CO2 and H2O Electrolysis Using Solid Oxide Electrolyzer Cell (SOEC) with La and Cl- doped Strontium Titanate Cathode

Abstract

The average CO2 concentration in atmosphere increased by 25 ppm in the last decade, and during the same period, the average global surface level temperature rose by 0.3 °C. CO2, one of the biggest contributors to climate change, is a greenhouse gas that traps the energy emitted by the earth’s surface, causing an increase in the temperature. Because of the greenhouse effect of CO2, a growing area of research is trying to find ways to minimize CO2 emission and decrease the CO2 concentration in the atmosphere. Besides reducing the CO2 emission, it is also important to develop technologies to convert CO2 into valuable products. One such product is syngas, a mixture of carbon monoxide and hydrogen that can be used as fuel, as well as for synthesis of hydrocarbons through Fischer–Tropsch synthesis. Intermediate and high temperature co-electrolysis of CO2 and water using Solid Oxide Electrolyzer Cell (SOEC) is a promising method to produce syngas from CO2. This work focuses on the use of La0.2Sr0.8TiO3±δClσ as an SOEC cathode for CO2 and H2O co-electrolysis, and its activity compared with conventional SOFC electrode material, Ni/NiO-YSZ. Electrocatalytically, it was found that Ni/NiO-YSZ outperforms La0.2Sr0.8TiO3±δClσ when only CO2 is reduced, however, La0.2Sr0.8TiO3±δClσ shows higher activity for co-electrolysis of CO2 and H2O. Post-reaction temperature-programmed oxidation testing performed on the co-electroylsis cells demonstrated less coking associated with La0.2Sr0.8TiO3±δClσ than Ni/NiO-YSZ, although both materials showed relatively lower levels of coking when H2O was not present. Interactions between the surfaces of these materials and CO2 were characterized using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and Raman spectroscopy. These showed that CO2 interacts more strongly with La0.2Sr0.8TiO3±δClσ than Ni/NiO-YSZ, forming carbonate species on the surface. The electrical conductivity of the materials was also compared, and while Ni/NiO-YSZ showed slightly higher values, the electrical conductivity of La0.2Sr0.8TiO3±δClσ increased more rapidly with temperature and was in the same order of magnitude as that of Ni/NiO-YSZ.