Electrocatalyst of Alkaline Water Electrolysis for Fluctuated Operation and SPE Membrane Electrolysis for Energy Carrier Synthesis with Water Decomposition
Shigenori MITSUSHIMA Green Hydrogen Research Center, Yokohama National University, Institute of Advanced Sciences (IAS), Yokohama National University 2 Hydrogen production, and transportation
Alkaline Water electrolysis Electrohydrogenation of toluene ✓ Start & stop impact for electrodes with water decomposition in a bipolar electrolyzer ✓ Introduction of a new electrolyzer ✓ Design of (Li)NiO/Ni durable system using PEFC technology anode o +3 H2O→ +3/2O2 U = 1.08 V o H2O→ H2+1/2O2 U = 1.23 V
Electrode-cathode assembly DSE® Anode
Production Solar cell Utilization Wind power
Electrolysis Hydrogen Dehydrogenation 3 Contents
1. Introduction
2. Analysis of bipolar electrolyzer for alkaline water electrolysis
3. Active and durable anode for alkaline water electrolysis
4. Direct electrohydrogenation of toluene with water decomposition
5. Conclusion 4 C and H cycle in global energy system
Fossil fuels: natural extremely slow cycle Photosynthesis Biomass: natural annually or decadal cycle Hydrogen: artificial carbon free cycle Renewal electricity
Photovoltaic power Wind power CO2(g)
H O(g) 2 Fuel cells e- Combustion engine
H for energy storage ~~~~~Equilibrium ~~~~~2 Biomass and transportation ・firewood Water electrolysis ・Biofuels H2O(l) - Hydropower e Fossil fuels Photosynthesis ・Natural Gas ・Petroleum ・Coal 5 Role of hydrogen and water electrolysis
Water Electricity
Water electrolyzer
➢ Conversion of electricity to chemical energy • Usage of excess renewable electricity to meet demand = Power supply following operation with start & stop operation Less expensive, compact & durable Hydrogen ➢ Storage electricity as chemical energy • Usage as energy carrier, but low volumetric energy density is a issue for long term storage and oversea transportation
Liquidification (L-H2, L-NH3, or Organic chemical hydride) 6 Performance of AWE and SPEWE
SPEWE has higher density for H2 production than AWE Both system should be designed around 1.8 ~ 2.0 V of cell voltage i / Acm-2 || 0 0.2 0.4 0.6 Almost same OPEX 2.5 Commercialized AEW Blue: Alkaline water electrolysis (designed for 0.2~0.4 Acm-2) (AWE) Ir / Pt23) 2.0 V 24)
/ / Ir / PtC RuO / PtC25) U NEDO2 project of‘17 IrO / PtC22) IrO2-SnO (2:1) / PtC22) Ir 2Ru O2 / PtC26) 1.5 Red： Solid polymer0.6 0.4 2 electrolyte water electrolysis (SPEWE) 0 0.5 1.0 1.5 2.0 -2 i / Acm 1. M. Carmo, D. L. Fritz, J. Mergel, and D. Stolten, Int. J. Hydrogen Energy 38, 4901 (2013). 2. S. Mitsushima, S. Fujita, ELECTROCHEMISTRY 85, 28 (2017). 7 Type of water electrolysis and its characteristics
Basic electrolyte Acidic electrolyte Solid polymer ~1 A cm-2 @1.8 V 2 – 3 A cm-2 @1.8 V electrolyte PGM → NPGM catalyst PGM catalyst SPEWE (Ion exchange ✓ Instable & low conductive Ti base materials membrane) electrolyte membrane ✓ High material cost ⇒ reverse current if electrolyte feed ✓ Pure water feed Diaphragm 0.2 – 0.6 A cm-2 @1.8 V (Porous NPGM catalyst AWE membrane) Stainless based materials ✓ Low current density ✓ KOH solution feed ⇒reverse current Today’s talk Basic electrolyte • Understanding of reverse current • Development of durable electrocatalyst Acidic electrolyte with SPE • Value added water electrolysis: direct energy carrier synthesis 8 Contents
1. Introduction
2. Analysis of bipolar electrolyzer for alkaline water electrolysis
3. Active and durable anode for alkaline water electrolysis
4. Direct electrohydrogenation of toluene with water decomposition
5. Conclusion 9 Reverse current for bipolar electrolyzer
After shut down operation: U 1.3 → 0.3 V
- - Anode: NiOOH + H2O + e → Ni(OH)2 + OH (reduction) - - Cathode: Ni + 2OH → Ni(OH)2 + 2e (oxidation) Degradation Anode：NiOOH/Ni Cathode: Ni H2
O2
- + Separator Bipolar plate KOH OH-
Y. Uchino, T. Kobayashi, S. Hasegawa, I. Nagashima, Y. Sunada, A. Manabe, Y. Nishiki, S. Mitsushima, Electrocatalysis. (2017). doi:10.1007/s12678-017-0423-5. 10 Measurement system of leak & reverse current
Leak and reverse current was measured as ionic current through manifolds using clamp meter H2 O2
Clamp meter NaOH • Electrodes: Ni mesh • Separator: Nafion 117 Cell 1 Cell 2 • End & bipolar plates: Ni
Y. Uchino, T. Kobayashi, S. Hasegawa, I. Nagashima, Y. Sunada, A. Manabe, Y. Nishiki, S. Mitsushima, Electrocatalysis. (2017). doi:10.1007/s12678-017-0423-5. 11 Equivalent circuit & performance of the electrolyzer
• Cell performances in a electrolyzer were almost the same • Reverse current was determined as a function of the condition of electrolysis to analyze potential change of electrodes after electrolysis Circuit breaker Power Sorce 44 I Cell 1 Breaker r_gi Power supply Rg-I I 33 r_hj Cell 2 Anode Rh-j Cathode endplateAnode Endplate Bipolar Plate
Bipolar plate Cathodeendplate Endplate / V / / V / R η η R η 2 ηa U0 int. c a U0 int. c
U 2 U U
I 11 r_bd Rb-d Ir_ac
R 00 a-c U1 U2 00 200200 400400 600600 U1 U2 i / mA·cm-2 -2 i / mA cm Cell 1 Cell 2 Cell 1 Cell 2 Y. Uchino, T. Kobayashi, S. Hasegawa, I. Nagashima, Y. Sunada, A. Manabe, Y. Nishiki, S. Mitsushima, Electrocatalysis. (2017). doi:10.1007/s12678-017-0423-5. 12 Reverse current and cell voltage as a function of time
• U1 and U2 decreased slightly and significantly, respectively • This behavior could be explained with discharge of the bipolar plate Reverse current is a function of cell voltage and ionic resistances
Ir = 4 {U2 - (U1_initial - U1)} / (Rmanifold + Rinternal) 4 Solid: measured Dashed: estimated with the model 2 After 1 h electrolysis of
2 After 1 h electrolysis of -2 - 3 -2 400 mA cm 600 mA cm 600 mA cm-2 -2 400 mA cm 200 mA cm-2 U1 -2
2 200 mA cm V / U U
/ mA cm mA / 1 400 mA cm-2 r i 200 mA cm-2 1 600 mA cm-2 U2
0 0 0 50 100 150 0 50 100 150 t / min t / min Y. Uchino, T. Kobayashi, S. Hasegawa, I. Nagashima, Y. Sunada, A. Manabe, Y. Nishiki, S. Mitsushima, Electrocatalysis. (2017). doi:10.1007/s12678-017-0423-5. 13 Electric charge of reverse current
Charge of reverse current increased with current density of electrolysis = Q was almost proportional to NiOOH formation
44 Change of surface with reverse current A Initial C A C 3 3 1.4[NiOOH [H2/ 0 1.4 [NiOOH [H2/ 0
/ C / /NiO2] H2O] /NiO2] H2O] /C 22 Middle r,total 1.3[Ni(OH) [Ni/ ~0.2 1.3 [Ni(OH) [Ni/ ~0.2 Q 2 2 reverse /NiOOH]Ni(OH) ] /NiOOH] Ni(OH) ] Q 1 2 2 1 Final
1.3[Ni(OH)2 [Ni/ ~0.2 ~0.2 [Ni/ [Ni/ ~0.2 0 0 /NiOOH]Ni(OH)2] Ni(OH)2] Ni(OH)2] 00 200200 400400 600600 i / mA cm-2 duringi / mA cm -2electrolysis
Y. Uchino, T. Kobayashi, S. Hasegawa, I. Nagashima, Y. Sunada, A. Manabe, Y. Nishiki, S. Mitsushima, Electrocatalysis. (2017). doi:10.1007/s12678-017-0423-5. 14 Conclusion for start & stop of AWE
The reverse current in alkaline water electrolyzer having relation between the electrolyzer operating conditions and cell voltage has been investigated using a bipolar-type electrolyzer which consists of two cells. ✓ The reverse current increased with the current density of the electrolysis. ✓ The increase in the charge of the reverse current would correspond to the increase of the surface oxide on the anode of the bipolar plate. ✓ Cell voltages were above 1.4 V at all cases just when the electrolyzer is opened the circuit to stop. Therefore, the major redox couple of the reverse current would be
[NiOOH/NiO2 and [H2/H2O]. ✓ Final surface of bipolar plate is 0.11 to 0.44 V vs.
RHE of [Ni/Ni(OH)2] for both sides 15 Contents
1. Introduction
2. Analysis of bipolar electrolyzer for alkaline water electrolysis
3. Active and durable anode for alkaline water electrolysis
4. Direct electrohydrogenation of toluene with water decomposition
5. Conclusion 16 Degradation of Ni under 1.0~1.8 V(1 Vs-1) of potential cycling
• OER current decreased with potential cycling • Redox charge for Ni(II)/Ni(III) increased and its potential decreased with potential cycling • OER current decreased a lot with formation of Ni(IV) 300 7.0MNi0 KOH, 0 cycle 5 250 o Ni5000 -1 Ni(II) ⇄ Ni(III) Ni10000 5000 2 25 C,5 mVs
- Ni15000
200 2 Ni25000 10000 - 150 x 0 15000 0 cycle 100 25000
/ mAcm / 5000 Ni0 i 50 mAcm / Ni5000
-5 10000 Ni10000 i Ni15000 0 15000 Ni25000 -50 25000 x -10 1 1.2 1.4 1.6 1.8 1 1.2 1.4 1.6 E / V vs. RHE E / V vs. RHE H. Ichikawa, K. Matsuzawa, Y. Kohna, I. Nagashimb, Y. Sunadc, Y. Nishikd, A. Manabd, and S. Mitsushima, ECS Trans., 58 (2014) 9-15. 17 Idea of anode stabilization for AWE
• Active site is hydrous oxide • In order to stabilize the hydrous layer, compact oxide layer must be stabilized = electronic conductive oxide layer that is synthesized at high temperature MetalCompact Hydrous Oxide Oxide
OH-
Na+(aq) Ni O doping❓ complex❓ Illustration: based M. Lyons, R. Doyle, I. Godwin, M. O’Brien, L. Russell, J. Electrochem. Soc., 159, H932(2012) 18 Preparation of the Li dope NiO coated Ni
Polished Ni LiOHaq
LiOH coating with
5 M LiOHaq Without LiOH Dry at 60oC LiOHsol 0~4 mg cm-2
o 5 μm 800 or 1000 C in air for 1 h With LiOH With LiOH
Ni (Li)NiO 5 μm 5 μm 1000oC 800oC
S. Fujita, I. Nagashima, Y. Sunada, Y. Nishiki, S. Mitsushima, Electrocatalysis. 8 (2017) 422–429. 19 Resistance measurement for the surface oxide
• 2-probe AC impedance was applied • Resistance was evaluated as high frequency side of intercept to real axis
• High concentration NaClaq was impregnated to decrease contact resistance
5 Carbon rod Pressure 1.0 MPa 4 Resistance of oxide Φ 0.5 cm
3 50 kHz 0.15 Hz electrode / Ω / 2
img Au plate Z 1 0 0 2 4 6 8 10 7.0 M NaCl was impregnated Z / Ω aq real at the contact
S. Fujita, I. Nagashima, Y. Sunada, Y. Nishiki, S. Mitsushima, Electrocatalysis. 8 (2017) 422–429. 20 Electrochemical measurements
0.7 V - 1.8 V, 5 mV s-1 1.0 V - 1.8 V, 1 V s-1 iR correction: AC impedance 20 25oC, 5 mVs-1
7M KOH
2 - 10 Ni electrode
OER / mAcm /
i 0 Ni(II) ⇄ Ni(III) -10 1.1 1.3 1.5 1.7 E / V vs. RHE S. Fujita, I. Nagashima, Y. Sunada, Y. Nishiki, S. Mitsushima, Electrocatalysis. 8 (2017) 422–429. 21 XRD analysis for the surface oxide
Peaks of (Li)NiO shifts o
: Trigonal (Li)NiO 800 C higher angle with Li (104) : Cubic (Li)NiO 4)
(200) dopeing (Trigonal > Cubic)
: Ni o 1000 C 800oC 42 43 44 45 46 • Thin oxide because of the
existence of Ni peak
(220)
(104)
(111)
(200) (003)
(012) • Multi phases with trigonal
(101)
(111)
(110)
(116) (107)
(220) and cubic Intensity [a.u.] Intensity
1000oC
(220)
(200)
(220)
(111) (200) (111) • Single phase of cubic 20 40 60 80 2θ / degree(CuKα)
S. Fujita, I. Nagashima, Y. Sunada, Y. Nishiki, S. Mitsushima, Electrocatalysis. 8 (2017) 422–429. 22 Relationship between resistance of oxide and composition
• Resistance of the oxide decreased with increase of the x • For 800oC, high resistance cubic phase affected the oxide resistance
(x is for trigonal phase)
x of LixNi2-xO2/Ni S. Fujita, I. Nagashima, Y. Sunada, Y. Nishiki, S. Mitsushima, Electrocatalysis. 8 (2017) 422–429. 23 Performance as a function of Li dope amount
Li dope amount optimum would be balance of catalytic activity and electronic conductivity
Electrolyte IR free
x of LixNi2-xO2/Ni S. Fujita, I. Nagashima, Y. Sunada, Y. Nishiki, S. Mitsushima, Electrocatalysis. 8 (2017) 422–429. 24 Durability under 1.0 to 1.8 V of potential cycling
OER activity of the LixNi2-xO2/Nis was stable under potential cycling
x = 0.57
x = 0.14 Electrolyte IR free
S. Fujita, I. Nagashima, Y. Sunada, Y. Nishiki, S. Mitsushima, Electrocatalysis. 8 (2017) 422–429. 25 EIS measurements of Ni and LixNi2-xO2/Nis
Ni: OER of low frequency arc increase with potential cycling 800oC: Relatively small OER and surface resistance of low and high frequency arcs were observed. 1000oC: Relatively large OER and surface resistance of low and high frequency arcs were observed.
S. Fujita, I. Nagashima, Y. Sunada, Y. Nishiki, S. Mitsushima, Electrocatalysis. 8 (2017) 422–429. -1 26 Tafel plot of the SSV at 5 mV s on the Ni and LixNi2-xO2/Ni
• Activity of Ni decreased with potential cycling with simultaneously formation Ni(IV) around 1.55 V vs. RHE
• Activities of the LixNi2-xO2/Nis increased with potential cycling without Ni(IV) formation x = 0.57
x = 0.57 x = 0.14
x = 0.14
Electrolyte IR free
S. Fujita, I. Nagashima, Y. Sunada, Y. Nishiki, S. Mitsushima, Electrocatalysis. 8 (2017) 422–429. 27 CVs of before and after potential cycling
x = 0.57 • Peaks of Ni(II)/Ni(III) for both Ni and LixNi2-xO2/Nis increased with potential cycling x = 0.57 • Peaks of Ni(II)/Ni(III) for 1000oC prepared was the most stable in these electrode.
x = 0.14
x = 0.14
S. Fujita, I. Nagashima, Y. Sunada, Y. Nishiki, S. Mitsushima, Electrocatalysis. 8 (2017) 422–429. 28 Control of (Li)NiO layer by thermal decomposition
Advantage of LixNi2-xO2/Ni • Improvement of the stability for specific activity without Ni(IV) formation
Disadvantage of LixNi2-xO2/Ni • IR loss of electronic resistance of the (Li)NiO
Solution: Control of (Li)NiO layer to thinner and denser by thermal decomposition
• Low temperature preparation of 550oC for thermal decomposition and sintering
• Comparison of LiNO3-Ni(NO3)2 and LiNiO3-Ni(COOH)2 precursor
S. Fujita, I. Nagashima, Y. Sunada, Y. Nishiki, S. Mitsushima, Electrocatalysis, 10.1007/s12678-017-0439-x 29 Thermal decomposed oxide film resistances
Surface oxide resistance of the 2 0.5 acetate precursor electrode was =Nitrate
/ Ωcm / 0.4 the lowest in the LixNi2-xO2/Nis, and close to Ni because of the thin 0.3 =Acetate and dense with Li doped 0.2 electroconductive layer 2 8 0.1 Ni / Ωcm / 6 0 Oxide film resistance film Oxide 0 5 10 15 20 4 n×10-3 / cycle Precursor o 2 =LiOH, 1000 C
0 Oxide film resistance film Oxide 0 5 10 15 20 n×10-3 / cycle S. Fujita, I. Nagashima, Y. Sunada, Y. Nishiki, S. Mitsushima, Electrocatalysis, 10.1007/s12678-017-0439-x 30 SSVs at 5 mVs-1 of acetate and nitrate precursors
• Acetate precursor, which formed thin and dens layer, showed higher OER current and Tafel slope than the oxidation with LiOH • Nitrate precursor, which formed porous layer, showed degradation like as Ni 0 After 20K 0
Precursor = Ni
)
) 2 2
2 2 Before
- Acetate -1 Before - -1 After 20K
-2 -2 / A cm A /
Before cm A / After 20K geo
geo -3
i i -3 i i =Nitrate
-4 =LiOH, 1000oC -4 Log Log ( Electrolyte IR free Log ( Electrolyte IR free -5 -5 1.4 1.5 1.6 1.7 1.8 1.4 1.5 1.6 1.7 1.8 E / V vs. RHE E / V vs. RHE S. Fujita, I. Nagashima, Y. Sunada, Y. Nishiki, S. Mitsushima, Electrocatalysis, 10.1007/s12678-017-0439-x 31 Activity and stability for LixNi2-xO2/Ni of acetate precursor
Acetate precursor electrode showed the highest OER current
in LixNi2-xO2/Nis, and the most stable in these electrodes 0
) Precursor 2 =Acetate
/ A cm A / -1 =Nitrate Ni
[email protected] [email protected] V i -2 =LiOH, 1000oC
Log( Log( IR free 0 5 10 15 20 n×10-3 / cycle
S. Fujita, I. Nagashima, Y. Sunada, Y. Nishiki, S. Mitsushima, Electrocatalysis, 10.1007/s12678-017-0439-x 32 Conclusion for LixNi2-xO2/Ni anodes
In order to develop anti-reverse current AWE anode, surface modification of Ni with Li doped oxide has been investigated
• Li doping increased electronic conductivity of the surface oxide with high valent Ni • Appropriate Li doping increased OER activity of the surface oxide • Excess Li doping decreased OER activity with the change of rate determining step • Thin and dens (Li)NiO layer, which could be prepared with acetate precursor, showed the high activity and durability under potential cycling
Durable AWE with high performance would be developed with improvement of electrocatalysts 33 Contents
1. Introduction
2. Analysis of bipolar electrolyzer for alkaline water electrolysis
3. Active and durable anode for alkaline water electrolysis
4. Direct electrohydrogenation of toluene with water decomposition
5. Conclusion 34Hydrogen energy carriers & secondary batteries
Energy density of energy carriers is as ten times as batteries (ca. 1/10 of fossil energies) Energy carriers: Energetic materials for energy storage and transportation Pressurized Toluene / Liquefied hydrogen Liquefied ammonia hydrogen Methylcyclohexane Formula H2 H2 NH3 C7H8/C7H14 B. P. (oC) -253 -253 -33.4 101 Density(g/cm3) 0.0392(70MPa) 0.0706 0.682 0.769 H2 ΔG density (Wh/kg) 32,900 32,900 5,810 2,010 (Wh/L) 1,290(70MPa) 2,330 3,960 1,550 Secondary batteries: Energy storage systems Redox flow Na-S Lead acid Lithium ion Ni-MH Zn-Br
Active material 2+ 2+ LiMO2 / NiOOH / VO / V S / Na PbO2 / Pb Br2 / Zn (+)/(-) LiC6 MH energy density Theoretical 100 786 167 392 - 585 225 428 Actual 110 35 120 60 (Wh/kg) 35 Hydrogenation using renewable energies
Electrohydrogenation of toluene has the most highest theoretical energy conversion efficiency for energy carrier synthesis 88%（=1.08/1.23） of hydrogen production of water electrolysis Direct electrohydrogenation Uo = 1.08 V
CH3 CH3
+ 3 H2O → + 3/2 O2
Renewable energies Water electrolysis (storage) hydrogenation
CH3 CH3 3 H2O → 3H2 + 3/2 O2 Exothermal o + 3H2 ―→ U = 1.23 V (▲0.15 V) S. Mitsushima, Y. Takakuwa, K. Nagasawa, Y. Sawaguchi, Y. Kohno, K. Matsuzawa, Z. Awaludin, A. Kato, Y. Nishiki, Electrocatalysis. 7 (2016) 238–131. 36 Direct electrohydrogenation electrolysis
A new efficient energy carrier synthesis process Combination of electrohydrogenation and water decomposition
CH3 CH3 Cathode: + 6 H+ + 6 e- → Eo = 0.15 V vs. SHE
+ - o Anode: 3 H2O → 6H + 3/2 O2+ 6e E = 1.23 V vs. SHE CH3 CH3 o Overall： + 3 H2O → + 3/2 O2 U = 1.08 V
CH3 e- O2 H+ H2O (MCH)
Cathode membrane CH assembly: PtRu/C 3 catalyst layer on DSE electrode Nafion 117 (TL) 37 Polarization curves for Pt/C and PtRu/C
•Onset potential of reduction was positive •Gas evolution was not observed •MCH was an only product •PtRu/C had larger reduction current than Pt/C 0 Cathode: Pt/C or PtRu/C TL100% - - e + e
H 2 - Pt/C Increase of MCH -80 reduction current
PtRu/C
mAcm /
TL H2 i Anode / Reference: Pt/C -160 60oC iR-free Fig. Configuration of a -0.04 0 0.04 0.08 membrane half cell . E / V vs. RHE S. Mitsushima, Y. Takakuwa, K. Nagasawa, Y. Sawaguchi, Y. Kohno, K. Matsuzawa, Z. Awaludin, A. Kato, Y. Nishiki, Electrocatalysis. 7 (2016) 238–131. 38 Hydrogenation current as a function of temperature •PtRu/C had larger reduction current than Pt/C below 70oC •PtRu/C had the maximum currents at 60 oC, while Pt/C increased with temperature / This might be affected by the adsorption of TL and MCH q / oC
80 60 40 )
2 Pt-Ru/C - 70
1.8 2
60 -
50 / mAcm /
i 1.6 40 -
Pt/C mAcm /
i -
log( log( 30 1.4 TL100% 0 V vs. RHE 20 2.8 3.0 3.2 T-1 x 103 /K-1 S. Mitsushima, Y. Takakuwa, K. Nagasawa, Y. Sawaguchi, Y. Kohno, K. Matsuzawa, Z. Awaludin, A. Kato, Y. Nishiki, Electrocatalysis. 7 (2016) 238–131. 39 Anode for oxygen evolution reaction
• TL inhibited OER and accelerated degradation for IrO2/Ti • TL inhabitation was suppressed for IrO2-Ta 2O5/Ti and IrO2-Ta 2O5-ZrO2/Ti • Activity improved not only increase of effective surface area by Ta and ZrO2 addition without TL with TL IrO2-Ta 2O5-ZrO2/Ti 40 IrO /Ti Ir/Ta/Zr=50/20/30
2 2 600 - 30 -2
2 (13.1 gm -Ir) -
20 / mA cm / mA 400 i 10 0 / mA cm mA / 1.5 1.6 1.7 IrO2-Ta 2O5/Ti i E / V vs. RHE 200 Ir/Ta=50/50 (7.2 gm-2-Ir) 60oC 0 IrO2/Ti 1.2 1.4 1.6 (12.2 gm-2-Ir) E / V vs. RHE Nagai, K. Nagasawa, and S. Mitsushima, Electrocatalysis, 7, 441–444 (2016) 40 Flow field design for cathode
Channels Ribs in flow field
a) Parallel flow channel c) Interdigitated flow channel
b) Serpentine flow channel c) Porous carbon flow field K. Nagasawa, A. Kato, Y. Nishiki, Y. Matsumura, M. Atobe, S. Mitsushima, Electrochim. Acta. 246 (2017) 459–465. 41 LSV curves for various flow fields • The cell voltages: Porous < Parallel < Interdigit < Serpentine • Activation overpotentials were almost same for all flow fields •0.18 ~ 0.25 Wcm2 of internal resistance could not explain the difference of the cell voltages • EIS showed cathodic mass transfer resistance affected to the cell voltages 2.5 60oC Serpentine 10% TL Interdigit Parallel
2.0 Porous
/ V / U 1.5
1.0 0 0.1 0.2 0.3 0.4 0.5 i / A cm-2 K. Nagasawa, A. Kato, Y. Nishiki, Y. Matsumura, M. Atobe, S. Mitsushima, Electrochim. Acta. 246 (2017) 459–465. 42 Current efficiency as function of current for 10% TL
• Porous flow field showed 100% of current efficiency up to 0.15 Acm-2 • Parallel was better than serpentine and interdigit a little • This turn is as same as cathodic reaction resistance 100 10% TL ℎ푦푑푟표𝑔푒푛푎푡𝑖표푛 휀 = 푎푝푝푙𝑖푒푑 푎푝푝푙푖푒푑 −퐻2 푒푣표푙푢푡푖표푛
. % . 90 =
푎푝푝푙푖푒푑 F F e
80 Serpentine Parallel Interdigit Porous 0 0.1 0.2 0.3 0.4 0.5 i / A cm-2 K. Nagasawa, A. Kato, Y. Nishiki, Y. Matsumura, M. Atobe, S. Mitsushima, Electrochim. Acta. 246 (2017) 459–465. 43 Decrease of H2 bubble residence with flow field catalyst
• H2 bubble reacts with TL on Pt catalyst • Interruption of TL transfer by H2 bubble is suppressed → Cathode reaction resistance decreases with hydrogenation catalyst on flow field Decrease of local Cathode catalyst layer TL concentration
CH3 CH3 O2 O2
H2O H2O ←H+ ←H+ H2 H2 CH CH3 3 H O H O X 2 2 H2O H2O Anode Anode Porous carbon flow field Pt catalyst loaded porous without Pt catalyst carbon flow field S. Mitsushima, K. Nagasawa, A. Kato, Y. Nishiki, 232nd ECS Meeting (2017) #1673 44 Improvement of current distribution with anode structure
Fine mesh anode makes uniform current flow lines in thin electrolyte membrane to decrease apparent reaction resistance caused by charge and mass transfer
Conventional mesh anode Conventional mesh + fine mesh anode Cathode catalyst layer
CH3 CH3
CH3 CH3
Current flow lines in proton exchange membrane S. Mitsushima, K. Nagasawa, A. Kato, Y. Nishiki, 232nd ECS Meeting (2017) #1673 45 Cell voltage reduction
Cell voltage reduced with the improvement of flow field and anode structure Parallel grooved channel + conventional mesh anode 2.2 Porous carbon flow field + conventional mesh anode Pt loaded porous carbon flow field 1.8 + conventional mesh anode / V / Pt loaded porous carbon flow field U + fine mesh anode 1.4 10% TL 60oC 1.0 0 0.1 0.2 0.3 0.4 0.5 i / A cm-2 S. Mitsushima, K. Nagasawa, A. Kato, Y. Nishiki, 232nd ECS Meeting (2017) #1673 46 Enhancement of current efficiency Current efficiency increased with the improvement of flow field and anode structure ℎ푦푑푟표𝑔푒푛푎푡𝑖표푛 푎푝푝푙𝑖푒푑 − 퐻 푒푣표푙푢푡𝑖표푛 휀 = = 2 F 푎푝푝푙𝑖푒푑 푎푝푝푙𝑖푒푑 100 60oC, 10% TL 95 Pt loaded porous carbon flow field 90 + fine mesh anode Pt loaded porous carbon flow field
. % . + conventional mesh anode
F 85 e Porous carbon flow field 80 + conventional mesh anode 75 Parallel grooved channel + conventional mesh anode 70 0 0.1 0.2 0.3 0.4 0.5 i / A cm-2 S. Mitsushima, K. Nagasawa, A. Kato, Y. Nishiki, 232nd ECS Meeting (2017) #1673 47 Conversion under one through operation • Cell voltage was almost independent from flow rate of TL • Conversion was almost as same as theoretical value, and 1.7 V @ 0.4 A cm-2 with more than 90% conversion and 95% current efficiency Flow rate / mL min-1 △, ▲: 10 1.0 0.5 100 2.5 Porous carbon flow field + conventional mesh anode 80 2.0 ○, ●: Pt loaded porous carbon flow field
60 1.5 + fine mesh anode
/ V / conversion. % 40 0.4 A cm-2 1.0 U 100%TL 20 60oC 0.5 One through Measured 0 0.0 0 20 40 60 80 100 Theoretical conversion. % S. Mitsushima, K. Nagasawa, A. Kato, Y. Nishiki, 232nd ECS Meeting (2017) #1673 48 Conclusion for direct energy carrier synthesis
As a high energy conversion efficiency for energy carrier synthesis process, membrane electrolysis for toluene hydrogenation with water decomposition is proposed
Present performance is 1.7 V of cell voltage at 0.4 A cm-2 with more than 90% conversion and 95% current efficiency
• Hydrogen is an energy carrier for artificial hydrogen redox system to decrease carbon dioxide emission
• Electrolysis is the most realistic technology to produce chemical energy using renewable electricity with development for fluctuated power supply
• Alkaline water electrolysis is less expensive hydrogen production process and will be able to improve durability under potential cycling to connect renewable energies
• Direct electrohydrogenation of toluene with water decomposition, which is very efficient energy career synthesis process with renewable energies 50 Acknowledgment
These works were supported and/or cooperated by following funding agencies, universities, and industrial partners. The Institute of Advanced Sciences (IAS) in YNU is supported by the MEXT Program for Promoting the Reform of National Universities. I appreciate person concerned.