## 2 Materials and Methods  
LiNH\({}_{2}\) was purchased from Sigma-Aldrich, St. Louis, MO, USA, with purity not less than 95%, and MgH\({}_{2}\) was procured from Alfa Aesar (Ward Hill, MA, USA) with a purity of 98%. All the materials were kept and handled in an inert nitrogen atmosphere in a glove box. LiNH\({}_{2}\) was used as received, whereas MgH\({}_{2}\) was preprocessed for 15 h in ball mill under Ar/H\({}_{2}\) medium to obtain nanoMgH\({}_{2}\) with finer particle/grain size (<10 nm) compared to as-received MgH\({}_{2}\). The catalyst TiF\({}_{3}\) was purchased from Sigma-Aldrich with 99.9% purity, nanoTi, nanoCo, nanoNi and nanoFe (purity of 90%, particle size range of 3-20 nm, and average surface area of 35-130 m\({}^{2}\)/g) were purchased from QuantumSphere Inc. (Santa Ana, CA, USA) and MWCNT (purity of at least 60%) was purchased from Sigma-Aldrich. All the catalysts were used without further purification. The samples were ball milled using an 80 mL stainless steel bowl, which had a custom-built lid to facilitate evacuating/purging with hydrogen/argon (5%/95%) before starting and after every 2 h of ball milling. High-energy ball milling was carried out by Fritsch Pulverisette P6 planetary mill, the ball milling parameters such as the ball-to-powder ratio, milling speed and milling time were to 20:1, 300 RPM and 1-5 h, respectively. The base materials, xLiNH\({}_{2}\)-MgH\({}_{2}\), were synthesized by milling xLiNH\({}_{2}\) (x = 1 or 2) and MgH\({}_{2}\) for 5 h, and then the desired catalysts were added. The resulting compound was ball milled again for 15 min to make sure a thorough dispersion of catalysts in the base materials was obtained. After the ball milling operation, all the samples were kept in a glove box until further characterization as explained below.  
The microstructural and chemical analyses were carried out to confirm the morphology and composition of chemical elements by scanning electron microscopy (SEM) and energy dispersive X-rays (EDX). The powder X-ray diffraction (XRD) of the samples was carried out by Philips X'pert diffractometer with CuK\(\alpha\) radiation of \(\lambda\) = 1.54060 A. The as-milled samples were prepared inside the glove box, and sealed with Parafilm\({}^{\text{\textregistered}}\) tape, which shows peaks at 20 angles of 21\({}^{\circ}\) and 23\({}^{\circ}\). The diffraction data was analyzed using PANalytical X'pert Highscore software version 1.0f.  
The Perkin-Elmer Spectrum One Fourier transform infrared (FTIR) spectrometer was utilized to measure the bond stretches of the complex hydride compound, and the instrument's working range was between 370-7800 cm\({}^{-1}\) with a resolution of 0.5 cm\({}^{-1}\).  
The gravimetric weight loss experiments were conducted by TA (New Castle, DE, USA) instrument's SDT-Q600 equipment, which is the combination of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The as-prepared samples and their catalyst doped versions were heated at a rate of 5 \({}^{\circ}\)C/min, and the data was analyzed with TA Universal Analysis 2000 software.  
The thermal volumetric sorption analyses of the pristine and catalysts loaded base materials were carried out by Setaram (Caluire FRANCE) HyEnergy's PCTPro 2000 (i.e., a fully automated Sievert's type apparatus) and Quantachrome's (Boynton Beach, FL, USA) Autosorb 1C thermal programmed desorption (TPD) equipment.