Advances in the Technology of Solid State Hydrogen Storage Methods Using Novel Nanostructured Materials

총 설

나노구조물질을 이용한 고체수소저장 기술 동향 Renju Zacharia^{·김근영·남기석†}

전북대학교화학공학과

561-756

1

664-14 (2005

7

12

, 2005

8

10

)

Advances in the Technology of Solid State Hydrogen Storage Methods Using Novel Nanostructured Materials

Renju Zacharia, Keun Young Kim and Kee Suk Nahm^†

National Nanotechnology Integration Center and School of Chemical Engineering and Technology, Chonbuk National University, 664-14, 1 Ga, Duckjin-dong, Duckjin-gu, Jeonju, Jeonbuk 561-756, Korea

(Received 12 July 2005; accepted 10 August 2005)

요 약

수소저장기술은수소경제를달성하기위해개발해야할핵심요소기술이다

.

.

(nanostructured carbon materials),

(metal organic framework, MOFs),

(metal hydrides),

(clathrate hydrates),

(complex

chemical hydrides)

.

수소저장용량은고체의표면적에비례하여증가함을알수있었다

.

.

Abstract −

This article provides a panoramic overview of the state-of-the-art technologies in the field of solid-state hydrogen storage methods. The emerging solid-state hydrogen storage techniques, such as nanostructured carbon mate- rials, metal organic framework (MOFs), metal and inter-metal hydrides, clathrate hydrates, complex chemical hydride are discussed. The hydrogen storage capacity of the solid-sate hydrogen storage materials increases in proportion to the surface area of the solid materials. Also, it is believed that new functional nanostructured materials will offer far-reach- ing solutions to the development of on-board hydrogen storage system for the application of the transportation vehicles.

Key words: Renewable Energy, Hydrogen, Nanostructure Materials, Clathrates, Metal Organic Frame Works, Metal Hydrides, Solid-state Hydrogen Storage, Greenhouse Gases

1. 서 론

올해들어기후환경협약이실질적으로가동되고

,

.

.

,

[1].

[2, 3].

적에가장부합되는미래의에너지원이다

.

수소는지구상어디에나풍부히존재하는물로부터지속적으로 제조할수있어서그원료가고갈될염려가없으며

,

[4, 5].

그러나수소를에너지원으로사용하는수소에너지경제가실현되기 위해서는수소의제조

,

,

직산적해있다

[6-8].

실화하는데가장중요한기술이다

[9].

술이다

[10, 11].

조건은수소를고밀도로저장하여야하며

,

.

†

To whom correspondence should be addressed.

E-mail: [email protected]

장기술은압축기체수소저장

(compressed gas hydrogen storage)

(liquid hydrogen storage)

,

.

.

(carbon nanotubes, CNTs),

(metal-organic frameworks, MOFs),

(metal hydrides),

(complex chemical hydrides),

(clathrate hydrates)

구개발되고있다

[12-15].

/

에관한연구가초보단계이지만장기적으로수송용수소저장기술을 해결해줄것으로예상되어국내외적으로많은관심을끌고있다

.

이논문에서는위에서언급한수소저장매체를중심으로고체수소 저장기술개발현황을고찰하고향후기술개발방향을논의하였다

.

먼저기존화석연료의문제점을점검하고수소에너지경제로전환의 필요성을제시하였다

.

.

.

2. 수소에너지경제의 필요성

화석연료는인류에게가장중요한에너지원으로크게석유

,

가스

,

[16].

형태로

,

,

,

.

렵다

. Fig. 1

내고있다

[7, 16].

개발도상국들의경제성장속도가빠르게진행되면서에너지소비 가급속히증가되어국제석유가의급등은당분간피할길이없게 되었다

.

40

,

는

60

,

164

것으로평가되고있다

[7, 15].

량은감소하여화석연료를기반으로하는경제시스템이한계에도 달하여에너지의안전한공급을위해서는재생가능한에너지경제 로의전환을과감히시도하여야한다

.

화석연료의사용으로인해인류가직면하고있는또하나의문제 는화석연료가연소하면서발생하는유해가스가환경을크게오염 시키고있으며

CO

하여생태계의파괴를초래하고있다

[17, 18]. CO

러지게증가시키는산업분야는

Fig. 2

,

,

전력산업

[19, 20]

,

량의

70

(Fig. 3[22]).

2025

.

수송산업의연료를재생가능한청정에너지로대체하면에너지 효율을높일수있으며

,

.

교토기후협약의정서의서명은

CO

스템을구축하게하였다

[23, 24].

Fig. 1. The global variation in the production and consumption of fos- sil fuels. All fuels are converted into the units of million tones of oil equivalent (Mtoe). The production and consumption between 2003 and 2040 are predicted based on past data [7].

Fig. 2. The contribution of various sectors to the emission of green- house gases(

) in U.S.[21]. It can be seen that the transporta- tion sector contributes significantly to increased emission of oxides of carbon and nitrogen, and VOCs.

Fig. 3. The relative proportions of fossil-fuel use in U.S. by different

transportation modes projected to year 2025 [22]. It is evi-

dent that the light trucks and cars that are predominantly

used for private conveyance use considerable proportion of

the fuels.

기관의에너지효율을크게향상시킨다

.

35

85

[25].

30

,

60

[26, 27].

위에서언급한경제적

,

.

.

.

3. 수소저장기술

수소는무색

,

,

,

.

(

75

)

.

물리적상태의변환이필요하다

(Fig. 4).

수소는−

262

C

70.6 kg/m

, 0

C

1 bar

0.089 kg/m

.

3

(triple point)

(critical point)

70.8 kg/m

(

253

C)

(Fig. 4

).

Van der Waals

.

.

.

한압력에따라수소의저장량은증가하며

700 bar

서는약

10 wt

.

압을견뎌주는용기재질의개발과실제이용에는위험성이항상뒤

따른다는문제점이있다

.

.

.

,

(specific energy)

(energy

density)

.

(net energy)

결정한다

.

/

(kWh/m

)

.

,

1/10

준으로낮다

[29].

저장기술은수송용응용에적합한수소저장기술이아니며

,

.

장기술의개발이필요하다

.

Fig. 5

커니즘에서잘예측할수있는바와같이높은표면적을갖는고체 저장재료에흡착의수단으로저장하거나

,

,

.

Fig. 6

.

4. 수송용 수소저장기술 개발 목표

수소를수송용연료로사용할때수소저장용량의목표치는나라 마다다소다르다

.

,

2,000 kg

600-700 km

목표를삼는반면

,

1,000 kg

으로기술개발의목표치를설정하고있다

[32].

(DOE)

US

(US Council for Automobile Research)

FreedomCAR

[33].

world-energy network

(WE-NET)

[34].

Fig. 4. The primitive phase diagram of hydrogen. Figure adapted

from [28]. Fig. 5. Schematic model of hydrogen adsorption on various materi-

als [30].

해필요한중요한수소저장기술요소들은비에너지

,

,

,

,

. FreedomCAR, WE-NET, IEA (International Energy Agency)

2010

Table 1

[32]. Table 1

이

FreedomCAR

.

Table 2

2010

2 kWh/kg

이다

[35].

산한다

.

6.5 wt

(2 kWh/kg)

[33].

비에너지측정시시스템중량에는연료공급인프라와관련된하 드웨어의중량도포함되어있다

.

준이되는척도는

Table 1

Table 2

FreedomCAR

.

마이크로

/

매체로많은관심을끌고있다

[13-14, 18].

연구개발되고있는재료는탄소나노튜브

(carbon nanotubes, CNTs),

유기금속구조물

(metal-organic frameworks, MOFs),

(metal hydrides),

(complex chemical hydrides),

(clathrate hydrates),

(zeolites)

.

/

.

.

다음에는이러한새로운고체수소저장물질의수소저장특성에대 하여논의하겠다

.

.

FreedomCAR

,

수소저장용량을기준으로두고논한다

.

/

체적수소저장용량을보인다면정지형대량에너지저장분야에서실 질적으로쓰일수있을것이다

.

5. 고체수소저장기술

5-1.

/

(metal/inter-metal hydrides)

금속과금속간합금이

250-650 K

소와반응한다는것은이미

1960

[36]. 2

란탄족및악티늄계열원소

, Ti, V

형성하는것으로알려져있다

[36].

2

성질을띄고있으며일반적으로금속수소화물이라명명한다

.

MH

라다양한상을형성한다

[37].

물중에가장잘알려져있는수소화물은

AB

H

.

A

,

,

(Mg)

2

,

B

(Al)

H

.

B

Ni, Co, Cr, Fe, Mn

금속이다

[37].

소저장체적밀도가극히높다는것이다

.

LaNi

115 kg/m

[28].

/

/

-

-

(pressure-composition-temperature, PCT)

/

.

은다음으로나타낸다

[36].

여기서∆

Q

van’t Hoff plots

. Fig. 7

van’t Hoff plots

[38].

비록금속간수소화물이높은수소저장량즉

, H/M

1

AB

+ xH

AB

H

+

Q Table 1. Technical benchmarks and selection criteria for on-board

hydrogen storage system proposed by different national and international organizations [32]

Storage parameter DOE WE-NET IEA

Gravimetric capacity (wt

) Volumetric capacity (kg H

/m

) Desorption temperature (

C) Cycle life (number) Refueling time (min)

6.5 6.2 NA 500

5

>3

<100 NA

>5000 NA

NA 5

<100 NA NA

Table 2. R&D targets for on-board hydrogen storage system for years 2010 and 2015. Based on the data from [33]

Storage parameter 2010 2015

Gravimetric capacity (kWh/kg) Volumetric capacity (kWh/L) Storage system cost ($/kg H

) Fuel cost ($/gallon gas equivalent) Min. and Max. operation temperature (

C) Cycle life (number)

Transient response time (s) Safety

1.5 2 1.5 4

−

30/85 1000 0.75 Meets applicable

standard

2.7 3 1.5 2

−

40/85 1500 0.5 Meets applicable

standard Fig. 6. Stored hydrogen by volume and by mass. The graph shows

volumetric hydrogen density

versus gravimetric hydrogen density

for various materials to store hydrogen by bulk absorption, surface adsorption, or compound formation; dec. is the decomposition temperature, m.p. is melting point, and b.p.

is boiling point. The container is not taken into account [31].

게나타내지만전이금속이나란타늄계원소의중량이높기때문에 일반적으로

1-2 wt

.

Mg

2

3.3-7.7 wt

.

/

1-10 bar

270-360 K

.

Mg

ZrNi, ZrMn

.

1 wt

.

수소화물을형성하는

7

Table 3

.

/

hysteresis

,

,

,

/

,

.

/

탈착속도가많은응용에서가장중요한기술적인자가된다

.

AB

.

A

A

,

B

. AB

것이다

. PCT

응을통해거의

2

.

Fig. 8

LiNi

Ni

Sn

2

.

체심입방구조를갖는수소흡착합금은높은수소저장량때문에많 은관심의대상이되고있다

[39].

Ti-V-Mn, Ti-V.Cr, Ti-Cr-(Mo,Ru)

3 wt

된다

.

PCT

2

2

[39]. 2

.

금속

/

(Mg)

.

2

MgH

7.6 wt

[40].

Mg

MgH

/

.

300-400

C

.

MgH

[41].

.

Mg

.

더빨리흡착되어산화막을형성하여수소의흡착을막는다

[41].

그러나이산화막은수소분위기에서

400

C

면제거된다

[42].

Mg

서수소분자가서서히해리되기때문이다

.

Ni

Pd

Mg

. Mg

Ni

Ni

의조성이

0-50

/

단조롭게증가한다

[43].

MgNi

성

,

.

Density functional theory

Mg

MgH

Fig. 7. Van’t hoff plots of some matals and intermetal alloys [38].

Table 3. The families of hydride forming intermetallic compound, their prototypes and structure [28]

Intermetallic compound Prototype Structure AB

AB

AB

A

B

A

B

AB A

B

LaNi

ZrMn

CeNi

Y

Ni

Y

Fe

TiFe Mg

Ni

Haucke phase, Hexagonal Laves phase, Hexagonal, cubic Hexagonal

Hexagonal cubic cubic cubic

Fig. 8. The change in the plateau pressure of LaNi

with substitution

of Ni with Sn [36].

인함을알수있다

[44].

bulk-to bulk

155 meV

.

bulk-to bulk

2.4×10

s

.

bulk

500 meV

.

4×10

s

Mg

/

.

.

[45-

47].

그레인경계주변에서수소의확산속도가빨라지기때문으로설명 된다

[48].

금속수소화물에질소가결합된금속

-N-Hx

(amides)

태는최근에

Chen

5 wt

[49].

고상재료중에서금속수소화물은수소용수소저장재료로이용하 기위한기술적연구가상당한수준으로이루어져상업화에가까운 수소저장재료이다

. Daimler-Benz, Toyota, Mazda

보유하고있다

[32].

는열전달연구가활발히진행되고있다

.

[30].

5-2.

(complex chemical hydrides)

Li, Mg, B

1, 2, 3

[50, 51].

금속착수소화물은중심원자가

AlHx

(alanate hydrides), BHx

(metal hydrobirates)

라고명명하기도한다

.

NaAlH

,

LiAlH

,

LiBH

, KBH

, NaBH

.

.

Mg

FeH

, Al(BH

)

등과같은금속착수소화물은수소저장밀도가

150 kg/m

[9].

LiBH

(18 wt

)

타내는물질이다

[9, 52].

,

높은수소

/

.

.

금속착수소화물의전형적인예는

NaBH

(sodium borohydride)

.

Fig. 10

(a)

(tetrahedral structure)

,

.

금속착수소화물의급격한수소화

/

NaAlH

.

2

[51, 53].

각반응단계에서는

3.7, 1.9 wt

5.6 wt

[53].

(1)

의수소분해공정은가역적이지만실제응용에알맞는조건에서

반응이일어나지않는다

[51].

Ti

용함으로서적당한조건에서도가역적인반응이일어난다

[38].

(nuclear magnetic resonance study)

Ti

NaAlH

의수소화

/

즘을밝히는연구도최근에활발히진행되고있다

[54].

된

Ti

. Fig. 11

FreedomCAR

2010

년과

2015

하였다

[55].

소저장중량및부피용량은

FreedomCAR

2010

장량을초과하고있다

.

.

그러나금속착수소화물은수소방출공정에서높은온도를필요로

3NaAlH

Na

AlH

+ 2Al 3H +

Na

AlH

3NaH Al 32---H + +

Fig. 9. Hydrogen sorption kinetics at 623 K of commercial magne-

sium hydride and of magnesium + graphite ball-milled under 4 bar of hydrogen at 563 K during 5 hrs (a) desorption under 0.07 bar of hydrogen, (b) adsorption under 10 bar of hydrogen.

Fig. 10. Molecular structure of NaBH

. (a) Sodium, boron and hydro-

gen are represented by green, blue and red spheres. Right

panel (b) shows the crystal structure of the same.