Carbon deposition during co-electrolysis in reversible solid oxide cells

Snowdon, Abigail Louise (2023). Carbon deposition during co-electrolysis in reversible solid oxide cells. University of Birmingham. Ph.D.

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Abstract

Syngas production via high temperature co-electrolysis of CO\(_2\) and H\(_2\)O is a promising pathway towards sustainable hydrocarbon fuels in a closed-loop cycle. However, the use of carbonaceous fuels in solid oxide cells (SOC) can lead to carbon deposition at the fuel electrode, particularly at the intermediate-temperature range.

One method for mitigating carbon deposition is changing the fuel electrode material away from the conventional Ni-Yttria Stabilised Zirconia (NiYSZ). Here, the benefits of Ni-Ceria-doped Scandia-Stabilised Zirconia (NiScCeSZ) SOCs are shown in terms of the superior performance at reduced temperatures and carbon resistance. Two methods of cell manufacturing are developed, both adopting the reverse aqueous tape casting technique. One method consists of a novel five-layer cell in which the GDC barrier layer and new composite layer are tape cast and sintered together. The other method incorporates a spin-coated GDC barrier layer onto a pre-sintered half cell. The cells and the properties of the starting materials are characterised by dilatometry, electron microscopy, and the performance is assessed by polarisation curves and electrochemical impedance spectroscopy (EIS). The best performance is achieved from the spin-coated cells due to a reduced ohmic and gas diffusion resistance resulting from thinner layers with less porosity. These spin-coated cells are therefore used for further co-electrolysis and carbon deposition testing.

For the first time, NiScCeSZ fuel electrode supported cells are used for the co-electrolysis reaction to identify carbon deposition thresholds with respect to operating temperature. Identical tests are also carried out on Ni-YSZ cells for comparison. This work reveals that NiSceSZ cells can operate at up to 58% higher current densities than NiYSZ cells, with half the amount of carbon being deposited. It is important to identify these carbon deposition thresholds in order to operate within the window of safe operation to maximise syngas yield and extend the lifetime of the cells.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):