(Invited) Large Scale PEM Electrolysis Stack Development - the Megastack Project

Abstract

In the MEGASTACK project, the existing PEM electrolyser stack designs of ITM power has been scaled up and combined with novel solutions to successfully achieve a MW-sized PEM stack design. Two-phase flow and structural mechanics modelling approach has been applied together with optimization of stack components such as MEAs, bipolar plates, current collectors and sealings. The development activities have focused on existing solutions, already proven in kW-sized electrolyser stacks, rather than aiming to use completely new, unproven concepts and materials. The two-phase flow model is based on the volume of fluid (VOF) model in ANSYS/Fluent 16.2 and implements sub-grid scale models for water electrolysis as a set of user-defined functions. These sub-grid scale models include, gas nucleation, gas-liquid mass transfer and bubble coalescence and breakup phenomena on subgrid length scales. Experiments using a transparent cell in combination with a high-speed digital camera as well as numerical image processing was used to quantify temporal and spatial gas distribution and flow velocities. The experimental results are compared to the two-phase flow model results and the validity and implications of the model are discussed. It is clear from both the modelling work and experimental results, that inlet and outlet manifolds, as well as the flow resulting from specific choices for current collector greatly impacts the water distribution of the electrolyser stack and therefore also on the gas distribution within the cell. The LCA compares in a life cycle (cradle-to-gate- plus use phase-) perspective the environmental aspects of the two design options by following practice guidance and required provisions developed by the FCH JU – a method that complies with the ISO 14040 and 14044 series. Results derived from the comparative LCA point towards an improved environmental performance of the new stack design demonstrated in the MEGASTACK project for all midpoint impact categories investigated in this study, i.e. for the abiotic depletion potential (ADP), global warming potential (GWP), acidification potential (AP), and eutrophication potential (EP). The lower environmental impacts resulting from the new stack design are linked to both increased current density that reduces the quantity of active materials required for a given hydrogen production capacity, and the reduction of material requirements through the improved stack design. Summary The FCH-JU project MEGASTACK has developed a PEM electrolyser stack design for MW-sized water electrolysers with the goal of significantly reducing the cost of large scale PEM electrolysers. This presentation will give a summary of the main achievements and results from the MEGASTACK project as well as a more detailed presentation of the results from two phase flow modelling of the liquid and gas transport in the anode flow field and results from a comparative life cycle analysis of the new stack.