Ph.D. Research Proposal: Durability study of solid oxide cells operated in pressurized electrolysis modes

Host laboratory: CEA-Grenoble/LITEN/LPH; Funding source: CTBU scholarship (CEA)

Dates: From 1/10/2017 to 1/10/2020 (3 years)

Context and issue:

The integration of renewable and intermittent energies to the global energy market implies electricity storage. However, the available technologies for electricity storage have a low energy capacity and a short time-span. In this context, H2 and/or carbon molecules produced via water and/or water + CO2 electrolysis open up excellent perspectives for storing renewable electricity, specially the High Temperature Electrolysis (600-900°C). This technology is based on Solid Oxide Cells (SOCs) which are composed of a ceramic assembly consisting of a dense electrolyte sandwiched between two porous electrodes. To date, however, the degradation rates in electrolysis modes and more particularly under pressurized conditions are too high and need to be decreased before considering the industrial deployment of the technology. Furthermore, the electrode reaction pathways and the basic degradation mechanisms under pressure (<30 bars) are still not understood.

The proposed PhD thesis aims to address this issue thanks to an original approach combining experimental testing, modelling and materials characterizations. This work will ensure a better understanding of the basic degradation mechanisms for electrolysis and co-electrolysis modes in comparison with the fuel cell one under pressure.

Work plan:

To achieve the objectives of the thesis, a multi-scale approach coupling modelling, electrochemical tests and post-test characterizations will be implemented. The work will be divided into three parts:

(1) Electrode characterizations under pressure. The first part of the thesis will be dedicated to the study of the electrochemical, physical and chemical properties of the electrodes under pressure. This work will be performed with symmetrical cells to identify the elementary mechanisms of each electrodes. The main characterization tool will be the electrochemical impedance spectroscopy.

2) Durability tests and post-test characterizations. Durability experiments will be carried out on complete cells to assess the influence of the operating conditions on degradation rates. A comparison between the electrolysis and fuel cell modes will be more specifically investigated. A set of physicochemical and microstructural characterizations will be conducted on the cells before and after the long-term testing. The microstructural evolutions of electrodes will be assessed by tomographic 3D reconstructions. Physicochemical destabilization of materials, characterization of the adsorbed species and the possible passivation of the electrode active sites will be also apprehended by several techniques such as electron microscopy, Xray diffraction etc… All of these characterizations will help to identify the physical processes inducing the degradation.

(3) Modelling. All data collected by the electrochemical tests and the post-test characterizations will be used in a multi-physics and multi-scale model already available in the laboratory. This model takes into account the elementary mechanisms at the scale of the microstructure up to the macroscopic cell response. This numerical tool will be first improved by the implementation of a relevant reaction pathway for an Operation under pressurized conditions. The validity of the proposed reactive mechanism will be verified by comparing the simulations with the experimental data. Once the model updated, it will be used to quantify the Impact of each degradation mechanism on the global durability curve.

All these works will ensure a better understanding of degradation mechanisms in order to offer innovative solutions to mitigate their effects. More precisely, it will provide new operating strategies for a SOC operating under pressure.

Applicant’s profile: Master degree with a specialization in electrochemistry and physics of materials.

Contacts: Joining CV, study marks and recommendation letter:

Marie PETITJEAN, marie.petitjean@cea.fr ; Jérôme LAURENCIN, jerome.laurencin@cea.fr