What are solid oxide electrochemical reactors?

Figure 1. Operation of solid oxide electrochemical reactors in fuel cell mode

Solid oxide electrochemical reactors (SOERs), also known as reversible solid oxide cells, are a type of fuel cell/electrolyser system, which typically operate in a high-temperature environment (500 °C – 800 °C). SOERs are one of the promising future energy generation system, demonstrating high fuel to electrical energy conversion efficiency, when operated in fuel cell mode (Figure 1). The system can use hydrogen and/or hydrocarbons as a fuel. When it is operated in electrolyser mode, the system can produce green hydrogen when it utilises electricity generated by renewable energy.  

Why three-dimensional structures?

 

Figure 2. Schematic illustration of the solid oxide electrochemical reactors with the planar structure (left side) and with 3D pillar structured electrolyte layer (right side) Reproduced with permission; Electrochim.Acta, 426, 140834. Copyright (2022) Elsevier.)

We fabricated 3-D structured electrodes or electrolyte layers for high-performance SOERs for clean and efficient power generation and CO2 electrolysis and H2 production. For the development of high-performance SOERs, it is crucial to boost the rates at which geseous species react on each electrode. The reactions occur at the interface between electronic conductors | ionic conductors | pores in the porous electrode; such interfaces are known as 'triple-phase boundaries' (TPBs). Hence, densities of such TPBs determine the reaction rate of gaseous species, reacting with the electrons and ions flowing-in or out through electronically-conducting electrodes and ionically-conducting electrolyte phases. Therefore, increasing TPB densities facilitate the conversion of the gases in the electrodes, leading to the enhanced SOER performance. Our goal is increasing these TPB densities through constructing 3-D structured electrodes or electrolyte layers to ultimately increase the performance of SOERs. The performance of 3-D structured electrodes was compared with planar structures, to elucidate geometric effects on reactor performance (Figure 2).

Prediction of optimal geometry & ink-jet printing of the 3D structures  

Figure 3. (a, b) Model-predicted effects of current density and YSZ pillar height on the potential difference in fuel cell mode with 3% H2O, and (c) designed cell configuration with various heights of YSZ pillars. Reproduced with permission; Electrochim.Acta, 427, 140902. Copyright (2022) Elsevier.

First, we predicted the optimal geometry of the 3-D structured pillars through computational modelling (COMSOL Multiphysics), by designing the SOERs cell with various YSZ pillar heights from 10 µm to 150 µm. Figure 3 shows calculated SOERs performance in fuel cell mode at each pillar height value, demonstrating the performance saturation from 90 µm pillar height. Subsequently, based on the predicted optimal pillar geometry, we moved on to the fabrication of micropillar structures for SOERs to validate our computational prediction.

Figure 4. Various printable 3-D microstructures through an ink-jet printing method

Fabrication of those structures is possible using an ink-jet printing method. Ink-jet printing technology enables the printing of 3D ceramic structures down to the micrometre scale with high precision and reproducibility. The schematic illustration in Figure 4 shows various types of micro 3D geometries that can be produced using inkjet printing method.

Figure 5. Printed micro size YSZ pillars with printing of 50 layers

Figure 5 shows the printed micro size YSZ pillars on the YSZ electrode layers using an inkjet 3D printer with 50 layers printing. By using inkjet printing technology, fabrication of the cell with those 3D structured components is possible, thereby increasing the performance of SOERs. Our printer is Ceradop X-Serie (France).

This project is being carried out by Dr Inyoung Jang.

Dr Inyoung Jang operating the 3D printer (Ceradrop, X-Serie)

 

Publications

The work of Dr Inyoung Jang and collaborators on 3-D inkjet printing and modelling of solid oxide electrochemical reactors: