Oxidative Self-Assembly of Au/Ag/Pt Alloy Nanoparticles into High-Surface Area, Mesoporous, and Conductive Aerogels for Methanol Electro-oxidation

The ability to assemble nanoparticles (NPs) into functional nanostructures is critical for the advancement of nanoscience. However, common assembling techniques utilize organic ligands or biomolecules, which are detrimental for charge transport and interparticle coupling and impede the efficient integration of low-dimensional properties. Herein, we report a methodology for the self-supported assembly of ultrasmall (3–6 nm) Au/Ag/Pt alloy NPs into large, freestanding alloy superstructures (aerogels) that exhibit direct NP connectivity, high surface area (125 ± 0.43 to 142 ± 0.93 m2/g) and mesoporosity (21.6 ± 2.2 nm), and superior electrocatalytic activity for the methanol oxidation reaction (MOR). Precursor Au/Ag/Pt alloy NPs and hydrogels were synthesized via a stepwise galvanic replacement reaction (GRR) of glutathione (GSH)-coated Ag NPs, followed by oxidative removal of the surfactant ligands. The composition of alloy aerogels was tuned by varying the oxidant/GSH molar ratio, which governs the extent of Ag dealloying with in situ generated HNO3 and increases the exposure of Au and Pt on the aerogel surface. The alloy aerogels exhibit superior MOR mass activity, which is 21.4 and 2.5 times higher than that of the precursor NPs and commercial Pt (40 wt %)/C electrocatalysts, respectively. The MOR surface-specific activity (MOR-SSA) of the aerogels was improved by >17% when the Pt content was increased from 22.4 to 31.2%. The aerogels exhibit improved electronic conductivity and enhanced tolerance for carbonaceous byproducts and maintained ∼94% of the initial MOR activity at −0.3 V for 24 h in alkaline medium. The interconnected porous superstructure of the aerogel provides a facile conduit for molecules to reach the pristine active surface, whereas the presence of oxophilic Au promotes the dissociative adsorption of methanol, providing the Au/Ag/Pt alloy aerogel as a high-efficiency, durable electrocatalyst for the next generation of energy conversion studies.