Performance Comparison between Ni–SDC and Ni–YSZ Cermet Electrodes for Carbon Dioxide Electrolysis on Solid Oxide Electrolysis Cell

Solid oxide electrolysis cells (SOECs) have already proven their ability to electrolyze steam (H₂O). Recently, the attention has been drawn towards the electrolysis of carbon dioxide (CO₂). In this paper, the electrochemical reduction of CO₂ over Ni–Ce_0.8Sm_0.2O_1.9 (SDC) and Ni–8 mol% Y₂O₃–ZrO₂(YSZ) electrodes was studied on SOEC device.

Cells used in this work consist of Ni–SDC or Ni–YSZ cermet electrodes, YSZ electrolyte, and (La_0.8Sr_0.2)_0.97MnO₃ (LSM) electrode. Electrochemical properties of SOEC were evaluated by impedance spectroscopy and current–voltage (I–V) curves with a supply of CO₂/H₂ and pure O₂ gases to the cathode and anode sides, respectively, at 1000 ^oC.

The results of preliminary experiments indicated that in CO₂/H₂ mixture, CO₂ reduction proceeds indirectly via kinetically fast reverse water-gas shift reaction (RWGSR, CO₂ + H₂ ⇌ CO + H₂O). The impact of cathode material on CO₂ reduction was studied as depicted in Fig. 1 (a) and (b), which shows I–V curves of single button cells employing Ni–SDC and Ni–YSZ electrodes, respectively. The cell with Ni–SDC electrode exhibited relatively high current density compared with Ni–YSZ electrode. The better performance of Ni–SDC electrode depends on the conductivity of doped ceria; it exhibits higher ionic conductivity than YSZ and shows electronic conductivity under a reducing atmosphere. These two factors are most likely extended the effective triple phase boundary (TPB) region and improved the electrochemical reactions at electrode/electrolyte interface.