Investigating the Role of Stabilizers in Enhancing the Electrocatalytic Activity of PdAu Nanoalloy Catalysts for Methanol Oxidation in Fuel Cells through an Oxidative Addition Mechanism

The formation of nanoalloys through borohydride reduction is an effective method for creating nanocatalysts. Surfactants and stabilizers are crucial for enhancing the stability, dispersion, and electrocatalytic activity of catalysts used in the methanol oxidation reaction (MOR) in fuel cells. This study investigates the effects of various capping agents and stabilizers─reduced graphene oxide, aminoclay, sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide, polyvinylpyrrolidone, and poly(vinyl alcohol)─on the morphology and electrocatalytic activity of PdAu nanoalloy thin films for methanol oxidation. In electrochemical tests, the PdAu/SDS catalyst demonstrated impressive activity of approximately 700.48 mA mg-1, significantly surpassing conventional Pt/C catalysts. Scanning electron microscopy (SEM), energy-dispersive analysis of X-ray, and elemental mapping analyses after accelerated durability tests revealed no significant structural changes or metal leaching following 200 MOR cycles. Our analysis aimed to clarify their functions while considering various stabilizers (cationic, anionic, nonionic) and proposed a new mechanism. The incorporation of SDS notably enhances the catalytic properties by increasing the electron density on the PdAu surface and facilitating the oxidative-addition of O-H bonds from methanol. Our proposed mechanism includes: methanol adsorption, O-H bonds activation (oxidative-addition), C-H bond activation, nucleophilic attack on a coordinated formyl group, and decarboxylation. As a result, the PdAu/SDS composite establishes itself as the most effective catalyst for methanol fuel cells, with anionic stabilizers outperforming nonionic and cationic surfactants.