INTRODUCTIONINTRODUCTION

Molten carbonate fuel cells (MCFC) are considered a new and alternative power source, promising for its low environmental emission and for its high efficiency. They convert into electricity the chemical energy of a fuel, either hydrocarbon based like natural gas or renewable like biogas or landfill gas, through a reaction with no intermediate conversion of heat into mechanical energy. For successful market-entry and competitiveness of MCFC systems cost reduction, reliability improvement, performance and endurance have to be maintained along time; so, it still needs a work of optimisation, especially aimed to extend cell life.In fact, to assure good lasting performance all the components interacting in the cell have to keep their main characteristics and the required operating conditions. But the severe working conditions, that are high temperature, a quite corrosive environment produced by alkali molten carbonates and an adequate gas composition and distribution, lead to different phenomena altering the components properties and interfering in the cell performance. Ansaldo Fuel Cells laboratories are concentrating the attention on single cell test facilities, on sub-scale laboratory stacks (tecnostacks) and stack units to study possible solutions to apply on full-size stacks.

MCFCMCFC: IN-SITU DIAGNOSTIC TECHNIQUES: IN-SITU DIAGNOSTIC TECHNIQUES

G.Durante, S. Dellepiane, E. Bergaglio, A. Scattolini, P. Capobianco

Ansaldo Fuel Cells S.p.a., Genoa, Italy

In-situ measurements and ex-situ characterisation onMolten Carbonate Fuel Cells: from laboratory cells to full-size stack

GAS ANALYSISGAS ANALYSIS to verify the correct composition

of the fuel-in and oxidant-in gas and to measure produced output gas

composition, related to effective reaction rates and competing reactions.

MCFCMCFC: EX-SITU AND POST-TEST CHARACTERISATION

SINGLE CELL TESTSINGLE CELL TEST

INTERNAL RESISTANCE (iR) INTERNAL RESISTANCE (iR) MEASUREMENTMEASUREMENT

to evaluate the total ohmic resistance of a fuel cell and stack of fuel cells

CHARACTERISATION VOLTAGE/CURRENT AND CHARACTERISATION VOLTAGE/CURRENT AND POWER/CURRENT DENSITY AS AN INDEX OF PERFORMANCESPOWER/CURRENT DENSITY AS AN INDEX OF PERFORMANCES

TEMPERATURE AND VOLTAGE MAPPINGTEMPERATURE AND VOLTAGE MAPPINGSingle cell voltages and local temperature

inside the stack are measured to monitor local operating conditions

Short time for testing

Modest cost of realization

High flexibility

Different configuration respect to full size stack

Difficult scalability to full scale stack

TECNOSTACKTECNOSTACK

Study of new operating procedures

Analysis of new cell configuration

Test on different materials

Design more similar to full size stack

Easier scalability to full size stack

Chronogram of single cell voltage/current characterisation.

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Characterisation Voltage and Power/Current Density

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Voltage single cell 1Voltage single cell 2Power density single cell 1Power density single cell 2

CONCLUSIONSCONCLUSIONS

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Single cell Voltage, Voltage iR free, iR trend

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After the test, the cell (single cell, tecnostack cell or full-size cell) is disassembled, verifying the expected typical features for all the components.

Complete post test analysis have to be planned for qualitative and quantitative determinations:

- Ni cathode dissolution and Ni distribution inside the matrix (Fig. 6) ;- the electrodes structure changes by porosimetric analysis (Fig. 5) and microscopy analysis (Fig. 7)

Main parameters tested on metallic materials:

▪ the penetration rate of the corrosion film; ▪ the carburation of alloys: ▪ the electrical conductivity of oxide; ▪ the mechanical resistance of corroded alloys.

Different techniques have to be used to investigate the properties of corroded alloys in different environments:

SEM with energy dispersive X-Ray spectrometer (EDS) and metallurgical microscope (Fig. 1 and Fig. 2);

Vickers micro-hardness measurements through the cross section of the corroded samples (Fig. 3);

Electrical conductivity measurements (Fig. 4)

Applied Applied techniquestechniques

Optical Microscope Scanning Electron Microscope (SEM) equipped

with Energy Dispersive X-ray Spectrometer (EDS) Atomic Absorption Mercury Porosimetry (Fig. 5)

Diagnostic tools and post-test analysis give important

informations about alternative configurations or processes or

new materials with the aim to improve life, reduce costs,

About materials, AFCo has pointed out three main phenomena:

cathode dissolution

matrix straightening

metallic components corrosion

The monitoring of cell life and performances passes by

V/I curve

iR measurements

Gas analysis

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Fig. 7

Cells voltage at Stand-by

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increase performance in full-size stack, investigating the degradation phenomena.

23rd-24th June 2009 Trondheim, Norway