Tuning geometry distortion of pyrochlore RE2Zr1.95Ni0.05O7+δ anodes with rich oxygen vacancies for ammonia-fed solid oxide fuel cell

Abstract

Pyrochlore oxide A2B2O7 is a potential anode catalyst of ammonia-fed solid oxide fuel cell (SOFC) due to its unique and open structure that can make some oxygen ions flow to occupy the hole position to form Frankel defect. Herein, various rare-earth ions with different radius are selected as the A site to construct defective pyrochlore oxide RE2Zr1.95Ni0.05O7+δ (REZN, RE = La, Pr, Nd, Sm, Gd, LZN/PZN/NZN/SZN/GZN) to gain insights into oxygen vacancies that can be the diffusion and adsorption active site for ammonia. In the n-type semiconductor REZN, the degree of crystal ordering decreases with the decrease of the radius of rare-earth RE3+ ions. Among them, GZN exhibits the most negative conduction band and the smallest band gap, making it easier to overcome the energy potential barrier and facilitate the movement of carriers. As a result, the conductivity of GZN is about 25 times higher than that of LZN. The average TEC value of GZN is 10.40 × 10-6 K−1, which matches that of electrolyte YSZ (10.50 × 10-6 K−1). The maximum power density of ammonia-fed SOFC supported by YSZ electrolyte based on GZN anode is 128.63 mW·cm−2 at 800 °C, which is 2.3 times higher than that of NiO-based SOFC. The single cell based on GZN anode can be run continuously for 100 h at 800 °C without significant degradation. The preliminary results suggest that GZN oxide is promising to be a candidate catalyst for ammonia-fed SOFC anode.