High‐Temperature CO₂ Electrolysis in Solid Oxide Electrolysis Cells: Developments, Challenges, and Prospects

Abstract

which has caused serious global warming. According to Intergovernmental Panel on Climate Change, global warming of 1.5 °C above preindustrial levels will come true by 2055 and bring about severe environmental and ecological issues, [2] such as ocean acidification, sea level rise, and species extinction. Therefore, it is urgently needed to reduce the atmospheric CO 2 concentration. [3] Apart from utilizing renewable energy resources to substitute for fossil fuels, CO 2 capture and storage (CCS) processes, and CO 2 capture and utilization (CCU) processes have been developed to effectively diminish the existing atmospheric CO 2 concentration. [4] The CCS processes are often expensive and laborious, and face the risk of CO 2 leakage, while the CCU processes are able to convert the captured CO 2 to value-added carbon-containing chemicals powered by external energy and has attracted more and more research interests recently. However, the conversion of CO 2 to target products is relatively difficult due to its extremely stable CO bonds. Several approaches for CO 2 conversion have been developed, such as photosynthesis, thermocatalytic reduction, electrochemical reduction, and photochemical conversion. Compared with other approaches, electrochemical reduction is more attractive because of two reasons: 1) electrochemical reduction process is controllable through adjusting the applied voltage and reaction temperature, and 2) the process can utilize renewable energy resources such as wind, solar, hydroelectric, and geothermal energies to electrochemically convert CO 2 to useful chemicals, which forms a carbon-neutral energy cycle and simultaneously provides an efficient storage method for renewable energy resources.Several types of electrolysis cell have been systematically investigated for CO 2 electroreduction as listed in Table 1. The first type operates in H-shaped electrochemical cells with liquid electrolyte at low temperatures (<100 °C).[5] Gaseous CO 2 reactant is dissolved into the liquid electrolyte and transported to the electrode surface, which is subsequently electroreduced to CO, HCOOH, CH 4 , C 2 H 4 , C 2 H 5 OH, and so on. [1,6] Although high Faradaic efficiency of products from CO 2 electroreduction has been achieved by exploring efficient catalysts recently, the current density of CO 2 electrolysis is relatively low due to the low CO 2 solubility and the competitive High-temperature CO 2 electrolysis in solid-oxide electrolysis cells (SOECs) could greatly assist in the reduction of CO 2 emissions by electrochemically converting CO 2 to valuable fuels through effective electrothermal activation of the stable CO bond. If powered by renewable energy resources, it could also provide an advanced energy-storage method for their intermittent output. Compared to low-temperature electrochemical CO 2 reduction, CO 2 electrolysis in SOECs at high temperature exhibits higher current density and energy efficiency and has thus attracted much recent attention. The history of its development and its fundamental mech...

Developments in CO2 Electrolysis of Solid Oxide Electrolysis Cell with Different Cathodes▴

“…The fundamental working mechanisms of an SOEC for CO 2 electrolysis are illustrated in Figure 1 [17]. The electrolysis reactions are nonspontaneous redox reactions.…”

“…Fundamental working mechanisms of an SOEC for CO 2 electrolysis (reproduced from[17] with permission from JohnWiley & Sons).…”

Research Progress in Conversion of CO2 to Valuable Fuels

“…To complete such a reaction, high temperature, high pressure environment, or highly efficient catalysts are typically required to provide the necessary energy. Till now, different strategies including thermal catalysis [ 9 , 10 , 11 , 12 , 13 ], photocatalysis [ 14 , 15 , 16 , 17 ], electrocatalysis [ 18 , 19 , 20 , 21 ], and photoelectrochemical (PEC) reactions [ 22 , 23 , 24 , 25 ] have been adopted to conduct the reduction of CO 2 , in which heat, light, or electricity were used to supply essential energy for the reaction. As is known, eight electrons are needed for each CO 2 molecule to complete the conversion to hydrocarbon compounds.…”

Three-Dimensional Cathodes for Electrochemical Reduction of CO2: From Macro- to Nano-Engineering

“…Table 1. Selected products and equilibrium potentials of electrochemical reduction of CO 2 [16] (this table is To date, electrochemical reduction of CO 2 has been demonstrated by systems operating under ambient conditions (H-cell, flow cells, membrane-electrode-assembly (MEA) cells) or under high temperatures such as solid oxide electrolysis cells (SOECs) [17][18][19][20]. Figure 1 illustrates configurations of different reactor designs commonly used for the electrochemical reduction of CO 2 [19].…”