Introduction

This project on the electrocatalytic pathway to transform carbon dioxide and water into products such as fuels is part of a multi-disciplinary project between teams from the Departments of Chemical Engineering, Chemistry and the Centre for Process Systems Engineering.

The Electrochemical Engineering group is focussing on the electrocatalytic route, to either split H2O or CO2 into H2 and CO, respectively, which is then to be fed to the downstream processing technologies.

In Phase 1 of the project (EP/H046380/1), we evaluated aqueous based CO2 splitting as well as high temperature solid oxide electrolysis of CO2.

Now in its 2nd project phase (EP/K035274/1), we are focusing solely on high temperature electrolysis with reactors or different geometries, fabrication technologies and testing cycles.

Principles of Solid Oxide Fuel Cells (SOFCs) and Electrolysers (SOEs)

SOEs and SOFCs convert electrical energy to chemical energy, and vice versa, respectively. We are most interested in the former application of this technology, as a means to efficiently produce H2 and CO, from H2O and CO2, respectively. H2 and CO can then be used as a vector for energy storage, and converted back into electrical energy using a fuel cell, or as reagents for industrial processes including the Haber Process and Fischer-Tropsch reactions. If the electrical energy used to electrolyse H2O and/or CO2 is generated from environmentally processes such as solar or wind, the electrical energy generated from their re-oxidation can be considered environmentally friendly.

SOEs and SOFCs comprise three components; two composite electrodes comprised of an electrically and ionically conducting components (cermets), and a solid oxide (ceramic) electrolyte phase. In comparison to other electrolyser and fuel cell technologies, i.e. alkaline and PEM cells, SOEs and SOFCs are more thermodynamically favourable (more negative Gibbs energy change) as they operate at ca. 1000 K, which is the temperature at which the electrolyte becomes conductive:

Thermodynamics equation

 

The downside of operating at ca. 1000 K is that the cells are practically more difficult to handle. Therefore we are interested in reducing the operating temperature while retaining high performance, and exploring innovative geometries to improve handling.

The equations for SOEs are given below, for both H2O and CO2 electrolysis:

[1.1] H2O(g)+2e-→H2 (g)+O2-

[1.2] CO2 (g)+2e-→CO (g)+O2-

The oxide ion conducts through the electrolyte phase and is oxidised at the following electrode:

[2] 2O2-→O2 (g)+4e-

The arrow directions and reaction chronology are reversed for SOFC operation. 

List of Publications

L. Kleiminger, T. Li, K. Li, G.H. Kelsall, Syngas (CO-H2) production using high temperature micro-tubular solid oxide electrolysers, Electrochim. Acta, 179, 2015, 565-577. (Download)

L. Kleiminger, G.H. Kelsall, T. Li, K. Li, Effects of Current Collector Materials on Performances of Micro-Tubular Solid Oxide Electrolysers for Splitting CO2, ECS Trans. 68, 2015, 3449-3458.

L. Kleiminger, T. Li, K. Li, G.H. Kelsall, CO2 splitting into CO and O2 in micro-tubular solid oxide electrolysers, RSC Adv. 4, 2014, 50003-50016.

C-y. Cheng, G.H. Kelsall, L. Kleiminger, Reduction of CO2 to CO at Cu-ceria-gadolinia (CGO) cathode in solid oxide electrolyser, J. Appl. Electrochem., 43, 2013, 1131-1144.Link

P. Bumroongsakulsawat, G.H. Kelsall, Tinned graphite felt cathodes for scale-up of electrochemical reduction of aqueous CO2, Electrochim. Acta, 159, 242-251.

P. Bumroongsakulsawat, G.H. Kelsall, Effect of solution pH on CO: formate formation rates during electrochemical reduction of aqueous CO2 at Sn cathodes, Electrochim. Acta, 141, 216-225.