Comparison of electrochemical impedance spectra for electrolyte-supported solid oxide fuel cells (SOFCs) and protonic ceramic fuel cells (PCFCs)

Hirofumi Sumi,Hiroyuki Shimada,Yasunobu Mizutani,Yuki Yamaguchi,Koji Amezawa,Yuji Okuyama

doi:10.1038/s41598-021-90211-9

Abstract

Protonic ceramic fuel cells (PCFCs) are expected to achieve high power generation efficiency at intermediate temperature around 400–600 °C. In the present work, the distribution of relaxation times (DRT) analysis was investigated in order to deconvolute the anode and cathode polarization resistances for PCFCs supported on yttria-doped barium cerate (BCY) electrolyte in comparison with solid oxide fuel cells (SOFCs) supported on scandia-stabilized zirconia (ScSZ) electrolyte. Four DRT peaks were detected from the impedance spectra measured at 700 °C excluding the gas diffusion process for ScSZ and BCY. The DRT peaks at 5 × 102–1 × 104 Hz and 1 × 100–2 × 102 Hz were related to the hydrogen oxidation reaction at the anode and the oxygen reduction reaction at the cathode, respectively, for both cells. The DRT peak at 2 × 101–1 × 103 Hz depended on the hydrogen concentration at the anode for ScSZ, while it was dependent on the oxygen concentration at the cathode for BCY. Compared to ScSZ, steam was produced at the opposite electrode in the case of BCY, which enhanced the cathode polarization resistance for PCFCs.

Highlights

Solid oxide fuel cells (SOFCs) are expected to be power generation systems with high energy conversion efficiency
H2:H2O:N2 = 20:3:77 vol.% and O2:H2O:N2 = 20:3:77 vol.% for solid oxide fuel cells (SOFCs) supported on scandia-stabilized zirconia (ScSZ) electrolyte and Protonic ceramic fuel cells (PCFCs) supported on BCY electrolyte
Capacitance (RC) elements. (b, c) Temperature dependence of polarization resistances in H 2:H2O:N2 = 20:3:77 vol.% and O2:H2O:N2 = 20:3:77 vol.% for SOFCs supported on ScSZ electrolyte and PCFCs supported on BCY electrolyte

Summary

Introduction

Solid oxide fuel cells (SOFCs) are expected to be power generation systems with high energy conversion efficiency. Owing to the supply of oxide ions ( O2−) from a cathode to an anode through an electrolyte at high temperatures above 700 °C, SOFCs can, in principle, directly use hydrocarbons and alcohol fuels as well as hydrogen[1,2,3,4,5]. Increasing the fuel utilization is limited in the case of SOFCs, because the fuel is diluted at the outlet by the steam production at the anode In this case, the fuel is not diluted by power generation, because steam is produced at the cathode. For S OFCs24–26 and polymer electrolyte fuel cells (PEFCs)[27], the anode and cathode polarization resistances were separated with high resolution. DRT analysis is a powerful tool for investigating the degradation mechanism during durability tests[32]

Methods

Results

Conclusion