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Hydrogen Generation by Both Acidic and Catalytic Hydrolysis of Sodium

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Hydrogen Generation by Both Acidic and Catalytic Hydrolysis of Sodium Catal. Sustain. Energy 2018; 5: 41–48 Short communication Olga V. Netskina*, Tihon N. Filippov, Oksana V. Komova, Valentina I. Simagina Hydrogen generation by both acidic and catalytic hydrolysis of sodium borohydride https://doi.org/10.1515/cse-2018-0006 most closely satisfy these severe requirements [8-13]. First, Received October 9, 2018; accepted October 16, 2018 they have no rivals in the mass content of hydrogen. For Abstract: Sodium borohydride tablets have been employed example, potassium borohydride, sodium borohydride as hydrogen-storage materials. Hydrogen release was and ammonia borane have hydrogen densities of 0.083, performed by acidic hydrolysis where solutions of sulfuric 0.112 and 0.145 g·cm-3, respectively, which exceeds the and hydrochloric acids were added to the tablets, and value for liquefied hydrogen (0.07 g·cm-3). Second, hydride by catalytic hydrolysis where water was added tablets interaction with water increases the hydrogen yield of solid-state NaBH4/Co composite. In acidic solutions twofold, water being involved in the gas generation. hydrogen evolution occurred instantaneously, and at high concentrations of acids the releasing hydrogen contained an MH n + nH2O → M(OH )n + nH2 , (1) (1) admixture of diborane. Hydrogen evolution from the solid- where M is an alkali or alkaline-earth metal. state NaBH4/Co composite proceeded at a uniform rate of 4CoCl + 8NaBH + 18H O ⎯⎯→ (4Co : 2B) + 6B(OH ) + 8NaCl + 25H (2) 13.8±0.1 cm3·min-1, water vapor being the only impurity in the However, hydrolysis2 of hydrides4 is not2 a totally safe catalyst 3 2 evolving gas. process, since it evolves a large amount of heat per mole of -1 -1 hydrogen: 2LiHBH –3 145→ kJ·molB2 H6; MgH 2 – 160 kJ·mol ; LiBH 4 – (4) -1 -1 -1 Keywords: Hydrogen, sodium borohydride, acid 90 kJ·mol ; LiAlH4 – 150 kJ·mol ; NaAlH4 – 142 kJ·mol ; AlH3 hydrolysis, diborane, catalyst hydrolysis 156 kJ·mol-1; CaH – 140 kJ·mol-1; NaH – 152 kJ·mol-1 [14,15]. 2NaBH2 + H SO → Na SO + B H + 2H (5) Unlike most hydrides,4 sodium2 4 borohydride2 4 interaction2 6 2 with water has a comparatively small heat effect (80 kJ per mole of2NaBH hydrogen)4 + so2 HClthat its→ complete2NaCl conversion+ B2 H6 + can2H 2 (6) 1 Introduction be achieved either at temperatures above 110 °С and in the presence of vapors of hydrochloric or acetic acids [16], The development of compact hydrogen sources is an + → + or over metalBH catalysts3 3H 2[17,18]O whichB(OH opens)3 the3H possibility2 (7) important direction of hydrogen energy research [1-7]. of the control of the process of hydrogen generation. Compact hydrogen sources must provide high yields Inexpensive but active+ cobalt +catalysts are→ most often+ + of hydrogen per unit of mass or volume without any 2NaBH 4 6H2O H2SO4 Na 2SO4 2B(OH )3 8H2 (8) used [19,20]. Acid catalysts prepared by modifying the additional heating, as well as purification of hydrogen support with sulfuric [21], boric, and citric [22] acids are from compounds that act as catalytic poisons for + + → + + also efficientNaBH in 4hydrogen3H2O generationHCl fromNaCl solutionsB(OH of )3 4H2 (9) electrodes of low-temperature proton exchange membrane sodium borohydride. fuel cells, requirements strongly narrowing the range of Along with the+ catalytic→ sodium borohydride+ hydrogen-generating materials suitable for energy-carrier NaBH 4 4H 2O NaB(OH )4 4H 2 (10) hydrolysis, hydrogen generation by adding inorganic or applications. Binary and complex hydrides of alkali metals organic acids to a solution of this hydride has also been discussed in the literature [23-25]. It has been demonstrated *Corresponding author: Olga V. Netskina, Laboratory of Hydrides that the addition of a weak solution (0.25 M) of phosphoric Investigation, Boreskov Institute of Catalysis SB RAS, Pr. Akademika acid to sodium borohydride in the presence of a copper Lavrentieva 5, Novosibirsk, 630090, Russia, [email protected] catalyst which has a low activity leads to a substantial Tihon N. Filippov, Photocatalysis group, Boreskov Institute of Cata- growth in the hydrogen generation rate [26]. Nevertheless lysis SB RAS, Pr. Akademika Lavrentieva 5, Novosibirsk, 630090, Russia in dilute solutions of acids, complete conversion of this Oksana V. Komova, Valentina I. Simagina, Laboratory of Hydrides hydride could not be achieved without catalysts and Investigation, Boreskov Institute of Catalysis SB RAS, Pr. Akademika increased concentrations of acids were used to increase Lavrentieva 5, Novosibirsk, 630090, Russia Open Access. © 2018 Olga V. Netskina et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution- NonCommercial-NoDerivs 4.0 License. 1 42 O.V. Netskina, et al. the hydrogen yield and the rate of gas generation [27]. No 7791-13-1, 97 wt%) in a 0.12 М aqueous solution of + → + An XRD analysis of the non-gaseous products of the sodiumMH n borohydridenH2O Mat( OH40 )°Сn withnH 2constant, stirring (1) interaction of sodium borohydride with acids has shown at 400 rpm. The Co:NaBH4 mole ratio was 1:25. them to be sodium boratesMH +andnH sodiumO → M salts(OH )of+ thenH , (1) n 2 n 2 4CoCl2 + 8NaBH 4 + 18H 2O ⎯⎯→ (4Co : 2B)catalyst + 6B(OH )3 + 8NaCl + 25H 2 (2) corresponding acids [28]. According to a chromatographic analysis, the hydrogen-containing4CoCl + gas8NaBH did not+ contain18H O any⎯⎯ → (4Co : 2B) + 6B(OH ) + 8NaCl + 25H (2) (2) 2 4 2 catalyst→ 3 2 impurities even in the case of hydrochloric acid [29]. This 2BH 3 B2 H6 (4) result is doubtful and needs additional investigation since After gas evolution the black ferromagnetic catalyst 2BH 3 → B2 H6 (4) hydrogen chloride easily evaporates and is always present precipitate2NaBH 4was+ Hseparated2SO4 → Nafrom2SO the4 +reactionB2 H6 + medium,2H2 (5) above a hydrochloric acid solution. washed with acetone (CAS No 67-64-1, 99 wt%) and dried 2NaBH 4 + H2SO4 → Na 2SO4 + B2 H6 + 2H2 (5) Despite the convenienceof aqueous sodium in a2 vacuumNaBH box+ 2 atHCl 70 →°С for2NaCl 2 hr. The+ B synthesizedH + 2H cobalt (6) borohydride solutions for hydrogen generation by catalyst was4 stored in desiccators under2 argon6 to prevent2 + → + + acidic and catalytic hydrolysis,2NaBH 4 in 2storageHCl the2NaCl sodiumB2 Hits6 oxidation2H2 by air. The reduction of the cobalt catalyst (6) borohydride slowly interacts with water even in the by sodiumBH 3 + borohydride3H2O → B leads(OH to)3 the+ 3 formationH2 of spherical (7) presence of sodium hydroxideBH 3 [30-32].+ 3H2O This→ Bnot(OH only)3 +leads3H2 particles (average size 30 nm) consisting of a core of (7) to a reduction in hydrogen content but also to changes in amorphous cobalt-boron and an oxygen-containing shell 2NaBH 4 + 6H2O + H2SO4 → Na 2SO4 + 2B(OH )3 + 8H2 (8) the character of the in situ2NaBH reduction4 + 6H of2 Ocobalt+ H2 SOcatalysts4 → Na 2(thicknessSO4 + 2B (3-5OH nm).)3 + 8InH an2 earlier study the molar ratio of (8) because of the forming sodium tetrahydroxoborate [33]. the elements in such cobalt-boron catalysts was found NaBH + 3H O + HCl → NaCl + B(OH ) + 4H (9) Considering the instability of sodium borohydride to be Co:B:O:H=3.2:1.5:1.4:14 2 [39]. The physicochemical3 2 NaBH 4 + 3H2O + HCl → NaCl + B(OH )3 + 4H2 (9) solutions it was suggested that this hydride in the form of properties of the prepared cobalt catalyst have been tablets may be stored and used for hydrogen generation describedNaBH in4 + detail4H 2 elsewhereO → NaB [39,40].(OH )4 + 4H 2 (10) NaBH 4 + 4H 2O → NaB(OH )4 + 4H 2 (10) [34-37]. The advantages of such an approach are: high The elemental composition of the catalyst was content of hydrogen (up to 10 wt %), the absence of an identified by atomic-emission spectroscopy with alkali, no losses of hydrogen in storage, simplicity of inductively-coupled plasma on an Optima 4300V operation using water from any natural source, as well instrument (Germany). The relative error of determination as the possibility to vary the rate of gas generation by of cobalt and boron did not exceed 5 %. varying the amounts of the added inexpensive cobalt For the hydrogen generation kinetic study, the tablets catalyst [38]. It is important to consider the composition were placed into a temperature-controlled glass reactor at 3 of the gas evolving from the NaBH4 tablet when used as 40 °С and then 5 cm of water or an acid solution of a given a hydrogen source since impurities can poison fuel cell concentration (H2SO4 – from 6.2 to 98 wt%, CAS No 7664- electrodes catalytically. To date, little attention has been 93-9; HCl – 34 wt%, CAS No 7647-01-0) was added. The paid to this issue in the literature. Also, there have been volume of the evolving gas was determined volumetrically no publications comparing the efficiencies of hydrogen using a gas burette and reduced to normal conditions generation from solid-state compositions of NaBH4 by (N refers to normal conditions, i.e., 0°C, 1 atm). Each acidic and catalytic hydrolysis. experiment was repeated three times and the average The aims of this work are (I) to compare the kinetic values were taken to construct the kinetic dependences. regularities of hydrogen generation from sodium The relative experimental error did not exceed 2 %. borohydride tablets in solutions of acids with different The qualitative analysis of the hydrogen-containing concentrations and from NaBH4/Co tablets upon addition gas was performed on a Nicolet 380 IR-spectrometer of water and (II) to determine the qualitative composition (Thermo Scientific, USA). The spectrometer was equipped of the forming hydrogen-containing gas. with a gas cell with an optical path length of 10 cm. The scan space was from 900 to 4000 cm-1, the resolution was 1 cm-1.
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