In-Situ Exsolved Co-Fe Alloy Nanoparticles on Double Layered Perovskite for the Cogeneration of Elethylene and Electricity in Proton Conducting Fuel Cell
Authors: Liu Subiao , Luo Jing-Li 
Published: February 2020

Ethylene plays a crucial role in modern society. Currently, tube furnace steam cracking is the dominant technology in ethylene production, and about 99% of global ethylene production employs the tube furnace pyrolysis method [1]. However, the cracking reactions are highly endothermic, reversible, and severely limited by thermodynamic equilibrium. Moreover, CO and CO2 are largely formed because of the existence of oxygen sources [2]. According to the mechanism of ethane dehydrogenation, if one of the products, hydrogen, can be selectively removed from the reaction system, the conversion is no longer limited by thermodynamic equilibrium, allowing ethane conversion rate to increase at a lower temperature and thus, making the ethylene production more economical. In response to the critical need for a cleaner energy technology, proton conducting solid oxide fuel cell (PCFC) has been investigated as a potential candidate for the ethane dehydrogenation. Desired chemicals (ethylene) and electricity can be produced simultaneously. For a typical PCFC for ethane dehydrogenation, ethane is dehydrogenated to ethylene at anode, protons from hydrogen pass through the proton conducting electrolyte to react with the oxygen ions at cathode. However, anode catalysts reported in PCFC have not met the requirements of excellent electrochemical performance and high ethylene yield. Therefore, it is of great interest to develop new catalysts with excellent catalytic activity and good coking tolerance for the ethane dehydrogenation [3]. Recently, double layered perovskites have been investigated as the anode materials due to their good stability and high mixed ionic and electronic conductivity for the partial oxidation of hydrocarbons [4]. Also, it is known that Co-Fe bi-metallic alloy is an excellent electrochemical catalyst, and has been widely used as a catalyst in fuel cell anode materials. Moreover, both Co and Fe have been utilized as effective alloying elements to enhance the performance of anode materials and the combination of Co-Fe alloy catalyst favors the formation of C2-C4 alkenes [5].

In this work, in-situ exsolved Co-Fe alloy nanoparticles uniformly distributed on a double layered perovskite (Pr0.4Sr0.6)3(Fe0.85Mo0.15)2O7 (CoFe-PSFM) anode backbone by reducing the cubic perovskite Pr0.4Sr0.6Co0.2Fe0.7Mo0.1O3-δ (PSCFM) in a 10% H2/N2 atmosphere was synthesized at 900 °C. It was fabricated as the anode in a BaCe0.7Zr0.1Y0.2O3-δ (BCZY) electrolyte-supported PEFC. The maximum output power densities of 348.84 mW cm−2 in C2H6 and 496.2 mW cm−2 in H2 were achieved at 750 °C. More importantly, a high ethylene yield, increasing from 13.2% at 650 °C to 41.5% at 750 °C with a remarkable ethylene selectivity over 91% and no CO2 emission, was achieved due to the considerably efficient catalysis of the in-situ Co-Fe alloy nanoparticles which were homogeneously distributed on the PSFM backbone. Furthermore, galvanic static test up to 100 h under a constant current load of 0.65 A cm-2 showed no detectable degradation. The results clearly indicate that the CoFe-PSFM anode material possesses high ethane partial dehydrogenation activity, enhanced electro-catalytic activity, and good stability. Based on its remarkable performance in cogeneration of electricity and ethylene in PCFC, CoFe-PSFM ceramic material is an attractive anode for a directly hydrocarbon fueled solid oxide fuel cell (SOFC).

Figure 1