Phase engineering of a donor-doped air electrode for reversible protonic ceramic electrochemical cells
Kang Xu, Hua Zhang, Yangsen Xu, Dongliang Liu, Feng Zhu, Fan He, Ying Liu, Haobing Wang, Yu Chen
Abstract
Reversible protonic ceramic electrochemical cells (R-PCECs) demonstrate great feasibility for efficient energy storage and conversion. One critical challenge for the development of R-PCECs is the design of novel air electrodes with the characteristics of high catalytic activity and acceptable durability. Here, we report a donor doping of Hf into the B-site of a cobalt-based double perovskite with a nominal formula of PrBa0.8Ca0.2Co1.9Hf0.1O5+δ (PBCCHf0.1), which is naturally reconfigured to a double perovskite PrBa0.8-xCa0.2Co1.9Hf0.1-xO5+δ (PBCCHf0.1-x) backbone and nano-sized BaHfO3 (BHO) on the surface of PBCCHf0.1−x. The air electrode demonstrates enhanced catalytic activity and durability (a stable polarization resistance of 0.269 Ω cm2 for ∼100 h at 600 °C), due likely to the fast surface exchange process and bulk diffusion process. When employed as an air electrode of R-PCECs, a cell with PBCCHf0.1 air electrode demonstrates encouraging performances in modes of the fuel cell (FC) and electrolysis (EL) at 600 °C: a peak power density of 0.998 W cm−2 and a current density of −1.613 A cm−2 at 1.3 V (with acceptable Faradaic efficiencies). More importantly, the single-cell with PBCCHf0.1 air electrode demonstrates good cycling stability, switching back and forth from FC mode to EL mode ±0.5 A cm−2 for 200 h and 50 cycles.