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Ruthenium nanoparticles (NPs) supported over carbon thin films (Ru/C thin films) catalysts were synthesized by pulsed laser deposition and used as catalysts for hydrolysis of ammonia borane (AB). Highly irregular and porous carbon films with high surface area were deposited by varying Ar gas pressures during the deposition. By taking the advantage of phase explosion phenomena, occurring at high laser fluence, the surface of the carbon films were decorated with crystalline Ru NPs with size below ∼10 nm. Ru/C thin film catalyst produced H 2 with 6 times higher H 2 generation rate as compared to unsupported Ru NPs assembled film, and with a high turnover frequency value of 70.5 mol H 2 mol −1 Ru min −1 . A combination of morphological features and high content of sp 2 bonded C atoms provides good dispersion of Ru NPs over a large surface area. Both these features contribute in generating large number of active sites leading to the increase in catalytic efficiency. A possibility of using the present form of catalyst as an ON/OFF switch for H 2 production was also tested. Although the catalytic activity decreased with the number of hydrolysis cycles, Ru/C thin film catalyst was able to generate the expected amount of H 2 gas in each cycle when it was reused several times. The observed low activation energy (∼28 kJ mol −1 ) and high H 2 generation rate (15.5 L H 2 min −1 g −1 of Ru) by hydrolysis of AB suggest that Ru/C thin film catalyst is highly efficient. [ABSTRACT FROM AUTHOR]

Highlights: [•] Co-B catalyst particles were supported over three type of mesoporous silica of different pore sizes. [•] Co-B supported over SBA-15 showed highest H2 generation rate for hydrolysis of AB. [•] Confinement of Co-B within the pores creates smaller NPs (6nm) with uniform size distribution. [•] Thicker pore walls of SBA-15 avoid agglomeration of Co-B NPs at elevated temperature (873K). [Copyright &y& Elsevier]

Abstract: Catalyst in the form of Co-B nanoparticles supported on mesoporous silica particles (MSP) was synthesized by chemical impregnation–reduction method. This catalyst powder was used for hydrogen production by hydrolysis of Ammonia Borane (AB) and was compared with Co-B catalyst supported on non-porous silica particles (NSP) and unsupported Co-B powder. It was found that the MSPs synthesized in the present studies have average pore size of about 3.1nm which were efficient to anchor the Co-B particles with average size of ~8nm on the surface to provide high active surface area and improved degree of dispersion. MSP-supported Co-B catalyst was able to produce expected amount of H2 gas from hydrolysis of AB with significantly superior generation rate, about 3 times higher than that produced by unsupported and NSP-supported Co-B catalyst. Availability of a large number of under-coordinated Co active atoms owing to the size of nanoparticles, better dispersion, high surface area and good stability against agglomeration during the reaction are the main features acquired by the Co-B nanoparticles supported on MSP that exhibit high catalytic efficiency. [Copyright &y& Elsevier]

Abstract: Co-B nanoparticles supported over carbon films were synthesized by using pulsed laser deposition (PLD) and used as catalysts in the hydrolysis of sodium borohydride (NaBH4) to produce molecular hydrogen. Amorphous Co-B-based catalyst powders, produced by chemical reduction of cobalt salts, were used as target material for nanoparticles-assembled Co-B film catalysts preparation through PLD. Various Ar pressures (10–50Pa) were used during deposition of carbon films to obtain extremely irregular and porous-carbon support with high surface area prior to Co-B film deposition. Surface morphology of the catalyst films was studied using scanning and transmission electron microscopy, while structural characterizations were carried out using X-ray diffraction. The hydrogen generation rate attained by carbon-supported Co-B catalyst film is significantly higher as compared to unsupported Co-B film and to conventional Co-B powder. Morphological analysis along with NaBH4 hydrolysis tests showed that the Co-B nanoparticles produced with PLD act as active catalytic centers for hydrolysis while the carbon support provides high initial surface area for the Co-B nanoparticles with better dispersion and tolerance against aggregation. The hydrogen generation rate obtained by the present catalyst film was also investigated as a function of Co-B loading, carbon morphology, and solution temperature. The high performance of our carbon-supported Co-B film is well supported by the obtained very low activation energy (∼31kJ (mol)−1) and exceptionally high H2 generation rate (8.1LH2 min−1 (gofcatalyst)−1) in the hydrolysis of NaBH4. [Copyright &y& Elsevier]

Abstract: A systematic and comparative study is conducted on Co–B-based ternary alloy catalysts for H2 generation by hydrolysis of NaBH4. Various transition metals, namely Ni, Fe, Cu, Cr, Mo, and W, were added to Co–B catalyst by chemical reduction of the corresponding metal salts. All the transition metals in the Co–B compounds behave in a dissimilar manner while influencing the catalytic activity. Cr, W, Mo, and Cu impose significant promoting effects on the Co–B catalyst by increasing the H2 generation rate by 3–4 times when compared to the undoped catalyst. On the contrary, Ni and Fe are only able to create a marginal increment in the catalytic performance of the Co–B catalyst. The metal/(Co+metal) molar ratio was varied in the catalyst in order to study the effect of metal doping on surface morphology, electronic interaction, and catalytic efficiency of the alloy catalyst. This systematic variation also contributed to clarify the role of each dopant metal in the electron exchange mechanism involved in NaBH4 hydrolysis. The promoting effects of the dopant metals are mainly discussed in terms of large active surface area, ability to act as Lewis acid sites for better absorption of OH− group, electronic interaction with Co active metal, and amorphous nature of the alloy catalyst. [Copyright &y& Elsevier]

Abstract: Nanoparticle-assembled Co-B thin films were synthesized by Pulsed Laser Deposition (PLD) and used as catalysts for the hydrolysis of NH3BH3 (ammonia borane, AB) to produce molecular hydrogen. Amorphous Co-B-based catalyst powders, produced by chemical reduction of cobalt salts, were used as target material for Co-B thin film catalysts preparation through PLD. Surface morphology of Co-B powder and film catalyst was studied using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Compositional and structural characterizations were carried out using X-photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) techniques, respectively. The efficiency of both powder and film catalysts was tested by comparative kinetic analysis of the AB hydrolysis for hydrogen production. It was observed that nanoparticles produced during the laser ablation process act as active catalytic centers to produce significantly higher rate (about 6 times) of H2 than the same amount of the corresponding Co-B powders. Almost complete conversion (95%) of AB was obtained, as confirmed by 11B NMR, by using Co-B films at room temperature. Active Co-B nanoparticles on the surface of the PLD-deposited films is able to decrease the activation energy, for hydrolysis of AB, to the very low value of 34kJmol−1. We also found that by adding small amount of NaBH4 to the NH3BH3 solution increases the efficiency of the Co-B catalyst films, thus generating H2 with higher rate. Maximum H2 generation rate of about ∼8.2LH2 min−1 (g of Co)−1 and ∼13LH2 min−1 (g of Co)−1 was measured by hydrolysis of AB and mixture of (AB+NaBH4) solutions, respectively. [Copyright &y& Elsevier]

Abstract: Cr-modified Co–B (Co–Cr–B) catalyst alloy powders have been synthesized by chemical reduction of cobalt and chromium salt at room temperature to study the hydrogen production by catalytic hydrolysis of NaBH4. The Cr/Co molar ratio was varied in the catalyst in order to study the effect of Cr doping on surface modification and catalytic efficiency of Co–B catalyst. The resulting catalyst powders were characterized by scanning electron microscopy, X-ray diffraction, X-photoelectron spectroscopy, and BET surface area measurement. When the molar ratio χ Cr =Cr/(Cr+Co) exceeds 9% the BET surface area of the Co–Cr–B catalyst increases by one order of magnitude as compared to that of Co–B catalyst. The catalytic activity of the Co–Cr–B for hydrogen production depends on Cr concentration: specifically, the activity increases by increasing χ Cr up to about 4% and then it gradually decreases by further increasing χ Cr. We established that the increased catalytic activity is related to the formation of chromium oxide on the catalyst surface, with the oxide favoring the dispersion of Co–B particles resulting in high catalyst surface area. However as χ Cr exceeds 4%, Cr starts to cover the Co active sites and the corresponding catalytic activity decreases. The highest catalytic activity was obtained at the optimum Cr-content, χ Cr =4%, in Co–Cr–B catalyst, showing nearly 4 times higher H2 generation rate than that of pure Co–B catalyst. Kinetic studies on the hydrolysis reaction of NaBH4 with Co–Cr–B catalyst reveal that the concentrations of both NaBH4 and NaOH have essentially no effects on hydrogen generation rate. The promoting effect of Cr in Co–Cr–B catalyst results in lower activation energy for hydrogen production, which is 37kJmol−1 as compared to 45kJmol−1 obtained with pure Co–B powder. Finally, the possible role of Cr3+ species in the electron exchange mechanisms involved in NaBH4 hydrolysis with the Co–Cr–B catalyst has been discussed. [Copyright &y& Elsevier]

Abstract: Amorphous catalyst alloy powders in form of Co–P, Co–B, and Co–P–B have been synthesized by chemical reduction of cobalt salt at room temperature for catalytic hydrolysis of NaBH4. Co–P–B amorphous powder showed higher efficiency as a catalyst for hydrogen production as compared to Co–B and Co–P. The enhanced activity obtained with Co–P–B (B/P molar ratio=2.5) powder catalyst can be attributed to: large active surface area, amorphous short range structure, and synergic effects caused by B and P atoms in the catalyst. The roles of metalloids (B and P) in Co–P–B catalyst have been investigated by regulating the B/P molar ratio in the starting material. Heat-treatment at 773K in Ar atmosphere causes the decrease in hydrogen generation rate due to partial Co crystallization in Co–P–B powder. Kinetic studies on the hydrolysis reaction of NaBH4 with Co–P–B catalyst reveal that the concentrations of both NaOH and catalyst have positive effects on hydrogen generation rate. Zero order reaction kinetics is observed with respect to NaBH4 concentration with high hydride/catalyst molar ratio while first order reaction kinetics is observed at low hydride/catalyst molar ratio. Synergetic effects of B and P atoms in Co–P–B catalyst lowers the activation energy (32kJmol−1) for hydrolysis of NaBH4. The stability, reusability, and durability of Co–P–B catalyst have also been investigated and reported in this work. It has been found that by using B/P molar ratio of 2.5 in Co–P–B catalyst, highest H2 generation rate of about ∼4000mlmin−1 g−1 can be achieved. This can generate 720W for Proton Exchange Membrane Fuel Cells (0.7V): which is necessary for portable devices. [Copyright &y& Elsevier]

Nanocatalysts, in the form of nanoparticles assembled coatings (NPACs) of Co 3 O 4 , were synthesized by pulsed laser deposition (PLD) with optimized parameters. Phase explosion phenomena occurring at high laser fluences produce nanoparticles (NPs) with an average size of ∼5 nm having narrow size distribution (3–10 nm) and low degree of agglomeration, which are randomly arranged in the form of coating on the substrate surface. In comparison with chemically synthesized Co 3 O 4 crystalline powder, the NPACs deposited by PLD showed significantly higher catalytic activity for H 2 generation by hydrolysis of NaBH 4 . Maximum H 2 generation rate obtained by NPACs (5010 ml min −1 g cat −1 ) is about 5 times higher than that produced by Co 3 O 4 powder (1000 ml min −1 g cat −1 ), which is mainly attributed to high surface area and large number of active sites provided by the Co 3 O 4 NPs in the coating owing to their size and shape. By varying the O 2 pressure during PLD, two different cobalt oxide phases, namely Co 3 O 4 and CoO, were formed in NPACs and found that Co 3 O 4 phase is more active for hydrolysis than CoO phase with lower oxidation number. The morphology and crystallinity of Co 3 O 4 NPACs were tuned by varying the laser fluence and substrate temperature respectively, and their effect on H 2 generation rate was studied. The results showed that the NPs with mixed amorphous-nanocrystalline phase on the surface act as active sites for favorable interaction and NaBH 4 conversion. [ABSTRACT FROM AUTHOR]