Accelerated Proton Transport Based on a p-i-n Heterostructure Membrane for Low-Temperature Solid Oxide Fuel Cells

The p-i-n junction structure has garnered great interest from researchers due to its increased photoactive area and wider space charger region compared with that of the p-n junction. Herein the ultrawide bandgap (∼6.7 eV) semiconductor alumina (Al2O3) has been introduced to construct a p-i-n junction with ZnO and NiO. ZnO–Al2O3–NiO powders are suitable for electrolyte membrane material of low-temperature solid oxide fuel cells (LT-SOFCs). The insulating Al2O3 brings a doubled depletion region and more effective charge separation compared with the p-n junction consisting of ZnO and NiO. The fuel cell based on the p-i-n junction membrane material delivers an enhanced maximum power density (MPD) of 917 mW cm–2 along with a high open-circuit voltage (OCV) of 1.013 V at 550 °C. An analysis based on the space charge region and energy band alignment in the p-i-n junction is proposed to account for the appreciable cell performance and ionic conductivity, as well as the electron blocking and charge separation ability. This study presents a practical p-i-n junction design based on ZnO–Al2O3–NiO via a solution process for LT-SOFC electrolyte material and sheds light on the extensive exploration of p-i-n junctions applied in LT-SOFCs.