Carbon Dioxide Reduction on a Metal-Supported Solid Oxide Electrolysis Cell

Abstract

Using iACRES, which is an ironmaking system based on the Active Carbon Recycling Energy System concept, to reduce or recycle CO₂ emitted from ironmaking processes, we electrolyzed CO₂ with a metal-supported solid oxide electrolysis cell (MS-SOEC) capable of providing a large cell surface area for the processing of large amounts of CO₂. The MS-SOEC current-density–voltage (I-V) curves reveal a change in slope at around 0.8 V, which is the theoretical decomposition voltage of CO₂. The CO production rate was 0.88 µmol cm⁻² s⁻¹ when 2.0 V was applied between the cathode and the anode at 800°C, while that for O₂ was 0.44 µmol cm⁻² s⁻¹, which is consistent with the stoichiometry for CO₂ electrolysis. The Faraday efficiency was 48% at 900°C. Gas was observed to leak from the cell; this leakage will need to be overcome through improvements in the layer-production process in order to achieve an efficiency close to 100%. On the basis of the cell-based experimental results, the feasibility of a blast furnace based on iACRES and driven by an HTGR (high-temperature gas-cooled reactor) was evaluated. To reduce CO₂ emissions by 30.0%, the required MS-SOEC surface area was estimated to be 8.30×10⁴ and 3.98×10⁴ m² with 968 and 480 MWth of HTGR thermal output under Faraday efficiency of 48% and 100%, respectively. We confirmed that iACRES using MS-SOEC contributes to realizing low-carbon ironmaking by recycling CO₂ and reducing its emissions into the atmosphere.