Improving the performance of hydrogen storing metal alloys: Scaling up of wash coating techniques
Creators: name: Puszkiel, Julián
Publisher: name: Zenodo
Year: 2024

description: Hydrogen production and storage offer a promising solution to the non-continuous nature of renewable energy sources such as solar and wind. Renewable energy can be converted into hydrogen by electrolysis and back into electricity through a fuel cell, balancing out production and demand, a concept known as Power-To-Gas. Hydrogen storage still represents a challenge. The most common methods of high-pressure storage (safety concerns and expansive tank design at higher pressure) and liquid storage (energy penalty for conversion and boil-off losses) have clear disadvantages. For the case of low-pressure storage, underground hydrogen storage in caverns offers a cheap and convenient solution. However, it is constrained by local availability and issues like the geochemical side reactions and hydrogen recovery. The storage of hydrogen in solid form as hydrides is a promising alternative. Special attention is paid to the so-called room-temperature metal hydrides since they combine reasonable working temperatures (20 - 100 °C) and pressure (1 - 50 bar) with fast kinetics and easy raw material handling. Nonetheless, there are still aspects to be optimized. The material's swelling behavior at the time to absorb in the interstices of the crystal structures is one of the aspects of research. Different approaches are applied to minimize the pressure effect of the swelling upon the vessel's internal walls to design a hydride-based hydrogen storage vessel. Adding glidant agents or simply leaving free space for expansion are the most common. The heat management of the hydride-based hydrogen storage vessel is another aspect. Metal hydrides are generally used in a powder form, and such powder bed has low thermal conductivity. Thus, the heat of the exothermic hydrogen absorption cannot be released, decreasing the kinetic performance. The low thermal conductivity of the powder bed is mainly counteracted by constructive means to the tank systems or by pressing into pellets. While showing promising results on the lab scale, most methods are difficult or expensive to scale up. Therefore, a method focused on scalability was developed: A modified wash-coating process, where axillar materials to improve heat conductivity and reduce the effect of expansion have been added to the commercially available hydride-forming alloy Hydralloy C5. The performance of the modified metal alloy was tested on the lab scale, where hydrogen capacity, temperature, and stress were measured in situ. Especially combinations of HydralloyC5 with ENG (expanded natural graphite, a graphite modification with improved heat conductivity) + elastomeric binder and ENG + Aerosil as a glidant agent have shown excellent results. Both samples showed improved heat management performance, but especially the sample with elastomeric binder could completely compensate for the expansion stress, while the sample with Aerosil as a glidant agent had the advantage of ease of preparation. Both samples were successfully prepared on the kg scale, and the first results to estimate the performance of the samples on the larger scale will be presented.