UNESCO Desire – Net project Molten Carbonate Fuel Cells State of the Art & Perspectives State of the Art & Perspectives Angelo Moreno, Stephen McPhail ENEA – Hydrogen and Fuel Cell Project Rome, 13 th March 2007 PART B

The Details…

Anode Ni-Cr or Ni-Al alloy MCFC – characteristics Requirements: Porous material: soak up electrolyte & provide interface with fuel gas 3-6 μm ) Good conductivity Structurally resistant (creep, sintering) Low cost

Anode Ni-Cr or Ni-Al alloy MCFC – characteristics Durability problem: Low tolerability to sulphur compounds (H 2 S, COS) → Poisoning of the anode: H 2 S + Ni → NiS + H 2 (H 2 S > 0.5 ppm) in raw coal gas: H 2 S≈1.5% Extensive Sulphur cleaning required (incorporate in reformer?)

Anode Ni-Cr or Ni-Al alloy MCFC – characteristics Cost issues: Slow manufacturing process (tape- casting) ► extrusion

Electrode manufacturing process Receipt of material Slurry check Component mixing Material check Preparation of recipe

Drying Sintering Chemical-physical analysis Measurement check Tape Casting Debinding Material check Electrode manufacturing process

Anode Ni-Cr or Ni-Al alloy MCFC – characteristics Alternative materials: Cu-Al, LiFeO 2, La-Cr, Mn- or Nb- doped, … Cost issues: Slow manufacturing process (tape- casting) ► extrusion Porous Ni is expensive and rare ► thin-layer coating, alternative materials

MCFC – characteristics Cathode Li-NiO Requirements: Porous material 7-15 μ m ) Good conductivity Low dissolution rate in alkali carbonates Structurally resistant Low cost

MCFC – characteristics Durability problem: Dissolution due to corrosive environment NiO → Ni 2+ + O = Ni 2+ migrates to anode → precipitation → cell shorting Cathode Li-NiO As-received nickel substrate (x ) Coating, trapping or alternative required Ni substrate coated with Mg-doped LiCoO 2

MCFC – characteristics Cathode Li-NiO Alternative materials: LiCoO 2, LiFeO 2, Li 2 MnO 2, Ni-Ce, La- Mg-doped, … Cost issues: Slow manufacturing process (tape- casting) ► extrusion Porous Ni is expensive and rare ► thin-layer coating, alternative materials

MCFC – characteristics Electrolyte Li 2 CO 3 /K 2 CO 3 or LiCO 3 /NaCO 3 in LiAlO 2 ( α or γ ) matrix Requirements: Hydrophilic Good ionic conductivity Low gas permeability Good structural & sealing properties Low cost

MCFC – characteristics Durability problems: 1.High acidity promotes cathode dissolution 2.Electrolyte is prone to evaporate 3.Matrix degradation 1.Basic additives: CaCO 3, SrCO 3, BaCO 3 2.Increase vapour pressure, create supply 3.Improve matrix structure (crack arrestors) Electrolyte Li 2 CO 3 /K 2 CO 3 or LiCO 3 /NaCO 3 in LiAlO 2 ( α or γ ) matrix

MCFC – characteristics Cost issues: Matrix manufacture from costly solvents with high discard ► high yield aqueous slurry LiAlO 2 most expensive active component material ► …? Electrolyte Li 2 CO 3 /K 2 CO 3 or LiCO 3 /NaCO 3 in LiAlO 2 ( α or γ ) matrix

MCFC – stack Requirements: Good conductivity Suitable strength and binding properties Stable corrosion layer Thermal expansion… Low cost Metallic components Current collectors, bipolar plates, sealing

Metallic components Current collectors, bipolar plates, sealing MCFC – stack Durability problem: Hot corrosion in contact with melt → structural degradation →

Metallic components Current collectors, bipolar plates, sealing MCFC – stack Durability problem: Hot corrosion in contact with melt → structural degradation → 654 h operation2064 h operation Electrolyte loss (>25%) Increased ohmic resistance R cell (B) R cell (A)

Metallic components Current collectors, bipolar plates, sealing MCFC – stack Cost issues: Differently treated metals for anode & cathode environments ► Single, cheap alloy

MCFC – Fuelling High efficiency conversion, CO acceptance, clean by-products MCFC ideal for green electricity generation Biomass gasification, Waste pyrolysis, digestion, ……

MCFC – Fuelling High efficiency conversion, CO acceptance, clean by-products MCFC ideal for green electricity generation BUT Fuel gas clean-up is still restrictive: low tolerance, high cost

MCFC – Fuelling High efficiency conversion, CO acceptance, clean by-products MCFC ideal for green electricity generation low tolerance, high cost Sulphur-tolerant (10 ppm) cell… Cost-effective clean-up…

MCFC – Heat Recovery Increase system efficiency by addition of bottoming cycle P cell ↓ Steam generator + Steam turbine P cell ↑ Direct expansion in GT + Steam generator + Steam turbine High-T heat + Simplicity in system Cell life - Large piping volume + Cell performance Co-Gen Possibility - Contaminants effect System pressurization

MCFC – Balance of Plant (BoP) Balance of Plant components: Pumps and fans Heat exchangers Spray nozzles Piping Filters Seals Gaskets Valves Regulators Majority of MCFC system shutdowns due to Grid/BoP failure Custom-made components → significant costs

MCFC – Balance of Plant (BoP) Stack-related shutdowns MTU, CFC Presentation IEA Meeting (2006)

Technological targets

So What?

Conclusions MCFC technology is proven and running (manufacturers in USA (2), D, I, K, J) Multi-fuel capability Strong potential in combination with renewables Strong potential for combined cycle waste heat utilisation Modular build-up → scale-up and scale-down BUT

Conclusions Need for continued product improvement: –increase power density (improve conductivity, utilization) –increase longevity (corrosion, dissolution resistance) –increase tolerance (resistance to contaminants) –reduce plant footprint (efficient, integrated plant design) –reduce costs (standard components, slim down prod. process) Solutions exist but are often contradicting

Conclusions Research & development activities: –Contributions possible from all sciences –No need for complete MCFC test rig –Catch up with improvements in conventional systems Openings possible at ENEA for aspiring MCFC contributors

THE END

Circular Single Cell 10 Cells Stack Square Single Cell 15 Cells Stack 0.1 m² 50 Cells Stack 0.1 m² 20 Cells Stack 0.75 m² MCFC – stack scale-up

Cell typeTolerance limits AFC 0% CO 2, 0% H 2 S PEFC CO < 10 ppm PAFC CO < 1% v H 2 S +COS < 50 ppm MCFC H 2 S, COS < 1 ppm HCl < 1 ppm, NH3 < 1% v SOFC H 2 S < 1 ppm, HCl < 1 ppm NH 3 < 1000 ppm