In situ tailored nickel nano-catalyst layer for internal reforming hydrocarbon fueled SOFCs

The authors gratefully thank the Engineering and Physical Sciences Research Council (EPSRC) SuperGen Hydrogen Fuel Cells Challenges Flame SOFC Project (Grant No EP/K021036/1) for financial supportConventional Ni cermet anodes suffer from carbon deposition when they are directly used with hydrocarbon fuels due to the negative effects of pyrolysis and Boudouard reactions. In this work, the use of a non-stoichiometric perovskite, La0.8Ce0.1Ni0.4Ti0.6O3, as a reforming layer in reducing atmospheres led to the surface being highly populated with homogeneously exsolved Ni nano particles. This catalyst layer was applied to Ni-GDC anode supported and ScSZ electrolyte supported cells to prevent carbon deposition and to stabilize operation with dry methane. The catalyst layer showed both excellent attachment to the Ni-GDC anode and resistance to carbon deposition. The performance of the Ni-GDC anode-supported cells with the catalyst layer was about 1.1 W/cm2 in hydrogen fuel which is similar to that seen without the use of a catalyst layer. For the ScSZ electrolyte supported cells, the catalyst layer improved the power density and stability when in operation with dry methane.Publisher PD

Ce(Mn,Fe)O2 –(La,Sr)(Fe,Mn)O3 composite as an active cathode for electrochemical reduction of CO2 in proton conducting solid oxide cells

We thank EPSRC (EP/I022570/1, EP/K015540/1, EP/I038950/1) and the Royal Society (Wolfson Research Merit award) for support.A solid oxide electrolysis cell concept for reducing CO2 to CO was studied using a proton conducting mixed oxide- BaCe0.7Zr0.1Y0.1Yb0.06Zn0.04O3-δ (BCZYYZ) as an electrolyte. The oxide composite mixture: Ce0.6Mn0.3Fe0.1O2 – La0.6Sr0.4Fe0.9Mn0.1O3 (12.5-87.5 wt%) was examined as enhancing catalyst electrode for CO2 reduction and proton oxidation reaction on the cathode side for avoiding coke formation. Here we demonstrate the successful electrochemical reduction of CO2 in proton conducting SOECs. During electrochemical reduction of CO2 at 700oC, current densities as high as 0.5 A/cm2 and 1 A/cm2 at 1.3 V and 2.2 V respectively, were withdrawn even though the cell employed a 400 μm thick BCZYYZ electrolyte support.Publisher PDFPeer reviewe

Enhancement of redox stability and electrical conductivity by doping various metals on ceria, Ce1-xMxO2-δ (M=Ni, Cu, Co, Mn, Ti, Zr)

This work was supported by EPSRC (EP/I022570/1, EP/K015540/1, EP/I038950/1, EP/K021036/1).Various metal oxide materials have been actively investigated to improve energy efficiency as exhaust-catalyst as well as electrodes in electrochemical devices such as fuel cells, ceramic sensors, photo-catalyst etc. Ceria-based materials are of great interest due to their wide applications; such as redox or oxygen storage promoter in automotive catalyst and solid state conductor in fuel cells. Here we report redox and electrical properties for Ce1-xMxO2-δ (M=Ni, Cu, Co, Mn, Ti, Zr) by X-ray diffraction (XRD) and simultaneous thermo-gravimetric analysis (TGA). Among various system, Ce1-xCuxO2-δ and Ce1-xNixO2-δ indicated relatively reversible redox behavior, although Cu2+ and Ni2+ had limited solid solubility in CeO2. The enhancement of oxygen carrier concentration and electrical conductivity as well as electrochemical activity in the ceria lattice by the introduction of small amounts transition metal cations have been considered in this study. Ce0.7Cu0.3O2-δ showed about 1015 μmol[O2]/g of oxygen storage capacity (OSC) with high redox stability at 700oC. We also demonstrated that Ce0.9Ni0.1O2-δ was used as an anode of the YSZ electrolyte supported SOFC single cell; the maximum power density was 0.15 W/cm2 at 850oC with hydrogen fuel.Publisher PDFPeer reviewe

Direct methane solid oxide fuel cells based on catalytic partial oxidation enabling complete coking tolerance of Ni-based anodes

Solid oxide fuel cells (SOFCs) can oxidize diverse fuels by harnessing oxygen ions. Benefited by this feature, direct utilization of hydrocarbon fuels without external reformers allows for cost-effective realization of SOFC systems. Superior hydrocarbon reforming catalysts such as nickel are required for this application. However, carbon coking on nickel-based anodes and the low efficiency associated with hydrocarbon fueling relegate these systems to immature technologies. Herein, we present methane-fueled SOFCs operated under conditions of catalytic partial oxidation (CPOX). Utilizing CPOX eliminates carbon coking on Ni and facilitates the oxidation of methane. Ni-gadolinium-doped ceria (GDC) anode-based cells exhibit exceptional power densities of 1.35 W cm−2 at 650 °C and 0.74 W cm−2 at 550 °C, with stable operation over 500 h, while the similarly prepared Ni-yttria stabilized zirconia anode-based cells exhibit a power density of 0.27 W cm−2 at 650 °C, showing gradual degradation. Chemical analyses suggest that combining GDC with the Ni anode prevents the oxidation of Ni due to the oxygen exchange ability of GDC. In addition, CPOX operation allows the usage of stainless steel current collectors. Our results demonstrate that high-performance SOFCs utilizing methane CPOX can be realized without deterioration of Ni-based anodes using cost-effective current collectors

Study on Direct Flame Solid Oxide Fuel Cell Using Flat Burner and Ethylene Flame

This paper presents an experimental investigation of direct flame solid-oxide fuel cell (SOFC) by using a flat-flame burner and fuel-rich ethylene/air premixed flames. A direct flame fuel cell (DFFC) setup is designed and implemented to measure electrochemical characteristics of electrolyte supported (i.e., single cell consisting of Ce0.9Ni0.1O2-? anode/GDC electrolyte/LSCF-GDC cathode) fuel cell. The fuel cell temperature and cell performance were investigated by operating various fuel/air equivalence ratios and varying distance between burner surface and the fuel cell. A maximum power density of 41 mW/cm2 and current density of 121 mA/cm2 were achieved. Experimental results suggest that the fuel cell performance was greatly influenced by the flame operating conditions and cell position in the flame. The uniformity of the flame temperature and the fuel cell stability were also investigated and calculations of equilibrium gas species composition were performed

Nano-composite structural Ni-Sn alloy anodes for high performance and durability of direct methane-fueled SOFCs

This work was supported by the Seoul R&BD Program (CS070157). It was also partially supported by a National Research Foundation (NRF) of Korea grant funded by the Korean government (MSIP) (no. 2012R1A3A2026417) and the third Stage of Brain Korea 21 Plus Project.Ni-based cermets have commonly been used as anode materials with good catalytic properties for hydrocarbon fuels. However, carbon deposition can occur due to the non-ideal electrochemical reaction of hydrocarbon fuel and the structural limitation resulting from the unsymmetrical Ni-based anode-supported single cells. This critical problem leads to loss of cell performance and poor long-term stability of solid oxide fuel cells (SOFCs). Our designed anode material with an extremely small amount (0.5 wt%) of Sn catalyst incorporated into the Ni and nano-composite structure was employed not only to prevent carbon deposition in oxygen deficient areas found for unsymmetrical cells, but also to increase the cell performance due to its excellent microstructure. The nano-composite Sn doped Ni-GDC cells showed a power density of 0.93 W cm-2 with stable operation in dry methane at 650°C.PostprintPeer reviewe