Effect of a mesoporous NiCo2O4 urchin-like structure catalyzed with a surface oxidized LiBH4 system for reversible hydrogen storage applications

Abstract

A mesoporous NiCo₂O₄ urchin-like structure was synthesized by applying a facile hydrothermal method. Different concentrations of NiCo₂O₄ urchin-like structures were mixed with a surface oxidized LiBH₄ system using a wet-impregnation method, followed by heat treatment. The hydrogen storage capacity of LiBH₄ + 25% NiCo₂O₄, LiBH₄ + 50% NiCo₂O₄ and LiBH₄ + 75% NiCo₂O₄ systems was investigated. Typically, hydrogenated LiBH₄ + 25% NiCo₂O₄, LiBH₄ + 50% NiCo₂O₄ and LiBH₄ + 75% NiCo₂O₄ systems desorbed 2.85 wt%, 3.78 wt% and 3.91 wt% of hydrogen, respectively, at the dehydrogenation temperature ranging from room temperature (RT) to 275 °C. Further, the LiBH₄ + 75% NiCo₂O₄ system exhibited better kinetics than other systems and released ∼5.8 wt% of hydrogen at a isothermal dehydrogenation temperature of 250 °C in 60 minutes. Hydrogen binding energies were calculated as 0.28 eV, 0.27 eV and 0.26 eV for LiBH₄ + 25% NiCo₂O₄, LiBH₄ + 50% NiCo₂O₄ and LiBH₄ + 75% NiCo₂O₄ systems, respectively. Moreover, the calculated activation energies of LiBH₄ + 25% NiCo₂O₄, LiBH₄ + 50% NiCo₂O₄ and LiBH₄ + 75% NiCo₂O₄ systems are 17.99 kJ mol⁻¹, 17.03 kJ mol⁻¹ and 16.92 kJ mol⁻¹, respectively. The calculated BET (Brunauer–Emmett–Teller) surface area of NiCo₂O₄ and LiBH₄ + 75% NiCo₂O₄ systems is 124.05 and 136.62 m² g⁻¹, respectively. These results showed that hydrogen sorption and desorption properties are significantly increased by the influence of mesoporous structure, lower binding energy and activation energy of LiBH₄ + 75% NiCo₂O₄ system.