The main objective of MEGASTACK is to develop a cost efficient stack design for MW sized PEM electrolysers and to construct and demonstrate a prototype of this stack. The prototype will demonstrate a capability to produce hydrogen with an efficiency of at least 75% (LHV) at a current density of 1.2 Acm-2 with a stack cost below €2,500/Nm3h-1 and a target lifetime in excess of 40,000 hours (< 15 μVh-1 voltage increase at constant load).

In the project we aim to take advantage of the existing PEM electrolyser stack designs of ITM power as well as novel solutions in the low-cost stack design concepts developed and further refined in the FCH-JU projects NEXPEL and NOVEL. In order to successfully up-scale the design concept from a 10-50 kW to a MW-sized stack, we will in the MEGASTACK project perform integrated two-phase flow and structural mechanics modelling together with optimization of stack components such as MEAs, current collectors and sealings which are important for stack scale up. The development activities will focus on existing solutions, already proven in kW-sized electrolyser stacks, rather than aiming to use completely new, unproven concepts and materials. The stack design will have ease of manufacture and stack assembly as a major goal, with necessary quality control processes and robust supply chains for components.

To reach these ambitious objectives, MEGASTACK will develop and demonstrate an enhanced stack design essential for cost-competitive, efficient and dynamic PEM electrolysis systems through the following key concepts:

• The stack design process will have an integrated approach, involving stack manufacturers, component and MEA suppliers as well as PEM electrolyser experts from research institutes.
• Evaluation and adaptation of existing solutions and commercially available components for use in large format stacks and increased ease of stack assembly by the reduction of stack part count.
• Advanced multiphase flow modelling coupled with multiphysics models for electrochemical kinetics, heat and momentum transport will be used as detailed design tools for cell and stack components.
• Implementation of quality control measures and supply chain evaluation of all components will be performed in order to reduce costs and minimise technology and manufacturing risks.

Clearly, the development of a large scale stack for PEM electrolysers is not a trivial endeavour. It is highly unlikely that a simple scale up of an existing stack design would be successful. It is thus necessary to take an integrated approach, involving a multidisciplinary team with expert knowledge of all aspects related to stack construction and operation, such as:

• Properties and behaviour of stack components such as MEAs, porous current collectors, bipolar plates, coatings and sealings.
• The importance of detailed understanding of heat and mass transport for securing designs with minimal pressure drop, proper heat management and efficient water supply and gas removal.
• Design for ease of assembly and minimization of the risk of misalignment of components and consequent failure of one or more cells in a stack.