Physical bottom Up Multiscale Modelling for Automotive PEMFC Innovative performance and Durability optimisation
The main goal of PUMA MIND is to establish a predictive modelling tool of PEMFC durability as a function of their components composition and operation conditions either representative or automotive applications. More precisely, this modelling tool will adhere to an integrative approach combining:
- a detailed model of the electrochemical phenomena in relation to the chemical and microstructural properties of the catalyst layers ;
- a detailed model of the transport processes, thermal management and mechanical stresses in relation to the microstructural properties of the components; - a 1D cell level multi-scale model describing the competitive mechanisms and allowing a calculation of their relative influence on the macroscopic performance and durability under current cycled conditions;
- a cell level multi-physics CFD model with 3D resolution of the processes, allowing for a recommendation of operation conditions for improved PEMFC durability;
- an innovative diagnostic and control oriented physical-model for online PEMFC diagnosis and real-time optimization of the operation conditions for enhanced durability.
Achievements to date
A web-site has been built and made available by VODERA: http://www.pumamind.eu/
The kick-off meeting of the project will be held in Grenoble on February 8th 2013.
The breakthrough outcomes expected from PUMA MIND are:
- a set of simulation tools providing a better understanding of the interplay between mechanisms at different scales regarding the electrochemistry (including degradation such as catalyst dissolution, support corrosion, ionomer degradation), water management and thermo-mechanical stresses, and their relative impact on the whole cell behaviour in real automotive application conditions;
- modelling strategies that scale up detailed physical descriptions of mechanisms into macroscopic models and provide a better understanding of the relationships between the operation conditions (e.g. type of current cycle, relative humidity, temperature, pressures…), the components structural and chemical properties, and the long-term cell durability;
- cell level models, in particular 3D CFD models, predicting durability as function of the materials chemical and structural properties, components and operation conditions;
- an on-line diagnostic model which allows for the maintenance of the PEMFC operation under the appropriate conditions at a given current cycle for enhanced durability;
- with a strong connection with novel validation experiments in ex situ and in situ conditions, operation strategies to enhance the PEMFC durability with good efficiency.
Since the first PEMFCs were developed in the late 1950s there has been a remarkable technological progress towards increasing their efficiency and reducing the platinum loading, through the development of new membranes and electro-catalytic nanoparticles or the improvement of the electrode structure attributed to by growing fundamentals and understandings in modern material and porous media science. On the other hand, the platinum loading reduction resulted in increasing the components’ structural complexity, especially of the Catalyst Layers (CLs): from this, even if the overall operating principle of a single cell remain relatively simple, complex mechanisms at different spatial scales form a strong interplay during the PEMFC operation, limiting the effectiveness of the catalysts’ activity. In fact, processes at the smaller scales, e.g. Oxygen Reduction Reaction (ORR) on the cathode platinum nanoparticles dominate the processes at the larger scales (e.g. liquid water transport through the cathode carbon support secondary pores) which in turn affect the processes at the smaller ones, e.g. through the water flooding limiting O2 transport in the cathode. It is extremely important for automotive applications to accurately predict PEMFC state-of-health and remaining lifetime. For that purpose, it is necessary to develop diagnostic schemes that can evaluate PEMFC state-of-health adequately.
In order to achieve this, several steps are required:
- to develop, via physical modelling, a better understanding of several individual processes in the cell components;
- to understand the interplay between individual scales over the spatiotemporal hierarchies with their possible competitive or synergetic behaviour;
- to identify the contribution of each mechanism into the global cell response under dynamic conditions;
- to design separated controllers for an online control of the PEMFC behaviour in order to enhance its durability under specific operation conditions (e.g. by controlling the dynamics of the reactant relative humidity, the temperature, etc.).
Because of the structural complexity and multi-physics character of modern PEMFCs, interpretation of experimental observations and ultimate PEMFC optimization is a challenge. An analysis through a consistent multiscale physical modelling approach, in particular consisting on CFD models at the device level with high predictive capabilities towards the materials atomistic, chemical and structural properties, is required to elucidate the efficiency limitations and their location, the degradation and failure mechanisms. The development of such multiscale modelling approach and associated CFD models must have several properties:
- predictive capabilities of the relative contributions of the different scales and mechanisms into the macroscopic PEMFC efficiency and durability;
- high flexibility towards its application to any type of chemical and structural properties of the used materials and components;
- easily adaptable to any type of operation condition and system.
The PUMA MIND approach, consisting of building up a diagnostic and control-dedicated physical model with large prediction capabilities, enables:
- the reduction of the amount of experiments (and thus the cost) currently needed to build up classical empirical models with limited prediction capabilities;
- a better targeting of experimental characterizations in representative conditions of the end user application;
- new operation strategies, reducing performance degradation and also strategies to improve the stability of the materials and components;
- integration, at EU level, of modelling efforts usually developed separately. This will be done with the development of a modelling platform for more efficient communication and coordination for higher impact of the use of modelling on the PEMFC optimization in engineering practice.