The Effect of B-Cation Disordered Structure on the Electrocatalytic and Electrochemical Performance of A2CrMoO6 (A= Ca, Sr, Ba)
Authors: Yang Xin , Chen Jing 
Published: February 2020

As a kind of promising candidate of anode material for solid oxide fuel cell (SOFC), A2BB'O6-δ  type double perovskites such as Sr2MnMoO6, Sr2MgMoO6, Sr2NiMoO6, Sr2FeMoO6, etc. have exhibited excellent catalytic activity, redox stability and other promising behaviors in high temperatures. Therefore oxide anodes has become a promising anode for SOFC instead of cermet anodes. Magnetic materials A2CrMoO6-δ  (A=Ca, Sr, Ba) (ACM oxide) was first found having a lower magnetic susceptibility and lower negative magnetoresistance than that of Sr
2
FeMoO6 due to the effect of B-cation disorder on electronic and magnetic properties. In this work, we would focus on the researchabout effect of B-cation disorder on electrocatalytic and electrochemical behaviors. 

B-site disordered double perovskite ACM oxide was synthesized by solid-state reaction under reducing atmosphere. Then it was refined to acquire the lattice parameters and characterized to investigate the comprehensive behaviors and properties of ACM oxide, such as electrical, catalysis and electrochemical behaviors. H2-TPR (temperature programmed reduction) analysis were conducted using a TP-5076 TPD/TPR dynamic adsorption instrument to investigate the catalytic activity and reversibility. Herein, the H2 consumption temperature corresponds to the catalytic activity area, and the H2 consumption (amount) refers to the extent of catalysis (See Figure). On the one hand, the material showing the lowest H2 consumption temperature has is easier to work as a catalysis under lower temperatures. On the other hand, the material displaying the lowest H2 consumption peak can play a part as catalysis with fewer H2. The H2-TPR results demonstrated ACM anode was catalytically activated for hydrogen which is the very fuel gas when a SOFC is operating in working temperature. The reduction temperatures gradually go up with the atomic radius, and H2-consumption saw a considerable growth in the same order so that BCM oxide is endowed with the highest catalytic activity, followed by SCM and CCM oxides. To study the stability and the reversibility of the anode samples, multiple runs of H2-TPR are needed. The results display that ACM oxide is relatively stable after multiple run of H2-TPR as well meaning the catalytic activity of ACM anode is steady and can be repeated multiple times. Obviously, the sample without peak shift is more stable. By comparison with BCM and SCM anodes, SCM anode possesses a stronger repeatability and more powerful reversibility.

As for the average thermal expansion coefficient (TEC) of SCM anode is 12.7×10-6 K-1 between 30 and 1000℃ in 5%H2/95%Ar matching the value of electrolyte La0.9Sr0.1Ga0.8Mg0.2O2.85 （LSGM） (∼12.5×10-6 K-1) , as well as the excellent chemical compatibility with LSGM we use LSGM as electrolyte in cell assembly. Then the symmetrical cells equipped with each anode as electrode and supported by electrolyte were fabricated and tested under reduction atmosphere within the operating temperature. Symmetrical cells impedance analysis would be operated under hydrogen atmosphere. Therefore, the polarization resistance of the symmetrical cells can be used to analyse the electrochemical performance. Finally, we'll analyse the effect of the B-cation disorder of structrue on the electrocatalytic and electrochemical properties combining the results of refined structure of ACM oxide.

Given the above superior electrocatalytic and electrochemical properties of ACM anode materials, we recommend them as a series of promising anode materials for SOFC.

Figure 1