Design, fabrication and testing of porous material-metal hydride composites for hydrogen storage

Hydrogen is widely acknowledged to be a promising renewable fuel for replacing petroleum. Current methods of storage focus on compression or cooling to increase the density of hydrogen. However, these often require cryogenic or high-pressure conditions which are costly to achieve and maintain. Alternatively, hydrogen can be stored via adsorption onto a solid nanoporous scaffold, or reversibly forming a metallic hydride. Both techniques have their own sets of advantages and disadvantages with neither method meeting all criteria for practical hydrogen storage simultaneously. Achieving solid-state hydrogen storage is an important goal within engineering and chemistry, and is the key to realising a safe, cost-effective, environmentally friendly fuel centred around hydrogen.

Producing metal-hydride particles at the nanometre scale has previously been used to improve the hydrogen storage capabilities of various metal hydrides through maximising the surface area, increasing surface energies, and reducing internal diffusion paths. Typically, these nanosized materials are synthesised through mechanical milling, which produces inconsistent materials that are prone to contamination. Recently, incorporating the metal hydride within a porous network has proven to be a practical pathway to control the synthesis of nanosized metal hydrides. Nanoporous materials with pore diameters of only several nanometres demonstrate good potential for synthesising porous material-metal hydride composites, and show several beneficial properties, including reduced exposure to moisture, reduced formation enthalpies, and improved stability. Confinement effects from the porous scaffolds can further alter the phase diagram of the guest material, stabilising phases which may otherwise be unstable under the same pressure and temperature conditions.

Nanoporous material-metal hydride composites provide an exciting avenue to overcoming the current challenges in hydrogen storage and producing confined phases with unique properties. In this project, carbonaceous micro-mesoporous host material properties will be explored to identify the effect the scaffold has on the behaviour of the encapsulated guest metallic hydride.

Several steps are required to be able to design nanoporous material-metal hydride composites, including:
- Systematically explore host properties such as pore size and pore geometry to determine the effect on the confined material arrangement.
- Identify the extent to which the porous scaffold affects the formation/decomposition and physical properties of the confined metal hydride lattice.
- Understand phase nucleation within the nanoporous material-metal hydride system and how the guest materials can vary throughout the composite.
- Investigate the effect of different manufacturing techniques and conditions on the final composite system.
- Perform computational simulations to understand underlying mechanisms within the material to predict the guest structure and composite properties.

The overarching goal of this project is to rationally design and fabricate novel nanoporous material-metal hydride composites to exploit desirable properties for hydrogen storage at commercially achievable temperature and pressure conditions. Furthermore, understanding and manufacturing of nanoconfinement composites may lead to developments in catalysts, electronics, and energy storage materials.

There are seven principal groups of beneficiaries for our new EPSRC Centre for Doctoral Training in Composites Science, Engineering, and Manufacturing.

1. Collaborating companies and organisations, who will gain privileged access to the unique concentration of research training and skills available within the CDT, through active participation in doctoral research projects. In the Centre we will explore innovative ideas, in conjunction with industrial partners, international partners, and other associated groups (CLF, Catapults). Showcase events, such as our annual conference, will offer opportunities to a much broader spectrum of potentially collaborating companies and other organisations. The supporting companies will benefit from cross-sector learning opportunities and

- specific innovations within their sponsored project that make a significant impact on the company;
- increased collaboration with academia;
- the development of blue-skies and long-term research at a lowered risk.

2. Early-stage investors, who will gain access to commercial opportunities that have been validated through proof-of-concept, through our NCC-led technology pull-through programme.

3. Academics within Bristol, across a diverse range of disciplines, and at other universities associated with Bristol through the Manufacturing Hub, will benefit from collaborative research and exploitation opportunities in our CDT. International visits made possible by the Centre will undoubtedly lead to a wider spectrum of research training and exploitation collaborations.

4. Research students will establish their reputations as part of the CDT. Training and experiences within the Centre will increase their awareness of wider and contextually important issues, such as IP identification, commercialisation opportunities, and engagement with the public.

5. Students at the partner universities (SFI - Limerick) and other institutions, who will benefit from the collaborative training environment through the technologically relevant feedback from commercial stakeholder organisations.

6. The University of Bristol will enhance their international profile in composites. In addition to the immediate gains such as high quality academic publications and conference presentations during the course of the Centre, the University gains from the collaboration with industry that will continue long after the participants graduate. This is shown by the

a) Follow-on research activities in related areas.
b) Willingness of past graduates to:

i) Act as advocates for the CDT through our alumni association;
ii) Participate in the Advisory Board of our proposed CDT;
iii) Act as mentors to current doctoral students.

7. Citizens of the UK. We have identified key fields in composites science, engineering and manufacturing technology which are of current strategic importance to the country and will demonstrate the route by which these fields will impact our lives. Our current CDTs have shown considerable impact on industry (e.g. Rolls Royce). Our proposed centre will continue to give this benefit. We have built activities into the CDT programme to develop wider competences of the students in:

a) Communication - presentations, videos, journal paper, workshops;
b) Exploitation - business plans and exploitation routes for research;
c) Public Understanding - science ambassador, schools events, website.