K doping as a rational method to enhance the sluggish air-electrode reaction kinetics for proton-conducting solid oxide cells
By Yang, Yi; Shi, Nai; Xie, Yun; Li, Xinyu; Hu, Xueyu; Zhu, Kang; Huan, Daoming; Peng, Ranran; Xia, Changrong; Lu, Yalin
Published in Electrochimica Acta
2021
Abstract
Proton-conducting solid oxide cells (P-SOCs), which can switch flexibly between operating as fuel cells (FCs) and operating as electrolysis cells (ECs), are deemed as a promising device that can highly efficiently realize the energy conversion between electrical power and chemical energy (e.g., hydrogen energy). Exploring an effective way to accelerate the sluggish reactions on air electrodes, including proton involved oxygen reduction reactions in FCs and steam electrolysis reactions in ECs, is of key importance to improve the electrochemical performance of P-SOCs. In this work, K doped Sr2Fe1.5Mo0.5O6-δ (K0.25Sr1.75Fe1.5Mo0.5O6-δ, KSFM) is prepared and investigated as a potential air electrode for P-SOCs. Here, K dopant which has higher basicity and larger ionic radius than Sr2+ is used to modulate the physical and chemical performance of air electrodes, and thus to improve their reaction kinetics. Compared with that taking SFM, improving factors of 53.3% and 93.4% at 600°C are achieved for the cell using K doped SFM air electrode operating in FC and EC mode, respectively. Density functional theory (DFT) calculations reveal that K can make the oxygen p-band center closer to the Fermi level, reducing the formation energy of oxygen vacancies; and meanwhile, it improves the hydration energy of SFM and reduces the energy barrier for proton migration. It is also found K could enhance the interaction between the surfaces and steam, yet the lower adsorption energy of steam compared to that of O2 would not isolate the O2 adsorption reaction. K doping is a rational way to design new air electrodes for P-SOCs.