Hydrogen production by sodium borohydride through hydrolysis in alkaline solutions has been extensively studied as a production/storage option due to the high volumetric and gravimetric efficiency exhibited. The potential application of this option is based on an easily controllable catalysed hydrolysis reaction, non-toxic and recyclable by-products, and the high purity hydrogen produced can be used in fuel cells. This work reports on a comparative study of own-developed, supported and non-supported, nonnoble catalyst. Ru based catalysts are taken as reference. Characterization of the catalyst was accomplished using a FEG-SEM scanning electron microscope and FTIR analysis. Obtained values amount to 10 NLmin-1g-1 for Ni-based catalyst while Ru-based catalyst amount to twice as much in the same experimental conditions. Typical solutions contain sodium borohydride of concentrations between 2 and 10 wt%, stabilized with 3 to 10 wt % NaOH. Produced hydrogen is measured at ambient pressure as a function of catalyst exposure time at controlled temperatures till completion of the reaction. A thorough study of the open literature rendered normalized values for the reaction rate with different catalyst, making comparisons valuable

Bonnetot, B.

Buni, A.

Fernandes, Vitor

Laversenne, L.

Minkina, V.

Perrin, J.

Rangel, C. M.

Silva, R. A.

Repositório do LNEG

PRODUCTION OF HYDROGEN BY BOROHYDRIDES:  IN SEARCH OF LOW COST NON-NOBLE EFFICIENT CATALYST   C. M. RANGEL1*, V.R. FERNANDES1, R.A. SILVA1,  B. BONNETOT2, L. LAVERSENE2, A. CUNI3, V. MINKINA4, J. PERRIN3  1INETI, Electrochemistry of Materials/ DMTP, Paço do Lumiar, 22 1649-038 Lisboa Portugal 2Laboratoire Multimatériaux et Interfaces, UMR CNRS 5615 Université Claude Bernard Lyon 1, 69622 Villeurbanne, France 3Air Liquide, Claude-Delorme Research Center, 1,  Chemin de la Porte des Loges  78354 Jouy-en-Josas France 4Heat and Mass Transfer Institute of the National Academy of Sciences of Belarus, 15, P. Brovki Str., Minsk, 220072, Republic of Belarus *carmen.rangel@ineti.pt   Key words: sodium  borohydride, non-noble catalyst, supported catalyst, hydrogen production  Abstract: Hydrogen production by sodium borohydride through hydrolysis in alkaline solutions has been extensively studied as a production/storage option due to the high volumetric and gravimetric efficiency exhibited. The potential application of this option is based on an easily controllable catalysed hydrolysis reaction, non-toxic and recyclable by-products, and the high purity hydrogen produced can be used in fuel cells. This work reports on a comparative study of own-developed, supported and non-supported, non-noble catalyst. Ru based catalysts are taken as reference. Characterization of the catalyst was accomplished using a FEG-SEM scanning electron microscope and FTIR analysis. Obtained values amount to 10 NLmin-1g-1 for Ni-based catalyst while Ru-based catalyst amount to twice as much in the same experimental conditions. Typical solutions contain sodium borohydride of concentrations between 2 and 10 wt%, stabilized with 3 to 10 wt % NaOH. Produced hydrogen is measured at ambient pressure as a function of catalyst exposure time at controlled temperatures till completion of the reaction.  A thorough study of the open literature rendered normalized values for the reaction rate with different catalyst, making comparisons valuable.     1. Introduction  Chemical borohydrides emerge as potential hydrogen carriers and media for storage due to their high volumetric and gravimetric efficiency. In the case of sodium borohydrides as much as 10.8 wt% hydrogen might be obtained, taking into account the reactants stoichiometric ratio [1-8 ].  Through catalysed hydrolysis, high purity hydrogen can be produced at low temperature; the reaction is exothermic and does not need energy input and the reaction products are non-toxic. Another advantage is that sodium borohydride dissolved in water is non-flammable, even though the option of using solutions as a storage media is impaired by self-hydrolysis that occurs even in stabilized solutions [9]. Cost effective recycling methods of the reaction products are also needed.  Furthermore, the development of compact and efficient reactors is limited by the availability of low cost catalysts that present high conversion rates. A number of supported catalysts are being proposed in the literature [1, 6, 9 ] since their use allows the recirculation of the working solution as well as water management, reaction products separation and the injection of borohydride for the repeated generation of hydrogen with minimal catalyst deactivation, as well as catalyst recovery.  This work reports on a comparative study of own-developed, supported and non-supported, non-noble catalyst.  A comparison of the results with those available in the open literature is made.   2. Experimental  In this work a number of non-noble metal catalysts, active in the hydrolysis of borohydride have been prepared by:   reactive sol-gel Co-based catalysts were prepared by forming a cobalt acetylacetonate complex followed by decomposition under reductive conditions.   ball milling   Ni and Ru catalyst were prepared from metal chlorides using ball milling with solid NaBH4 in order to produce pre-catalysed samples and avoid long induction times at the beginning of the hydrolysis.  wet chemistry: A Ni-based catalyst in the form of a finely divided powder was prepared from nickel salts in a reducing environment, the catalyst is bimetallic with small amounts of ruthenium. For comparison Ru nanoparticles have been also produced using the same method.   Some of the best performing catalysts were fixed on different support and their effect on reaction rate tested:    catalyst supported on α-Al2O3 and α- α-Al2O3 /SiO2  Ni, Co and Ru catalysts were used with loadings of 5 wt% metal loadings. Particle size of the metal powder varied between 19 and 34 nm.  catalyst supported on metallic foams  Ni foams with a density of 380 gm-2 and a thickness of 1.6 mm, using doctor blade technique [6].  Typical experiments used 0.1g of catalyst in solutions containing 2 to 10 wt % sodium borohydride (from either Rohm and Haas or Aviabor ) stabilised solution with either 3 or 10 wt %  NaOH, as indicated. Concentrations up to 20% NaOH were also used to ascertain the effect of NaOH as stabiliser of the self-hydrolysis of sodium borohydride.   The catalysts have been characterised using XPS, FTIR and SEM.  A study of the hydrolysis reaction was first conducted at ambient pressure in order to determine reaction rates in different conditions. The volume of generated gas was measured by a water displacement method rendering values at standard pressure and temperature. Some experiments were also conducted in a batch type reactor. The produced gas volumes were measured as a function of time at controlled temperature, till complete exhaustion of the reactant.     3. Results and Discussion  Non-supported catalyst    Pre-catalysed samples prepared by reactive sol-gel were tested using a 10 wt%  NaBH4 solution stabilized with 3 wt% of NaOH. Figure 1a) shows the amount of generated gas which exhibits a linear relationship with exposure time and increases with Co concentration in the samples for concentrations up to 5 wt% Co. An increase in the amount of Co brings about a drop in the reaction rate, furthermore, the production rate is variable slightly increasing after the first 20 minutes of exposure but never reaching or surpassing the generation rate for sample with 5 wt% Co. It is noticeable that the borohydrides present in the catalyst is also reacted to produce hydrogen. For the case of the catalyst containing 1 wt% Co the reaction was slower and was not allowed to proceed till the end.  Since the sample containing 5 wt %Co showed the best results, the effect of temperature was studied with this catalyst concentration. Results are shown in figure 1b).  Borohydride from the solution and that incorporated in the catalyst reacted to full extent to produce hydrogen.                      (a)                                                                    (b)   Figure  1.  The effects of concentration of the catalyst (a) and temperature for the pre-catalysed 5 wt % Co catalyst powder (b) in a 10 wt % NaBH4 solution stabilised with 3 wt% of NaOH. (All sodium borohydride present reacted to form hydrogen gas, when the reaction was slow as in the case of 1% Co catalyst, the measurements were interrupted after 80 minutes).   Using the Ni-based nanopowder prepared by wet chemistry, the variation of the hydrogen production rates exhibited a maximum at 10 wt% NaOH [9]. Variation with the temperature up to 60ºC give more than 10 L gas per minute per gram of catalyst, see figure 2. Ruthenium nanoparticles were also tested in the same conditions giving a rate of 26 Lmin-1g-1.  Supported Catalyst  On α-Al2O3 and α-Al2O3 / SiO2  Co, Ni catalysts supported on α-Al2O3 and α-Al2O3 / SiO2 were also tested both at ambient pressure and in a small batch reactor. Ru catalyst was supported only on α-Al2O3.  Ru presented the highest reaction rates. The catalyst support was observed to dissolve in the reaction media, as suggested by EDAX analysis of the powders, before and after use of the catalyst in the hydrolysis of NaBH4, see figure 3. In the case of the alumina /silica support, the silica appears preferentially lost. The powder preparation for observation under the scanning electron microscope, 020040060080010001200140016000 20 40 60 80 100time /minVgas/ml1% Co + NaBH45% Co + NaBH410% Co + NaBH4020040060080010001200140016000 50 100 150time/minVgas/ml25ºC37ºC45ºCincluded coating of the powder with gold justifying the observed corresponding peak. Na and B are also identified.     Figure  2. Reaction rates as a function of temperature for Ni-based catalyst for 10 wt% NaOH.       Figure 3. Typical EDAX spectra for supported catalyst before and after testing in sodium borohydrides. Ru catalyst supported on Alumina (a); Ni catalyst supported in Alumina –Silica (b), showing Aluminium loss in the first case and Si loss in the second case. The blue line represents the spectrum recorded for the sample after reaction.   02468101220 30 40 50 60 70T/ºCReaction rate / Lmin-1g-1 (a) (b)  On Ni metallic foam   Ni-based catalyst formulations were fixed on a Ni metallic foam with a density of 380g.m-2 and a thickness of 1.6 mm.   Figure 4a) shows a SEM picture of the used foam with applied catalyst. Figure 4b) shows the volume of gas produced as a function of time in a 2 wt % sodium borohydride solution at 45 and 65ºC.  Three different regions were identified: a region of adsorption of species where there is no hydrogen production, which represents a reaction induction time; this region is activated by temperature. A second region, associated to a linear variation of the volume of produced gas with time and a third region where the rate of H2 decreases before it stops due to total consumption of sodium borohydride.   Even though a comparative analysis of data obtained from the open literature revealed itself difficult, due to the different experimental conditions used, an attempt was made to collect relevant results that could be compared with the data obtained in the present work, see table 1.                          (a)                                                                          (b)  Figure  4.   SEM view of Ni-based catalyst supported on a Ni foam (a). Hydrogen volume produced using a Ni based supported catalyst at room temperature and 65ºC using a 2 wt % NaBH4 solution stabilised with 10 wt% NaOH.   It is observed that the data obtained in this work compare well with the highest rates obtained by other authors when using own synthesised Ru powder or with supported Ni-based catalyst.  Regarding Ru catalyst high surface area powders were reported to reach 60 Lmin-1g-1 [10].    FTIR analysis of the catalyst indicate characteristics band for groups  Ni--OOH and Ni—OH at 463 and 651 cm-1, respectively as well as a wide band at 3640-3250 cm-1 and peaks  between 1430-980 cm-1 and 1633 cm-1 attributed to stretching and deformation vibrations of OH groups and bending vibrations of H--O—H.   More comprehensive results accounting for the characterisation of the catalyst used will be the subject of publication elsewhere.     010002000300040005000600070000.10 1.00 10.00 100.00t (min)V (ml)  Table1. Data on supported and non-supported catalyst used for the production of hydrogen from sodium borohydride solutions stabilised with NaOH in various experimental conditions.   Catalyst Solution composition/  Amount of catalyst H2 generated (Lmin-1g-1) / T  Reference Ru/IRA400  10wt% NaOH;10wt% NaBH4 / 250 mg (5 wt%Ru)  12         (45ºC) Amendola 2000   10wt% NaOH, 1,5 wt% NaBH4;     0.29     (40ºC) Ni/B 10wt% NaOH, 1,5 wt% NaBH4 / 200 mg (2 wt%Ru)    0.83     (60ºC) Hua 2003 Ni Filaments 10wt% NaBH4, KOH 0,01M, /Ni Filaments, 1g    0.057    (RT) Ni Filaments 20wt% Co 10wt% NaBH4, KOH 0,01M, /Ni Filaments 20 wt% Co 1g    0.089    (RT) Kim 2004 Co/B 2wt% NaBH4, 5wt%NaOH / 100 mg 1.4 (without T control) Wu 2005 Ru  5wt% NaOH;20wt% NaBH4/ 50 mg    1.6       (20ºC) Co/B  5wt% NaOH;20wt% NaBH4/ 50 mg    0.88     (20ºC) Jeong 2005 Pt- LiCoO2 5wt%NaBH4, 5wt%NaOH / 239 mg (Pt 10 wt%)  16          (25ºC) Ru- LiCoO2 5wt%NaBH4, 5wt%NaOH / 125 mg (Ru 10 wt%)    9.6       (25ºC) PtRu-LiCoO2 5wt%NaBH4, 5wt%NaOH,/ 125 mg (PtRu 10 wt%)    3.8       (25ºC) Ru em IRA-400 5wt%NaBH4, 5wt%NaOH / 185 mg (Ru 6.78 wt%)    3.3       (25ºC) Krishman 2005 Ru  26          (45ºC) Ni-based bimetallic 10wt% NaOH; 10wt% NaBH4 /  50 mg     8.5       (45ºC) Ni-based bimetallic / Ni foam 10wt% NaOH;2wt% NaBH4 / 60 mg  10          (60ºC) This work       CONCLUSIONS  A number of catalysts have been synthesised and tested in sodium borohydride stabilized solutions in a search for cheap, stable and efficient catalyst for hydrogen production. Ni-based catalyst performed well at temperatures up to 60ºC. Supporting on Ni foams gave excellent results allowing re-use of the catalyst and repeated injection of the borohydride solution with no catalyst de-activation. Ru catalysts were taken as a reference both from literature data and own-synthesized powder giving always higher rates.   Acknowledgements :  Partial funding by the European Commission DG Research (Contract SES6- 2006-518271/ NESSHY) is gratefully acknowledged by the authors.     References  [1] Amendola S.C., Sharp-Goldman S.L., Janjua M.S., Kelly M.T., Petillo P.J, Binder M. (2000). An Ultrasafe Hydrogen Generator: Aqueous, Alkaline Borohydride Solutions and Ru Catalyst. J. Power Sources, 85:186–189. [2] Amendola S.C., Sharp-Goldman S.L., Janjua M.S., Spencer N.C., Kelly M.T., Petillo P.J., Binder M. (2000). A Safe Portable Hydrogen Gas Generator using Aqueous Borohydride Solutions and Ru Catalyst.   Int. J. Hydrogen Energy, 25:969-975. [3] Hua D., Hanxi Y., Xinping A., Chuansin C. (2003). Hydrogen Production from Ctalytic Hydrolysis of Sodium Borohydride using Ni Boride Catalyst. Int. J. Hydrogen Energy, 28:1095-1100. [4] Kim J-H, Lee H., Han S-Ch., Kim H-S., Song M-S, Lee J-Y. (2004). Production of Hydrogen from Sodium Borohydride in Alkaline Solutions: Development of Catalyst with High Performance Int. J. Hydrogen Energy, 29 263-267. [5] Jeong S.U., Kim R.K., Cho E.A., Kim H.-J., Nam S.-W., Oh I.-H., Hong S.-A., Kim S.H. (2005). A Study of Hydrogen Generation using High Performance Co-B Catalyst. J. Power Sources 144:129-134. [6] Krishmnan P., Yang T-H, Lee W-Y, Kim Ch-S. (2005). Pt-Ru-LiCoO2- An Efficient Catalyst for Hydrogen Generation from Sodium Borohydride Solutions. J. Power Sources, 143:7-23. [7] Rangel C.M, Silva R.A., Fernandes V.R., Hydrogen Storage and Production at Low Temperatures from Borohydrides, 16th World Conference on Hydrogen Energy, paper 598, Lyon, 2006. [8] Pinto AMFR, Falcão D.S., Silva R.A., Rangel C.M. (2006).Hydrogen Generation ans Storage from Hydrolysis of Sodium Borohydride in Batch Reactors. Int. J. Hydrogen Energy, 31:1341-1347.  [9] Rangel C. M., Fernandes V.R., Silva R.A, “Producción de Hidrógeno por Borohidruros sobre Catalizadores Soportados” CONAPPICE, Madrid, 2006. [10] S.Ozkar, M. Zahmakiran. (2005). Hydrogen Generation from Hydrolysis of Sodium Borohydride using Ru(0) Nanoclusters as Catalyst. J. Alloys Comp., 404-406:728-731. 

Production of hydrogen by borohydride: in search of low cost non-noble efficient catalyst

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Production of hydrogen by borohydride: in search of low cost non-noble efficient catalyst

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