripping. Therefore, this work revealed that HBE is the dominant parameter for improving the kinetics of Pt sites for alkaline HOR.