CO2 and steam electrolysis using a microtubular solid oxide cell

Hernán Monzón,Miguel A Laguna-Bercero

doi:10.1088/2515-7655/ab4250

Abstract

Nickel-yttria stabilized zirconia (Ni-YSZ) supported tubes were fabricated by plastic extrusion molding (PEM). YSZ was used as the electrolyte and LSM-YSZ (lanthanum-strontium doped manganite) as the oxygen electrode. Both layers were deposited by dip coating and were then sintered at 1500 °C and 1150 °C, respectively. Coelectrolysis experiments were performed in these cells at 850 °C, using different fuel gas conditions varying the amount of steam, carbon dioxide, nitrogen and hydrogen. Area specific resistance (ASR) values ranged from 0.47 Ωcm2, when rich steam and CO2 flows are used, to 1.74 Ωcm2, when a diluted composition is used. Gas chromatography was used to examine the amount of H2 and CO in the output gas. The obtained results are consistent with the equilibrium of the water gas shift reaction. For all the different analysed conditions, faradaic efficiency was found to be close to 100%. This experiment confirmed that there is no electronic conduction taking place through the YSZ electrolyte. The threshold for electronic conduction in the diluted feeding conditions (Poor H2O and CO2) for these particular YSZ-based cell was found at voltages of about 1.65 V.

Highlights

Simultaneous coelectrolysis of H2O and CO2 is becoming as an emerging technology to produce syngas from CO2 waste and steam
High temperature electrolysis could be performed with solid oxide fuel cells (SOFC) which are operated in reverse mode
Area specific resistance (ASR) values for steam electrolysis (Rich H2O) and coelectrolysis (Rich H2O and CO2) are very similar, and much lower than the one for CO2 electrolysis (Rich CO2), which is consistent with the results of Stoots et al [7], where they found that the cathodic reactions are probably dominated by the reduction of steam to hydrogen, whereas carbon monoxide is mainly produced via the RWGS

Summary

Introduction

Simultaneous coelectrolysis of H2O and CO2 is becoming as an emerging technology to produce syngas from CO2 waste and steam. The use of this technology will be predominantly of interest combined, for example, with waste heat from other industrial processes In this case, an increase of the electrolysis temperature implies that the heat-to-electric energy ratio required for the process will be higher. Similar studies were performed by Yu et al [16] Their tubular cells were composed of Ni-YSZ-based fuel electrode supports, YSZ or ScSZ electrolytes, and composite air-electrodes of LSM or LSCF. Direct synthesis of CH4 from a CO2–H2O feedstock was recently demonstrated using a tubular design by combining the CO2–H2O co-electrolysis and methanation reactions in a single tubular unit [17, 18] Those previous works have demonstrated the feasibility of using microtubular configurations, it is still lacking in the literature about the factors governing the selectivity of the different reactions for the microtubular configuration, where the temperature along the length of the tube is not uniform. Detailed gas chromatography (GC) analysis will be performed in the present work in order to give some insight to this issue

Experimental details

Results and discussion

Conclusions