Locally Topological Disorder of Ag Sites in Medium-Entropy Alloys for Methanol Electrocatalytic Oxidation

Pd-based nanostructures are emerging as novel catalysts for alkaline direct methanol fuel cells (ADMFCs), but enhancing their activity and stability for electrocatalytic methanol oxidation reaction (MOR) remains a significant challenge. Herein, the medium-entropy principle is employed to modify the structure of Pd-based catalysts. An electrospinning method combined with subsequent thermal treatment is proposed to synthesize PtPdCuAg medium-entropy alloy (MEA) nanoparticles dispersed on carbon nanofibers (CNFs) (PtPdCuAg MEAs/CNFs). During the in situ electrochemical activation process, Ag migrates to the surface of PtPdCuAg MEAs, forming an Ag-rich outer layer. The incorporation of various elements to create the medium-entropy structure lowers the d-band center of the catalyst. Moreover, the Ag skin facilitates the formation of oxygen-containing intermediates, which can further oxidize toxic intermediates, thereby refreshing the catalyst surface. Additionally, the 1D CNF substrates effectively prevent the aggregation and sintering of MEA catalysts. Consequently, PtPdCuAg MEAs/CNFs demonstrate an enhanced MOR activity of 1598.5 mA mg^-1 under alkaline conditions, which is 2.5 and 3.1 times higher than that of PtPdCu MEAs/CNFs and commercial Pd/C catalysts, respectively. This work not only provides a facile route to fabricate Pd-based MEAs but also highlights the critical role of Ag in MOR, greatly advancing the application of ADMFCs.