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

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.

Pd–Co-Based Electrodes for Hydrogen Production by Water Splitting in Acidic Media

“…Furthermore, considering the excellent results obtained in the case of Ni-based nanostructured electrodes for alkaline electrolyzers [ 49 , 50 , 51 ], in this work, the Pd–Co alloys have been obtained in the form of an array of nanowires using alumina membranes (AAM) as the template [ 52 , 53 , 54 , 55 ]. In fact, as demonstrated in [ 56 , 57 , 58 , 59 , 60 , 61 , 62 ], due to the high surface area, the electrodes based on the arrays of nanowires showed very good performance compared to the planar ones. This is generally true for all electrochemical devices with nanostructured electrodes [ 4 , 63 ] such as batteries [ 64 , 65 , 66 ], sensors [ 67 , 68 , 69 , 70 ], supercapacitors [ 71 , 72 , 73 ] and solar cells [ 74 , 75 , 76 ].…”

SrTiO3-SrVO3 Ceramics for Solid Oxide Fuel Cell Anodes: A Route from Oxidized Precursors

“…SrTiO 3 and SrVO 3−δ form a continuous series of perovskite-like solid solutions under reducing conditions [28,31,32]. Balancing fractions of titanium and vanadium cations in the B sublattice enables a reasonable compromise between phase stability and the level of electrical conductivity and also allows one to adjust the thermochemical expansion [28,33]. In particular, SrTi 0.5 V 0.5 O 3−δ perovskite ceramics with intermediate titanium and vanadium content showed electrical conductivity of ~20 S/cm at 900 • C combined with a phase stability domain extended up to p(O 2 ) of at least 10 −11 atm at 900 • C and average TEC of 15 ppm/K [28].…”

“…Due to phase stability issues, Sr(Ti,V)O 3 -based anodes may be prepared either under reducing conditions or under an inert atmosphere where oxidation kinetics are sluggish [28,33]. However, from a practical point of view, it would be of interest to fabricate anodes of solid oxide cells under an ambient atmosphere (air) with a subsequent in-situ reduction, similar to what is practiced in the case of Ni-YSZ cermets.…”