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INTERN A TfON A LJOURNA L Of' HYDROGtN E:NE:RGY XXX ( 2 014) J - I O

Available online at www.sclencedirect.com 65 66 1 ScienceDirect 67 2 68 3 69 4 70 5 journal homepage: www.elsevier.com/locate{he 71 6 ELSEVIER 72 7 73 8 74 9 Synthesis and characterization of 75 10 76 11 (sulfonated poly--ether-) based 77 12 78 13 nanocomposite (h-boron nitride) membrane 79 14 80 15 for storage 81 16 82 17 83 18 R. Naresh Muthlia .·,J?. Rajashaballl. a,b, R. Kanna'l c 84 19 ~ 1 1 85 20 • School of Physics, Madurai Kamaraj University, Madurai 625021, TamU Nadu, 86 21 "Department of and Biochemistry, Utah State Uniuersity, Logan, UT 84322-0300, USA 87 22 • Department of Physics, Uniuersity College of Engineering, Anna Uniuersity, Dindigul624622, TamU Nadu, India 88 23 89 24 90 25 ARTICLE INFO ABSTRACT 91 26 92 27 Article history: The development of light weight and compact hydrogen storage materials is still prereq­ 93 28 94 29 Received 7 August 2014 uisite to fuel-cell technology to be fully competitive. The present experimental study reports Received in revised form the hydrogen storage capability of sulfonated poly-ether-ether-ketone (SPED<)-hexagonal 95 30 96 20 November 2014 boron nitride (h-BN) (SPEEK-h-BN) nanO

Please cite this article in press as: Naresh Muthu R, eta!., Synthesis and characterization ofpolymE!!' (sulfonated poly-ether­ ether-ketone) based nanocomposite (h-boron nitride) membrane for hydrogen storage, International Journal of Hydrogen .Energy (2014), http://dx.doiorgl10.10161j1jhydene. 2014.11.136 HEI5080_proof • 13 December 2014 • 2/10

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1 alternative to conventional systems (4]. Although hydrogen is with platinum (P~ nanoparticles was analyzed and a 66 2 often presented as the fuel of the future, the developmentofa maximum storage capacity of0.21 wt.% at298.15 K and 19 bar 67 3 hydrogen-based fuel is rather difficult Hydrogen has to be was noticed (28]. Hypercrosslinked - Pt nano­ 68 4 produced, stored, distributed and used, but each ofthese steps particles display a hydrogen uptake of 0.36 wt.% at 294 K and 69 5 is hindered due to several factors (5]. Multiple challenges must 100 atrn (29]. The PANl impregnated with tin oxide, multiwall 70 6 71 be overcome to achieve the vision of secure, abundant, inex­ nanotubes (MWCNTs) and aluminum powder (AI) 7 72 pensive, and clean hydrogen production with low carbon exhibit 0.31, 0.38, 0.5 wt. %of hydrogen adsorption at 115 •c 8 73 9 emissions (4,6,7]. and 70 bar (30]. Hydrogen storage capacity of halloysite 74 10 In the prospect of a hydrogen-based economy, the major nanotubes (HNT) - PANl nanocomposite was examined by 75 11 issue is to address how to reversibly store hydrogen while Attia et al. (31] and noticed 0.78 wt% of hydrogen was stored 76 12 minimizing energy consumption. Three major approaches at room temperature and a pressure of0.5 MPa. The hydrogen 77 13 (8,9], compression for storage in tank, storage by purely storage capacity of poly (ether-ether-ketone) functionalized in 78 14 physical absorption and storage via chemical reaction or situ by manganese oxide formation, showed a hydrogen 79 15 chemical storage are in the forefront of current research ef­ storage capacity of 1.2 wt.% at 77 K (6]. The hydrogen storage 80 16 forts. Direct use ofcompressed hydrogen as a fuel encounters capacity of treated -soluble polymers such as 81 17 major constraints due to large tank volumes, short lifetimes of polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP) doped 82 18 83 the storage system and stringent safety measures, in addition single-walled carbon nanotubes (SWCNTs) has shown to be 19 84 20 to high investment costs and portability. 1.2 and 1.5 wt. %, respectively at 50 •c (32]. Kim et el (33]. re­ 85 21 A lot of research works have been carried out on hydrogen ported that the PAN! - vanadium oxide nanocomposites 86 22 rich materials like chemical hydrides (10], complex hydrides (VON C) showed storage capacity of1.8 wt.% at 77 K and 70 bar. 87 23 (11] and metal hydrides (12] that store hydrogen by chemi­ The activated rectangular PANl-based carbon tubes (ARP-CTs) 88 24 sorption. In the last two decades, over 350 distinct materials exhibited the hydrogen adsorption of 5.2 wt. % at 77 K and 89 25 have been investigated experimentally (13] and more than 70% 5 MPa and 0.62 wt.% at 293 K and 7.5 MPa respectively (34]. 90 26 have been discontinued as potential candidates for hydrogen­ Makridis et al. (4] studied Mg doped polymethylmethacrylate 91 27 fuel cells. Although some complex metal hydrides (such as, (PMMA) which exhibited 6 wt. % at 250 •c. The Li-conjugated 92 28 93 MgH , NaBH , Ca(BH,}.,, AlH , K,LiAIH , etc.) have advantages of microporous polymers could able to store more than 6 wt % 29 2 4 3 6 94 high gravimetric (-15- 20 wt. % of H.) and high volu­ of hydrogen at 77.3 K and at 1 bar (35]. 30 95 31 metric density (about 150 g H,/IJ, major disadvantages were Up to date, none of the proposed hydrogen storage systems 96 32 found to be high desorption energy, slow kinetics and toxic appears able to match US-DOE targets. Recent studies showed 97 33 byproducts, besides cyclability as a major issue. that the polymer nanocomposites could be an attractive ma­ 98 34 Large specific surface area materials such as carbon terial for hydrogen storage. The present work is aimed at the 99 35 nanotubes (14], metalorganic frameworks (15,16] and zeolites synthesis and characterization of light weight and compact 100 36 (15,17] store hydrogen by physisorption and in most of these hydrogen storage material based on polymer nanocomposite 101 37 cases hydrogen uptake are not so high. Recent reports have using sulfonated poly (ether-ether-ketone) (SPEEK) and hex­ 102 38 demonstrated that boron nitride (BN) nanomaterial can be agonal boron nitride (h-BN) nanoparticles, where the PEEK has 103 39 used as a potential hydrogen storage medium (18- 22]. Hex­ excellent mechanical and chemical properties and thermal 104 40 105 agonal boron nitride (h-BN) is an analoL of , has stability (36,37]. The dipolar nature of B~bonds in hexagonal 41 106 unique physical and chemical properties, including high boron nitride (h-BN) can have stronger absorption of hydrogen 42 107 43 specific surface area, low density, high mechanical strength from . where phase inversion technique is 108 44 and oxidation resistance (22- 24]. Weng et al. (18] reported the employed for the preparation of microporous SPEEK-h-BN 109 45 ability of BN porous microbelts to exhibit high and reversible nanocomposite membranes. So it is expected that the light 110 46 hydrogenuptakeof23wt.% at n Kand 1 MPa. Wangetal. (19] weight and more micro porous nature of SPEEK could accom­ 111 47 reported a hydrogen storage capacity of 2.6 wt % in h-BN modate more h-BN nanoparticles which in tum can adsorb 112 48 powders under the hydrogen pressure of 1.0 MPa. The con­ more hydrogen molecules. 113 49 ventional BN nanopowder, multiwalled BNNT and bamboo­ 114 50 like BNNTs can absorb hydrogen up to 02, 1.8 and 2.6 wt. %, 115 51 respectively at room temperature and at 10 MPa (20]. The Experimental methods 116 52 117 hydrogen storage capacity of 4.2 wt. % at 10 MPa in BNNTs 53 118 collapsed walls (21] and 5.6 wt.% at 3 MPa at room tempera­ 54 Materials 119 55 ture in BN porous whiskers were noticed (22]. 120 56 The other promising route is the use of polymers/polymer The PEEK polymer from Sigma Aldrich and h-BN (99.99% pu­ 121 57 nanocomposites that have also been considered for hydrogen rity) with average particle size of 70 nm from Sisco Research 122 58 storage (4,6,25- 35]. Keown et al. (25] found that polymer of were purchased. Concentrated sulfuric acid 123

59 intrinsic microporosity (PIMs) stores 1.7 wt. % of hydrogen at (H 2S04) (98%) and N, N-Dimethylformamide (DMF) were 124 60 77 K and 10 bar. The hypercrosslinked polystyrene could store received from Merck. 125 61 2.75 wt.% of hydrogen at 77 K and 10 bar (26]. The hydrogen 126 62 storage capacity of HCl treated conducting polymers like Preparation of SPEEK 127 63 polyaniline (PANl) and polypirrole (Ppy) were found to be 6 and 128 64 129 8 wt. %, respectively at room temperature and at 9.3 MPa (27]. The present work involves preparation of sulfonated PEEK and 65 130 The hydrogen storage ability of the hypercrosslinked SPEEK-h-BN nanocomposite membranes for the hydrogen

Please cite this article in press as: Naresh Muthu R, et al., synthesis and characterization of polymer (sulfonated poly-ether­ ether-keJone) based nanocomposite (h-boron nitride) membrane for hydrogen s10rage, International journal of Hydrogen Energy (2014), http://dx.doi.Of!f10.10I61j.ijhydene20I4.11.136 HEI5080_proof• 13 December 2014 • 3/10

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1 66 Vacuum H 2 2 67 3 Pressure ..., Pressure 68 4 Gauge ...~ ~ Gauge 69 5 i"" 70 6 71 7 72 8 - 73 9 Flow ...... 74 10 ...... 75 Meter ermocouple 11 Th 76 12 77 Control 13 !) Hz Chamber 78 14 Valve ~ 79 15 Inlet 80 16 ..... 81 17 ....r- ..... 82 18 Sample 83 19 H·• 84 20 Vacuum Gas Sample Holder ;= 85 21 Pump 13= 86 22 I Furnace '\ 87 23 H• Outlet 88 24 89 25 Fig. 1 - Schematic diagram of Sieverts·like hydrogenation setup. 90 26 91 27 92 28 adsorption studies. Poly (ether-ether ketone) (PEEK) was sul­ as follows. Before hydrogenation, the chamber should be free 93 29 fonated as described in literature (36,38,39]. The pure PEEK fyom leak. The prepared membranes were loaded in the 94 30 polymer was dried in a vacuum oven at 100 •c for 12 ~ then sample container and the hydrogen was flushed few times 95 31 dissolved in concentrated sulfuric acid (98%) and heated to within the chamber for proper flow. The membranes were 96 32 40 •c under constant stirring for 24 9.: This solution was dec­ maintained in a vacuum at 1so•c for 11). Then the hydrogen 97 33 anted into large excess ofice-cold water to precipitate the acid was allowed to react with these membranes at a constant flow 98 34 99 polymer. The precipitate obtained was repeatedly washed rate of J!!.S Umin for 15 min, where the equilibrium pressure 35 2 100 36 with distilled water until the rinsed water has a pH value of the chamber was maintained at 1 kg/cm . The hydroge­ 101 37 above 6. The washed precipitate was further dried at 1oo•c for nated membranes were kept in the chamber to attain room 102 38 12 9.: The final product obtained was sulfonated PEEK, which temperature. 103 39 has the desired degree of sulfonation. 104 40 Characterization 105 41 Preparation of SPEEK·h·BN nanocomposite membranes 106 42 Powder X-ray diffraction (XRD) technique (X'Pert PAN analyt­ 107 43 The SPEEK-h-BN nanocomposite membranes were prepared ical diffractometer), Micro-Raman spectroscopy (Labram 108 44 109 with 0, 1, 3 and 5 wt % of h-BN using a phase inversion HR800), Fourier Transform Infrared (ITIR) spectroscopy (FTIR- 45 110 46 technique (38,40,41}. To fabricate SPEEK-h-BN nanocomposite 8400, cr. Shimadzu mode~. Scanning Electron Microscopy 111 47 membranes, SPEEK polymer was dissolved in N, N-Dirne­ (SEM, ]EOL-MODEL 6390), Atomic force microscopy (AFM, A- 112 48 thylformamide and water (non-). Then h-BN nano­ 100 SGS), CHN - elemental analysis (Elementar Vario EL DI), 113 49 particles were taken with N, N-Dimethylfonnamide at 100 mg/ Thermo Gravimetric Analysis (TGA, Sll EXSTAR 6000), Proton 114 50 5 ml concentration. To allow h-BN nanoparticles to be Nuclear Magnetic Resonance ('H NMR) spectroscopy (Bruker 115 51 dispersed uniformly the mixture was kept in an ultrasonic 300 MHz) were used to examine the structure, composition, 116 52 bath at room temperature for 1 h. Then both the solutions functional groups, desorption temperature and degree of 117 53 were magnetic stirred. After getting homogeneous solution it sulfonation of the prepared nanocomposite membranes. 118 54 was casted on a glass plate. Then it was heated at 60 •C for 5 11_ 119 55 120 and dried at 100 •c for 20 11_ in vacuum in order to avoid 56 121 57 moisture. The thickness of the resulting membranes was Results and discussion 122 58 found to be in the range of 52 ± 10 ~m. 123 59 The Degree of Sulfonation (DS) is estimated from 1H NMR 124 60 Hydrogenation studies spectrum by finding the ratio of peak area of the distinct H, 125 61 signal (AHt) to the peak area of all the other aromatic hydro­ 126 62 Hydrogen adsorption studies have been carried out for the gens (AH._.-,u·c.ol· The aromatic are denoted by the 127 63 128 developed SPEEK-h-BN nanocomposite membranes using symbol "H;' in the SPEEK structure, where x = A,A, B,B'C,D 64 129 Sieverts-like hydrogenation setup and its schematic diagram (38}. Scheme 1 shows the presence of various aromatic pro­ 65 130 is shown in Fig. 1. The details of hydrogenation procedure are tons in the SPEEK structure (37, 38}.

Please cite this article in press as: Naresh Muthu R, eta!., Synthesis and characterization ofpolymE!!' (sulfonated poly-ether­ ether-ketone) based nanocompositl! (h-boron nitride) membrane for hydrogen storage, International Journal of Hydrogen .Energy (2014), http://dx.doiorg/10.1016/j1jhydene.2014.11.136 HEI5080_proof • 13 December 2014 • 4110

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1 0 210 66 HA' HA 2 He Ho "·· "· (d) 67 3 II 140 68 0 c 4 ~0 ;f ~ j ~ j n 69 5 ~ 70 70 H, HB' HA' HA 6 "· 71 so,H 180 7 (c) 72 8 73 S<:heme 1 - Sttucture of SPEEK. 120 9 ~. 74 10 " 75 ~"' 60 11 ~ 1.... 76 12 1 ·- 90 77 f1g. 2 displays the H NMR spectrum of SPEEK and has a "'c 13 distinct signal at 7.5 ppm lhat indicates the presence of pro­ ...... a (b) 78 14 c 60 79 tons of lhe - SO,H group. DS can be calculated from the - 15 - 80 16 following formula (36,37,39]. 30 81 17 n Au. 82 18 100 83 12- 2n - L;Au.._.~•c.c ...... 19 (a) 84 20 '1here 'n' is the number of H, per so J 85 21 r"" 86 .I 22 DS(%) = n x 100 87 23 88 The estimated degree of sulfonation of our prepared 0 24 10 20 30 40 so 60 70 80 89 25 SPEEK is 65%. In general, the DS of 40- 70 % produces a 90 20 (d~ree) 26 more mechanically and thermally stable polymer of SPEEK 91 27 (39,42]. Fig. 3 - XRD profile of (a) SPEEK-O%h-BN (b) SPEEK-1%h-BN 92 28 f1g. 3 shows the XRD patterns of SPEEK-O%h-BN, SPEEK-1% (<:) SPEEK-3'l'oh-BN and (d) SPEEK-S'l'oh-BN nanocomposite 93 29 h-BN, SPEEK-3%h-BN and SPEEK-5%h-BN nanocomposite membranes. 94 30 membranes. Fig. 3(a) shows a very broad peak centered at 22•, 95 31 which indicaJes the amorphous nature (43) of SPEEK mem­ 96 32 brane. A characteristic sharp reflection at 28 = 27• in 97 33 Fig 3(b- d) confirms lhe presence of h-BN in the prepared The presence of functional groups has been determined 98 34 nanocomposile membranes (44]. It is noticed that the in­ from the bands appearing in lhe FTffi spectrum and f1g. 5 99 35 tensity ofh-BN peak increases with increase of h-BN content shows the fTIR spectra of SPEEK and SPEEK-h-BN nano­ 100 36 101 composites. The m spectrum of SPEEK (Fig. 5(a)) has the 37 in the nanocomposite membranes and it is the clear evidence 102 38 for the crystalline nature of nanocomposite membranes 103 39 (45,46). The absence ofany other peak exceptSPEEK andh-BN 4000 104 40 proves that the prepared nanocomposile membranes are free (d) 105 41 from impurities. 106 2000 42 ng. 4 shows lhe Raman spectra ofSPEEK-O%h-BN, SPEEK- 107 43 1%h-BN, SPEEK-3%h-BN and SPEEK-5%h-BN nanocomposite ..) "- .,.,/ 108 44 membranes. Fig. 4(a) indicates a Raman mode for SPEEK 4000 - 109 45 polymer at 1149 em-•and is attributed to the sulfonation (47). (c) 110 46 In Fig 4(b-d), the sharp peak of£, mode appears at1367 em- • ~ 111 47 8 =: 2000 112 corresponding to the h -BN and is due to the in-plane a lx)lnic 48 \. A_ ...... 113 49 displacement of Band N atoms against each other (48]. The ...... 114 50 intensity of the h-BN mode (1367 em-' ) increases compared to 115 1 (b) 51 SPEEK mode (1149 cm- ) as the content ofh-BN nanoparticles 116 52 increases in SPEEK and enhances the crystalline nature ofthe 2000 117 53 nanocomposite membranes and it is confirmed by XRD 118 54 \. .A 119 results. 4000 .... 55 (a) 120 56 121 57 2000 122 58 1 1.... h ...... J \. 123 59 ... 124 0 60 125 1000 1100 1200 1300 1400 1500 61 ·I 126 62 \__ Wavenumber (em ) 127 __ ..,... / _A____ 63 Fig. 4 - Raman spectra of(a) SPEEK-O'l'oh-BN (b) SPEEK-l 'l'oh­ 128 64 ...... '-' ).! 129 ••• ..' '"' '·' '·' BN (<:) SPEEK-3%h-BN and (d) SPEEK-S'l'oh-BN 65 130 Fig. 2 - 1H NMR spectrum of Sulfonated PEEK in DMS0-<1,;. nano<:ornposite membranes.

Please cile this article in press as: Naresh Muthu R, et a!., synlhesis and characterization of polymer (sulfonated poly-ether­ ether-keJone) based nanocomposite (h-boron nitride) membrane for hydrogen s10rage, International journal of Hydrogen Energy (2014), http://dx.doi.Of!f10.10161j.ijhydene20I4.U.136 HEI5080_proof• 13 December 2014 • 5/10

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1 prominent absorption peaks at 3470, 1652, 1078 1016 and 66 2 (d) 864 em- •. The characteristic peak at 3470 em- • is assigned to 67 3 the 0-:[1 vibra lion ofsulfonic acid groups. in addition the peak 68 4 at 1652 em- • is assigned to the carbonyl band of SPEEK. The 69 5 absorption bandsat1078,1016 and864 em- • correspond to the 70 6 71 ""'c \ O=S=O symmetric vibration, symmetric stretching of sulfo­ 7 72 5 nated 5'1.0 modes and out-of-plane C'1.H bending of an iso­ 8 ·~ L - 1--.. 73 s~ lated hydrogen in a 1,2,4-trisubstituted phenyl ring 9 = 74 10 E respectively. These characteristic modes confirmed the pres­ 75 !- 11 ence of groups in the prepared SPEEK (49-52]. 76 12 In addition to the peaks observed for SPEEK, some new 77 13 prominent peaks are noticed (Fig. 5 (b-d)) at 3460, 2367 and 78 14 1190 em - • in the case of prepared polymer nanocomposite 79 15 membranes. These new characteristic peaks are due to the 80 16 4000 3500 3000 2500 1500 1000 81 ·I presence of h-BN nanoparticles in SPEEK. The peak at 3460, 17 Wavenumber (em ) 2367 and 1190 em- • correspond to N'1.H stretching vibration, 82 18 83 asymmetric stretching mode of B'1.H and bending mode of 19 Fig. 5 - FTIR spectra of(a) SPEEK-O%h-BN (b) SPEEK-l'l'oh-BN 84 20 (c) SPEEK-3'l'oh-BN and (d) SPEEK-sr.h-BN nanocomposille B'1.H of SPEEK-h-BN nanocomposite and this confirms the 85 21 membranes. incorporation of h-BN nanoparticles in the SPEEK matrix 86 22 [53- 55]. 87 23 11g. 6 shows the SEM images which are helpful to examine 88 24 the presence and distribution ofh-BN nanoparlicles in SPEEK­ 89 25 h-BN nanocomposite membranes. The SPEEKhas smooth and 90 26 91 27 92 28 93 29 94 30 95 31 96 32 97 33 98 34 99 35 100 36 101 37 102 38 103 39 104 40 105 41 106 42 107 43 108 44 109 45 110 46 111 47 112 48 113 49 114 50 115 51 116 52 117 53 118 54 119 55 120 56 121 57 122 58 123 59 124 60 125 61 126 62 127 63 128 64 129 Fig. 6 - SEM photograph of (a) SPEEK-0%11-BN (b) SPEEK-1%h-BN (c) SPEEK-3%h-BN and (d) SPEEK-5%11-BN nanocomposite 65 130 membranes.

Please cite this article in press as: Naresh Muthu R, et al., Synthesis and characterization ofpolymE!!' (sulfonated poly-ether­ ether-ketone) based nanocomposite (h-boron nitride) membrane for hydrogen storage, International Journal of Hydrogen Energy (2014), http://dx.doiorgl10.1016/j1jhydene. 2014.11.136 HEI5080_proof • 13 December 2014 • 6/10

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1 66 2 67 3 68 4 69 5 70 6 71 7 72 8 73 9 74 10 75 11 76 12 77 13 78 14 79 15 80 16 81 17 82 18 83 19 84 20 85 21 86 22 87 23 88 24 89 nm 25 f 90 26 91 27 92 28 93 29 94 30 95 31 96 32 97 33 98 34 99 35 100 36 Fig. 7 - AFM images of (a) SPEEK-1%h-BN (b) SPEEK-:W.h-BN (c) SPEEK-5%h-BN nanocomposite membranes (rwo 101 37 102 dimensions) (d) SPEEK-l'l'.h-BN (e) SPEEK-:W.h-BN (f) SPEEK-5%h-BN nanocomposite membranes (rhree Dimensions). 38 103 39 104 40 uniform surface morphology (see Fig. 6a). This smooth distribution ofh- BN nanoparlicles wilh lhe particle size in the 105 41 106 morphology confirms the amorphous nature of SPEEK poly­ range of 70-.190 nm and some of h-BN nanoparticles agglom­ 42 107 eratecd in SPEEK matrix. The presence of pores in the micro­ 43 mer which agrees well with our XRD results. The remaining 108 44 micrograph depicts lhe porous strucrure, indicating the strucrure is mainly due to the non-solvent removal and 109 45 110 46 111 1500 47 150 (b) Hydrogenated SI,_E£K-S%h-BN 112 (a) Uydrogcnatcd S f'EEK-S'~h-UN 48 100 113 49 750 114 so }\, 50 - ...... J\ 115 1400 51 120 Rydrogcnntcd SP££K.-3%h-8N 116 U,-drogen:lted SJ,E£K-3, ob-UN 52 =80 j 117 53 118 ~ - ~ _!\., ..:!. 40 .0 54 c· ·;; 1000 119 -~ 90 -~ = llydrogenated SPKEK""'- t % h-BN 55 llydrogennted SI•EEK· I~.h-llN .. 120 " ...J 56 :!= 60 ..:- 500 121 57 - 30 -../' A 122 I.A. ~ 58 3200 123 78 Hydrogenated S PEEK~%11 -BN 59 ..ol.. Uydrog~n:1ted Sf•t:EK-O'Yob-UN 124 60 50 .,.....Jr' 1600 125 61 25 ...... '-.. .! 126 0 - "'"' 62 127 0 1000 II 00 1200 1300 1400 1500 63 10 20 30 40 50 60 70 80 128 64 20 {degree) Wavenumber (em"') 129 65 130 Fig. 8 - (a) XRD spectra (b) Raman spectra of hydrogenated SPEEK-h-BN nanocomposille membranes.

Please cile this article in press as: Naresh Muthu R, et a!., 5ynlhesis and characterization of polymer (sulfonated poly-ether­ ether-keJone) based nanocomposite (h-boron nitride) membrane for hydrogen s10rage, International journal of Hydrogen Energy (2014), http://dx.doi.Of!fl0.10161j.ijhydene2014.U.l'l6 HEI5080_proof• 13 December 2014 • 7/10

INTERN A TfON A L JOURNA L Of' HYDROGtN E:NE:RGY XXX ( 2014) J - I O 7

1 nanocomposite membranes. The hydrogen storage capacity 66 2 (d) of the prepared nanocomposite membrane is estimated by 67 3 finding the difference of hydrogen content in the membranes 68 4 before and after hydrogenation. The storage capacity of 69 5 ~ 70 ~ SPEEK-O'Y.b-BN, SPEEK-1'Y.b-BN, SPEEK-3%h-BN and SPEEK-5% 6 ~ (c) h-BN nanocomposite membranes are found to be 0.66, 0.91, 71 7 .. 72 '"'c: 1.66 and 2.98 wt %, respectively. The presence of more pores 8 73 1:!" in SPEEK matrix and more adsorption sites in the h-BN 9 c:~ 74 10 "'c \ ~b~ nanoparticles could be the reason for increased storage ca­ 75 11 pacity in nanocomposite membranes. Therefore, it is 76 1-.." 12 concluded that the SPEEK-5'Y.b-BN membrane is a more 77 13 \ effective hydrogen storage medium than other membranes. 78 14 The results obtained are compared with earlier reports and 79 15 are given in Table 2. However, most of the hydrogenation 80 16 experiments reported in Table 2 have been conducted either 81 4000 3500 3000 2500 2000 1500 I 000 500 17 at low temperarure or at different pressure conditions. Since 82 18 ·I 83 Wa••enumber (em ) the present work is conducted at 150 •c, a proper interpreta­ 19 84 20 Fig. 9 - FTIR spectra of hydrogenated (a) SPEEK·O'r.b·BN (b) tion of our results with earlier works could not be possible. 85 21 SPEEK·l'Y.b·BN (c) SPEEK·3'Y.b·BN and (d) SPEEK·S'Y.b·BN Moreover, the storage of hydrogen at low temperature and 86 22 nanocomposite membranes. high pressure conditions are not realistic for automobile 87 23 application. 88 24 89 25 solvent retention ability of the system (56]. Moreover, some of 90 26 h-BN nanoparticles are distributed unifonnly and are high­ Desorption analysis 91 27 lighted (see Fig. Gb- d). 92 28 The topographic images of 2D and 3D of SPEEK-h-BN Fig. 10 displays the TG plot of hydrogenated nanocomposite 93 29 nanocomposite membranes are captured by AFM and are membranes and the inset shows the region where hydrogen 94 30 presented in Fig 7. From the AFM image, it is evident that the desorption takes place. The TGA spectrum of SPEEK-5%h-BN 95 31 96 smoothness ofmembrane surface decreases as the content of (see Fig. 10d) exhibits two weight loss, one at the tempera­ 32 97 h-BN increases in the prepared nanocomposite membranes. ture interval of 214- 218 •c and another above 250 •c. The 33 98 initial weight loss of2.98% is attributed to desorption ofstored 34 Since the phase inversion method has been adopted in the 99 hydrogen in the hydrogenated membrane. The second weight 35 present study, a porous top-layer is formed due to non-solvent 100 36 removal and creates more pores in the prepared polymer loss starts above 250 •c whiclt corresponds to the disintegra­ 101 37 nanocomposite membrane (48]. It is observed that, as the tion of SPEEK (36,39,57]. Hence, one can confirm that the initial 102 38 quantity ofh-BNincreases, the number ofporesincreasesand weight loss is due to the release ofstored hydrogen and not by 103 39 simultaneously the pore size decreases. Our AFM observa­ the hydrogen in SPEEK From the desorption temperature, the 104 40 tions are consistent with the SEM results. activation energy of desorption (E.,) was calculated using the 105 41 following equation (54,58]. 106 42 Adsorption analysis 107 43 108 44 lnrf) = R~m 109 It is expected that hydrogenated nanocomposite membranes 45 110 46 exhibit peculiar behavior. The XRD/Raman spectra (Fig. 8) of where, T m is the desorption temperature, I! is the heating rate 111 47 hydrogenated SPEEK-h·BN nanocomposites are lower in in­ (10 •C/min) and R is the universal gas constant. Furthermore, 112 48 tensity compared to unhydrogenated membranes and the binding energy (E8) of hydrogen is calculated using the 113 49 confirm the adsorption of hydrogen. The FTIR spectra of the van·t Hoff equation (59,60]. The calculated values of desorp­ 114 50 hydrogenated SPEEK-h-BN nanocomposite membranes are tion temperatureofhydrogen, activation energy of desorption 115 51 shown in Fig. 9. Due to hydrogenation, some prominent and binding energy are displayed in Table 1. 116 52 modes are noted that are indicated by arrows in the spectra. In order to make use of these prepared light weight and 117 53 C!iN-elemental analysis is performed to find the quantity compact membranes for fuel cell applications, the recom­ 118 54 119 of hydrogen incorporated in hydrogenated SPEEK-h-BN mended binding energy of stored hydrogen should be 55 120 56 121 57 122 58 Table 1 - The desorption parameters in hydrogenated SPEEK·h·BN nanocomposite. 123 59 Polymer H2 Desorption Desorption activation Binding energy range 124 60 nanocomposite Weight loss temperature range rCJ energy range (kJ/mol) (eV) 125 61 (wt. %) 126 62 127 SPEEK·O%h· BN 0.66 190-192 25.53-25.67 0.362-o.364 63 SPEEK·1%h· BN 0.91 201-204 26.32-26.54 0.371-o.373 128 64 SPEEK· 3%h· BN 1.66 204-214 26.54-27.26 0.373-o.381 129 65 SPEEK· 5%h· BN 2.98 214-218 27.26-27.56 0.381-o.384 130

Please cite this article in press as: Naresh Muthu R, eta!., Synthesis and cltaracterization ofpolymE!!' (sulfonated poly-ether­ ether-ketone) based nanocomposite (h-boron nitride) membrane for hydrogen storage, International Journal of Hydrogen .Energy (2014), htrp://dx.doiorg/10.1016/j1jhydene. 2014.11.136 HEI5080_proof • 13 December 2014 • 8110

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1 nanocomposite membranes are stable at room temperature. 66 Table 2 - Hydrogen stomge capacity of various polymer 2 67 composites. Hence, it is expected that the SPEEK-h -BN nanocomposite 3 membranes could be an effective hydrogen storage medium 68 4 Polymer H2 Conditions Reference in near future. 69 5 nanocomposite (wt %) 70 6 Hypercrosstinked 0.21 298.15 K and 19 bar {28) 71 7 polymers - Pt 72 8 Hypercrosstinked 0.36 294 K and 100 attn {29) Conclusion 73 9 Polystyrene - Pt 74 10 PANI - Sn00 0.31 115 •c and 70 bar [30) A lightweight and compact hydrogen storage medium using 75 115 •c and 70 bar 11 PANI - MWCNTs 0.38 (30) SPEEK and h-BN was prepared by phase inversion technique. 76 12 PANI - Al 0.5 115 • c and 70 bar (30) 77 The prepared hydrogen storage medium was subjected to 13 ARP-crs 0.62 293 K and 7.5 MPa [34) 78 various characterization studies like XRD, micro-Raman, FTIR, 14 HNr - PANI 0.78 RT and O.S MPa (31) 79 15 PEEK-Manganese oxide 1.2 77K (6) SEM, AFM, CHN and TGA The XRD and micro-Raman results 80 16 PVA - SWCNTs 1.2 so• c [32) demonstrated the presence of h -BN nanoparticles in SPEEK 81 PVP - SWCNTs so •c 17 1.5 (32) polymer. The distribution ofh- BN nanoparticles on lhe surface 82 PANI - VONC 1.8 77 K and 70 bar (33) 18 ofSPEEKwas con fumed by SEM and theAFM images indicating 83 SPEEK/h-BN 2.8 150 • c Present 19 lhe porous nature of membranes. The hydrogenated SPEEK-h­ 84 work 20 85 ARP-crs 5.2 77 K and5MPa [34) BN nanocomposite membranes (hydrogen storage medium) 21 86 U-conj ugated 6 77.3 K and 1 bar (35) were characterized by XRD, micro-Raman, FTIR, CHN and TGA 22 microporous polymers The XRD, m icro - Raman and FTIR confirm lhe adsorption of 87 23 PMMA - Mg 6 2so • c (4) hydrogen in the synlhesized SPEEK-h-BN nanocomposite 88 24 89 membranes. The hydrogen storage capacity of SPEEK-h-BN 25 90 26 nanocomposite membrane increases with increasing h-BN 91 27 0.2-0.4 eV (54,58,59,61]. The obtained binding energy of hy­ and is due to the larger number ofadsorption sites offered by h­ 92 28 drogenated SPEEK-h-BN nanocomposite membranes lies BN. The hydrogenated membranes are stable at room tem­ 93 29 wilhin this range. Moreover lhe nanocomposite membranes perature. A 2.98 wt. % of hydrogen storage capacity was ach­ 94 30 exhibit 100% desorption which is estimated by comparing ieved in SPEEK-5'Y.h-BN nanocomposite membrane. The 95 31 the amount of stored hydrogen from CHN-elemental analysis average binding energy of hydrogen was found to be 0.38 eV 96 32 and desorption of stored hydrogen from TG analysis, where and the nature of hydrogen binding is weak chemisorption. 97 33 the amount of stored hydrogen is equal to the amount of Moreover the desorption tempera rure was found to be 98 34 desorbed hydrogen. Moreover, the hydrogenated SPEEK-h-BN 214-218•C for the stored hydrogen to be released and SFEEK-h- 99 35 100 36 101 37 100~------~ 102 38 (b) 103 39 104 40 80 105 41 106 42 107 ~.0- 70 ~··r==:::---, 43 ·.,- - J1.l 108 44 ::: •., 109 45 60 •' "... 110 46 , 111 47 .. . 112 48 300 400 500 113 49 Temperature <-C) Temperature (•C) 114 50 115 lOOT""------, lOOT""------, 51 (c) (d) 116 52 117 53 90 118 54 119 55 120 56 121 57 122 i 58 ; 9 1 123 59 \ 60 124 - "''-----;;,..-...::::=;! 60 114 ~ » l lO'I J U lU ~~ l " Jilt 125 61 so+---~··~ ··=-=-~~~· ~~--r--~ 50T~--~ ·~·~==~-~·~· ~----~----~ 126 62 I 00 200 300 400 500 I 00 200 300 400 500 127 0 63 Temperature ( C) Temperature ("C) 128 64 129 Fig. 10 - TGA spectra of hydrogenated (a) SPEEK-Q'Yoh-BN (b) SPEEK-l'Y.h-BN (c) SPEEK-3%h-BN and (d) SPEEK-5%h-BN 65 130 nanocomposite membranes.

Please cile this article in press as: Naresh Muthu R, et al., synlhesis and characterization of polymer (sulfonated poly-ether­ ether-ketone) based nanocomposite (h-boron nitride) membrane for hydrogen s10rage, International journal of Hydrogen Energy {2014), http://dx.doi.oqf10.10161j.ijhydene20I4.U.136 HEI5080_proof• 13 December 2014 • 9/10

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Please cite this article in press as: Naresh Muthu R, et al., synthesis and characterization of polymer (sulfonated poly-ether­ ether-ketone) based nanocomposite (h-boron nitride) membrane for hydrogen storage, International journal of Hydrogen Energy (2014), http://dx.doi.Of!fl0.10161j.ijhydene2014.U.136