T. S. Zhao Chair Professor of Mechanical & Aerospace Engineering - - PowerPoint PPT Presentation
T. S. Zhao Chair Professor of Mechanical & Aerospace Engineering Director of the HKUST Energy Ins@tute Senior Fellow of the HKUST Ins@tute for Advanced Study Use of fossil fuels vs. Environmental problems Electricity Vehicles Heat Engines
Chair Professor of Mechanical & Aerospace Engineering Director of the HKUST Energy Ins@tute Senior Fellow of the HKUST Ins@tute for Advanced Study
Heat Engines
O2 Fuel
Combus@on
Use of fossil fuels vs. Environmental problems
CO2
NOx, SOx Par@culates
Vehicles Electricity
Sustainable Energy Future
Consumers need motion, sound, light, heat, communication
Utilization: Wind Solar Biomass Electrical Energy Storage Biofuels Heat Electricity Thermal Energy Storage Fuel Cells
Water Heat Electricity Clean products
AIR
Hydrogen Methanol Ethanol methane
Fuel Cell
Electrolyte frame Bipolar plate Anode catalyst Cathode catalyst
O2 H2
Stack of several hundred
e-
Direct Alcohol Fuel Cell
Alcohols
e-
Solid Oxide Fuel Cell (SOFC)
Biogas
Fuel Volume per WaV hour
360 ml
Hydrogen – uncompressed gas Liquid Hydrogen 0.4 ml Hydrogen from Chemical Hydride 0.6 ml 0.2 ml Methanol & Ethanol Li-ion BaVery 2 ml
DMFC is a carbon neutral, sustainable tech
n Opera@ng at room temperature n Quiet & no moving parts
Voltage, V Current density 1.15 Polariza@on curve Icell Vcell
Issues with DMFC
Catalyst ac@va@on loss Ion transport loss Mass transport loss Voltage loss Performance is low : a decade ago, 30-50 mW/cm2
Complexity in the fuel cell process
Reac@ons (e-, H+, Heat…); Rate (T, C); Transport (mul@- component, Mul@-phase); Structure (Mul@-scale..)
Flow channel (macroscale) Diffusion layer (microscale) Catalyst layer (nanoscale)
Liquid Gas Liquid Gas
Our Approach
Theore@cal framework
Theory
Revealing intricacy of cell opera@on & Improving cell performance
Experimenta@on + Simula@ons
Flow behavior Current Mass transport Current Current Heat transport Mass transport
Experimenta@on
Int J Heat Mass Transfer, 47 (2004) 5725-5739. Journal of Power Sources, 139(1-2) 79-90. Electrochemistry Communica@ons 7 (2005) 288-294. Electrochimica Acta 52 (2007) 6125-6140
Breakthrough: DMFC performance boost
0.25 0.50 0.75 200 400 600 800 1000 1200 50 100 150 200 250
16.5 wt.% PTFE 11.7 wt.% PTFE 8.0 wt.% PTFE 3.8 wt.% PTFE non-wetproofed
Current density, mA/cm2 Cell voltage, V Power density, mW/cm
2
Power density (200 mW/cm2)
Breakthrough: DMFC performance boost
J Power Sources 171 (2007) 268-274
Innova@on:
High-performance DMFC electrode
Energy & Environmental Science, 4, 1428-1433
World-record power density: 180 mW/cm2
Breakthrough: Direct ethanol fuel cell
Previous Now
J Power Sources 187 (2009) 387-392 Energy & Environmental Science 2012,5,5333-5339
Discovery: DMFC Opera@on
Electrochemical and Solid-State LeVers, 8 (1) A52-A54 (2005)
Discovery: DMFC Opera@on
Electrochemical and Solid-State LeVers, 8 (1) A52-A54 (2005)
Implica@ons
A new method for hydrogen produc@on
— Instant — Applicable at room temperature — No CO species
n Ceramic electrolyte
conduc@ng oxygen ions
n High temperature (700oC);
inexpensive catalysts
SOFC is a clean, carbon neutral, efficient tech
n High efficiency (~70%) n No combus@on; clean n Fuel flexibility
Biogas from sewage sludge in HK
Sludge treatment works in HK produce biogas for 9.7 Million m3 (2014)
Biogas composi@on Average percentage%
CH4 65 CO2 35 H2S(ppm) 100-4075 Others(%)
Current biogas u@liza@on
Biogas water boiler at Tai Po STW Dual fuel engine generator at Sha Tin STW CHP generator at the Shek Wu Hui STW
Biogas: 9.7 Million m3 Heat Engines (η=30%-40%) Electricity: 2.35-3.12×1010 W-hour ~3500 people
Biogas: 9.7 Million m3 SOFC (η=70%-75%) Electricity: 5.48-5.86×1010 W-hour
~7000 people
Change to SOFC
Added benefits:
— Clean (no NOx, no SOx) — Quite opera@on — Compact system
Challenging issue: Carbon deposi@on
Mechanisms:
n Breaking down C-H bonds @Nickel catalyst → free radicals n CH4→C+2H2 n Polymeriza@on of free radicals n Deposi@on in pores of the anode
Ni-YSZ anode Deposited C filament
Challenging issue: Sulfur poisoning
n Auer desulfuriza@on, ~ppm level H2S can lead to cell
performance degrada@on.
n Commercial electrodes can only withstand 2 ppm H2S
Mechanism of sulfur poisoning
Int J of Hydrogen Energy 33 2008 6316 Energy & Environ. Sci 4 2011 4380
SOFC demos with biogas from anaerobic diges@on sludge treatment
Loca>on Scale Remarks Year Spain 5 kWe No external biogas reforming 2009-2011 Germany 1 kWe External reformer 2014 Italy 175 KWe External reformer Under construc@on
Steam reforming CH4+H2O→CO+3H2 H2+O2- →H2O+2e- CO+O2- →CO2+2e-
Biogas + Steam
( ~65% CH4, 30% CO2, 0.3% CO, H2O)
H2O + CO2
SOFC
Dry reforming CH4+CO2→2CO+2H2 H2+O2- →H2O+2e- CO+O2- →CO2+2e-
Biogas
( ~65% CH4, 30% CO2, 0.3% CO)
H2O + CO2 △Ho=206 kJ/mol △Ho=247.3 kJ/mol Par@al oxida@on CH4 + 1/2O2 → CO + 2H2 H2+O2- →H2O+2e- CO+O2- →CO2+2e-
Biogas + O2
( ~65% CH4, 30% CO2, 0.3% CO, O2)
H2O + CO2 △Ho=-35.6 kJ/mol
J Power Sources 142 2005 75 J Eng. Gas Turbines Power 127 2005 86
n DIR-SOFC is more energy efficient with the highest heat u@liza@on. n Steam produced on the DIR-SOFC anode will help facilitate the anode reac@on.
Cathode side Reformer Anode side
Biogas H2O
Air Cathode side Anode side
Biogas H2O
Air
Indirect internal reforming-SOFC (IIR-SOFC) Direct internal reforming-SOFC (DIR-SOFC)
External Reformer Cathode side Anode side
Biogas H2O
Air
External reforming-SOFC (ER-SOFC) H2 CO CO2 CH4 H2 CO CO2 CH4
Find good electrode materials that can tolerate S to generate high power output with improved durability.
p Ni-based cermet anode with YSZ replaced by other oxygen ion
conductors;
p Cermet anodes with Ni replaced by other metals; p Conduc@ve metal oxides: such as Sr2MnMoO6-δ.; Sr2MgMoO6-δ.
n
Cu-ceria anode
Fast oxygen ion conducEon might enhance S removal
Electrochemical and Solid-State LeJers, 8 2005 A279
n
Ni-YSZ with Ni par@ally replaced by
800 ºC, H2S 20 ppm
Applied Catalysis A: General 486 2014 123
n
Conduc@ve metal oxide anodes
On oxide anode materials there is reduced S adsorpEon.
Science 254 2006 312
Study of La0.75Sr0.25Cr0.5Mn0.5O3−δ impregnated anodes
cell-1: a cell with 5 wt.% LSCrM-impregnated YSZ anode; cell-2: a cell with 35 wt.% LSCrM-impregnated YSZ anode; cell-3 a cell with 32 wt.% LSCrM+6wt.% Ni + 2wt.% Ag-impregnated YSZ anode; cell-4: a cell with 32 wt.% LSCrM and 6 wt.% Ni impregnated YSZ anode cell-5: a cell with 30 wt. % Ni impregnated YSZ anode
C deposi@on on cell-5 @ Ni-YSZ anode
CO CO2 CH4 H2S
MFC MFC MFC MFC Evaporator
SOFC
Tailgas analyzer Electrochemical Interface & Impedance Analyzer
Power output
H2O Tailgas treatment system Peristal@c pump recircula@on T Temperature controller Gas flow control system Temperature control system
Cell opera@ng temperature: 600-800 oC
n Fuel cell is an enabling technology to increase the use
climate change and air pollu@on problems.
n We have made breakthroughs in direct alcohol fuel
cells.
n Solid oxide fuel cells offer the promise to convert
biogas from sewage sludge treatment to electricity in a cleaner way with much higher efficiency.
n We will address the issues with the use of biogas in
solid oxide fuel cells (carbon deposi@on and sulfur poisoning)…