Rh-hydrogen system under high pressure and low temperature

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Nov 15, 2013 (3 years and 10 months ago)

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Rh
-
hydrogen system


under high pressure and low temperature


Bing Li
1,4, *
, Yang Ding
1
,
Duck Young Kim
2
,
Rajeev
Ahuja
3
, Viktor Struzhkin
2
,
Wenge

Yang
1
,
Guangtian

Zou
4
, Ho
-
Kwang

(Dave) Mao
1,2,*
.

1

HPSynC
, Carnegie Institution of Washington, 9700 South Cass Avenue, Argonne, Illinois 60439, USA

2

Geophysical Laboratory, Carnegie Institution of Washington, Washington, D.C. 20015, USA

3

Condensed
Matter Theory Group, Department of Physics and Astronomy, Uppsala University, Box 530 SE
-
751 21, Uppsala, Sweden

4

State Key Laboratory of
Superhard

Materials, Jilin University, Changchun 130012, China (*: Email address: bingli.001@gmail.com and hmao@ciw.edu)

Methods

Heavy

metal

hydrides

are

of

great

scientific

interest

for

they

can

become

potential

high

T
c

superconductors

and

hydrogen

storage

materials
.

Rhodium

metal,

as

a

member

of

platinum

group

metals,

is

the

second

one

after

palladium

found

to

form

hydride
.

At

ambient

condition,

rhodium

metal

adopts

FCC

structure

and

it

forms

a

hydride,

namely

RhH,

under

high

hydrogen

pressure

around

3
.
8

GPa
.

RhH

remains

in

FCC

structure

but

expands

a

lot

from

its

Rhodium

metal

matrix
.

To

further

explore

rhodium
-
hydrogen

system,

we

performed

some

in
-
situ

studies

on

this

system

to

higher

pressures

and

low

temperatures

range
.

We

discovered

that

RhH

transforms

to

RhH
2

at

around

8

GPa,

which

still

remains

in

an

FCC

structure
.

Compared

with

RhH,

RhH
2

has

much

larger

volume

expansion

during

the

phase

transition

(~

1
.
5

times

larger

than

the

first

one)
.

Low

temperature

transport

measurement

results

showed

that

RhH

and

RhH
2

both

showed

metal

behaviors
.

Moreover,

our

thermodynamic

stability

study

of

RhH
2

showed

that

it

can

be

quenched

up

to

liquid

nitrogen

temperature

at

ambient

pressure
.

These

results

promise

the

practical

applications

using

this

higher

hydrogen

storage

capability

of

RhH
2

at

ambient

pressure

in

the

future

containing

very

high

amount

of

hydrogen

per

volume

(
163

kg

H
2
/m
3
)
.


Abstract

Conclusions

Results 1

1
.
We

discovered

a

new

high

pressure

phase

of

rhodium

hydride



RhH
2



above

8

GPa

at

room

temperature
.

The

phase

transitions

are

reversible

with

large

hysteresis

at

room

temperature
.

The

RhH
2

contains

very

high

amount

of

hydrogen

per

volume

(
163

kg

H
2
/m
3
)

and

moderate

amount

by

mass

(
1
.
9

mass
%
),

and

is

the

only

dihydride

in

the

platinum

group

metals
.

2
.
This

new

RhH
2

phase

can

be

quenched

to

ambient

pressure

up

to

100

K
.

Upon

warming

up

to

room

temperature,

RhH
2

losses

hydrogen

in

two

steps,

firstly

to

RhH
1

and

finally

to

rhodium

metal
.

The

results

indicate

the

practical

application

with

much

higher

hydrogen

storage

capability

of

RhH
2

at

ambient

pressure
.


3
.
Low

temperature

resistance

measurement

results

show

that

both

RhH

and

RhH
2

are

metallic

phases
.

Fig. 1 Diamond
anvil cell

Fig. 2 sample con
-
figuration in DAC

Diamond

anvil

cell

(DAC)

is

used

to

generate

pressure

(Fig

1
)
.

Sample

preparation

is

done

in

Geophysical

Lab

using

the

gas

loading

system
;

powder

rhodium

was

loaded

with

gaseous

hydrogen

into

a

gasket

hole

to

form

the

rhodium
-
hydrogen

system

(Fig

2
)
.

X
-
ray

experiments

were

done

in

Sector

16
-
IDB

and

IDD

(HPCAT)

at

Advanced

Photon

Source,

Argonne

National

Lab

(Fig

3
,

4
)
.

Low

temperature

was

achieved

in

a

liquid

flow

He

type

cryostat,

a

gear

box

was

used

to

adjust

pressure

during

low

temperature

experiments
.

4
-
probe

electrical

resistance

measurement

were

done

in

GL

(Fig

5
)

Fig. 4 XRD setup at
16
-
IDB

Fig. 6 XRD
images

Fig. 7 Evolution of XRD with increasing (left) and
decreasing (right) pressure at room temperature

Fig. 9 Crystal structures of Rh, RhH and RhH2 (left). Volume changes of rhodium
-
hydrogen
system depending on pressure at room temperature. The second volume expansion is
about 1.5 times larger than the first one.

Fig. 11 T
-
dependence
of the electrical resistance of
Rh,
RhH and RhH
2

measured at temperatures below 50 K
.

Fig. 10 XRD of RhH2 at 6Kelvin when releasing pressure (a)
and XRD at
ambient pressure when warming
up (b).

From

the

X
-
ray

diffraction

experiment

combined

with

theoretical

calculations,

we

assigned

the

new

high

pressure

phase

RhH
2
.

It

is

interesting

that

all

these

Rh,

RhH

and

RhH
2

are

fcc

structures

(Fig

9

left),

the

hydrogen

atoms

first

occupy

octahedral

sites

in

RhH,

and

then

go

into

the

tetrahedral

site

in

RhH
2

phase
.

Fig

9

(right)

shows

the

unit

cell

volume

changes

according

to

pressure,

there

are

two

abrupt

volume

expansion

during

the

phase

transitions,

the

second

expansion

is

about

1
.
5

times

larger

than

the

first

one
.

The

dash

lines

are

from

theoretical

calculations,

which

are

well

agreed

with

experiment

data
.

At

room

temperature

u
pon

releasing

pressure,

RhH
2

transforms

back

to

RhH

at

about

4

GPa

and

then

back

to

rhodium

at

around

3

GPa,

suggesting

the

phase

transition

is

reversible


with

some

hysteresis
.

Room temperature high pressure experiment

Low temperature high pressure experiment

We

also

performed

low
-
temperature

high
-
pressure

experiments

on

the

new

high

pressure

phase

RhH
2
.

Fig

10
(a)

shows

the

results

when

pressure

was

released

from

19

GPa

to

1

bar
.

The

x

ray

diffraction

patterns

did

not

change

dramatically,

which

indicates

the

new

high

pressure

phase



RhH
2

is

quenchable

to

ambient

pressure

at

6
.
1

Kelvin
.

When

the

system

was

warmed

up

to

about

100
K

(Fig

10
b),

RhH
2

partially

transformed

to

RhH

forming

a

RhH
-
RhH
2

mixture

phase

between

100
~
150

Kelvin
.

K
eeping

warming

up,

the

sample

turned

back

to

rhodium

metal

above

199
K

(the

peak

marked

with

*

comes

from

gasket)
.

So

with

temperature

goes

up,

RhH
2

lost

hydrogen

step

by

step,

finally

turned

back

to

Rh

metal
.

We

also

performed

transport

measurement

on

this

system,

Fig

11

shows

the

temperature

dependence

of

the

electrical

resistance

of

Rh,

RhH

and

RhH
2

below

100
K
.

The

curves

indicate

the

metallic

behavior

for

RhH

and

RhH
2
,

and

no

superconductivities

were

found

above

5
K

in

these

phases
.

[1]
J.
-
M.
Joubert

International
jonual

of hydrogen energy 35 (2010) 2104
. [2]
Marek

Tkacz

J. Chem. Phys., Vol. 108, No. 5, 1 February
1998 [3]
V.E.
Antonov
, T.E.
Antonova
, V.K.
Fedotov
,
and
B.A
.
Gnesin
, Journal of Alloys and Compounds 446

447 (2007)
508. [4]
V.E.
Antovov
,
I.T.
Belash
,
O.V.
Zharikov
.
a
nd
A. V.
Palichenko
, phys
. stat. sol. (b)
142 (1987) K155.

References

HPSynC

is supported as part of
EFree
, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Office of Basic
Energy Sciences (BES) under Grant Number DE
-
SC0001057.

Acknowledgement

Fig. 5 Four
-
probe
setup in GL

Fig. 3 X
-
ray absorption
setup at 16
-
IDD

Fig. 8 Evolution of absorption spectra with increasing
pressure at room temperature (from top to bottom)

Results 2

At

room

temperature,

we

performed

high

pressure

experiments

on

rhodium
-
hydrogen

system

(Fig

6
-
7

XRD

experiment
;

Fig

8

Absorption

spectra)
.

Our

results

confirmed

previous

high

pressure

work

that

at

about

4

GPa

rhodium

metal

starts

to

react

with

hydrogen

and

forms

a

rhodium

hydride

(RhH)
.

Furthermore,

at

higher

pressure,

a

new

high

pressure

phase

is

formed

above

~
8

GPa
.


Results 3

100um