Page 12 - PR 2014 2016 05 Renewable Energies

114 Renewable Energies | Progress Report

Solid Oxide Fuel resistant, and tolerant to carbon deposits
Cell (SOFC) and sulphur contamination. The reduction of

the operating temperature from 800-1000°C
Solid Oxide Cells (SOCs) is a general classifi- down to 500-800°C range, in order to mini-
cation for Solid Oxide Fuel Cells (SOFCs) and mize degradation of components, improve
Solid Oxide Electrolysis Cells (SOECs) -SOFCs design flexibility, and lower material and
operated in electrolysis mode- are solid-state manufacturing costs, is also a key issue for
devices that can be used to i) convert between disseminating SOCs. Nevertheless, reducing
chemical and electrical energy and/or ii) drive the operating temperatures requires new
chemical reactions. These capabilities make materials for high-performance SOCs.
them attractive for energy conversion, energy
storage, chemical sensing, chemical separa- The main activities of the SOFC research group
tion, and chemical synthesis applications. at IPEN have been the synthesis, processing,
Most of the research focus has been given to and characterization of the SOFC components,
the development of reversible SOCs devices along with single cell testing, aiming at direct
capable of operating in both modes (fuel cell ethanol SOFCs. Ethanol is an available, efficient
and electrolysis) for advanced application and cost competitive renewable fuel. Differ-
involving energy storage and generation in ently from hydrogen, which still requires an
one device. SOFCs are the most efficient elec- infrastructure for widespread use, ethanol
trochemical devices to directly convert the brings strategic advantages such as easy stor-
chemical energy of fuels into electricity, thus age and good distribution. Moreover, it allows
they are regarded as promising power sourc- SOFCs to run in a carbon neutral cycle.
es for several applications due to important
characteristics such as: i) wide range of power Yttria-stabilized zirconia (YSZ) and nickel (Ni)
outputs (from centralized power plants of composite is the standard anode for solid oxide
MWatt to auxiliary portable units of a few fuel cell. This composite is the best anodes
Watt); ii) fuel flexibility, SOFCs potentially run for hydrogen electrochemical oxidation, but
on different fuels such as hydrogen, natural it lacks of stability when carbon containing
gas, and ethanol; and iii) high efficiency and fuels are used. In order to use available fuels
carbon neutral energy generation with rather such as methane (natural gas) with the stan-
low noise and harmful emissions. dard anodes, it is necessary to add an oxidant
agent, typically water. However, adding water
Basically, SOCs consist of two porous elec- to the fuel stream adds complexity to the fuel
trodes separated by a dense electrolyte. Such cell system and decreases its efficiency. There-
a ceramic cell requires complex fabrication fore, developing new concepts of SOFC anode
technologies and each component must fulfill remains a one of the challenges to advance
several criteria. Physical and chemical com- SOFC technology to commercialization. In this
patibility and stability at high temperature context, two main strategies can be identified.
and oxidizing/reducing environments along The first one is replacing the standard anode
with good electrochemical properties are im- for more stable materials. Several compounds,
portant properties for materials used in these mainly ceramic single-phase perovskites and
devices. Important goals in SOCs research alternative ceramic-metal composites, have
include the development of fuel-flex anodes, been proposed, but so far none of them can
capable of operating in different fuel, redox reach the same performance of the Ni-YSZ

Instituto de Pesquisas Energéticas e Nucleares