A p–n–n heterostructure composite for low-temperature solid oxide fuel cells

Abstract Recent advances have presented a promising p-n heterostructure strategy to develop highly ionic conducting electrolytes for low-temperature solid oxide fuel cells (LT-SOFCs). In this study, a p–n–n heterostructure approach is further proposed to develop new electrolytes for LT-SOFCs based on p-type Ni0.8Co0.15Al0.05LiO2−δ (NCAL), n-type ZnO, and n-type SnO2. Material characterization reveals that the developed NCAL-ZnO-SnO2 electrolyte gains a desirable heterostructure with homogenous distribution and hetero-interface as well as enriched oxygen vacancies. Electrochemical studies find that the electrical conductivity and fuel cell performance are significantly correlated with the mass ratios of p/n phases in the samples. The 2NCAL-1(ZnO-SnO2) exhibits a highest ionic conductivity of 0.389 S cm−1 at 530 ℃ along with a remarkable fuel cell power density of 1267 mW cm−2, which are apparently superior to those of p–n heterostructure electrolytes of NCAL-ZnO and NCAL-SnO2. By considering the semiconductor features of the used materials, further investigation in terms of energy band structure and rectifying characteristic studies indicate the possible existence of p-n-n heterojunction in the NCAL-ZnO-SnO2 fuel cell with rectifying behavior for charge carrier modulation. On basis of which, an energy band alignment effect is propounded to illustrate the electronic blocking and ionic acceleration processes of the p–n–n heterostructure electrolyte. The successful demonstration of 2NCAL-1(ZnO-SnO2) thus provides a new approach to develop advanced electrolytes for LT-SOFCs.