Rationally designed negative electrode for selective CO2-to-CO conversion in protonic ceramic electrochemical cells

Protonic ceramic electrochemical cells (PCECs) are solid-state electrochemical devices that employ proton-conducting oxides as electrolytes, which offer a promising approach for electrification of chemical manufacturing, including CO2 reduction to produce value-added chemicals (e.g., CO). The primary advantage of PCECs is their intermediate operating temperatures (300–600 °C), which thermodynamically and kinetically favor the CO2 reduction chemistry at the negative electrode. However, the conventional negative electrodes of PCECs, such as BaZr0.8−xCexY0.2O3-δ-Ni or BaZr0.8−xCexY0.1Yb0.1O3-δ-Ni, cannot reduce CO2 to either CH4 or CO with a selectivity of >99 %, leading to the production of a CO and CH4 mixture. Herein, an oxide-supported in-situ exsolved Ni-Fe alloyed nanoparticle electrocatalyst, Sr2Fe1.4Mo0.5O6-δ-Ni0.175 (SFM-Ni0.175), is first employed as the negative electrode of PCECs. The PCECs equipped with this new negative electrode selectively favor the CO2-to-CO conversion. A selectivity of ~100 % toward CO has been demonstrated over a wide range of operating temperatures (400–600 °C) and applied potentials/current densities. The negative electrode demonstrated in this work fully suppresses the CH4 production. In situ diffuse reflectance infrared spectroscopy (DRIFTS) was performed to probe the CO2 reduction mechanisms over both SFM-Ni0.175 and the traditional negative electrode (BCZYYb7111 +Ni), which indicates SFM-Ni0.175 inhibits the formation of formate species, leading to selective production of CO. This work validates that PCECs equipped with the rationally designed negative electrode can selectively manufacture chemicals.