Probing the Mechanism of Plasmon-Enhanced Ammonia Borane Methanolysis on a CuAg Alloy at a Single-Particle Level

Abstract

Plasmon-enhanced ammonia borane (AB) methanolysis, as an efficient, controllable, and safe method for hydrogen release, has attracted increasing attention. However, the mechanism remains controversial since it is difficult to directly observe the interface interaction in the plasmonic field. Here, CuAg alloy nanoparticles (NPs) with controlled compositions are synthesized and exhibit an excellent H2 yield (17.1 μmol min–1) under light illumination. Theories and experiments show that both hot carriers and photoinduced local-field enhancement contribute to the improved catalytic activity under light irradiation. More impressively, plasmon-induced interfacial charge transfer between single CuAg NPs and reactant molecules was explored in situ by a single-particle confocal microscope system, and a complete photoluminescence (PL) quenching phenomenon of CuAg NPs was observed when immersed in a methanol solution, not ammonia borane. The PL quenching indicates the transfer of hot electrons to methanol, which is the rate-limiting step of the AB dehydrogenation reaction. In contrast, charge transfer from the plasmonic NP to AB (the most widely proposed path to date) does not work here. This work provides direct evidence for the hot electron transfer from CuAg to methanol via single-particle PL measurement and provides insights for plasmon-enhanced AB methanolysis.