The pellets were subjected to reciprocating rubbing under vacuum (10-7 mbar range) using an alumina sphere, 3 mm in diameter. A specially designed friction cell with nearly zero own gas emission was used. The motion frequency was 1 Hz. One motion cycle consisted of one forth and one back stroke, each of which lasted for about 40 ms. The indenter stood still for around 50 ms after the forth stroke and 870 ms after the back one. The stroke length was la = 7 mm, the mean sliding speed was Vs = 0.18 m s-1 and the normal load was in the range 0.22 – 0.88 N. The total and partial gas pressures were measured in the experimental vacuum chamber, where the pellets were rubbed, using an ionization Bayard-Alpert type vacuum gauge and a quadrupole mass-spectrometer, correspondingly. To quantify minute gas emission rates (<1 nmol/s) the experimental chamber was connected to a gas-expansion chamber through a diaphragm, which conductance under molecular gas flow was carefully measured. Before starting the experiments, the chamber was pumped out for at least 48 hours to achieve stable background pressure (the rate of change of low-pass filtered pressure signal ≤10-11 mbar s-1). The gas emission was evaluated from the pressure time series during the mechanical action and benchmarked against the stable background. The gas composition and the emission rates were determined using a previously developed statistical matrix method. X-ray diffraction (XRD) with Cu Kα (λ = 0.15418 nm) radiation was employed for the structural characterization of NaAlH4. To assess the thermal stability of NaAlH4 Temperature-Programmed Desorption Mass-Spectrometry (TPD-MS) was used. A portion of NaAlH4 powder was placed into an alumina crucible in a glove box under Ar atmosphere (MBraun, <1 ppm H2O, <10 ppm O2). Alumina crucible was used instead of a Pt one to avoid possible decomposition of NaAlH4 due to the catalytic effect of Pt. The crucible was transferred to the TPD-MS system, where it was set into another Pt crucible. During the transfer, the sample was briefly exposed to the atmospheric air (about 5 min). The test was carried out under an Ar flux of 50 ml/s and a heating rate of 5 ºC/min. The mechanically affected zones were characterized using FTIR spectrometry, Raman confocal spectroscopy (incident laser wavelength  = 532 nm and power 5.6 mW) and Scanning Electron Microscopy (Hitachi S 800) to contrast possible structural and chemical variations induced in the material by the mechanical action. All the results were benchmarked against the measurements on the pristine zones of the same pellets.

Datasets of mass-spectrometry signals were obtained in the experiments with non-thermal dehydrogenation of sodium alanate through the application of mechanical energy. An application of mechanical energy was explored as a new non-thermal method to drive H2 emission from undoped sodium alanate at room temperature. Dehydrogenation reactions were studied on a micrometer scale using localized rubbing under ultrahigh vacuum. Mechanically Stimulated Gas Emission Mass-Spectrometry (MSGE-MS) including the Dynamic gas expansion method was used to determine the kinetic parameters of hydrogen emission as well as the composition and emission behaviour of trace gases. It was found that mild rubbing of NaAlH4 pellets under vacuum led to intensive and almost instantaneous gas emission. The dominating species in the emitted gases was H2 (>99%). Traces (~0.1%) of mono- and polyalanes, NaAlH4 vapours, CO2 and other no identified gases were registered. Several H2 emission modes, which characteristic time constants ranged widely from 0.6 to 465 s, were observed. None of the dehydrogenation reactions involved could be connected to either the thermal effect of friction or the direct coupling of mechanical forces to the energy landscape of chemical reactions. The study was complemented by structural, morphological, tribological, mechanical and surface analyses. It was suggested that the tribochemical reactions can be triggered by plastic deformation and shearing.

1.Dataset of mass-spectrometry time series of mechanically stimulated gas emission from sodium alanate (NaAlH4) pellets under vacuum.-- 2. Dataset of Thermal Programmed Desorption – Mass-Spectrometry (TPD-MS) analysis of sodium alanate.-- 3. Dataset of X-ray diffraction of sodium alanate.-- 4. Dataset of micro-FTIR spectra of pristine and mechanically activated surfaces of pellets of sodium alanate.-- 5. Dataset of Raman spectra measured on the surfaces of pellets of sodium alanate.

This study was co-funded by Spanish Ministry for Science and Innovation (grants PID2019-111063RB-I00, PID2020-112770RB-C22 and RTI2018-099794-B-I00) and the Basque Government via the EMAITEK Plus 2020 programme.

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