Realization of the near-linear relationship between cumulative carbon dioxide (CO2) emission and the rise in the global surface temperature is pushing society to a profound change in the way we produce and consume energy. In principle, the strategic deployment of a diverse portfolio of CO2 mitigation technologies could stabilize human-induced global temperature. The activation of the reverse chemical pathways in which CO2 is reduced into high-energy molecules is an appealing route to recycle CO2 into our economy. In this direction, the utilization of solid oxide electrochemical cells (SOECs) is a promising approach to facilitate the electrochemical reduction of CO2 with high rates and selectivity owing to favorable kinetics at high operating temperatures. However, these systems are limited by the high activation overpotential losses induced by the sluggish kinetics of CO2 and O2 electrocatalysis – central reactions at the SOECs electrodes. Moreover, the current knowledge gap on the mechanisms governing the surface reactivity of suitable electrocatalysts towards CO2 and O2 electrocatalysis at high temperatures is still an appreciable challenge that hinders the optimization of SOEC electrode reactions. This work combines theoretical calculations, controlled synthesis, advanced characterization, and testing to obtain insights on the chemical/electrochemical steps that govern CO2 and O2 electrocatalysis in SOECs. Structure/performance relations are developed to guide the identification of highly active and stable electrocatalysts for these electrode reactions. It is found that a compromise in the oxophilicity of the electrocatalyst is required to achieve optimal material activity and stability. Our theory-guided design principles successfully identified: (i) Cobalt-doped La2NiO4 as a highly active material for O2 electrocatalysis, and (ii) Iron as a highly active metal for CO2 electrochemical reduction, however, electrochemically unstable. This phenomenon ratifies the role of the strength of surface oxygen-binding as a stability descriptor.

Oxygen & carbon dioxide electrocatalysis in high-temperature solid oxide electrochemical cells

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ACS Fall 2022

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