Electroless-deposited Co–P catalysts for hydrogen generation from alkaline NaBH4 solution

Cobalt–phosphorus (Co–P) catalysts, which were electroless deposited on Cu sheet, have been investigated for hydrogen generation from alkaline NaBH₄ solution. The microstructures of the as-prepared Co–P catalysts and their catalytic activities for hydrolysis of NaBH₄ are analyzed in relation to pH value, NaH₂PO₂ concentration, and the deposition time. Experimental results show that the Co–P catalyst formed in the bath solution with pH value of 12.5, NaH₂PO₂ concentration of 0.8 M, and the deposition time no more than 6 min presents the highest hydrogen generation rate of 1846 mL min⁻¹ g⁻¹. Furthermore, the as-prepared catalyst also shows good cycling capability and the corresponding activation energy is calculated to be 48.1 kJ mol⁻¹. The favorable catalytic performance of the electroless-deposited Co–P catalysts indicates their potential application for quick hydrogen generation from hydrolysis of NaBH₄ solution.     

Fabrication of porous Co–Ni–P catalysts by electrodeposition and their catalytic characteristics for the generation of hydrogen from an alkaline NaBH4 solution

Porous Co–Ni–P catalysts were made on Cu substrates by electrodeposition in order to generate hydrogen from an alkaline sodium borohydride (NaBH₄) solution. We investigated the effects of the cathodic current density and the electrodeposition time on the surface morphology and chemical composition of the Co–Ni–P catalysts. The hydrogen generation characteristics from an alkaline NaBH₄ solution using these catalysts in an alkaline NaBH₄ solution were then investigated. The cathodic current density significantly affected the growth behavior and catalytic properties of the Co–Ni–P electrodeposits. Co–Ni–P catalysts grew two-dimensionally at a low cathodic current density of 0.01 A cm⁻². By contrast, at a cathodic current density of more than 0.05 A cm⁻², three-dimensional growth of the catalysts occurred due to the large cathodic overpotential. In addition, the rates of hydrogen generation were found to be higher for the three-dimensional catalysts than the two-dimensional catalysts. Three-dimensional growth of the Co–Ni–P catalysts continued as the electrodeposition time increased from 1 to 10 min at a cathodic current density of 0.1 A cm⁻². The surface areas of the three-dimensional Co–Ni–P catalysts increased gradually with electrodeposition time, resulting in their catalytic efficiency for the hydrolysis of NaBH₄ being improved. The hydrogen generation rate was also influenced by the concentrations of the NaOH and NaBH₄ in the alkaline NaBH₄ solution. The hydrogen generation rate increased gradually with increasing NaOH concentration. By contrast, there was an optimum concentration of NaBH₄, above which the hydrogen generation rate decreased. Finally, the hydrogen generation rate from Co–Ni–P catalysts was found to decrease due to the precipitation of by-products.     

Efficient catalytic properties of Co–Ni–P–B catalyst powders for hydrogen generation by hydrolysis of alkaline solution of NaBH4

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 573 K 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 (29 kJ mol⁻¹) for hydrolysis of NaBH₄.     

Performance evaluation of hydrogen generation system with electroless-deposited Co–P/Ni foam catalyst for NaBH4 hydrolysis

In this work, the performance of a hydrogen generation system with an electroless-deposited Co–P/Ni foam catalyst for NaBH₄ hydrolysis was evaluated. The performance of a hydrogen generator using a combination of Co/γ-Al₂O₃ and Co–P/Ni foam catalysts was also evaluated in order to address the shortcomings with the individual catalysts. The generator had high conversion efficiency, fast response characteristics, and strong catalyst durability. Hydrogen generation tests were performed to investigate the effect of the composition of the NaBH₄ solution on the hydrogen generation properties. The generator's conversion efficiency decreased with an increase in the amount of solute dissolved in NaBH₄ solution because of the accumulation of precipitates on the catalyst, and NaOH concentration had a greater effect on the hydrogen generation properties than did NaBH₄ concentration. According to these results, the hydrogen generation system with the Co–P/Ni foam catalyst is suitable as a hydrogen supplier for proton exchange membrane fuel cells owing to the strong durability and inexpensive cost of the catalyst.     

Ni–Fe–B catalysts for NaBH4 hydrolysis

A series of Ni–Fe–B catalysts with different Fe/(Fe + Ni) molar ratios, used for the hydrolysis of NaBH₄, were prepared by chemical reduction of NiCl₂ and FeCl₃ mixed solution with NaBH₄. The measurements revealed that the catalysts with the molar ratio of Fe/(Fe + Ni) (30%) exhibited the highest catalytic activity, and the optimal reduction temperature is 348 K. In addition, the effects of the concentration of NaBH₄, NaOH and the hydrolytic temperature of NaBH₄ were discussed in detail. The results show that the reaction rate of hydrolysis first rises up and then goes down subsequently with the increase of NaBH₄ concentration, as well as the concentration of NaOH. The activation energy of the hydrolysis for Ni–Fe–B catalysts is fitted to 57 kJ/mol. The maximum value of hydrogen generation is 2910 ml/(min g) at 298 K.     

New electroless plating method for preparation of highly active Co–B catalysts for NaBH4 hydrolysis

Supported non-noble transition metal catalysts are ideal for use in NaBH₄-based hydrogen storage systems because of their low cost, robustness, and ease of handling. We have developed a new low-temperature electroless plating method for preparation of Co–B catalysts supported on Ni foam. This method requires only one plating step to achieve the desired catalyst loading, and has higher loading efficiency than conventional multi-step methods. The produced Co–B catalyst shows higher NaBH₄ hydrolysis activity than those prepared by conventional methods due to increased boron content and nanosheet-like morphology. The pH and NH₃ concentration of the precursor solution were found to have considerable influences on both the catalyst loading and activity. Temperature dependence of hydrogen generation suggests that the catalytically active phase is formed in situ above a certain temperature threshold, which is supported by XPS analysis. The maximum specific hydrogen generation rate is in excess of 24,000 mL min⁻¹ g⁻¹, which is among the highest values for catalysts of this type reported in the literature.     

Multifunctional Co–B–O@CoxB catalysts for efficient hydrogen generation

The development of efficient and non-noble catalyst is of great significance to hydrogen generation techniques. Three surface-oxidized cobalt borides of Co–B–O@Co_xB (x = 0.5, 1 and 2) have been synthesized that can functionalize as active catalysts in both alkaline water electrolysis and the hydrolysis of sodium borohydride (NaBH₄) solution. It is discovered that oxidation layer and low boron content favor the oxygen evolution reaction (OER) activity of Co–B–O@Co_xB in alkaline water electrolysis. And surface-oxidized cobalt boride with low boron content is more active toward hydrolysis of NaBH₄ solution. An alkaline electrolyzer fabricated using the optimized electrodes of Co–B–O@CoB₂/Ni as cathode and Co–B–O@Co₂B/Ni as anode can deliver current density of 10 mA cm⁻² at 1.54 V for overall water splitting with satisfactory stability. Meanwhile, Co–B–O@Co₂B affords the highest hydrogen generation rate of 3.85 L min⁻¹ g⁻¹ for hydrolysis of NaBH₄ at 25 °C.     

The effects of plasma treatment on electrochemical activity of Co–W–B catalyst for hydrogen production by hydrolysis of NaBH4

A plasma treatment of Co–W–B catalyst increases the rate of hydrogen generation from the hydrolysis of NaBH₄. The catalytic properties of Co–W–B prepared in the presence of plasma have been investigated as a function of NaBH₄ concentration, NaOH concentration, temperature, plasma applying time, catalyst amount and plasma gases. The Co–W–B catalyst prepared with cold plasma effect hydrolysis in only 12 min, where as the Co–W–B catalyst prepared in known method with no plasma treatment in 23 min. The activation energy for first-order reaction is found to be 29.12 kJ mol⁻¹.     

Hydrogen generation by hydrolysis of NaBH4 with efficient Co–P–B catalyst: A kinetic study

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 773 K 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 (32 kJ mol⁻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 ∼4000 ml min⁻¹ g⁻¹ can be achieved. This can generate 720 W for Proton Exchange Membrane Fuel Cells (0.7 V): which is necessary for portable devices.     

Hydrogen generation from catalytic hydrolysis of sodium borohydride solution using supported amorphous alloy catalysts (Ni–Co–P/γ-Al2O3)

The supported amorphous alloy catalysts Ni–Co–P/γ-Al₂O₃ were synthesized by electroless plating for hydrogen generation from catalytic hydrolysis of sodium borohydride solution. The influences of deposition time, pH, NaBH₄ concentration and the Co/Ni atomic ratio on the hydrogen generation rate were investigated in this paper. The reported work also includes the full experimental details for the collection of a wealth of kinetic data to determine the activation energy (E_a = 52.05 kJ mol⁻¹). Energy dispersive X-ray spectrometer (EDS), field emission scanning electron Microscope (SEM), inductively coupled plasma-atomic emission spectrometer (ICP-AES) and X-ray diffraction (XRD), nitrogen adsorption–desorption isotherm were used to characterize surface element composition, morphology and structure of the amorphous alloy.     

Amorphous cobalt–boron/nickel foam as an effective catalyst for hydrogen generation from alkaline sodium borohydride solution

Low cost and catalytically effective transition metal catalysts are of interest for the development of on-board hydrogen generation systems for fuel-cell vehicles. In the present study a modified electroless plating method was developed for the preparation of amorphous Co–B catalyst supported on Ni foam. Compared to the conventional electroless plating method, the newly developed method is more effective and produces Co–B catalyst with much higher catalytic activity. The catalytic activity of the supported Co–B catalyst was found to be highly dependent on the plating times and calcination conditions. Through optimization of these preparation conditions we were able to prepare a catalyst capable of a hydrogen generation rate of 11 l (min g)⁻¹ (catalyst) in a 20 wt.% NaBH₄ + 10 wt.% NaOH solution. Preliminary phase analyses and microstructure characterization were performed to understand the effects of preparation conditions on the catalytic activity of the Co–B catalyst.     

Effects of electroless deposition conditions on microstructures of cobalt–phosphorous catalysts and their hydrogen generation properties in alkaline sodium borohydride solution

Cobalt–phosphorous (Co–P) catalysts with a high hydrogen generation rate in alkaline sodium borohydride (NaBH₄) solution are developed by electroless deposition. The microstructures of the Co–P catalysts and their catalytic activities for hydrolysis of NaBH₄ are analyzed as a function of the electroless deposition conditions such as the pH and temperature of the Co–P bath. The electroless-deposited Co–P catalysts are composed of nano-crystalline Co and amorphous Co–P. The size of the nano-crystalline Co particles dispersed in amorphous Co–P matrix depends largely on the electroless deposition conditions. Moreover, Co–P catalysts with finer crystalline Co exhibit a higher hydrogen generation rate. In particular, the Co–P catalysts formed in a pH 12.5 bath at 60–70 °C exhibit the best hydrogen generation rate of 3300 ml min⁻¹ g⁻¹-catalyst in 1 wt.% NaOH + 10 wt.% NaBH₄ solution at 30 °C, which is 60 times faster than that obtained with a Co catalyst.     

High-performance cobalt–tungsten–boron catalyst supported on Ni foam for hydrogen generation from alkaline sodium borohydride solution

Low cost and catalytically effective transition metal catalysts are highly wanted in developing on-demand hydrogen generation system for practical onboard application. By using a modified electroless plating method, we have prepared a robust Co–W–B amorphous catalyst supported on Ni foam (Co–W–B/Ni foam catalyst) that is highly effective for catalyzing hydrogen generation from alkaline NaBH₄ solution. It was found that the plating times, calcination temperature, NaBH₄ and NaOH concentrations all exert considerable influence on the catalytic effectiveness of Co–W–B/Ni foam catalyst towards the hydrolysis reaction of NaBH₄. Via optimizing these preparation and reaction conditions, a hydrogen generation rate of 15 L/min g (Co–W–B) has been achieved, which is comparable to the highest level of noble metal catalyst. In consistent with the observed pronounced catalytic activity, the activation energy of the hydrolysis reaction using Co–W–B/Ni foam catalyst was determined to be only 29 kJ/mol. Based on the phase analysis and structural characterization results, the mechanism underlying the observed dependence of catalytic effectiveness on the calcination temperature was discussed.     

Effects of deposition time on the H2 generation kinetics of electroless-deposited cobalt–phosphorous catalysts from NaBH4 hydrolysis,and its cyclic durability

The effect of electoless-deposition time of a Co–P catalyst on the kinetics of H₂ generation in an alkaline NaBH₄ solution, and its cyclic durability are investigated. The electroless-deposited Co–P catalyst is composed of both outer spherical Co–P particles and an inner flat Co–P layer. As the deposition time of the Co–P catalyst is increased, the outer spherical Co–P particles grow, and their H₂ generation kinetics increase. However, the weight-normalized reaction rates differ as a function of deposition time, although the weight of the deposited material is proportional to the deposition time. Specifically, the Co–P catalyst deposited for 3 min shows the highest weight-normalized H₂ generation rate than those deposited for other lengths of time. The rate of H₂ generation for the Co–P catalyst is decreased dramatically after one cycle (10 h) due to separation of the Co–P particles from the Co–P plate. Up to the sixth cycle (60 h), the rate of H₂ gradually decreases due to a powerful shock on the catalyst support by expansion of H₂ volume. Beyond six cycles, the catalytic performance of the Co–P catalyst was stable enough for repetitive use.     

Study of Co–W crystalline alloys as hydrogen electrodes in alkaline water electrolysis

Binary Co–W crystalline alloys, Co₉₅W₅, Co₉₀W₁₀, Co₈₅W₁₅, Co₈₀W₂₀ and Co₇₀W₃₀ (atomic %) were investigated in view of their possible applications as electrocatalytic materials for hydrogen evolution reaction (HER). The electrocatalytic efficiency of the electrodes was studied on the basis of electrochemical data obtained from steady-state polarization and electrochemical impedance spectroscopy (EIS) techniques in oxygen-free 1 M NaOH solution at 298 K. The results were compared with those obtained on polycrystalline Co. Moreover, literature data concerning the electrocatalytic activity of polycrystalline Ni and Ni–Mo alloys, which are considered good electrocatalyst materials for the hydrogen evolution reaction in alkaline solutions, were also reported for comparison. The values of Tafel slope, b, exchange current density, j₀, and overpotential at the current density of 250 mA cm⁻², η₂₅₀, indicated outstandingly high electrocatalytic activity of Co–W electrodes. The best performance towards the HER demonstrates the Co₉₀W₁₀ alloy in accordance with the prediction based on the electronic structure calculations and the enhanced density of states at the Fermi level of the 3d Co band.     

Fe–P and Fe–P–Pt co-deposits as hydrogen electrodes in alkaline solution

Fe–P and Fe–P–Pt alloys for use as electrodes for alkaline water electrolysis are prepared by an electroplating technique which employs an acidic complex bath solution. After heat treatment, the plated alloys act as effective electrocatalytic materials by lowering the hydrogen overpotential sufficiently. The improved electrocatalytic activity is due to an increase in effective surface area, a change in surface features upon heat treatment, and the presence of traces of platinum. Electrodes of the plated alloys are stable even in a highly corrosive electrolytic medium (6 M KOH).     

Iron incorporated Ni–ZrO2 catalysts for electric power generation from methane

On the purpose to perform as functional layer of SOFCs operating on methane fuel, NiFe–ZrO₂ alloy catalysts have been synthesized and investigated for methane partial oxidation reactions. Ni₄Fe₁–ZrO₂ shows catalytic activity comparable to that of Ni–ZrO₂ and superior to other Fe-containing catalysts. In addition, O₂-TPO analysis indicates iron is also prone to coke formation; as a result, most of NiFe–ZrO₂ catalysts do not show improved coking resistance than Ni–ZrO₂. Anyway, Ni₄Fe₁–ZrO₂ (Ni:Fe = 4:1 by weight) prepared by glycine-nitrate process shows somewhat less carbon deposition than the others. However, Raman spectroscopy demonstrates that the addition of Fe does reduce the graphitization degree of the deposited carbon, suggesting the easier elimination of carbon once it is deposited over the catalyst. Ni₄Fe₁–ZrO₂ has an excellent long-term stability for partial oxidation of methane reaction at 850 °C. A solid oxide fuel cell with conventional nickel cermet anode and Ni₄Fe₁–ZrO₂ functional layer is operated on CH₄–O₂ gas mixture to yield a peak power density of 1038 mW cm⁻² at 850 °C, which is comparable to that of hydrogen fuel. In summary, the Ni₄Fe₁–ZrO₂ catalyst is potential catalyst as functional layer for solid-oxide fuel cells operating on methane fuel.     

Revision of the NaBO2–H2O phase diagram for optimized yield in the H2 generation through NaBH4 hydrolysis

The binary phase diagram NaBO₂–H₂O at ambient pressure, which defines the different phase equilibria that could be formed between borates, end-products of NaBH₄ hydrolysis, has been reviewed. Five different solid borates phases have been identified: NaBO₂·4H₂O (Na[B(OH)₄]·2H₂O), NaBO₂·2H₂O (Na[B(OH)₄]), NaBO₂·2/3H₂O (Na₃[B₃O₄(OH)₄]), NaBO₂·1/3H₂O (Na₃[B₃O₅(OH)₂]) and NaBO₂ (Na₃[B₃O₆]), and their thermal stabilities have been studied. The boundaries of the different Liquid + Solid equilibria for the temperature range from −10 to 80 °C have been determined, confirming literature data at low temperature (20–50 °C). Moreover the following eutectic transformation, Liq. → Ice + NaBO₂·4H₂O, occurring at −7 °C, has been determined by DSC. The Liquid–Vapour domain has been studied by ebullioscopy. The invariant transformation Liq. → Vap. + NaBO₂·2/3H₂O has been estimated at 131.6 °C. This knowledge is paramount in the field of hydrogen storage through NaBH₄ hydrolysis, in which borate compounds were obtained as hydrolysis reaction products. As a consequence, the authors propose a comparison with previous NaBO₂–H₂O binary phase diagrams and its consequence related to hydrogen storage through NaBH₄ hydrolysis.     

Ni–MoS2 composite coatings as efficient hydrogen evolution reaction catalysts in alkaline solution

It remains an important project for the development of water splitting electrolyze to design and synthesis of more efficient non-noble metal catalyst. In this work, a structured Ni–MoS₂ composite coating has been synthesized under supergravity fields with nickel sulphamate bath containing suspended MoS₂ submicro-flakes. X-ray diffraction patterns indicate that the MoS₂ submicro-flakes have been successfully incorporated into the Ni matrix. Additionally, SEM shows that the prepared Ni–MoS₂ composite coatings display finer grain size than the pure Ni coatings, which can increase the electrochemistry surface area and the active site of hydrogen evolution reaction. Therefore, due to the synergistic effect of molybdenum disulfide and nickel, the Ni–MoS₂ composite coatings are directly used as binder-free electrode, which exhibits outstanding electrocatalytic activity for HER in 1.0 M NaOH solution at room temperature. The Ni–MoS₂ composite coatings demonstrated an outstanding performance toward the electrocatalytic hydrogen production with low overpotential (100 mA cm^?2 at η = 207 mV), a Tafel slope as small as 65 mV dec^?1, and stable cycling performance (1200 cycles). The preeminent HER performance of this catalyst suggests that it may hold great promise for practical applications.