Development of Ni-Sr(V,Ti)O3-δ Fuel Electrodes for Solid Oxide Fuel Cells.

Bernardo F Serôdio Costa,Blanca I Arias-Serrano,Aleksey A Yaremchenko

doi:10.3390/ma15010278

Abstract

A series of strontium titanates-vanadates (STVN) with nominal cation composition Sr1-xTi1-y-zVyNizO3-δ (x = 0–0.04, y = 0.20–0.40 and z = 0.02–0.12) were prepared by a solid-state reaction route in 10% H2–N2 atmosphere and characterized under reducing conditions as potential fuel electrode materials for solid oxide fuel cells. Detailed phase evolution studies using XRD and SEM/EDS demonstrated that firing at temperatures as high as 1200 °C is required to eliminate undesirable secondary phases. Under such conditions, nickel tends to segregate as a metallic phase and is unlikely to incorporate into the perovskite lattice. Ceramic samples sintered at 1500 °C exhibited temperature-activated electrical conductivity that showed a weak p(O2) dependence and increased with vanadium content, reaching a maximum of ~17 S/cm at 1000 °C. STVN ceramics showed moderate thermal expansion coefficients (12.5–14.3 ppm/K at 25–1100 °C) compatible with that of yttria-stabilized zirconia (8YSZ). Porous STVN electrodes on 8YSZ solid electrolytes were fabricated at 1100 °C and studied using electrochemical impedance spectroscopy at 700–900 °C in an atmosphere of diluted humidified H2 under zero DC conditions. As-prepared STVN electrodes demonstrated comparatively poor electrochemical performance, which was attributed to insufficient intrinsic electrocatalytic activity and agglomeration of metallic nickel during the high-temperature synthetic procedure. Incorporation of an oxygen-ion-conducting Ce0.9Gd0.1O2-δ phase (20–30 wt.%) and nano-sized Ni as electrocatalyst (≥1 wt.%) into the porous electrode structure via infiltration resulted in a substantial improvement in electrochemical activity and reduction of electrode polarization resistance by 6–8 times at 900 °C and ≥ one order of magnitude at 800 °C.

Highlights

IntroductionNi–YSZ cermets have poor redox stability, and significant volume changes upon occasional nickel oxidation/re-reduction cycles cause irreversible microstructural degradation [3,4,5]
Concerns about the disadvantages of traditional Ni–YSZ (YSZ = yttria-stabilized zirconia) anodes of solid oxide fuel cells (SOFCs) have boosted significant research activities on the development of alternative anode materials [1,2]
Oxide ceramic materials such as SrVO3 - and SrTiO3 -based perovskites are considered as promising alternative components for anodes of hydrocarbon-fueled SOFC [2,8,9,10,11]

Summary

Introduction

Ni–YSZ cermets have poor redox stability, and significant volume changes upon occasional nickel oxidation/re-reduction cycles cause irreversible microstructural degradation [3,4,5] Nickel agglomeration is another common degradation mechanism that leads to a loss of electrical connectivity between Ni particles and a decrease in electrocatalytic activity [5,6]. Ni–YSZ anodes are readily poisoned by sulfur and suffer from carbon deposition, which are key issues for direct operation with hydrocarbon fuels [7,8]. Oxide ceramic materials such as SrVO3 - and SrTiO3 -based perovskites are considered as promising alternative components for anodes of hydrocarbon-fueled SOFC [2,8,9,10,11].

Methods

Results

Conclusion