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MgH2-based hydrogen storage materials are promising candidates for solid-state hydrogen storage allowing efficient thermal management in energy systems integrating metal hydride hydrogen store with a solid oxide fuel cell (SOFC) providing dissipated heat at temperatures between 400 and 600 °C. Recently, we have shown that graphite-modified composite of TiH2 and MgH2 prepared by high-energy reactive ball milling in hydrogen (HRBM), demonstrates a high reversible gravimetric H storage capacity exceeding 5 wt % H, fast hydrogenation/dehydrogenation kinetics and excellent cycle stability. In present study, 0.9 MgH2 + 0.1 TiH2 +5 wt %C nanocomposite with a maximum hydrogen storage capacity of 6.3 wt% H was prepared by HRBM preceded by a short homogenizing pre-milling in inert gas. 300 g of the composite was loaded into a storage tank accommodating an air-heated stainless steel metal hydride (MH) container equipped with transversal internal (copper) and external (aluminium) fins. Tests of the tank were carried out in a temperature range from 150 °C (H2 absorption) to 370 °C (H2 desorption) and showed its ability to deliver up to 185 NL H2 corresponding to a reversible H storage capacity of the MH material of appr. 5 wt% H. No significant deterioration of the reversible H storage capacity was observed during 20 heating/cooling H2 discharge/charge cycles. It was found that H2 desorption performance can be tailored by selecting appropriate thermal management conditions and an optimal operational regime has been proposed.

In energy systems, multi-generation including co-generation and tri-generation has gained tremendous interest in the recent years as an effective way of waste heat recovery. Solid oxide fuel cells are efficient power plants that not only generate electricity with high energy efficiency but also produce high quality waste heat that can be further used for hot and chilled water production. In this work, we present a concept of combined cooling, heating and power (CCHP) energy system which uses solar power as a primary energy source and utilizes a reversible solid oxide fuel cell (R-SOFC) for producing hydrogen and generating electricity in the electrolyser (SOEC) and fuel cell (SOFC) modes, respectively. The system uses “high temperature” metal hydride (MH) for storage of both hydrogen and heat, as well as “low temperature” MH's for the additional heat management, including hot water supply, residential heating during winter time, or cooling/air conditioning during summer time. The work presents evaluation of energy balances of the system components, as well as heat-and-mass transfer modelling of MH beds in metal hydride hydrogen and heat storage system (MHHS; MgH2), MH hydrogen compressor (MHHC; AB5; A = La + Mm, B Ni + Co + Al + Mn) and MH heat pump (MHHP; AB2; A = Ti + Zr, B Mn + Cr + Ni + Fe). A case study of a 3 kWe R-SOFC is analysed and discussed. The results showed that the energy efficiencies are 69.4 and 72.4% in electrolyser and fuel cell modes, respectively. The round-trip COP's of metal hydride heat management system (MHHC + MHHP) are close to 40% for both heating and cooling outputs. Moreover, the tri-generation leads to an improvement of 36% in round-trip energy efficiency as compared to that of a stand-alone R-SOFC.

Metal hydrides show great potential for hydrogen storage. However, for efficient hydrogen storage, thermal management is the technical barrier. Among the different heat exchangers proposed in the literature, finned tube heat exchangers are of great technological interest due to their adaptability to wide range of practical applications, high compactness and high heat transfer efficiency. In the present paper, the optimization of finned heat exchanger considering both enhanced heat transfer and vessel volume efficiency is conducted. A semi-analytical expression of heat transfer rate from a single fin is derived. The effects of fin dimension (fin thickness and radius) on the heat exchanger performance are studied. It was shown that the thermal resistance of the whole heat exchanger can be reduced by increasing the fin radius and decreasing the fin thickness, while the fin volume is kept fixed. In the second part of the study, a 2-D numerical simulation was performed in order to validate the results of the analytical study. The effects of two parameters (cooling tube diameter, the fin length) on the hydrogen charging time were highlighted. The increasing in the tube diameter from 2.5 mm to 5 mm results to 25% reduction of the charging time, which is very noticeable. On the other hand, given a reactor radius, increasing the length of fin reduces the overall thermal resistance of the reactor-heat exchanger. The results showed that the decreasing of the thermal resistance of 13% leads to a decreasing in charging time of 42%. Finally, it was found that the results of the numerical simulation agreed qualitatively with those of analytical study. Therefore, the analytical solution presented can be used for a quick assessment of the finned tube heat exchanger design without significant errors.

Metal hydride systems are utilized in many practical applications such as hydrogen storage, heat pumps, etc. The establishment of a metal hydride system requires the expression of reaction rate for the first step design, from an engineering standpoint. However, improper experimental determination of intrinsic kinetics usually leads to significant errors in the kinetic data. This paper presents a novel methodology of estimating these errors based on the entropy generation analysis. For this purpose, numerical simulation is performed taking into account the experimental conditions for a real case. The results showed that if the operating conditions (i.e. hydrogen pressure, heat transfer coefficient) and the size of the experimental setup are not chosen properly, the kinetic data obtained from the experiments will be largely misled. Therefore it should be carefully taken into account in order to minimize the relative errors induced on the kinetic data.