Single-layerMoS2 Nanopores asPowerGenerators

PI: Narayana R. AluruPresenter: Mohammad Heiranian

DepartmentofMechanicalScienceandEngineering,BeckmanInstituteforAdvancedScienceandTechnology,

UniversityofIllinoisatUrbana−Champaign

Node PeakMemoryGB/s

BlueWater CrayXE 102

NICS KrakenCrayXT 25.6

NERSC HopperXE 85.3

ANL IBMBG/Q 42.6

* BW nodes have sufficiently high memory of 64 GB per node (A Stampede node has 32 GB)

* Efficient for calculations requiring reading and writing large amount of data

* Power can be generated from salt concentration gradients (e.g. seawater & river)

* Charged nanoporous membranres are selective to counter ions

* Because of the selectivity, more counter ions diffuse down the gradient

Siria,Alessandro,etal. Nature(2013).

( ) lncisKCl

diff is transKCl

RT aV SF a

é ù= S ê ú

ë û

Selectivity factor Experimentally, a boron nitride nanotubve was shown to generated large electric currents

Corresponding diffusion potential

µm nm

* 2D membranes are ideal as the thinness leads to higher transport rates

* MoS2 : 1. Thickness of less than 1 nm2. Selective pore charge density ranging from

-1 to -9 e/nm2 depending on pH* With the few-atom thick membrane, a stronger

power generation is expected

Membrane Power density(W/m^2)

Membrane thickness

Weinstrin and Leitz, 1976 0.17 1 mmAudinos, 1983 0.40 3 mmTurek and Bandura, 2007 0.46 0.19 mmSuda et al, 2007 0.26 1 mmVeerman et al, 2009 0.95 0.2 mmKim et al, 2010 7.7 0.14 mmSiria et al, 2013 4000 1umThis work ? 0.65 nm

AMoS2 nanopore intheexperiment

Boron nitride MoS2

* Different salinity ratios of 10, 100, 500 and 1000 of KCl in MD simulations

* Short circuit current and open circuit voltage are characteristics of a power generator in porous membranes

-0.002 -0.001 0.000 0.001 0.002-6

-4

-2

0

2

4

6

Cur

rent

(nA

)

Applied electric field (V Å-1)

Cmax/Cmin= 10 Cmax/Cmin= 100 Cmax/Cmin= 500 Cmax/Cmin= 1000

MDExperiment

* Flux of each ion depends on its concentration and velocity inside the pore

* Potassium ions are attracted to the charged surface of the pore

* A double layer near the surface

* Selectivity decreases with concentration ratio

0 2 4 6 8 10 12

0

1

2

3

4

5

6

7

Con

cent

ratio

n (M

)Distance from the center of the pore (Å)

K+ Cma x/Cmin=10 Cl- C

max/C

min=10

K+ Cma x

/Cmin

=100

Cl- Cmax/Cmin=100

K+ Cma x/Cmin=500

Cl- Cmax/Cmin=500 K+ C

ma x/C

min=1000

Cl- Cmax

/Cmin

=1000Concentration ratio JK

+ [#/ns] JCl- [#/ns] Potassium selectivity coefficient

10 2.34 0.34 0.7462

100 15.34 2.67 0.7034

500 12.67 2.34 0.6882

1000 10.34 2.00 0.6758

K Cl

K Cl

J JJ J

+ -

+ -

-

+Potassium selectivity

* Open circuit voltage

(or electric field)

increases with salinity

ratio

* Non monotonic

behavior for current

and salinity ratio

10 100 10000.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

Sho

rt ci

rcui

t cur

rent

(nA)

Cmax/Cmin

10 100 10000.0000

0.0005

0.0010

0.0015

0.0020

Ope

n ci

rcui

t ele

ctric

fiel

d (V

Å-1

)

Cmax/Cmin

Experiment

MD

* Continuum based analysis is carried out to understand the non-monotonic behavior

* Dominant component of the current is due to diffusion and migration of ions

* At high salinity ratios, migration current starts to contribute more suppressing the

total current

* A non-monotonic relationship between short circuit current and pore size in both the experiment and continuum analysis

* For larger pore, the selectivity of the pore decreases * This results in mixing of ions with an equal and opposite diffusive current

* Symmetric concentration of 1M KCl in MD* Variation of conductance with inverse

thickness is not linear* ionic mobility also influences the

conductance

-1.0 -0.5 0.0 0.5 1.0-30

-20

-10

0

10

20

30

Cur

rent

(nA

)

Applied voltage (V)

1 Layer-MoS2

2 Layer-MoS2

3 Layer-MoS2

4 Layer-MoS2

6 Layer-MoS2

12 Layer-MoS2

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35

0

5

10

15

20

25

30

Con

duct

ance

(nS

)

Reciprocal thickness, L-1 (Å-1)

1 2 3 4 5 6 7 8 9 10 11 12

0

2

4

6

8

10

K+

Cl-

mob

ility

(s k

g-1 1

011)

Number of MoS2 layers

* Abrupt reduction is due to the strong adsorption of counter-ions to the surface

* A double layer near the surface* Mobility of ions decreases sharply within

double layer* Residence time increases for multilayer

membranes 0 2 4 6 8 10 120

2

4

6

8

10

12

14

16

18

20

22

Con

cent

ratio

n (M

)

Distance from the center of the pore (Å)

K+ 1 layer Cl- 1 layer K+ 2 layers Cl- 2 layers K+ 3 layers Cl- 3 layers K+ 4 layers Cl- 4 layers K+ 6 layers Cl- 6 layers K+ 12 layers Cl- 12 layers

l region

1 2 3 4 5 6 7 8 9 10 11 12

0

2

4

6

8

10

12

Mob

ility

(s k

g-1 1

011)

Number of MoS2 layers

K+ within l Cl- within l K+ outside l Cl- outside l

Number of MoS2 layers Residence time of K+ within l [ns]

1 0.08

2 1.52

3 3.46

4 5.53

6 7.26

12 15>

* Maximum power is proportional to both the conductance and the square of open-circuit voltage

* A multilayer MoS2 reduces the power substantially

* Power for a twelve-layer MoS2 is ~3% of that of the single-layer membrane 1 2 3 4 5 6 7 8 9 10 11 12 13

0.0009

0.0012

0.0015

0.0018

0.0021

Ope

n ci

rcui

t ele

ctric

fiel

d (V

Å-1

)

Number of MoS2 layers

1 2 3 4 5 6 7 8 9 10 11 12

0.0

0.2

0.4

0.6

0.8

1.0

Pn m

ax (P

1 max

)-1

Number of MoS2 layers

Reverse electrodiialysis cells Power density(W/m2) Membrane thicknessWeinstrin and Leitz, 1976 0.17 1 mmAudinos, 1983 0.40 3 mmTurek and Bandura, 2007 0.46 0.19 mmSuda et al, 2007 0.26 1 mmVeerman et al, 2009 0.95 0.2 mmKim et al, 2010 7.7 0.14 mmSiria et al, 2013 4000 1umThis work 106 0.65 nmMultilayer MoS2 (Simulations) 30000 7.2 nm

* MoS2 membranes are promising in power generation from chemical potential* Giant power is generated, 106 W m-2, 3 orders of magnitudes higher than previously

reported results * Thinness of a single-layer MoS2 is the key to this giant power generation* In addition to length effect, the ion mobility decreases with length of membranes

(multilayer MoS2)* Non-monotonic short circuit current behavior is due to the competition between

diffusive and migration currents* The decrease in short circuit current with pore size originates from the loss of

selectivity in large pores

Special thanks to Blue Waters for making this possible!