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ALMA forum 20182018/11/10, Tokyo

Magnesiumasan energy carrier
I. Nakatsugawa
National Institute of Advanced
Industrial Science (AIST), Japan2Content◼ Introduction◼ Magnesium as thermal energy carrier◼ Magnesium as hydrogen carrier◼ Magnesium as thermal energy + hydrogencarrier◼ Magnesium as electrical energy carrier◼ Recycling of used magnesium◼ Concluding remarks

What is “energy carrier”?
Definition： Chemical substance which serves as a carrier of energy
transportation / storage
lossesPrimary
EnergySourceEnergyFor Energy

lossesEnergyCarrier

End Useη2

η1Conversion #1

Net Energy
To Society

Conversion #2

Fossil fuels-Sunlight
Earth activity

Renewable electricpower-SolarHydro
Geothermal
Tidal power- Coal- Oil- Natural gas

For renewable energy- Hydrogen- Ammonium- Methanol- Magnesium- Aluminum

Energy carrier that
contributes to reduce
environmental impact andsecure energy
https://commons.wikimedia.org/w/index.php?curid=16124211

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Requirement for energy carrier1)◆ Abundant (low cost)◆ Convert to various kinds of energy◆ High energy conversion efficiency◆ User friendly◆ Available when and where needed◆ Stockpile in large/small volume◆ Transport easily in short/long distance◆ Release no harmful substances after use
There are no energy carrier which can satisfy all therequirements. ‘Hydrogen’ is considered as the mostpromising candidate.
1) A. Ishihara and K. Ohta, Introduction to renewable energy, Nikkankogyo (2012),141.

Magnesium working with hydrogen carrier

Magnesium it is expected to work alongside with H2 energy
carrier.
Liquid Hydrogen

Combustion（Heat）

Hydrogen
MethanolRenewableelectric power
Organic hydride-SolarHydro
Geothermal
Tidal powerNH3

BatteryMgH2
Magnesium（Electricity）

Conversion between
energy carriers

MagnesiumOxide/hydroxide
5Magnesium as thermal energy carrier
Difficult to use as
thermal source

Apply tosteam turbine

Unutilizedheat

Property of heat storage material 2)
Heatstorage

Material(reaction)

Operatingtemp.

StoragedensityLatentheat
storageIce (ice⇔ water)

0℃

0.34 GJ/m3

Erythritol

121℃

0.48 GJ/m3

MgO+H2O⇔ Mg(OH)2350℃

CaO+H2O⇔Ca(OH)2500℃

Chemicalheatstorage

1.0~1.5 GJ/m3

Snowcollection site
(120,000 m3)

Heat storage material to utilize
waste heat effectively
1) S. Kobayashi, Panasonic Technical Journal, 62(2016)121-125.
2) Y. Kato, High Density Thermal Energy Storage
Workshop (2011).

Sapporo Chitose Airport utilizes collected snow forcooling in summer.
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7Magnesium as thermal energy carrier
MgO + H2O = Mg(OH)2 -DH = 81 kJ/mol

Heat pump: A device that transfers heat
energy from cold area to hot area using
heat storage material

Heat storage

Conversion
rate

Heat release
Chemical heat pump based on MgO/Mg(OH)2 1),2)

Regeneration
efficiencyWater content

3.76 kg

Water collection

2.96 kg

Utilization rate

78 %Theoretical heat collection

13616 kJ

Released heat collection

8400 kJ

Regeneration efficiency

62 %1) Y. Kato, High Density Thermal Energy Storage Workshop (2011).
2) S. Kobayashi, Panasonic Technical Journal, 62 (2016)121-125.

Magnesium as hydrogen carrier
Magnesium can absorb H2 up to 7.6 wt%. High desorption temperature(~350 ℃) and sluggish reaction kinetics are concerned.
A process of H2 production at room temperature via hydrolysis of MgH2 isdeveloped.
MgH2 + 2H2O → Mg(OH)2 + 2H2, ΔH = -268 kJ/mol MgH2 = Mg + H2 ΔH = 75 kJ/mol(a) 0.3~0.5 L/min.
Evolution of H2 gas via hydrolysis of MgH2
with different concentration of citric acid atroom temperature1).

(b) 10 L/min.

MgH2 reactors2).
1) I. Nakatsugawa, unpublished results2) http://www.biocokelab.com

8Magnesium as hydrogen carrier

Fuel cell

MgH2 powder and 40W MgH2 FC portablebriquette form1)
power generator1)

Slowaging

Moistureretainingflexible

MgH2

Additives for health care, cosmetics1)
1) http://www.biocokelab.com

Mg(OH)2H2 production system based on the hydrolysis ofMgH2 2)2) http://www.safehydrogen.com/technology.html
9Mg + 2H2O → Mg(OH)2 + H2
DH = -924 kJ/mol
Mg + H2O → MgO + H2
DH = -602 kJ/mol

Combustion of H2
H2 + ½O2 → H2O
DH = -285 kJ/mol

H2 yield (cm3/cm3)

Corrosion of Magnesium

Reactioncompleteness (%)

Metal-water reaction

H2 yield (cm3/g)

Magnesium as thermal energy + hydrogen carrier

Hydrogen yield and reaction completeness of various metals with hotwater1).
1) Y. Yavor et al, Int J Hydrogen Energy 40 (2015) 1026-1036.
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Magnesium as thermal energy + hydrogen carrier
Feasibility study of Mg combustion with 3-5 kW pilot scale
Mg particles(20-70mm)
Pressurized air

Pressurized N2

Scheme of Mg/air ignition and combustion
process

Results

Self sustained Mg flame

Calibration of aerosol andexhaust gas• Combustion completion ratio : 91-100%• Mg/O2 molar ratio : 1.8-2.3

Task• Emission of NOx and fine particles
1) Y. Yavor et al, Int J Hydrogen Energy 40 (2015) 1026-1036.

11Magnesium as electrical energy carrier

12Magnesium as electrical energy carrier
AnodeStandard potential(VNHE)ElectroAh/gchemical
3
equivalent Ah/cm

Primary /secondary battery

Fuel cell

Basic feature

H2

CH3OHLi

Mg

Al

Zn

0-

-3.01

-2.38

-1.66

-0.76

26.59

5.02

3.86

2.20

2.98

0.82

-

4.58

2.06

3.8

8.1

5.8

As electric energy carrier
AnodeH2CH3OHLiMg

AlZn

Cell performance〇△◎△△◎

Scalability

△△△△

△

△

Compatibility◎◎△〇〇×Safety××△〇〇〇Reserves〇〇×〇〇△Price△〇×△△△14Magnesium as electrical energy carrier
Mg-MnO2 battery

Primarybattery

Mg water-activatedbattery
Mg- air battery

Mg fuel cell
（supply anode/electrolyte）

Mg-MgX battery

Mg battery

Secondarybattery

Mg-air battery
Mg- molten salt
battery
Ni-MgH2 battery

MgH2 desorption

Fuel cell（H2 supplysource）

MgH2 hydrolysis
Mg-hot wateroxidation

Mg-based batteries* blue is under
R&D stage

Commercialized Mg primary batteries
MnO2dry-battery

Water-activatedbattery

Airbattery

ExampleCathodeSea waterElectrolyteOCP (V)Potential at
5mA/cm2 (V)Energy density(Wh/kg)

Comment70
DiscontinuedSpecialuse15

Water activated Mg batteryPrinciple
Anode：Mg → Mg2+ + 2e
Cathode：2MnO2 + H2O + 2e → Mn2O3 + 2OHOperation• Start discharging by adding water• Stack 3-4 cells to supply voltage ~6.4V• Illumination for a week by adding water
LED① Current
collector（Cu)② MnO2 catalyst③ Separator④ Anode (Mg)

Size
WeightCasing

Add water (1~2 ml)
Structure of LED light

Illuminance (lux)FeatureTime (day)Time change of illuminance of LED light(30 cm distance from light source)1)
1) I. Nakatsugawa: 3rd Mg technical seminar, Japan Magnesium Association （2016).

Water activated Mg battery

Change of cell voltage under constantdischarge of 2.4 mA/cm2
Nyquist diagram of water activated Mg battery at
the terminal voltage.

••••
Dependence of energy density and current
efficiency on discharge current density.

Anode and cathode impedance increase withwater injection cycle.
Warburg impedance was observed at cathode,suggesting the depression of MnO2.
Gravimetric energy density took the maximum
at 0.48mA/cm2.
Current efficiency was decreased by staking
cells.
I. Nakatsugawa, H. Nakano: J. Jpn Inst. Light Metals, 67 (2017) 503-510.

18Mg - air battery
Principle
Anode：Mg → Mg2+ + 2e
Cathode：1/2 O2 + H2O + 2e → 2OH-

LoadFeature• Start discharging by adding 5~10% NaCl
• Continuous operation is possible by replacingused Mg anode and electrolyte.
• The current efficiency is ~60 %.

① Cathode② Electrolyte③ Anode（Mg)

O2O2Electrolyte

catalyst

2.2W unit cell

30W stacked cell

An example of Mg-air battery1)

Gas diffusion layer(water repellent)

Structure of Mg-air battery1) photo: courtesy of ARV corporation, Japan.

Mg - air battery

Discharge performance of Mg-air cell at 10 mA/cm2

C

40 mA cm-2

ACA

Anode

Cell enclosure

5 mA cm-2

Appearances of Mg anode after discharging

Current efficiency of Mg-air battery.

•••

Stable discharge is possible up to 40 mA/cm2.
Adherent reaction product tends to form at
higher discharge current.
Current efficiency increases with higherdischarge current.
I. Nakatsugawa, Y. Chino, H. Nakano, J. Power Sources, submitted.

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Magnesium as electrical energy carrier
Verification test of Mg-air battery (MAB) as an emergency power supply

EV1)

Trailer house2)

275 Wh unit cellController
Solar power

Mg-air battery
Li-ion battery

stack of 100 unit cells
1) photo: courtesy of ARV corporation, Japan.
2) photo: courtesy of Seven corporation, Japan.

MAB: 300 Wh x 12-16pcs

LIB: 2.5kWh
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Recycling of used magnesium

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Recycling of used magnesium

Hot water oxidation, battery
Mg + 2H2O → Mg(OH)2 + ½ H2
Mg + H2O → MgO + H2

Hydrolysis
MgH2 + 2H2O → Mg(OH)2 + H2

BatteryMg + 2e → Mg2+
½ O2 +H2O → 2OH-Mg + 1/2O2 +H2O = Mg(OH)2Mg
Recycle, Reuse of MgO/Mg(OH)222

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Recycling of used magnesium
Reuse MgO/Mg(OH)2 as chemical additives
Collection

Mg(OH)2
slurryDry~100℃

Mg(OH)2
powderFiring~350℃

MgO
powderMgO powder- Flue gas
desulfurization- Neutralizer ofacid waste- Additives for plastic- Ceramics- Additives for fuel oil- Insulator- Refractory material- Additives for cement- Fertilizers

Global production of Magnesium compound : 7,000 ktpy (2014) 1)
 Magnesium metal :900 ktpy (2014)1)
1) http://www.discoveryinvesting.com/blog/2015/8/10/a-closer-look-at-magnesium

24Reduction to Mg metal⚫ Thermal reduction: MgO → Mg + ½O2⚫ Electrolysis: Mg2+ + 2e → Mg

(MgO + C → Mg + CO)(MgCl2 → Mg + Cl2)

Electrolysis of molten MgO1),2)
Cathode：Mg2+ + 2e → Mg
Anode：O2- → 1/2O2 + 2eSOM：Y-stabilized ZrO2
Operation T.：1150~1300℃
Molten Mg efficiency：48~63%

Mass transfer
IR drop
Contact resistanceElectrolysis

Principle of Mg electrolysis using SOM.

1) X. Guan et al., J. Sustain. Metall., 2 (2016) 152–166.
2) http://energy.gov/sites/prod/files/2014/03/f11/lm035_derV-I curve of Mg
reduction using SOM. ezinski_2011_o.pdf

25Conclusion
Evaluation of Magnesium as energy carrier
Requirement
Abundant (low cost)

Evaluation△

Easily converted from/to variouskinds of energy
High energy conversion efficiency△Easy to handle by consumers〇

Available when and where needed〇〇

Stockpile large / small quantity

Easy to transport in short/longdistanceDo not release harmful substances
after use△〇〇

Comment
Abundant Ores. Metal price is high.
The cost competitive and green
production is anticipated.
Need economical/green refining
process for full-scale operation
Need to improve current efficiency
for electrical energy application.
In the forms of plate, consolidated
powder and slurry are available
Mg and MgH2 are stable in theatmosphere. Attention to powder
explosion.
NO2 is released in hot wateroxidation process.

Thank you!

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