Metal doped ceria for two-step thermochemical water splitting

Transcription

1 International Workshop on Solar Thermochemistry September 12-14, 2017, Ju lich, Germany Metal doped ceria for two-step thermochemical water splitting Tatsuya Kodama Professor, Dept. Chemistry & Chem. Eng., Faculty of Engineering, (Director, Pacific Rim Solar Fuels Research Center) Niigata University 8050 Ikarashi 2-nocho, Niigata , Japan

2 Two-step Water Splitting Cycle by Non- stoichiometric Ceria Water Decomposition (W-D) Step H 2 CeO 2 Thermal Reduction (T-R) Step T > 1300 Under low O 2 partial pressure T < 1000 H 2 O CeO 2-δ O 2 Overall reaction : H 2 O H 2 + 1/2 O 2

3 Content (1) Metal Doping Effect for Ceria on Reactivity (2) Preparation of Fine, Spherical Ceria Particles (3) Future Research Plan

4 (1) Metal doping effect for ceria on reactivity 1) N. Gokon, T. Suda, T. Kodama, Thermochemical reactivity of 5-10 mol Fe, Co, Ni, Mndoped cerium oxides in two-step water-splitting cycle for solar hydrogen production, Thermochemica Acta, Vol. 617, pp. 179~190, ) N. Gokon, T Suda, T. Kodama, Oxygen and hydrogen productivities and repeatable reactivity of 30-mol%-Fe, Co, Ni, Mn-doped CeO 2 -d for thermochemical two-step watersplitting cycles, Energy, Vol. 90, pp. 1280~1289, ) E. Shida, K. Naito, T. Hatamachi, S. Bellan, H.-S., Cho N. Gokon, T. Kodama, Reactivity of Mn-Doped Ceria for a Thermochemical Two-Step Water-splitting cycle at low temperature, Proceedings of the Annual Conference of The Japan Institute of Energy, The 26th Annual Conference of The Japan Institute of Energy, Nagoya, Japan, August 1-2, 2017, Abstract No , pp

5 Relation between T-R step temperature on O 2 and H 2 production amounts O 2 Production amount /Ncm 3 g -1 -CeO O 2 H 2 (1000 ) H 2 Production amount /Ncm 3 g -1 -CeO T-R step temp. /

6 Outline In order to lower the T-R step temperature of the two-step water splitting by non-stoichiometric ceria, the metal doping effects of Fe, Co, Ni and Mn into ceria on reactivity were investigated. M-doped ceria power (M = Fe, Co, Ni and Mn: M-CeO 2 ) with 0 30 mol%-m were synthesized by a wet process of the coprecipitation. of the aqueous mixed solution of cerium nitrate and other metal salt such as nitrate or sulfate. Characterization of the power materials was done by X-ray powder diffractometry, and the reactivities of the metal doped ceria powers for two-step water splitting were examined using a fix-bed quartz chamber or tube with infrared furnaces, and/or thermogravimetry.

7 Preparation of Mn doped-ceo 2 (Mn-CeO 2 ) by Co-Precipitation Water Stirring at room temp. Ce(NO 3 ) 3 6H 2 O MnSO 4 5H 2 O Mn 5, 10, 15, 30mol% ph=8.5 NaOH solution Precipitates Calcination at 900 for 2 hours

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13 Lattice parameter changes of M-CeO 2 ( 0 15 mol%-m).

14 Experimental set-up Thermal Reduction (T-R) Step Mass spectrometer Quartz chamber Infrared furnace Sample N 2 Capillary Vacuum pump Exhaust Platinum cup (Purity %) 1dm 3 min -1 Thermocouple Quartz tube Water Decomposition (W-D) Step Sample GC analysis Infrared furnace (TCD) Outlet N 2 Heater Thermocouple Distilled water water trap Stirrer Oil bath (80-95ºC)

15 T-R step reactivity test for M-CeO 2 with 0 15mol%-M Production rate of O 2 / μmol min -1 g -1 material mol%Fe 10mol%Fe 5mol%Fe CeO (a) Fe-CeO (b) Co-CeO mol%Ni 10mol%Ni 5mol%Ni mol%Co 10mol%Co 5mol%Co mol%Mn 10mol%Mn 5mol%Mn 80 (c) Ni-CeO 2 60 (d) Mn-CeO Time / min Time / min Time variation of Oxygen production rate (per gram of material) during the T-R step (at 1500 C) of 1 st cycle.

16 T-R step reactivity test for M-CeO 2 with 30 mol%-m Mn Produced amount of O 2 [Ncm 3 / g-material] Co Fe CeO T-R Temperature [ºC] Oxygen production amount (per gram of material) for a different T-R step temperature ( C).

17 Oxygen (T-R step) and Hydrogen (W-D step) reactivities for 5 mol% M-CeO T-R step at 1500 C W-D step at 800 C Production rate of O 2 / μmol min -1 g -1 material CeO2 5mol%Fe-CeO2 5mol%Ni-CeO2 5mol%Co-CeO2 5mol%Mn-CeO2 Temp Temperature / ºC Production rate of H 2 / μmol min -1 g -1 material CeO2 5mol%Fe-CeO2 5mol%Ni-CeO2 5mol%Co-CeO2 5mol%Mn-CeO2 Temp Temperature / ºC Time / min Time / min

18 Hydrogen (W-D step) reactivity at different W-D step temperature for 5 mol% Fe-CeO 2 Production rate of H 2 / μmol min -1 g -1 material W-D step temperature Time / min Note: T-R step temperature is 1500 C

19 Thermogravimetric analysis for two-step water splitting cycle Electric furnace Metal-doped CeO 2 power (about 200 mg) T-R step: N cm 3 min -1 W-D step: H 2 O/N 2 50 cm 3 min -1 P H2O = 0.3 Balance R-type thermocouple Mass change logging Gas out Platinum cup E. Shida, K. Naito, T. Hatamachi, S. Bellan, H.-S., Cho N. Gokon, T. Kodama, Reactivity of Mn-Doped Ceria for a Thermochemical Two-Step Water-splitting cycle at low temperature, The 26th Annual Conference of The Japan Institute of Energy, Nagoya, Japan, August 1-2, 2017.

20 Remarkable results Some of the metal-doped ceria powder samples showed the greater productivities of O 2 and H 2 in the repeated cycles than those with pure ceria powder. Especially, in the thermogravimetric experiments, about 8 times greater reactivity could be obtained with one of the metal-doped ceria samples than pure ceria. 3) E. Shida, K. Naito, T. Hatamachi, S. Bellan, H.-S., Cho N. Gokon, T. Kodama, Reactivity of Mn-Doped Ceria for a Thermochemical Two-Step Water-splitting cycle at low temperature, Proceedings of the Annual Conference of The Japan Institute of Energy, The 26th Annual Conference of The Japan Institute of Energy, Nagoya, Japan, August 1-2, 2017, Abstract No , pp

21 (2) Preparation of Fine, Spherical Ceria Particles 4) T. Etori, N. Gokon, A. Takeuchi, T. Miki, M. Yokota, T. Kodama, Flowability control of bed materials in a fluidized bed reactor for solar thermochemical process, Energy Procedia, Vol. 69, pp , ) S. Ito, S. Abe, T. Hatamachi, H.S. Cho, N. Gokon, T. Kodama, Synthesis of CeO 2 particles by spray dryer method for solar hydrogen production, International Symposium on Fusion Tech 2016, Harbin Institute of Technology, Harbin, China, January 19, 2016.

22 Solar Particle Fluidized Bed Reactor for Two-Step Water Splitting being developed T-R step CeO 2 CeO 2-δ + δ/2o 2 W-D step CeO 2-δ + δh 2 O CeO 2 + δh 2 T-R step W-D step Solar Flux Solar Flux O 2 H 2 T > 1300 T < 1000 N 2 gas Steam+N 2

23 Outline Conventionally, pulverized particles of ceria with the particle size of µm were used to demonstrate our solar fluidized bed reactor (FBR). Pulverized particles have ununiform particle shape and size. Fine, spherical particles are ideal for particle fluidization. Minimum fluidization gas velocity of ceria particles can be decreased and pressure drop through the fluidized bed will be decreased if fine, spherical particles are used for our FBR in comparison to the case using conventional, pulverized particles. Synthesis of fine, spherical ceria particles was examined by spry dry method of cerium nitrate aqueous solution. Minimum fluidized gas velocity and pressure drop of the fluidized bed of the synthesized particles were investigated.

24 Spry drying for fine, spherical ceria particles Fine and spherical cerium nitrate particles can be prepared by spry drying method. Then, cerium nitrate particles are calcined at

25 Spry Dryers Apparatus 1L-8i 2F0C-20 3OUDT-25 Moisture Evaporation Capacity 3kg/h 15Kg/h 30Kg/h OHKAWARA KAKOHKI CO., LTD.

26 Sample after calcination of spry-dried ceria nitrate Spherical CeO2 100μm S. Ito, S. Abe, T. Hatamachi, H.S. Cho, N. Gokon, T. Kodama, Synthesis of CeO 2 particles by spray dryer method for solar hydrogen production, International Symposium on Fusion Tech 2016, Harbin Institute of Technology, Harbin, China, January 19, 2016.

27 Flowability test of CeO 2 particles by small-scale quartz tube. Experimental set-up N 2 outlet N 2 Differential pressure gauge (manometer) Fluidized bed Distributor N 2 Flow controller N 2 Experimental conditions Gas : N 2 Distributor diameter: 25 mm Loaded particle : CeO 2 inlet N 2 Max 50 L/min N 2 flow

28 Remarkable results Spherical ceria particles with the particle diameters of about 100 µm were successfully synthesized via the spry dry method. Minimum fluidized gas velocity of the spherical ceria particles was less than 1/10 of that for conventional, pulverized ceria particles with the particle size range of µm. The pressure drop of the fluidized bed with the spherical particles was less than one seventh of that for conventional, pulverized ceria particles. 5) S. Ito, S. Abe, T. Hatamachi, H.S. Cho, N. Gokon, T. Kodama, Synthesis of CeO 2 particles by spray dryer method for solar hydrogen production, International Symposium on Fusion Tech 2016, Harbin Institute of Technology, Harbin, China, January 19, 2016.

29 (3) Future Research Plan 1) The solar FB reactor test at Miyazaki BD system using μm pulverized ceria particles. (CPC will be canted by (2017): presented by S. Bellan, in this Workshop) 2) Preparation of fine, spherical particles of metal-doped ceria. (2017) 3) The FB reactor test using fine, spherical ceria and metal-doped ceria particles using a sun-simulator. (2018) 4) Mass production of fine, spherical ceria and metal-doped ceria.(2018) 5) The solar FB reactor test at Miyazaki BD system using fine, spherical ceria or metal-doped ceria (2019)