Evaluation of ZIF-8 and ZIF-90 as Heat Storage Materials by Using Water, Methanol and Ethanol as Working Fluids

The increasing demand for heating/cooling is of grave concern due to the ever-increasing population. One method that addresses this issue and uses renewable energy is Thermochemical Energy Storage (TCES), which is based on the reversible chemical reactions and/or sorption processes of gases in solids or liquids. Zeolitic imidazolate frameworks (ZIFs), composed of transition metal ions (Zn, Co, etc.) and imidazolate linkers, have gained significant interest recently as porous adsorbents in low temperature sorption-based TES (sun/waste heat). In this study, we examined two different sodalite-type ZIF structures (ZIF-8 and ZIF-90) for their potential heat storage applications, based on the adsorption of water, methanol and ethanol as adsorbates. Both ZIF structures were analysed using PXRD, TGA, SEM and N2 physisorption while the % adsorbate uptake and desorption enthalpy was evaluated using TGA and DSC analysis, respectively. Among the studied adsorbent–adsorbate pairs, ZIF-90-water showed the highest desorption enthalpy, the fastest sorption kinetics and, therefore, the best potential for use in heat storage/reallocation applications. This was due to its significantly smaller particle size and higher specific surface area, and the presence of mesoporosity as well as polar groups in ZIF-90 when compared to ZIF-8.

A Study of K/Ti-co-doped NaAlH4 on Thermodynamic Tailoring, Surplus Hydrogen Amount and Metal Hydride Molar Volume

A remarkable finding of metal hydride hydrogen storage is that substituting 4 mol % sodium by potassium in 4 mol % Ti-doped NaAlH₄ raises the reversible hydrogen storage capacity from 3.3 % w/w H to 4.7 % w/w H. This increase by 42% is concomitant with a slightly lower desorption enthalpy: intriguingly enough, it is substantially more hydrogen capacity at slightly less desorption enthalpy. The general solution to that puzzle has been already derived from a gas phase point of view, taking advantage of the equilibrium nature of the matter, which thus comes in terms of an ideal gas chemical potential. However, it is also interesting to investigate for the flipside effect in the sorbent phase, affecting molar volume. This paper elucidates by the example of K/Ti-co-doped NaAlH₄ the relation of doping modifications to surplus hydrogen amount and hydride molar volume, defining the term “reaction pathway” in this context, yielding the according figures.<br>

A Study of K/Ti-co-doped NaAlH4 on Thermodynamic Tailoring, Surplus Hydrogen Amount and Metal Hydride Molar Volume

A remarkable finding of metal hydride hydrogen storage is that substituting 4 mol % sodium by potassium in 4 mol % Ti-doped NaAlH₄ raises the reversible hydrogen storage capacity from 3.3 % w/w H to 4.7 % w/w H. This increase by 42% is concomitant with a slightly lower desorption enthalpy: intriguingly enough, it is substantially more hydrogen capacity at slightly less desorption enthalpy. The general solution to that puzzle has been already derived from a gas phase point of view, taking advantage of the equilibrium nature of the matter, which thus comes in terms of an ideal gas chemical potential. However, it is also interesting to investigate for the flipside effect in the sorbent phase, affecting molar volume. This paper elucidates by the example of K/Ti-co-doped NaAlH₄ the relation of doping modifications to surplus hydrogen amount and hydride molar volume, defining the term “reaction pathway” in this context, yielding the according figures.<br>

Innovative Carbon Based Materials for Solid State Hydrogen Storage and Energy Storage

Alkali cluster-intercalated fullerides (ACIF) consist of crystalline nanostructures in which positively charged metal clusters are ionically bond to negatively charged C60 molecules, forming charge-transfer salts. These compounds have been recently investigated with renewed interest, appearing as a novel class of materials for hydrogen storage, thanks to their proven capability to uptake reversibly high amounts of hydrogen via a complex chemisorption mechanism. In this presentation, after a short summary on the hydrogen storage topic, the synthesis, the structural investigation, and the hydrogen storage properties of Li, Na, and mixed Li-Na clusters intercalated fullerides belonging to the families NaxLi12-xC60 (0 ≤ x ≤ 12) and NaxLi6-xC60 (0 ≤ x ≤ 6) will be presented. By manometric and thermal analyses, it has been proved that C60 covalently binds up to 5.5 wt% H2 at moderate temperature and pressure, thanks to the catalytic effect of the intercalated alkali clusters. Moreover, the destabilizing effect of Na in the co-intercalated NaxLi6-xC60 compounds leads to an improvement of the hydrogen-sorption kinetics by about 70%, linked to a decrease in the desorption enthalpy from 62 to 44 kJ/mol H2. The addition of Pt and Pd nanoparticles to Li fullerides increases up to 5.9 wt% H2 the absorption performances and of about 35 % the absorption rate. The ammonia storage properties of Li6C60 have also been investigated, resulting in quite appealing. Being the price of C60 quite high, cheaper C based materials are under examination. Porous biochar from agricultural waste is giving interesting results as electrode materials for high-performance supercapacitors.

The Influence of Fe on the Structure and Hydrogen Sorption Properties of Ti-V-Based Metal Hydrides

Ti-V-based metal hydrides have decent overall performance as hydrogen storage materials, but V is expensive and it is therefore tempting to replace it by less expensive ferrovanadium containing about 20% Fe. In the present work we have investigated how Fe influences the structure and hydrogen storage properties of (Ti0.7V0.3)1−zFez alloys with e r r o r t y p e c e z ∈ { 0 , 0.03, 0.06, 0.1, 0.2, 0.3} using synchrotron radiation powder X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry and manometric measurements performed in a Sieverts apparatus. The alloys form body-centered cubic (bcc) crystal structures for all considered values of z, and the addition of Fe causes the unit cell to contract. When exposed to hydrogen gas, the bcc alloys form face-centered cubic (fcc) hydrides if e r r o r t y p e c e z ≤ 0 . 1 while other hydrogen-containing phases are formed for higher Fe-contents. The hydrogen capacities of the fcc hydrides at 20 bar are not significantly influenced by the addition of Fe and reach 3.2(3) wt% in (Ti0.7V0.3)0.9Fe0.1H1.6(2). For higher Fe contents the hydrogen capacity is decreased. The absorption kinetics are fast and the reactions are complete within minutes when the alloys are exposed to 20 bar H2 at room temperature. Increasing Fe content reduces the desorption enthalpy, onset temperature and activation energy.

THE EFFECT OF MAGNETITE (Fe3O4)CATALYST FROM IRON SANDS ON DESORPTION TEMPERATURE OF MgH2 HYDROGEN STORAGE MATERIAL

One of the future technologies for a safe hydrogen storage media is metal hydrides. Currently, Mg-based metal hydride has a safety factor and efficient for vehicle applications. However, the thermodynamic properties of magnesium hydride (MgH2) found a relatively high temperature. High desorption temperatures caused MgH2 high thermodynamic stability resulting desorption enthalpy is also high. In this study, natural mineral (iron ore) has been extracted from iron sand into powder of magnetite (Fe3O4) and used as a catalyst in an effort to improve the desorption properties of MgH2. Magnetie has been successfully extracted from iron sand using precipitation method with a purity of 85 % , where the purity of the iron sand before extracted was 81%. Then, MgH2-Fe3O4 was milling using mechanical alloying method with a variety of catalysts and milling time. The observation by XRD showed the material was reduced to nanocrystalline scale. MgH2 phase appears as the main phase. DSC test results showed with the addition of Fe3O4, the desorption temperature can be reduced up to 366oC, compared to pure pure MgH2 reached by 409o C. Furthermore, based on gravimetric test, the hydrogen release occurs at a temperature of 388o C, weight loss of 0.66 mg during 16 minutes.

Kinetics and Thermodynamics of Nanostructured Mg-Based Hydrogen Storage Materials Synthesized from Metal Nanoparticles

Mg, Ni, Co, Cu and Fe nanoparticles with a particle size of 30-300 nm were synthesized by hydrogen plasma metal reaction method. Nanostructured Mg-based hydrogen storage materials (Mg-H, Mg-Ni-H, Mg-Co-H, Mg-Cu-H and Mg-Fe-H systems) were synthesized from these metal nanoparticles. In this work, the kinetic and thermodynamic properties of these nanostructured hydrogen storage materials were studied. It was found that nanostructure could significantly enhance the hydrogen absorption kinetics but the thermodynamics (desorption enthalpy and entropy) does not change with downsizing in the size range of 50 to 300 nm.

Thermodynamic and mechanical characterisation of kaolin clay

This study deals with experimental thermodynamic and rheological characterization of kaolin. Water sorption isotherms of kaolin were determined for three temperatures (30, 50 and 70°C). Desorption isotherms were fitted by using five models (GAB, BET, Henderson modified, Adam and Shove, Peleg) among the most used ones in literature. The GAB model was found to be the most suitable for describing the relationship between equilibrium moisture content and water activity for the whole range of temperature (30-70°C) and relative humidity(0-100%). Desorption enthalpy and entropy were determined. The desorption enthalpy decreases with increasing moisture content. The density and the shrinkage of the material and the Young’s modulus variations as a function of moisture content were determined experimentally. The Young modulus varies between 0.1 MPa and 14 MPa. The viscoelastic parameters of kaolin were also determined by using a series of Prony.

Chemically B-N Modified Activated Carbon and its Thermal Stability and Desorption Enthalpy With Methanol

A chemical modification of activated carbon is demonstrated through boron and nitrogen incorporation via microwave-assisted heating. The surface modification of the activated carbon was imaged by scanning electron microscope. The crystallinity of the material was quantified by X–ray diffraction, and the chemical content as well as bonding environment were investigated using X-ray photoelectron and Raman microscopies. The observed increment in desorption enthalpy of modified activated carbon with methanol as measured through differential scanning calorimetry and its superior thermal stability in air as measured by thermogravimetric analysis suggest that the modified material is a promising candidate for efficient sorption processes in waste thermal and solar energy driven cycles.