Nanostructured surface coatings for the improvement of AB₅-type hydrogen storage intermetallics

Abstract

SUMMARYHydrogen absorption behaviour of intermetallic absorbers strongly depends upon the contribution of the surface layers into the overall rate of the hydrogenation process. Activation process, which is normally required to initiate and facilitate the initial hydrogen uptake, may be waved by modifying the surface behaviour, thus offering obvious practical benefits. In the present work a surface nanoengineering approach was developed to enhance the hydrogenation ability of rare earth-containing AB 5 -type hydride-forming intermetallics. The modification involves three successive steps; (a) fluorination to form a surface-covering REF 3 layer with a high specific surface area; (b) surface functionalization by g-APTES; (c) deposition of Pd nanoparticles into the surface nanocavities of the fluoride. The surface functionalization step was applied to immobilize Pd nuclei inside the nanocavities of the REF 3 layer. The deposited Pd nanoparticles exhibited a high degree of coalescence, and were further transformed into a continuous surface layer. Pd/fluoride modified materials exhibited exceptional Pd coating densities and imposed a large facilitation in the kinetics of hydrogenation compared with the conventional nonmodified intermetallics. The approach has a potential in the directed design of new classes of highly efficient and robust composite hydrogen sorption materials for hydrogen storage, separation and purification. Large improvements in the kinetics of hydrogenation of the Pd/fluoride modified intermetallics also manifested by extraordinary surface poisoning tolerance towards oxygen and water vapour, as compared with that of the nonmodified, or just fluorinated/Pd modified intermetallic alloys. The developed classes of highly efficient and robust composite hydrogen sorption materials have the potential for application as sorption media for the high efficiency hydrogen storage, separation and purification systems and may facilitate progress towards the implementation of the key elements of future hydrogen economy.

Application of surface-modified metal hydrides for hydrogen separation from gas mixtures containing carbon dioxide and monoxide

“…Surface modification of the AB 5 substrate (powder 200 mesh/ 74 lm) was carried out by fluorination, followed by aminosilane functionalization and electroless deposition of Pd, according to the procedure described in [10,11]. Distinct from the previous studies, http://repository.uwc.ac.za 3 where small quantities ("'5 g) of the sample were prepared, the present work attempted to upscale the surface modification procedure.…”

Electrochemical kinetic performances of electroplating Co–Ni on La–Mg–Ni-based hydrogen storage alloys

“…After charge-discharge cycling, the surface of the alloy is passivated, resulting in a deterioration of the alloy performance, such as a reduction in the electrocatalytic activity and the anti-corrosion [7][8][9]. Modifying surface structure has been proved to an effective way for improving performances of metal hydride electrodes [10,11]. In recent years, several surface treatment methods have been applied to the alloys.…”

Poisoning-tolerant metal hydride materials and their application for hydrogen separation from CO2/CO containing gas mixtures

“…The corresponding surface modification procedures for the preparation of the advanced materials were developed [29,30], and feasibility of their application for hydrogen purification from (CO 2 þ CO)-containing gases was demonstrated [31,32]. The novel features of the developed surface modification procedures include (i) enhancement of PGM deposition by surface functionalisation of the metallic hydride-forming material [25,28,29], and (ii) combination of fluorination and enhanced PGM deposition procedures [24,28,30].…”

“…The fluorination and autocatalytic deposition of Pd were applied to w300 g batch of the La(Ni,Co,Al,Mn) 5 substrate. Further details on the surface modification procedure and characterisation (including activation performances) of the surface-modified materials can be found elsewhere [21,24,28,30,32].…”

“…http://repository.uwc.ac.za 9 In doing so, the electroless deposition of Pd onto fluorinated AB 5 material results in the "plugging" of micro-cavities in the fluoride layer by Pd nanoparticles that, in turn, results in the improvement of hydrogen absorption performances and poisoning tolerance of the surface-odified material [24,28].…”