Influence of cathode on electric power of solid oxide fuel cells

Abstract

The electric power produced by a Ni/Gd-doped ceria (GDC) anode-supported solid oxide fuel cell with a GDC electrolyte (40¯m thick) and a (La 0.8 Sr 0.2 )(Co 0.8 Fe 0.2 )O 3 (LSCF) cathode using a 3 vol % H 2 O-containing H 2 fuel was measured. The addition of 10 or 50 mass % GDC powder (Ce 0.8 Gd 0.2 O 1.9 ) to the LSCF cathode reduced the power density from 320 mW/cm 2 in the case of no GDC to 137 or 122 mW/cm 2 , respectively. The added GDC particles blocked the conduction path between LSFC particles. The as-prepared LSCF powder was ball-milled using ¡-Al 2 O 3 balls. The milling decreased the charge transfer resistance at the cathode and increased the power density of the fuel cell.©2014 The Ceramic Society of Japan. All rights reserved.Key-words : Solid oxide fuel cell, Cathode, Power density, Overpotential, Gd-doped ceria [Received September 2, 2013; Accepted December 24, 2013] Solid oxide fuel cells (SOFCs) are attractive electric power generators because of their high energy conversion efficiency, their ability to utilize a variety of fuels, the possibility of utilizing their high-temperature exhaust gas, and their leakage-proof property because of the use of solid electrolytes. A conventional SOFC with a yttria-stabilized zirconia (YSZ) electrolyte is typically operated at approximately 800°C to enhance the diffusion of oxide ions formed at its cathode. Gd-doped ceria (GDC) and Sm-doped ceria are also candidate electrolytes for SOFCs because they exhibit greater oxide-ion conductivity than YSZ. Decreasing the charge transfer resistance of electrochemical reactions at the electrodes (especially the cathode) is another strategy to increase the electric power generated by SOFCs. At the cathode, the diffusing oxygen molecules adsorb onto the cathode material and dissociate into oxygen atoms. The oxygen atoms react with electrons to form oxide ions at the triple-phase boundary (TPB, the gascathodeelectrolyte interface). The cathode material is a mixed conductor of electrons and oxide ions. A cathode composed of a mixture of GDC and LSCF is expected to exhibit enhanced electrocatalytic activity for the reaction of O 2 and electrons. Shah et al.3) measured the performance of a cathode fabricated by impregnating a porous GDC scaffold with a mixed nitrate solution of LSCF precursor. The formed nanometer-scale (50 nm) LSCF network reduced the charge transfer resistance at an operating temperature of 650°C over 300 h. Liu et al. 4) prepared an LSCFGDC composite cathode by impregnating the porous GDC scaffold with a mixed nitrate solution of La, Sr, Co, and Fe and measured the degradation in the composite cathode performance at 750°C in air over 500 h. The GDC scaffold method was effective in expanding the triple-phase boundary (GDC electrolyteLSCF cathodeO 2 gas). However, the charge transfer resistance and ohmic resistance increased because of grain growth of the LSCF nanoparticles. The authors suppressed the grain growth of LSCF by adding MgO and LaNi 0.6 Fe 0.4 O 3 particles.In this study, a GDCLSCF mixed cat...

Carbonate-Based Lanthanum Strontium Cobalt Ferrite (LSCF)–Samarium-Doped Ceria (SDC) Composite Cathode for Low-Temperature Solid Oxide Fuel Cells

“…The composite cathode microstructure (Figure 2c) reveals that the particle connectivity among LSCF particles was poor due to the presence of molten carbonate and SDC particles. This finding could considerably affect the electronic network over the LSCF surface, consequently blocking the conduction paths between the LSCF and SDCC particles, and decreasing the single-cell performance [20]. The results of our study proved that the single-cell performance decreased with increased SDCC composite electrolyte content.…”

“…Constructing the composite cathode by mixing LSCF with pure ionic conducting electrolyte material is an effective strategy for suppressing the compositional changes within the LSCF structure. However, the presence of pure ionic conducting materials, such as SDC electrolyte, could affect the electronic network at the surface of the LSCF cathode, thus causing significant decreases in the electronic conductivity of the LSCF cathode material itself [20]. This eventually increases the charge transfer resistance at the LSCF cathode during the fuel cell operation, consequently affecting the overall performance of the cell.…”

A Review on the Process-Structure-Performance of Lanthanum Strontium Cobalt Ferrite Oxide for Solid Oxide Fuel Cells Cathodes

“…In addition, LSCF-LSCF grain contact is substantially influenced by the electrical conductivity of the device, which markedly affects in-plane electronic conduction through the composite surface for the ORR and the overall ORR performance of the LSCF-based composite cathode. Furukawa et al [126] claim that combining an LSCF cathode with a pure oxide ion conducting material lowers catalytic activity. The oxide ion conducting particles restrict the conduction path between LSCF-LSCF particle networks, increasing ohmic and charge transfer resistance.…”