This is a continuation proposal describing an "in situ" muSR experiment on hydrogen storage materials. For the two previous beam-time allocated for RB1510262 and RB1520259, we have made a special cell for measuring the muSR spectrum and the amount of gas desorbed from the sample simultaneously. Using such cell, we have found that hydrogen starts to diffuse in the milled MgH2 sample below its hydrogen desorption temperature (RB1610029). This indicates the importance of H diffusion in solids to determine the desorption temperature in MgH2. In order to check whether such relationship is a common phenomenon in complex hydrogen storage materials, we wish to perform the "in situ" muSR experiment on borohydrides. Note that we already measured the muSR spectra for LiBH4 and other samples at temperatures far below their desorption temperature (RB1520259).