Electrochemical Reduction of CO₂ on Metal-Based Cathode Electrocatalysts of Solid Oxide Electrolysis Cells

Abstract

Electrochemical reduction of CO2 using solid oxide electrolysis cells (SOECs) has emerged as an attractive approach for converting CO2 to high energy molecules, such as CO, a key precursor for the synthesis of fuels and chemicals using the commercially established Fischer–Tropsch process. The in situ generation of syngas (CO and H2) has also been demonstrated in SOECs through the coelectrolysis of CO2 and H2O. However, conventional Ni-based SOEC cathodes exhibit high overpotential losses associated with CO2 activation, leading to the disproportional activation of CO2 and H2O during coelectrolysis, facilitating the equilibrium-limited thermochemical reverse water gas shift (RWGS) reaction. Thus, identification of factors that govern CO2 activation on transition metal electrocatalysts is important toward optimizing the performance of SOEC cathodes for modulated production of syngas. Herein, we experimentally assess the electrocatalytic performance of monometallic transition metal electrocatalysts (Fe, Ni, and Pd) toward electrochemical CO2 reduction in SOECs with the aim of understanding the electrocatalyst characteristics that govern this performance. We report that metal oxophilicity (a property correlated to the strength of metal–oxygen bonding) plays an important role in the energetics associated with electrochemical CO2 reduction and electrocatalyst deactivation via oxidation. We suggest that a compromise in the oxophilicity of the metal is required to achieve optimal electrochemical activity and stability because CO2 activation is facile on highly oxophilic transition metals to the left of Ni (i.e., Fe); however, strong oxygen binding on these metals leads to their deactivation via oxidation. Potential approaches that facilitate the electronic structure modulation of transitional metals to optimize their surface oxophilicity, such as alloying, are suggested.

Enhancing CO2 Catalytic Adsorption on an Fe Nanoparticle-Decorated LaSrFeO4 + δ Cathode for CO2 Electrolysis

“…Obviously, the current density sharply drops from 900 to 681 mA cm –2 in the first 1.5 h, and then, a slight degradation of current density was observed during the test. The fast degradation at beginning is likely associated with the strong oxygen binding of metallic Fe . In addition, the slight decrease might be owing to partial oxidation of Fe nanoparticles and destruction of the cathode microstructure at elevated temperature.…”

“…It was reported that Fe has a strong oxophilicity, which is related to the strength of metal-oxygen bonding. The metallic Fe is, therefore, often present in the form of alloy in the nanoparticles . For instance, the enhanced stability of Ni particles and decreased diffusion resistance were achieved after addition of Fe in the metallic Ni, resulting in a high electrolysis current density of −1840 mA cm –2 .…”

“…The metallic Fe is, therefore, often present in the form of alloy in the nanoparticles. 32 For instance, the enhanced stability of Ni particles and decreased diffusion resistance were achieved after addition of Fe in the metallic Ni, resulting in a high electrolysis current density of −1840 mA cm −2 . 33 However, the effect of monometallic Fe nanoparticles on CO 2 electrolysis performance was rarely reported due to the lower catalytic activity of Fe than that of Ni/Co.…”

Process Development and Technoeconomic Analysis of Different Integration Methods of Coal-to-Ethylene Glycol Process and Solid Oxide Electrolysis Cells

“…Fresh water mixed with recycled condensate is pressurized by a pump and fed into the cathode heat exchanger (heater model). Part of the product gas of the cathode is recycled and mixed with inlet gas to maintain the hydrogen content of the inlet gas at ∼10% to prevent nickel from being oxidized at the cathode . The mixture of steam and hydrogen is heated in cathode heat exchange to meet the operating temperature of the SOEC.…”

“…Part of the product gas of the cathode is recycled and mixed with inlet gas to maintain the hydrogen content of the inlet gas at ∼10% to prevent nickel from being oxidized at the cathode. 33 The mixture of steam and hydrogen is heated in cathode heat exchange to meet the operating temperature of the SOEC. The rest of the product gas of the cathode is used as the hydrogen source of the EGS unit, which is mainly modeled by the RPlug and five RadFrac models.…”