OECD Conference on Potential Environmental Benefits of Nanotechnology: Fostering Safe Innovation-Led Growth, Session 3. Clean Car Technology Paris, July 15-17, 2009 Nanostructured electrochemical reactors for NOx/PM decomposition and micro SOFCs Masanobu Awano Institute of Advanced Industrial Science and Technology(AIST) Nagoya 463-8560, JAPAN Ceramic electrochemical reactors are expected for their high performance on conversions of energy and substances; for examples, electric power generation (solid oxide fuel cells: SOFCs), synthesis of hydrogen, and decomposition and purification of environmental pollutants. Development of novel electrochemical modules for denox/pm reactor by nanostructure control Combination with thermoelectric ceramic module for harvesting of waste heat energy New type MicroSOFC development of high performance APU unit for vehicles by nano-micro structure control as clean energy source
Various applications of electrochemical reactor (O 2- -conducting ceramics ) Air O 2- e - 1 H 2 2 CH 4 e - H 2 O (SOFC) H 2 O + CO 2 (SOFC) e - Air 3 NO N 2 (de-no X ) 4 H 2 O H 2 (H 2 generation) O 2- O 2- e - O 2 5 CH 4 CO + H 2 (Syngas) 6 O 2 pumping 7 CH 4 CH 3 OH (GTL) 8 C CO 2
6th Pacific Rim Conference on Ceramic and Glass Technology, September 15th 2005, Hawaii, USA Nitrogen oxides ( NOx ) in exhaust gas are known - to cause air pollution problems (acid rain, photochemical smog) - to give damage to human nerves and respiratory organs The reduction of NO X emission has become one of the greatest challenges in environment protection. 100 % NO 2 50 H C C O 0 Japanese regulation 14.3 14.5 14.7 A/F Active at higher PO 2 atmosphere near zeroemission
Environment purifying / Saving energy NO x N 2 +O 2 NOx/PM DECOMPOSITION NANOSTRUCTURED DE-NOx REACTOR ELECTROCHEMICAL/THERMO ELECTRIC MODULE
Contents 1. Ceramic electrochemical reactor for NOx decomposition 2. Ceramic electrochemical reactor for PM (particulate matter) decomposition 3. Thermoelectric ceramic module for enhanced denox property by using waste heat energy
1. Ceramic electrochemical reactor for NOx decomposition
Example: scheme of NOx purifying by an electrochemical cell (under excess oxygen coexistence such as diesel engine exhaust gas) 高温排ガス クリーンガス N O x 高温における N O x 高選択性 Oxygen as an inhibitor to de-nox reaction O 2 e N 2 Catalytic Activation Site ガス分子吸着サイト 多孔質触媒電極層 Porous Cathode 熱電変換による電力供給 e O 2- O 2 Solid 固体電解質 Electrolyte Oxygen ( 酸素イオン ion conductor 伝導体 ) Porous 多孔質電極 Anode Large amount of electrical current supply is required difficulty to the application
Proposed Mechanism of Selective DeNOx Reaction high conc. oxygen defects layer nano particles 2nm N Ox m olecules Ni nano particles Exhaust gas O-N N 2 YSZ YSZ N io Ni NiO nano pores e - nano redox-reaction zone O-ion O 2 O 2- ( O 2 ) N 2 TEM image of an NiO and YSZ interface, and reaction model of selective NO molecule decomposition. The expected mechanism nano-space - of the absorption and decomposition of N to Ni, and oxygen capturing and pumping in the region of high defects concentration is also displayed
Improvement of de-nox / current efficiency NOx decomposition (%) NOx Conversion (%) 80 70 60 50 40 30 20 10 t=600 0 C oxygen 2% 1000ppm-NO EC electrode mesoscale control nanoscale control @2003 Energy efficiency of ordinary catalyst system @2001 oxygen 2% t=700 0 C 1000ppm-NO Pt-1300 0 C Ag-800 0 C Pd-800 0 C Pd-130 0 C Pd-Pt-130 0 C Literature previous results 0 0 50 100 150 200 250 Current (ma) C ellcurrent (m A) Improved de-nox efficiency for applied current by nano- and meso-scale structurally controlled electrochemical cells in comparison with previous results.
Microstructure development of electro-catalytic electrode by the factors of applied voltage and temperature YSZ(covering layer) NiO+YSZ (catalytic electrode) YSZ+Pt(electrode) YSZ(electrode)
Optimization of Nano-space reaction zone (applied voltage) Microstructure development of electrocatalytic electrode at the interface of NiO-YSZ grain boundaries as a function of applied voltage; (a)before applying current, (b)voltage 1V, (c)1.5v,(d)2v,(e)2.25v, (f)2.5v,(g)2.75v,(h)3v.
Research for application of de-nox cell to diesel engine exhaust gas purification Large size cell (10cm square) 100 Current 実験セルの efficiency of typical 電流効率 small (1.65%) cell %NFC-4-1 500C NOx decomposition NOx 転換率 (%) (%) 80 60 40 20 denox property of large size cells %NFC-7-2 500C %NFC-7-2 600C %NFC-4-1 600C(2) %NFC-10-2 500C データ 14 7:26:24 2003/09 0 0 10 20 30 40 50 Cell 電流密度 current (ma/cm 2 )) Gas DC Cell stack (20sheets) Image of a denox module of diesel engine exhaust gas Sequential development of the electrochemical cell from laboratory to a real application and NOx decomposition properties of a large size electrochemical cell (10cm square). Inserted photograph is a stack model of 20 cells assembled for exhaust gas purification of vehicles.
Measurement of denox performance of a stack by large cells Stack using 20 cells
70 60 Durability under operating conditions C 2 H 2 70 60 SO 2 NO Conversion [%] 50 40 30 20 10 0 : 0 % : 0.2% : 0.3% 0 200 400 600 800 Power [mw] NO Conversion [%] 50 40 30 20 10 0 : 0ppm : 3ppm :30ppm 0 200 400 600 800 Power [mw] NOx conversion (ratio) NO 転化率 (-) 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0 4 8 12 16 20 24 経過時間 (h) Time(h) No degradation for CO,CH / high conc.sox causing damage in the electrode Initial degradation less than 10% --- stable for prolonged operation over 200h
Electrochemical cell operation at low temperature by introduction of a nano-wired structure Nano-wire electrode Nano particles Exhaust gas Network of metallic nano- wires between electrolyte micron particles wire Electrochemical reaction Clean air power cathode electrolyte Electric wire to power source anode DeNOx property at 250 C under 20%O 2 coexistence
Selective reduction of NOx using our electrochemical cell Exhaust gas Cleaned gas NOx-selective layer O 2- conductor N 2 - DC NO - O 2 N 2
2. Ceramic electrochemical reactor for PM (particulate matter) decomposition
Oxidation of graphite on Ca 12 Al 14 O 33 / Ag composite anode Cathode : 2NO + 4e - N 2 + 2O 2- Anode : C + 2O 2- CO 2 + 4e -
Mechanism of Oxidation using Active oxygen on Anode of Electrochemical Reactor Microstructure of Ag/Ca 12 Al 14 O 33 /8YSZ Porous Anode Nanostructure controlled electrode C12A7(O*) Porous Anode YSZ,CGO 1µm O* CO 2 Reaction Between C and O* at Anode Supplying High Partial Voltage O Ion to Catalysts Graphite (PM) e- + - Cathode O2- Pump O ion into YSZ from NO NO e-
Simultaneous clean up of solid carbon (PM) and nitrogen oxide (NOx) Reducing electrode : 2NO + 4e - N 2 + 2O 2- Cathode Electrolyte Ag CGO + NiO CGO Oxidizing electrode : C + 2O 2- CO 2 + 4e - NOx decomposition (%) 100 NOx 100ppm(50ml/min) Graphite 0.8mg 80 60 40 20 Anode 475 Ag CGO + Ag graphite 50 40 30 20 10 0 Degree of CO 2 formation By graphite oxidation(ppm) cell surface through electrochemical reaction 0-10 0 0.5 1 1.5 2 2.5 Voltage /V
Effect of C 12 A 7 addition on Reaction Rate Removed Graphite (mol) 2x10-5 1x10-5 Theoretical Value ( C + O 2- = CO 2 +2e - ) Pt+YSZ+Ca 12 Al 14 O 33 (14%) Pt + YSZ 0 10 0 0 50 100 150 200 Amount of Applied Charge (c)
Table 1. Amount of electrochemical decomposition of graphite on the surface of anode at 2.5V and 475q C. Anode material Decomposed graphite(mol/cm 2 -h) Pt+8YSZ Ag+8YSZ Ca 12 Al 14 O 33 +8YSZ 0.3x10-5 0.7x10-5 1.3x10-5 12CaO 7Al 2 O 3 2000cc Diesel Engine Estimated Amount of PM from Exhaust Gas Electrochemical Reactor(ca 1 m 2 ) Cubic 1.9 g/h 1.199nm 1.6 g/h
3. Thermoelectric ceramic module for enhanced denox property by using waste heat energy
Application of thermoelectric energy conversion for supplying electric power from waste heat Thermoelectric conversion Heat O 2 N 2 Electrochemical Ceramic Reactor High-T electron hole heating e - NO x T Power generation for Electrochemical Reaction Thermoelectric Ceramic module Exhausted Gas ΔT Low-T N-type Total energy 100% Current P-type 15% 30% torque operation FUEL 5-10% Alternator 5% Pressure / (efficiency<50%) Friction loss 30% Exhaust gas 40% radiator Electric Battery components & system Waste heat h energy