Electrochemical Synthesis of Highly Ordered Porous Al Scaffolds Melt-Infiltrated with LiBH4 for Hydrogen Storage

Abstract

Two highly ordered porous Al scaffolds were synthesized by applying a soft template assisted electrodeposition method, using an ionic liquid as the electrolyte. Polystyrene (PS) spheres with an average diameter of 399 ± 2 nm or 89 ± 20 nm were deposited on a polished Cu electrode using a dip-coater. An imidazolium-based ionic liquid mixed with aluminium chloride [EMIm]/AlCl3 (40/60 mol%) was used as the electrolyte for the Al electrodeposition. The PS spheres that were used as a soft template were removed after the Al electrodeposition method by chemically dissolving them in tetrahydrofuran (THF). Lithium borohydride (LiBH4) was then melt-infiltrated into the porous Al scaffold. Morphological observations of the dip-coated Cu electrodes with the PS spheres, the as-synthesized porous Al scaffolds, and the LiBH4 melt-infiltrated samples were carried out using Scanning Electron Microscopy (SEM). The scaffolds exhibited a highly ordered porous Al structure with an open network of pores and an average pore size of 355 ± 25 and 56 ± 20 nm respectively. The porous Al acts as a reactive scaffold which interacts with LiBH4 at elevated temperature. Temperature Programmed Desorption (TPD) experiments revealed that the melt-infiltrated LiBH4 samples exhibited faster H2 desorption kinetics in comparison to the bulk material. In particular, the 56 ± 20 nm Al scaffold showed a H2 desorption onset temperature (Tdes) at 100°C which is 250°C lower than for bulk LiBH4. This temperature drop can be attributed to the size reduction of LiBH4 down to the nanoscale, together with the high contact surface area with the Al scaffold.