Journal of Alloys and Compounds 458 (2008) 223–230 Hydrogen storage behavior of ZrNi 70/30 and ZrNi 30/70 composites Diego Escobar, Sesha Srinivasan ∗ , Yogi Goswami, Elias Stefanakos Clean Energy Research Center, College of Engineering, University of South Florida, Tampa, FL 33620, USA Received 9 March 2007; received in revised form 30 March 2007; accepted 2 April 2007 Available online 6 April 2007 Abstract The Zr–Ni compositional alloys, namely (i) ZrNi 70/30 and (ii) ZrNi 30/70 (both by weight) have been investigated for the reversible hydrogenation behavior. These composites show Zr–Ni intermetallic multi-phase formation as explored by X-ray diffraction studies. The sorption kinetics of ZrNi 70/30 seems much faster (∼3–4 times) than that of ZrNi 30/70 alloys. The initial desorption rate increasing with an increase in temperature. A well-defined plateau region was obtained for the ZrNi 70/30 with an equilibrium pressure range from <1 bar (300 ◦ C) to 10 bars (390 ◦ C). For ZrNi 30/70, the sloppy plateau region extends to higher equilibrium pressures. It is estimated that the total effective hydrogen concentration for ZrNi 70/30 (∼1.0 wt.%) is at least 2 times that of ZrNi 30/70 (∼0.5 wt.%) composites. From the PCT isotherms, the enthalpy of reaction (H) has been calculated to be ∼39 kJ/mol H 2 for the ZrNi 70/30. The surface morphologies of the hydrogenated materials exhibit the presence of cracks and particle size pulverization in comparison to the pristine alloys. © 2007 Elsevier B.V. All rights reserved. Keywords: Hydrogen storage; Zr–Ni intermetallics; Thermogravimetric analysis; PCT isotherms; Desorption kinetics 1. Introduction Hydrogen is a highly reactive element and has been studied to form hydrides and solid solutions with thousands of metals and alloys [1]. The majority of the 91 natural elements below the H element in the periodic table will hydride under appropriate conditions such as: VH 2 , NaH, LaH 2 , ZrH 2 , etc. Unfortunately, the pressure–composition–temperature (PCT) properties are not very convenient relative to the 1–10 atm, 0–100 ◦ C range of util- ity used for practical hydrogen storage applications or a good content of hydrogen for device applications. For practical applications of reversible hydrides, it is required to combine strong hydride forming elements A with weak hydriding elements B to form alloys (especially intermetallic compounds) that have the desired intermediate thermody- namic affinities for hydrogen. A good example to show this characteristic is the combination of La (forming LaH 2 at 25 ◦ C, P d =3 × 10 -29 atm and H f = -208 kJ mol -1 H 2 ) with Ni (NiH, 25 ◦ C, P d = 3400 atm, H f = -8.8 kJ mol -1 H 2 ) to form the intermetallic compound LaNi 5 (LaNi 5 H 6 , 25 ◦ C, P d = 1.6 atm, H f = -30.9 kJ mol -1 H 2 ). This incredible abil- ∗ Corresponding author. Tel.: +1 813 974 0759; fax: +1 813 974 2050. E-mail address: sesha.srinivasan@gmail.com (S. Srinivasan). ity to ‘interpolate’ between the extremes of elemental hydriding behaviour has opened the door to the modern world of reversible hydrides. Intermetallic alloys such as AB 5 (e.g. LaNi 5 ), AB (e.g. FeTi, ZrNi, etc.), AB 2 (e.g. ZrFe 2 ) and A 2 B (e.g. Mg 2 Ni) have been explored in the past for their effective hydrogen sorption behavior [2–4]. In recent years, many new and novel hydrogen storage systems are being investigated, namely, (i) Mg-transition metal hydrides (e.g. Mg 2 FeH 6 ) [5,6]; complex hydrides such as (ii) alanates [7–9], (iii) borohydrides [10] and (iv) amides [11,12], (v) amino-boranes [13]; physisorbed sys- tems such as (vi) fullerenes [14], (vii) carbon nanotubes [15,16] (viii) graphitic nanofibres [17] (ix) metal organic frameworks [18,19] and (x) polymer nanocomposite matrices [20,21], etc. However, none of the hydride systems typified above satisfy all of the desired characteristics of hydrogen storage such as high volumetric and gravimetric hydrogen density, low temperature, rapid desorption kinetics, tolerance hysteresis, insensitivity to impurities, cost and weight, etc. The first example of a reversible intermetallic hydride was demonstrated with the AB compound, ZrNi [22]. The hydride ZrNiH 3 has a 1 atm desorption temperature of about 300 ◦ C, too high for hydrogen storage applications, whereas it is significant for hydrogen compression. These intermetallic alloys show good volumetric and gravimetric reversible H-capacities, competitive 0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2007.04.012