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

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 H-2) 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 metaloxygen 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.