UCL Department of Chemical Engineering

Paul Shearing was the first author of the most cited paper in Chemical Engineering Science in the period 2009-10 for the paper entitled: 3D reconstruction of SOFC anodes using a focused ion beam lift-out technique (Chem. Eng. Sci., 64(17) 3928-3933, 2009.) 

The paper, which was amongst the first to utilise focused ion beam techniques to characterise the microstructure of a solid oxide fuel cells (SOFC), has been cited by 52 other authors to date.

SOFCs are high temperature electrochemical energy conversion devices which demonstrate significant potential for green and economic power generation. Reactions in these fuel cells are typically supported by complex porous composite materials, which provide enable transport of electronic, ionic and gaseous species to so-called “triple-phase boundaries” where the reactions can be catalysed. The abundance and distribution of these TPBs is thought to have a direct influence on the overall performance of the electrode – in this paper the authors present a method to characterise this in three-dimensions. Focused ion beam (FIB) systems utilise the nano-milling capability of a focused Ga⁺ beam coupled with the imaging capacity of a scanning electron microscope to sequentially mill and image a material, yielding a sequence of 2D images that can be effectively recombined in 3D space. This is demonstrated in Figure 1, where this process has been utilised to obtain a 3D map of the SOFC electrode microstructure:

Figure 1- sequential SEM images (Left) are combined to make a 3D image (right) of a Ni-YSZ SOFC Electrode

Abstract: Improvements to electrode performance are essential to accelerate the commercialisation of SOFC technology. A key metric of performance for SOFC electrodes is the length and distribution of three or triple phase boundaries (TPBs) which provide an indication of electrochemical performance. Techniques that can be used to characterise TPB length are highly valuable; with an increasing knowledge of electrode microstructures, electrochemical performance can be optimised. One such technique for electrode characterisation uses focused ion beams (FIB) to sequentially mill and image an electrode surface, obtaining a sequence of 2D images that may be reconstructed in a 3D space. In this paper we present a technique to maximise the quality of the raw data obtained via ex-situ characterisation of electrode micro-sections based on FIB lift-out. With improved raw data, we have been able to conduct semi-automated image analysis to extract key microstructural information, including the length and distribution of TPBs. Reconstructions have been carried out using both single and dual beam instruments; two reconstructions of Ni–YSZ anode structures are presented here.