Mechanism insight into enhanced oxygen reduction reaction over heterovalent ion incorporated pyrochlore Pr₂Zr₂O₇ for direct ammonia solid oxide fuel cells

An effective B-site doping strategy through heterovalent ions was developed to synthesize a series of pyrochlore Pr2Zr1.95X0.05O7+delta (PZX, X = Mn, Sc, Sn, Nb, Mo, Al, Ga, In) for the direct ammonia solid oxide fuel cell (DA-SOFC) cathode. To guide the design of efficient cathodes for DA-SOFC, we explore the relationships between the ionic radius/valence of dopant and electrochemical performance. In view of the energy matching and interaction between the dopant and the host lattice, the substitution of trivalent Sc3+ with similar ionic radius for tetravalent Zr4+ can greatly improve the oxygen reduction reaction activity of Pr2Zr2O7 due to the reduced bond energy of 48f-oxygen ions in octahedral [ZrO6] units. As a result, the anode-supported single cell Ni-YSZ|YSZ|PZSc-60YSZ yields an output power density of 0.44 and 1.45 Wcm(-2) at 600 and 800 degrees C with ammonia fuel, outperforming PZX (X = Mn, Sn, Nb, Mo, Al, Ga, In) and common La0.8Sr0.2MnO3 (LSM)-based DA-SOFC. The detailed characterizations are employed to gain insight into the structure-activity relationship and reaction mechanism.