Modular Solid State Solutions for Portable H2 Applications · Modular Solid State Solutions for...
Transcript of Modular Solid State Solutions for Portable H2 Applications · Modular Solid State Solutions for...
Modular Solid State Solutions for Portable H2 Applications
James M. Hanlon,* Laura Bravo Diaz, Marek Bielewski, Aleksandra Milewska, Cédric Dupuis and Duncan H. Gregory
* School of Chemistry, University of Glasgow
Outline
Introduction
- HYPER project
- Solid state H2 system
Experiment methods
Results:
- Synthesis of nanostructured Mg(OH)2and LiH/MgH2
- Mg(OH)2 + MgH2
- Mg(OH)2 + LiH
Approaches to progress forward
HYPER Project Introduction
HYPER Project
EC project launched in 2012 to develop a fully integrated fuel cell and storage
system for portable applications
Gaseous and solid state hydrogen storage to be employed
Solid state hydrogen storage (WP 3/4):
- University of Glasgow: synthesis, characterisation, testing
- JRC (EC): testing
- JEN: Theoretical calculations and cell design
- McPhy: Synthesis, testing and cell design
Introduction
Requirements for the solid state storage system
Low onset temperature of H2 release
Good wt.% of H2 released
Favourable kinetics
Recyclability of end products
Introduction- Solid State H2 storage system
Cell design
The cell will consist of a MgH2 matrix with an exothermic filler
The exothermic filler will be used to initiate dehydrogenation from the MgH2
matrix. A glow plug will be employed for initialisation
Designed from the following parameters:
- 3rd order of reaction (kinetics)
- Heat generated by reaction when T>Tonset
- Constant properties:
1) Density = 1000 kg/m3
2) Heat conductivity = 0.5 W/(mK)
3) Heat capacity = 1600 J/(kg K)
- Insulated walls (apart from initialiser)
Introduction
Filler Material
Efforts have been concentrated on two systems:
Mg(OH)2 + MgH2 2 MgO + 2 H2 (wt% H2= 4.5)
Mg(OH)2 + 2 LiH MgO + Li2O +2 H2 (wt .% H2= 5.44)
These have been extensively tested to determine their suitability as a ‘one shot’
exothermic filler material
(1) F Leardini, J R Ares, J Bodega, J F Fernandez, I J Ferrer, C Sanchez, Phys. Chem. Chem. Phys, 2010, 12,
572-577
Experimental techniques
Characterisation
Thermal analysis (TGA-DTA-MS) has been carried out using a Netszch STA409C coupled
to a Hiden HPR 20 MS inside an Ar recirculating glove box
Kinetic and stability measurements performed using a PCT Pro and Hiden volumetric
Sievert’s appartus
Bruker D8 and Panalytical X’pert Pro have been employed for PXD characterisation
For more information- please see poster by Laura Bravo Diaz!
Experimental techniques- Synthesis
Synthesis techniques
Nanostructured Mg(OH)2 has been synthesised hydrothermally in the MW
Due to air-sensitive nature of hydrides, nanostructuring options are limited
Ball milling using a Retsch PM100 has been used. Typical parameters used are 5 mins
mill followed by 5 mins rest and inverse rotation @ 450 rpm
Mg(OH)2 – MgH2 system
Preparation
H2 release
Nano(chemical) synthesis of Mg(OH)2
Dehydration of nano Mg(OH)2 (Mg(OH)2 MgO +H2O)
Dehydration commences at 290 oC with MgO as the final product
Morphology of the Mg(OH)2 is retained after heating
(2) J.M. Hanlon, L. Bravo Diaz, G. Balducci, B. A. Stobbs, M. Bielewski, P. Chung and D.H. Gregory, Submitted to
Green Chem.
Results- Mg(OH)2 + MgH2
Stability
Mixture must be stable at 65 oC- ‘rest temperature’
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Time/ minutes
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H2 uptake (micromoles) - 65C
Mg(OH)2 and MgH2 system
STA of stoichometric Mg(OH)2 + MgH2 system
STA/MS have been performed using bulk and nano materials
Hand mix for 5 minutes
264 oC vs 317 oC
Mg(OH)2 and MgH2 system
Ball milling
Mixing must be improved
Ball milling has been employed @450 rpm
Effect of ball milling and reactivity?
153 oC vs 120 oC
Mg(OH)2 and MgH2 system
Effect of excess MgH2?
Excess MgH2 has been ball milled with Mg(OH)2 for 2 hours
Improvement in onset to 185 oC
Small weight loss < 3wt. % H2
Ignition simulations performed on this sample. 1100 oC needed to initiate the reaction:
density = 1000 kg/m3, k = 0.5 W/(mK), Cp=1600 J/(kg K), 3% H2
Tint= 30 oC
Hydrolysis of MgH2
How to improve hydrolysis?
Hydrolysis process could be constrained by the formation of a shell on the MgH2: (3)
(3) Tayah et al., Int. J. Hydrogen Energy , 2014, 39, 3109-3117
(4) Hiraki et al., Int. J. Hydrogen Energy , 2012, 17, 12114-12119
Could catalysts disrupt this?
Citric acid has also been used to lower the pH during hydrolysis to disrupt
this shell (4)
MgH2 + catalyst
H2 evolution
Hydrogen evolution - Thermal ramp 5 C/min
0.0E+00
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00:21:36 00:50:24 01:19:12 01:48:00Time
Fara
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torr
H2 MgH2 - Mg(OH)2
H2 MgH2-10wt SiC +
Mg(OH)2 sampleH2O MgH2 - Mg(OH)2
H2O MgH2 - 10 wt% SiC +
Mg(OH)2
Conclusions on Mg(OH)2 + MgH2
Conclusions From the STA/MS profiles the reaction is a 2-step process:
1) Dehydration of Mg(OH)2 and hydrolysis of some MgH2
2) Remaining hydrolysis of MgH2 due to a shell forming on the MgH2
Carbon and Silicon Carbide have been employed to try and disrupt this shell and improve
dehydrogenation of the mixture with some improvement
Kinetics for this system are too slow for its end use (please see poster by LBD)
First stage of reaction is exothermic, however total energy is too low to initialise the matrix
From calculations, this system may not produce enough heat to initiate the matrix
The end products are MgO and Mg so the starting materials can be regenerated
Results- Mg(OH)2 + LiH
Stability
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0 2000 4000 6000 8000 10000 12000 14000
Time/ minutes
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H2 uptake (micromoles) -65C
Mg(OH)2 – LiH system
STA of nano Mg(OH)2 + LiH
TG curve onset of ~92 oC with the main exothermic DTA peak is at 233 oC
Improved over bulk (onset of ~150 oC)
One step H2 release process
Kinetic testing- Mg(OH)2 – LiH system
Kinetic testing
System still needs further improvements for use as the exothermic filler
material, i.e first step of reaction, kinetics…
Improvement over MgH2 counterpart system
Conclusions on Mg(OH)2 + LiH
Conclusions
This system has improved performance to its MgH2 counterpart system in terms of kinetics
and its thermal profile
Nanostructuring improves the performance of the system
No stability issues with the system
Same issues with the ‘core shell’ forming on the hydride that limits H2 release
Calculations show the exothermic release from this system would be insufficient to
encourage MgH2 dehydrogenation from the matrix
Issues with reactivity during regeneration of the matrix?
Approaches Forward
Next Steps…
Further work needs to be undertaken on the ‘core shell’ of the hydrides
For the matrix approach to be successful, alternative exothermic filler
materials/matrix materials need to be investigated
Ideal ratio of filler to matrix composite needs to be investigated
Alternative, different solution required?
Acknowledgements
The research leading to these results has received funding from the European
Union’s Seventh Framework Programme (FP7/2007-2013) for the Fuel Cells and
Hydrogen Joint Technology Initiative under Grant Agreement number 303447
HYPER Project Introduction
Introduction- Solid State H2 storage system
Initialisation of the System
A glow plug is ideal for initialise the system
Glow plug can heat to 1000 oC in seconds time spans
Require external source to switch on the plug- increase ‘parasitic’ load
Synthesis of nanostructured Mg(OH)2
MW hydrothermal synthesis of Mg(OH)2
Kinetic experiments: Mg(OH)2 + MgH2
Very slow kinetics!
MgH2 + catalyst
TGA/MS Analysis
MgH2 + Mg(OH)2 hand mixed for 5 min of milled 5h MgH2/nano Mg(OH)2
MgH2 – 10 wt% C + Mg(OH)2 hand mixed for 5 min of milled 5h MgH2 + 10wt C/nano Mg(OH)2
MgH2 – 10 wt % SiC + Mg(OH)2 hand mixed for 5 min of milled 5h MgH2 + 10wt SiC/nano Mg(OH)2
MgH2 – 5 wt % SiC – 5 wt SiC + Mg(OH)2 hand mixed for 5 min of milled 5h MgH2 + 5wt SiC + 5 wt C/nano
Mg(OH)2
Mass change: 7.14 % - 8.19 %
Mass change: 9.80 % - 10.80 %
Mass change: 8.59 % - 9.36 %
Mass change: 9.2% - 9.93 %