Reversible hydrogen sorption behaviors of the 3NaBH4-(x)YF3-(1-x)GdF3 system: The effect of double rare earth metal cations

Abstract In the present work, NaBH 4 based hydrogen storage materials, 3NaBH 4 -(x)YF 3 -(1-x)GdF 3 composites, were prepared via mechanical ball milling with different values of x (2/3, 1/2, 1/3). The de-/rehydrogenation thermodynamic and kinetic behaviors of 3NaBH 4 -(x)YF 3 -(1-x)GdF 3 composites were systematically investigated. These composites showed a single endothermal peak of hydrogen desorption even though two metal fluorides were added simultaneously into NaBH 4 . All the 3NaBH 4 -(x)YF 3 -(1-x)GdF 3 composites showed reversible hydrogen sorption ability and the best hydrogen absorption kinetics was observed in the 3NaBH 4 -0.5YF 3 -0.5GdF 3 composite, with about 2 wt% hydrogen absorbed at 370 °C under 3.2 MPa H 2 pressure in 1 h. Its hydrogen absorption kinetic behaviors were correlated closely to a First-order reaction model based on experimental results. According to the pressure-composition-temperature (PCT) tests, the reversible hydrogen storage capacity increases, and the hydrogen desorption enthalpy decreases along with more GdF 3 addition. In particular, the desorption enthalpy with regard to the apparent Pauling's electronegativity (χ p ) of added metal cations can be described as Δ H d  = −2748.21χ p +3852.99 kJ/mol H 2 , where χ p =(x)∙χ p (Y 3+ )+(1-x)∙χ p (Gd 3+ ). This research helps us to clarify the effect of co-addition of two rare earth metal fluorides on reversible hydrogen sorption in NaBH 4 .