Ni/ScCeSZ anode-supported cell manufacturing and development of carbon tolerant anodes for methane-fuelled SOFCs

Jiang, Zeyu (2023). Ni/ScCeSZ anode-supported cell manufacturing and development of carbon tolerant anodes for methane-fuelled SOFCs. University of Birmingham. Ph.D.

Preview

Jiang2023PhD.pdf
Text - Accepted Version
Available under License All rights reserved.
Download (11MB) | Preview

Abstract

Solid oxide fuel cells (SOFCs) are highly efficient energy conversion devices with flexible fuel choices. However, SOFCs suffer thermal degradation from the high operating temperature (> 600°C) and display a coking issue at the anode when operating with hydrocarbon fuels. To overcome these issues, it is crucial to reduce the operating temperature and develop carbon-tolerant anode materials. This thesis aims to optimise the fabrication process for intermediate operating temperature (600 to 800°C) SOFCs and develop carbon-tolerant anode materials for operation under dry methane reforming conditions.

This thesis presents a comparative study of different cell fabrication approaches for anode-supported SOFC button cells with a ScCeSZ-GDC bi-layer electrolyte. Sequential tape casting coupled with spin coating were found to be the most appropriate techniques for fabricating defect-free SOFC single cells. It was found that sintering the ScCeSZ and GDC layers at different temperatures was necessary to avoid the interdiffusion of Zr and Ce during co-sintering. The successfully prepared bi-layer electrolyte SOFC showed promising electrochemical performance in hydrogen operation, with maximum power densities (P\(_{max}\)) of 1.10, 1.00, and 0.80 W•cm\(^{-2}\) at 800°C, 750°C, and 700°C, respectively. The cell also exhibited good operational stability with hydrogen operation at current densities of 0.2 and 1.0 A•cm\(^{-2}\) for 1200 and 500 hours, respectively. Electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS) were used to investigate the main factors causing performance degradation. It was found that Ni coarsening at the anode and migration of Sr from the LSCF cathode to the ScCeSZ electrolyte were the main contributions to cell performance degradation.

In this study, 1wt.% of Sn, Ag, Cu, or Fe dopant (with respect to Ni content) was infiltrated into the porous Ni/ScCeSZ anode to modify its catalytic activity and carbon resistivity under dry methane reforming conditions (CH\(_{4}\), CO\(_{2}\) and N\(_{2}\)). The concentration of dopant on the anode surface was found to be higher than 1wt.%, suggesting that the dopant preferentially remained on the anode surface after the infiltration process. Electrochemical performance of the 1wt.% Sn, Ag, Cu, and Fe-doped cells operated with simulated biogas was further evaluated at 750°C. Adding Sn to the Ni/ScCeSZ anode showed a significantly improved electrochemical performance in biogas operation at 750°C, with a P\(_{max}\) of 0.963 W•cm\(^{-2}\). However, no obvious enhancement on the power output of the Ag and Cu-doped cells was observed in biogas operation, suggesting unchanged catalytic activity towards dry methane reforming. Notably, modifying the Ni/ScCeSZ anode with 1wt.% of Fe showed a negative impact on the cell performance with hydrogen operation compared to other dopants. This was largely attributed to the accumulation of Fe dopant on the anode surface and the presence of low electrically conductive NiFe-ZrO\(_{2}\) catalyst.

All metal-infiltrated cells showed stable voltage output with simulated biogas operation for 120 hours. No carbon formation on the anode surface was identified from the Sn, Ag, and Cu-doped cells after biogas operation, resulting from stable operation in biogas. However, fibrous carbon was found on the Fe-doped cells after 120 hours of operation in simulated biogas. Raman spectroscopy results suggested that the carbon deposited on the Fe-doped cell had a lower graphitisation degree than on the undoped cells. The reduced formation of graphitic carbon suppressed the dissolution of carbon into the Ni catalyst, resulting in an improved operational stability of the Fe-doped cell in simulated biogas.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):