Gallium Plasmonic Nanoantennas Unveiling Multiple Kinetics of Hydrogen Sensing, Storage, and Spillover

Hydrogen is the key element to accomplish a carbon-free based economy.
Here, the first evidence of plasmonic gallium (Ga) nanoantennas is provided
as nanoreactors supported on sapphire (α-Al2O3) acting as direct plasmon-
enhanced photocatalyst for hydrogen sensing, storage, and spillover. The role
of plasmon-catalyzed electron transfer between hydrogen and plasmonic Ga
nanoparticle in the activation of those processes is highlighted, as opposed to
conventional refractive index-change-based sensing. This study reveals that,
while temperature selectively operates those various processes, longitudinal
(LO-LSPR) and transverse (TO-LSPR) localized surface plasmon resonances
of supported Ga nanoparticles open selectivity of localized reaction pathways
at specific sites corresponding to the electromagnetic hot-spots. Specifi-
cally, the TO-LSPR couples light into the surface dissociative adsorption of
hydrogen and formation of hydrides, whereas the LO-LSPR activates hetero-
geneous reactions at the interface with the support, that is, hydrogen spill-
over into α-Al2O3 and reverse-oxygen spillover from α-Al2O3.
This Ga-based plasmon-catalytic platform expands the application of supported plasmon-
catalysis to hydrogen technologies, including reversible fast hydrogen sensing
in a timescale of a few seconds with a limit of detection as low as 5 ppm and
in a broad temperature range from room-temperature up to 600 °C while
remaining stable and reusable over an extended period of time.