Hydrogen storage in a layered flexible [Ni<inf>2</inf>(btc)(en)<inf>2</inf>]<inf>n</inf> coordination polymer

© 2016 Hydrogen Energy Publications LLC [Ni2(btc)(en)2]n coordination polymer exhibits a layered two-dimensional structure with weak interaction between the layers. Correlation of experimental measurements, DFT calculations and molecular simulations demonstrated that its structural features, primarily the inherent flexibility of the layered polymeric structure, lead to improved hydrogen storage performance at room temperature, due to significant enhancement in isosteric heats of hydrogen adsorption. Volumetric measurements of hydrogen adsorption at room temperature show up to 0.3 wt.% hydrogen absorbed at 303 K and 2.63 bar of hydrogen pressure, with isosteric heats of adsorption of about 12.5 kJ mol−1. Predicted performance at room temperature is 1.8 wt.% at 48 bar and 3.5 wt.% at 100 bar, better than both MOF-5 and NU-100, with calculated values of isosteric heats for adsorption of hydrogen in 8–13 kJ mol−1 range at both 77 K and 303 K. Grand canonical Monte Carlo calculations show that this material, at 77 K, exhibits gravimetric hydrogen densities of more than 10 wt.% (up to 8.3 wt.% excess) with the corresponding volumetric density of at least 66 gL−1, which is comparable to MOF-5, but achieved with considerably smaller surface area of about 2500 m2 g−1. This study shows that layered two-dimensional MOFs could be a step towards MOF systems with significantly higher isosteric heats of adsorption, which could provide better room temperature hydrogen storage capabilities

Influence of mechanical activation and heat treatment on magnetic properties of nano structured mixture Ni <inf>85.8</inf> Fe <inf>10.6</inf> Cu <inf>2.2</inf> W <inf>1.4</inf>

© 2019, Journal of Mining and Metallurgy. Mehanicka aktivacija Ni 85.8 Fe 10.6 Cu 2.2 W 1.4 praškaste smeše, u vremenskim intervalima od 30-210 min, u kombinaciji sa termickom obradom na temperaturama u rasponu od 393-873 K, dovela je do mikro strukturnih promena, stvarajuci nanostrukturnu smešu istog sastva, ali sa poboljšanim magnetnim osobinama. Najbolji rezultat je ostvaren za mehanicku aktivaciju u trajanju od 120 min, prilikom termicke obrade na temperaturama oko Kirijeve tacke (693K), kada je specificna magnetizacija pocetne smeše povecana za 57%. Mikrostrukturne promene, koje obuhvataju strukturnu relaksaciju, smanjenje slobodne zapremine, gustine dislokacije i mikronaprezanja, dovode do poboljšanja strukturnih osobina materijala, i na taj nacin omogucuju bolju pokretljivost zidova magnetnih domena, kao i njihovo usmeravanje u primenjenom magnetnom polju, samim tim doprinose boljoj specificnoj magnetizaciji materijala. Sa dužim mlevenjem, veci stres akumuliran u uzorku podložniji je oslobadanju, pri cemu se procesi oslobadanja stresa pomeraju ka nižim temperaturama