No abstract

Solid oxide electrolysis cell (SOEC) is a potential technique to efficiently convert CO 2 greenhouse gas into valuable fuels. Thus, there is significant interest in developing highly active and stable electrocatalysts for the CO 2 reduction reaction (CO 2 RR). Herein, a Ni and F co-doping strategy is proposed to facilitate the exsolution reaction and form a new cathode, Ni−Fe alloy nanoparticles embedded in ceramic Sr 2 Fe 1.5 Mo 0.5 O 6−δ (SFM) doped with fluorine. F-doping and Ni−Fe exsolution enhance CO 2 adsorption by a factor of 2.4 and increase the surface reaction rate constant (k chem ) for CO 2 RR from 6.79 × 10 −5 to 18.1 × 10 −5 cm s −1 , as well as the oxygen chemical bulk diffusion coefficient (D chem ) from 9.42 × 10 −6 to 19.1 × 10 −6 cm 2 s −1 at 800 °C. Meanwhile, the interfacial polarization resistance (R p ) decreases by 52%, from 0.64 to 0.31 Ω cm 2 . At 800 °C and 1.5 V, an extremely high current density of 2.66 A cm −2 and a stability test over 140 h are achieved for direct CO 2 electrolysis in the SOEC.

BaCo0.4Fe0.4Zr0.1Y0.1O3−δ (BCFZY) has been demonstrated to be a highly active yet large thermal expansion cathode catalyst for solid oxide fuel cells (SOFCs). In this work, gadolinia doped ceria (GDC) was mixed with BCFZY (BCFZY-GDC) to investigate its oxygen reduction reaction activities and chemical/thermal compatibility with electrolyte. Improved thermal compatibility of BCFZY-GDC with electrolyte and cathodic activity in symmetric cells were obtained, while, in contrast to the results of the common composite approach, the addition of ceria reduced surface exchange and bulk diffusion coefficient and subsequently decreased electrochemical performance under typical fuel cell condition. This interesting phenomenon was explored based on the limited electronic conductivity and using distinct modes of action of measurement techniques. Besides, SOFCs with BCFZY-GDC showed remarkable stability in 100 h of testing, during which 54 times of thermal cycling operations at 600–800 °C with a ramp rate of 20 °C min–1 were performed, whereas SOFCs using BCFZY showed gradually reduced performance in 9 times of thermal cycling and failed within 20 h of testing under the same operational condition, highlighting the crucial role of thermal compatibility among SOFC key components for efficient and durable energy conversion in practical application.