Modulating d-d orbitals coupling in PtPdCu medium-entropy alloy aerogels to boost pH-general methanol electrooxidation performance

Abstract

Unraveling the essence of electronic structure effected by d-d orbital coupling of transition metal and methanol oxidation reaction (MOR) performance can fundamentally guide high efficient catalyst design. Herein, density functional theory (DFT) calculations were performed at first to study the d–d orbital interaction of metallic PtPdCu, revealing that the incorporation of Pd and Cu atoms into Pt system can enhance d-d electron interaction via capturing antibonding orbital electrons of Pt to fill the surrounding Pd and Cu atoms. Under the theoretical guidance, PtPdCu medium entropy alloy aerogels (PtPdCu MEAAs) catalysts have been designed and systematically screened for MOR under acid, alkaline and neutral electrolyte. Furthermore, DFT calculation and in-situ fourier transform infrared spectroscopy analysis indicate that PtPdCu MEAAs follow the direct pathway via formate as the reactive intermediate to be directly oxidized to CO₂. For practical direct methanol fuel cells (DMFCs), the PtPdCu MEAAs-integrated ultra-thin catalyst layer (4∼5 μm thickness) as anode exhibits higher peak power density of 35 mW/cm² than commercial Pt/C of 20 mW/cm² (∼40 μm thickness) under the similar noble metal loading and an impressive stability retention at a 50-mA/cm² constant current for 10 h. This work clearly proves that optimizing the intermediate adsorption capacity via d-d orbital coupling is an effective strategy to design highly efficient catalysts for DMFCs.