hydrogen sensing and storage new materials solutions are needed to reduce thermodynamic (process-temperatures limitations) and kinetic (process rate limitations) barriers and meet the challenges of sensing of a response time of less than 1 s, an operating temperature of −30 to 80 degrees Celsius, and a measurement of 0.1% to 10%, [1] as well as of hydrogen storage with low hydrogen refilling time and output power.The integration of plasmonics [2] with the recently introduced concept of novel catalytically-active liquid metal hydrides and hydrogen trapping mechanisms represents a breakthrough toward creating a new generation of plasmonic-enhanced photocatalytic nanosystems for enhancing both hydrogen sensing [3] and storage. [4] Surface-plasmon-resonance (SPR) induces electromagnetic field enhancement on common hydrogen-absorbing metals such as magnesium (Mg), palladium (Pd), titanium (Ti), and nickel (Ni) which may be exploitable in the microwave region for hydrogen storage. [5,6] Previous studies have reported SPR hydrogen sensing platforms based on Pd, [7,8] gold (Au), [9][10][11] aluminum (Al), [12] and Mg [13] nanoparticles (NPs). Considering the essential requirements for hydrogen storage, such as high storage capacity and fast hydrogen adsorption kinetics, requirements of hydrogen 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-Al 2 O 3 ) acting as direct plasmonenhanced 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. Specifically, the TO-LSPR couples light into the surface dissociative adsorption of hydrogen and formation of hydrides, whereas the LO-LSPR activates heterogeneous reactions at the interface with the support, that is, hydrogen spillover into α-Al 2 O 3 and reverse-oxygen spillover from α-Al 2 O 3. This Ga-based plasmon-catalytic platform expands the application of supported plasmoncatalysis 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.