Metal/Oxide Heterojunction Boosts Fuel Cell Cathode Reaction at Low Temperatures

Abstract

Among several types of low‐temperature solid oxide fuel cells, hydrogen‐permeable metal‐supported fuel cells (HMFCs) are devices that can achieve outputs of approximately 1.0 W cm−2 at 400 °C. This work clarifies the mechanism for promoting the cathode reaction on proton‐conducting ceramics at such low temperatures. Combined numerical and electrochemical analyses demonstrate that blocking minor oxide ion conduction at metal/oxide heterojunctions promotes proton transfer at the cathode/electrolyte interfaces, thereby enhancing the turnover frequency of the cathode reaction at the triple‐phase boundary. The electrolyte membrane in HMFCs is forced to gain extra protons to compensate for the charge of oxide ions that accumulate because of the blocking, resulting in an increment of the proton concentration gradients near the cathode/electrolyte interfaces so as to eject the excess amount of proton. The interfacial proton concentration gradient increases and thus the cathode polarization resistance of HMFCs decrease with the cell bias. An HMFC with a highly oxygen‐deficient BaZr0.5Sc0.5O3−δ electrolyte accumulates a large amount of oxide ions, thereby developing large concentration gradients. Thus, it achieves a cathode reaction resistance of 0.54 Ω cm2 at 400 °C with conventional cathode materials, La0.6Sr0.4Co0.2Fe0.8O3−δ. These findings demonstrate that HMFCs can efficiently utilize overpotential.

Enhanced Performance of Protonic Solid Oxide Steam Electrolysis Cell of Zr-Rich Side BaZr0.6Ce0.2Y0.2O3−δ Electrolyte with an Anode Functional Layer

“…Assuming the linear dependence of R O on electrolyte thickness reveals the existence of an R O of about 0.7 Ω cm 2 at zero thickness. Recent studies reported that proton-conducting solid oxide fuel cells (H-SOFCs) possess large impedances (∼10 5 Hz) due to slow proton transfer at the electrolyte–anode–gas TPB. − On the basis of these, the BZCY622 cells involve relatively large resistances related to the interfacial proton transfer from the electrolyte to the anode. The value estimated for the zero thickness electrolyte cell without AFL, i.e., 0.7 Ω cm 2 , is comparable to 80% of R O for the 15-μm-thick electrolyte cell without AFL (0.81 Ω cm 2 ), which confirms that the interfacial resistances are a dominant component in the R O of the BZCY622 base cells.…”

Perovskites for protonic ceramic fuel cells: a review

“…Jeong et al employed H 2 permeable metal-supported fuel cells (HMFCs), using Sc doped BaZrO 3Àd (BZS) electrolytes, and LSCF6428 as a cathode, to investigate the electrochemical mechanism of HMFCs. 204 Interestingly, as concluded in the literature, the proton concentration gradients and the cathode reaction at the TPBs could be harshly prompted by blocking the oxide ion conduction at the anode. Consequently, the polarization resistances of the HMFCs with LSCF6428 were decreased by a factor of 2-3.…”

Structural Engineering of Cobalt‐Free Perovskite Enables Efficient and Durable Oxygen Reduction in Solid Oxide Fuel Cells

“…[3,4] Accordingly, intensive efforts have been dedicated to pursuing novel cathode compositions with remarkable oxygen reduction reaction (ORR) activity. [5][6][7][8][9] Mixed ionic-electronic conducting perovskite-type oxides are judged as one of the potential candidates in cathode development, which considerably expand the ORR active sites from the three-phase boundary to the entire exposed electrode surface. Significant research progresses include La 0.6 Sr 0.4 CoO 3-δ , Sm 0.5 Sr 0.5 CoO 3-δ , Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ (BSCF), and PrBa 0.5 -Sr 0.5 Co 1.5 Fe 0.5 O 5+δ , [10][11][12][13] all of which are based on cobalt-rich perovskite materials.…”