Boosting Oxygen Reduction Reaction Selectivity in MetalNanoparticles with Polyoxometalates

The lack of selectivity toward the oxygen reduction reaction (ORR) in metalnanoparticles can be linked to the generation of intermediates. Thisconstitutes a crucial constraint on the performance of specific electrochemicaldevices, such as fuel cells and metal–air batteries. To boost selectivity of metalnanoparticles, a novel methodology that harnesses the unique electrocatalyticproperties of polyoxometalates (POM) to scavenge undesired intermediates ofthe ORR (such as HO2−) promoting selectivity is proposed. It involves thecovalent functionalization of metal nanoparticle’s surface with anelectrochemically active capping layer containing a new sulfur-functionalizedvanadium-based POM (AuNP@POM). To demonstrate this approach,preformed thiolate Au(111) nanoparticles with a relatively poor ORRselectivity are chosen. The dispersion of AuNP@POM on the surface ofcarbon nanofibers (CNF) enhances oxygen diffusion, and therefore the ORRactivity. The resulting electrocatalyst (AuNP@POM/CNF) exhibits superiorstability against impurities like methanol and a higher pH tolerance rangecompared to the standard commercial Pt/C. The work demonstrates for thefirst time, the use of a POM-based electrochemically active capping layer toswitch on the selectivity of poorly selective gold nanoparticles, offering apromising avenue for the preparation of electrocatalyst materials withimproved selectivity, performance, and stability for ORR-based devices.