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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]

Abstract: Two types of mesoporous Co–B nanocatalysts were prepared by the reduction of cobalt chloride with Sodium Borohydride (SBH) in the presence of cationic and non-ionic surfactant templates, namely n-cetyl-trimethyl-ammonium bromide (CTAB) and Pluronic (P123) respectively. Nitrogen adsorption–desorption isotherms revealed the presence of slit-like pores on the catalyst surface which provide high effective surface area. These surface enhanced catalysts were tested for hydrogen production by hydrolysis of sodium borohydride. The mesoporous Co–B catalysts showed much higher activity (4 times) in comparison to the non-porous Co–B, which can be attributed to the higher surface area of the mesoporous structures. Co–B/P123 catalyst showed the highest hydrogen generation rate owing to the presence of wide uniform pores which facilitated easier interaction of the reactants to release hydrogen. The lack of stability in the pore structure is observed at elevated temperatures for both the mesoporous Co–B catalyst. [Copyright &y& Elsevier]

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: Co–M–B–P quaternary alloy catalyst powders (where M = Cr, Mo, W, and Cu) were synthesized by chemical reduction method to improve the catalytic performance of Co–B catalyst for hydrogen production by hydrolysis of Ammonia Borane (AB). The catalytic activity increases significantly due to the combined promoting effects induced by M and P in quaternary alloy as compared to binary Co–B catalyst. The promoting roles of each doping element in Co–B catalyst during AB hydrolysis were studied using XPS, XRD, SEM, and BET surface area analyses. Each transition element, present in the form of either oxides or metal, acts as an atomic barrier to prevent Co–B particle agglomeration to increase the effective surface area. At the same time these species also act as Lewis acid sites to improve the absorption of the reactants on to the surface. Inclusion of phosphorous, in addition, is able to create higher number of Co-active sites on the surface, which was inferred from XPS analysis. Among all the alloy catalysts, Co–Cr–B–P showed the highest H2 generation rate, which was mainly attributed to the collective effects of Cr and P in forming the catalyst surface having higher surface area and more Co-active sites. On the contrary, in the case of Cu doped Co–B catalyst, the inclusion of P considerably lowers the surface area, which decreases the catalytic activity. [Copyright &y& Elsevier]

Systematic studies of Co-Mo-B-P alloy catalysts, synthesized by chemical reduction methods, were conducted for H generation by hydrolysis of ammonia borane (AB). The molar concentrations of Mo and P were optimized in the alloy to obtain the best catalytic activity. The combined promoting effects induced by Mo and P in the quaternary alloy caused the H generation rate to increase by ~7.5 times as compared to the undoped-Co-B catalyst. XPS, XRD, SEM, and BET surface area analyses were carried out to understand the promoting role of each dopant element during AB hydrolysis. In the Co-Mo-B-P alloy catalyst, Mo in form of oxides acts as an atomic barrier to avoid Co-B particles agglomeration to preserve the effective surface area. These oxidized species also act as Lewis acid sites to enhance the absorption of reactant to further assist the hydrolysis reaction over alloy catalysts. The role of P in the alloy catalyst is to create a higher number of Co active sites on the catalyst surface as confirmed by XPS. These combined promoting effects provided by P and Mo doping in the Co-B catalyst reduce the activation energy to the lowest value (23 kJ/mol) in the hydrolysis of AB. [ABSTRACT FROM AUTHOR]

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: Thin films of Carbon-supported Co–B nanoparticles were synthesized by using Pulsed Laser Deposition (PLD) and used as catalysts in the hydrolysis of 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 nanoparticles-assembled Co–B film catalysts preparation through PLD. Various Ar pressures (10–50 Pa) 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 Electron Microscopy, while structural characterization was 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 conventional Co–B powder. Almost complete conversion (95%) of AB was obtained at room temperature by using present film catalyst. Morphological analysis showed that the Co–B nanoparticles produced after the laser ablation process 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 efficient nature of our carbon-supported Co–B film is well supported by the obtained very low activation energy (∼29 kJ (mol)−1) and exceptionally high H2 generation rate (13.5 L H2 min−1 (g of Co)−1) by the hydrolysis of AB. [Copyright &y& Elsevier]

Abstract: In addition to high catalytic efficiency the catalyst must also comprise important features like high stability in severe conditions, ability to be recycled several times and should have high tolerance against deactivation. This work is oriented specifically to study these properties of already developed efficient transition-metal doped Co–B alloy catalyst. Various transition metals, namely Ni, Fe, Cu, Cr, Mo, and W, were singly added as dopants in Co–B catalyst by chemical reduction of the corresponding metal salts. These alloy catalysts were calcinated, in Ar atmosphere, at 673, 773, and 873 K in order to investigate the stability of the powders at elevated temperatures. The catalytic performances of these treated catalyst powders were tested for H2 generation by catalytic hydrolysis of sodium borohydride (NaBH4). The alloy powders were exposed to ambient condition for several days to test their tolerance against deactivation and self life. After separation from the reaction course and after rinsing, the catalyst powders were tested for several cycles to evaluate the reusability property. The observed changes in the catalytic activity were discussed on the basis of structural and morphological variations. The Co–B catalyst, when doped with Ni, Mo, and W metals showed high stability and resistance against deterioration, as function of both time and use, as compared to Cr- and Fe-doped alloy powders. A much lower performance with respect to calcination temperature, holding time, and number of cycles was established for Cu doped Co–B catalyst powder. [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: In order to sensitize TiO2 in visible light and to reduce photo-induced charge recombination, the multilayer films of Indium–Tin Oxide (ITO)/V-doped TiO2 were synthesized by radio-frequency magnetron sputtering. V-doped TiO2 thin films showed red shift in TiO2 absorption edge with increasing dopant concentration and, most importantly, the dopant energy levels are formed in the TiO2 band gap due to V5+/V4+ ions as confirmed by UV–Visible and XPS spectra. Multilayer films with different numbers of ITO/V-doped TiO2 (6 at.%) bilayers (namely, 2-, 3-, 4-, 5-, 6- and 7-bilayers) were deposited, in order to reduce the charge recombination rate, by keeping the total thickness of TiO2 constant in each multilayer film. In multilayer films, when exposed to visible light the photocurrent increases as function of the number of bilayers by reaching the maximum with 6-bilayers of ITO/V-doped TiO2. The measured enhanced photocurrent is attributed to: 1) ability of V-doped TiO2 to absorb visible light, 2) number of space-charge layers in form of ITO/TiO2 interfaces in multilayer films, and 3) generation of photoelectrons just in/or near to the space-charge layer by decreasing the V-doped TiO2 layer thickness. The reduced charge recombination rate in multilayer films was also confirmed by the photocurrent kinetic curves. The superior photocatalytic efficiency of the 6-bilayers film is also reflected in hydrogen production rate through water-splitting: we obtained indeed 31.2 μmol/h of H2 production rate. [Copyright &y& Elsevier]

Abstract: Cr-doped-TiO2 thin films, with three different Cr concentrations (2, 5.5, and 9 at.%), have been synthesized by radio-frequency magnetron sputtering in order to sensitize TiO2 in visible light. UV–visible spectra showed that maximum narrowing (2.1 eV) of the TiO2 band gap is obtained for the highest Cr concentration. However, negligible photocurrent was measured with Indium Tin Oxide (ITO)/Cr-doped-TiO2 (9 at.%) single bilayer sample due to the increased recombination rate of the photo-generated charges on the defects associated to the Cr3+ ions. To lower the charge recombination rate in the Cr-doped-TiO2, multilayer films with different numbers of ITO/Cr-doped-TiO2 (9 at.%) bilayers (namely, 3-, 4-, 5-, 6- and 7-bilayers) were deposited by keeping the total thickness of TiO2 constant in each multilayer film. When the multilayer films were exposed to visible light, we observed that the photocurrent increases as function of the number of bilayers by reaching the maximum with 6-bilayers of ITO/Cr-doped-TiO2. The enhanced photocurrent is attributed to: 1) higher absorption of visible light by Cr-doped-TiO2, 2) number of space charge layers in form of ITO/TiO2 interfaces in multilayer films, and 3) generation of photoelectrons just in/or near to the space charge layer by decreasing the Cr-doped-TiO2 layer thickness. The reduced charge recombination rate in multilayer films was also confirmed by studying the photocurrent kinetic curve. The superior photocatalytic efficiency of the 6-bilayers film implies higher hydrogen production rate through water-splitting: we obtained indeed 24.4 μmol/h of H2 production rate, a value about two times higher than that of pure TiO2 (12.5 μmol/h). [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: Cr- or Fe-ion-doped TiO2 thin films have been synthesized by radio-frequency magnetron sputtering and a sol–gel method to study hydrogen generation by photocatalytic water-splitting under visible light irradiation. The doping method, dopant concentration, charge transfer from metal dopants to TiO2, and type of dopants used for modification of TiO2 were investigated for their ability to enhance photocatalytic activity. UV–Visible spectra show that the metal-doped-TiO2 obtained by sputtering is much more efficient than that obtained by the sol–gel technique at inducing a red shift of the absorption edge in the visible light range. Low concentration metal ion doping must be done near the conducting indium tin oxide (ITO) – TiO2 interface to avoid the formation of recombination centers for photo-generated electron–hole pairs. H2 production rate (μmol/h) is higher for Fe-doped TiO2 (15.5μmol/h) than for Cr-doped TiO2 (5.3μmol/h) due to the ability of Fe ions to trap both electrons and holes, thus avoiding recombination, while Cr can only trap one type of charge carrier. A constant H2 generation rate is obtained for long periods of time by all the investigated TiO2 films because of the separate evolution of H2 and O2 gases, thus eliminating the back-reaction effect. [Copyright &y& Elsevier]

Abstract: The aim of the present work is to study the catalytic efficiency of amorphous Co–Ni–P–B catalyst powders in hydrogen generation by hydrolysis of alkaline sodium borohydride (NaBH4). These catalyst powders have been synthesized by chemical reduction of cobalt and nickel salt at room temperature. The Co–Ni–P–B amorphous powder showed the highest hydrogen generation rate as compared to Co–B, Co–Ni–B, and Co–P–B catalyst powders. To understand the enhanced efficiency, the role of each chemical element in Co–Ni–P–B catalyst has been investigated by varying the B/P and Co/Ni molar ratio in the analyzed powders. The highest activity of the Co–Ni–P–B powder catalyst is mostly attributed to synergic effects caused by each chemical element in the catalyst when mixed in well defined proportion (molar ratio of B/P=2.5 and of Co/(Co+Ni)=0.85). Heat-treatment at 573K in Ar atmosphere causes a decrease in hydrogen generation rate that we attributed to partial Co crystallization in the Co–Ni–P–B powder. The synergic effects previously observed with Co–Ni–B and Co–P–B, now act in a combined form in Co–Ni–P–B catalyst powder to lower the activation energy (29kJmol−1) for hydrolysis of NaBH4. [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]

Abstract: TiO2 thin films have been synthesized by radio-frequency magnetron sputtering and sol–gel method to study the hydrogen generation by photocatalytic water splitting under visible light irradiation. Photoelectrochemical cell with chemical bias, involving photo-anode in form of TiO2 film deposited on conducting indium tin oxide (ITO) film and Pt as cathode, is developed. The effect of conducting ITO layer on photo-voltage is studied by varying the thickness of ITO films. Constant H2 generation rate is obtained for long period of time by both the TiO2 films because of the separated evolution of H2 and O2 gas, thus eliminating the back-reaction effect. Sputter-deposited film as compared to sol–gel-synthesized film showed better H2 generation rate, mainly explained in terms of the higher visible light absorption achieved by oxygen vacancies created in the TiO2 film by the energetic target ions during deposition in pure Ar gas pressure. [Copyright &y& Elsevier]

Nanoparticles assembled Co-B-O thin film catalysts were synthesized by pulsed laser deposition (PLD) technique for hydrolysis of Sodium Borohydride (SBH). Surface morphology of the deposited films was investigated using SEM and TEM, while compositional analysis was studied using XPS. Structural properties of Co-B-O films were examined using XRD and HRTEM. Laser process is able to produce well separated and immobilized Co-B-O NPs on the film surface which act as active centers leading to superior catalytic activity producing hydrogen at a significantly higher rate as compared to bulk powder. Co-B-O thin film catalyst produces hydrogen at a maximum rate of ∼4400 ml min −1 g −1 of catalyst, which is four times higher than powder catalyst. PLD parameters such as laser fluence and substrate-target distance were varied during deposition in order to understand the role of size and density of the immobilized Co-B-O NPs in the catalytic process. Films deposited at 3–5 cm substrate-target distance showed better performance than that deposited at 6 cm, mainly on account of the higher density of active Co-B-O NPs on the films surface. Features such as high particle density, polycrystalline nature of Co NPs and good stability against agglomeration mainly contribute towards the superior catalytic activity of Co-B-O films deposited by PLD. [ABSTRACT FROM AUTHOR]

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]