Efficient hydrogen evolution from ammonia borane hydrolysis with Rh decorated on phosphorus-doped carbon

Development of supported ligand-free ultrafine Rh nanocatalysts for efficient catalytic hydrogen evolution from ammonia borane (AB) is of importance but remains a tremendous challenge. Here, ultrafine and ligand-free Rh nanoparticles (NPs) (2.19 nm in diameter) were in-situ decorated on porous phosphorus-functionalized carbon (PPC) prepared by pyrolyzing hyper-cross-linked networks of triphenylphosphine and benzene. The resultant Rh/PPC showed excellent hydrogen production activity from AB hydrolysis (Turnover frequency: 806 min⁻¹). Kinetic investigations indicated that AB hydrolysis using Rh/PPC exhibited first-order and zero-order reactions with Rh and AB concentrations, respectively. Activation energy (E_a) toward hydrogen generation from AB with Rh/PPC is as low as 22.7 kJ/mol. The Rh/PPC catalyst was recyclable and reusable for at least four times. The oxygen- and phosphorus-functional groups are beneficial for the affinity of Rh complex on the PPC surface, resulting in ultrafine and ligand-free Rh NPs with high dispersity and ability to supply abundant surface accessibility to catalytically active sites for AB hydrolysis. This study proposes a feasible approach for the synthesis of ultrafine and ligand-free metal NPs supported on heteroatom-doped carbon by using hyper-cross-linked networks.     

Bamboo fungus-derived magnetic porous carbon encapsulated nickel stabilized Rh nanoparticles as efficient catalysts for hydrolytic dehydrogenation of ammonia borane

Biomass-derived porous carbons are generally used as supports for metal nanoparticle (NP) stabilizations, while the strong hydrophilicity of such materials makes the as-prepared catalysts hard to be isolated after reaction, significantly affecting their potential applications. Herein, magnetic N-functionalized carbon (CN) encapsulated Ni composite (Ni@CN) prepared via pyrolysis of bamboo fungus pre-absorbed with nickel nitrate is exploited as a matrix to synthesize Rh/Ni@CN hybrid, which can be used as a magnetically recoverable catalytic material for hydrolytic dehydrogenation of ammonia borane (AB) to generate hydrogen. The Rh/Ni@CN (Rh loading: 0.84 wt%) exhibits an optimal activity (turnover frequency: 351 min⁻¹) for hydrogen evolution from hydrolytic dehydrogenation of AB. Most importantly, this catalyst can be simply isolated by a magnet and reused at least five times with complete conversion of AB to hydrogen. The strong interaction between the two metals and the small size of Rh NPs are responsible for the improved catalytic activity for hydrolytic dehydrogenation of AB. This work provides an eco-friendly and efficient strategy to fabricate excellent catalysts in catalytic applications.     

Facile and eco-friendly synthesis of porous carbon nanosheets as ideal platform for stabilizing rhodium nanoparticles in efficient hydrolysis of ammonia borane

Carbon materials have been demonstrated as excellent carriers for preparing supported metal nanocatalysts in catalytic applications. However, numerous chemical activators including strong acids and bases were applied, leading to the entire process dangerous and hazardous. Eco-friendly, economic, and convenient synthesis of carbon materials with desired properties as supports for metal nanoparticle (NP) stabilization to boost performance is important but remains challenging. Here, we developed a facile and eco-friendly strategy to synthesize porous carbon nanosheets (PCNs) with ultrahigh specific surface area (2575.1 m²/g) via pyrolysis the mixture of potassium oxalate and glucose. The resultant PCNs can be used as ideal platform for in-situ distribution of small Rh NPs (Rh/PCNs) as efficient catalysts in hydrogen production from ammonia borane (AB) under ambient conditions. Specifically, Rh/PCNs displayed high activity for AB hydrolysis, with a turnover frequency (TOF) of 513.2 min⁻¹. Small and well-distributed Rh NPs on PCNs with large catalytically active surface atoms are contributed to the high catalytic property of Rh/PCNs for the reaction. Present study has demonstrated that the PCNs is a superior catalyst support for preparing a series of metal NPs in other catalytic applications beyond hydrolysis reaction.     

Synergistic catalysis of Pd–Ni(OH)2 hybrid anchored on porous carbon for hydrogen evolution from the dehydrogenation of formic acid

The development of a facile yet efficient strategy to boost the catalytic performance of supported Pd nanoparticles (NPs) toward the dehydrogenation of formic acid (FA) is essential but remains challenging. Here, a novel hybrid nanocatalyst comprising Pd and Ni(OH)₂ supported on porous carbon (PC) is developed. The obtained Pd–Ni(OH)₂/PC nanocatalyst exhibits an excellent catalytic performance for FA dehydrogenation to produce hydrogen. The introduction of Ni(OH)₂ in PC support can significantly promote the catalytic activity of Pd NPs toward FA dehydrogenation. Additionally, the catalytic property of Pd–Ni(OH)₂/PC is correlated with the Pd/Ni ratio. The ₂Pd–₁Ni(OH)₂/PC with the optimum Pd/Ni ratio of 2/1 exhibits the maximum turnover frequency (TOF) of 3409 h⁻¹ at 60 °C for FA dehydrogenation. The highly dispersed ultrafine Pd–Ni(OH)₂ hybrid NPs with numerous accessible active sites and Ni(OH)₂−induced positive synergetic effects with Pd NPs considerably boost the catalytic performance for FA dehydrogenation.     

Oxygen vacancy-engaged interfacial charge transfer modulation for upgrade Rh-catalyzed hydrogen and oxygen productions

Developing efficient modulation strategies to upgrade the catalytic activity and reusability of Rh-catalyzed hydrogen evolution from ammonia borane (AB) hydrolysis are definitely profitable but remains a grand challenge. Here, we develop a stepwise activation strategy to produce highly active and reusable Rh/CoFe₂O₄-SB-H₂ with abundant oxygen vacancies and strong electronic metal-support interaction through stepwise reduction of Rh/CoFe₂O₄ precursor using sodium borohydride and H₂ as the reducing agents. Under ultrasonic irradiation, Rh/CoFe₂O₄-SB-H₂ with an ultralow Rh loading of 0.20 wt% can be utilized as an excellent catalyst for hydrogen production from room-temperature AB hydrolysis with a high turnover frequency (TOF) of 1894 min⁻¹. The TOF value could be further promoted to 15,570 min⁻¹ in the alkaline ultrasonic environment. The catalyst has a superior reusability with 75% maintaining activity of initial one in the 10^th cycle. The strong electronic metal-support interaction, rich oxygen vacancies and ultrasound irradiation promote the oxidative cleavage of the O–H bonds in attracted H₂O and thus account for high performance toward hydrogen production from AB. This catalyst can also be utilized as an active catalyst for oxygen generation from H₂O₂ decomposition. The developed strategies can be applied to upgrade the performance of other reducible metal oxides supported metal catalysts toward catalytic applications.     

Water soluble nickel(0) and cobalt(0) nanoclusters stabilized by poly(4-styrenesulfonic acid-co-maleic acid): Highly active, durable and cost effective catalysts in hydrogen generation from the hydrolysis of ammonia borane

This paper reports the in-situ generation and catalytic activity of nickel(0) and cobalt(0) nanoclusters stabilized by poly(4-styrene sulfonic acid-co-maleic acid), PSSA-co-MA, in the hydrolysis of ammonia borane (AB). PSSA-co-MA stabilized nickel(0) (PSMA-Ni) and cobalt(0) nanoclusters (PSMA-Co) having average particle size of 2.1 ± 0.6 and 5.3 ± 1.6 nm, respectively, were generated by in-situ reduction of nickel(II) chloride or cobalt(II) chloride in an aquoues solution of NaBH₄/H₃NBH₃ in the presence of PSSA-co-MA. The in-situ generated nanoclusters were isolated from the reaction solution and characterized by UV-Vis, TEM, XRD and FT-IR techniques. Compared with the previous catalyst systems, PSMA-Ni and PSMA-Co are found to be highly active catalysts for hydrogen generation from the hydrolysis of AB with the turnover frequency values of 10.1 min⁻¹ for Ni and 25.7 min⁻¹ for Co. They are also very stable during the hydrolysis of AB providing 22450 and 17650 turnovers, respectively. The results of mercury poisoning experiments reveal that PSMA-Ni and PSMA-Co are heterogeneous catalysts in the hydrolysis of AB. Herein, we also report the results of a detailed kinetic study on the hydrogen generation from the hydrolysis of AB catalyzed by PSMA-Ni and PSMA-Co depending on catalyst concentration, substrate concentration, and temperature along with the activation parameters of catalytic hydrolysis of AB calculated from the kinetic data.     

Hydrolysis of ammonia–borane catalyzed by an iron–nickel alloy on an SBA-15 support

An unsupported iron–nickel (Fe–Ni) alloy and several Fe–Ni alloy deposited on SBA-15 (Santa Barbara Amorphous-15) supports (Fe–Ni/SBA) with various Fe–Ni contents are prepared and used as catalysts in the hydrolysis of ammonia–borane (AB) for hydrogen generation. By maintaining a constant concentration of Fe–Ni in the AB aqueous solutions, we investigate the influence of the SBA-15 support on the Fe–Ni catalytic activity in the AB hydrolysis reaction. The SBA-15 support helps disperse the Fe–Ni alloy particles on its surface, which consequently improves the catalytic activity of the Fe–Ni. However, the presence of SBA-15 particles in the aqueous solution also retards the migration of the AB molecules in solution toward the Fe–Ni catalysts, increasing the induction time of the AB hydrolysis reaction. Therefore, there is an optimal Fe–Ni content in Fe–Ni/SBA for the catalysis of the AB hydrolysis reaction.     

Oxygen vacancies and morphology engineered Co3O4 anchored Ru nanoparticles as efficient catalysts for ammonia borane hydrolysis

Developing efficient but facile strategies to modulate the catalytic activity of Ru deposited on metal oxides is of broad interest but remains challenging. Herein, we report the oxygen vacancies and morphological modulation of vacancy-rich Co₃O₄ stabilized Ru nanoparticles (NPs) (Ru/V_O-Co₃O₄) to boost the catalytic activity and durability for hydrogen production from the hydrolysis of ammonia borane (AB). The well-defined and small-sized Ru NPs and V_O-Co₃O₄ induced morphology transformation via in situ driving V_O-Co₃O₄ to 2D nanosheets with abundant oxygen vacancies or Co²⁺ species considerably promote the catalytic activity and durability toward hydrogen evolution from AB hydrolysis. Specifically, the Ru/V_O-Co₃O₄ pre-catalyst exhibits an excellent catalytic activity with a high turnover frequency of 2114 min^?1 at 298 K. Meanwhile, the catalyst also shows a high durability toward AB hydrolysis with six successive cycles. This work establishes a facile but efficient strategy to construct high-performance catalysts for AB hydrolysis.     

Hydrogen evolution from hydrolysis of ammonia borane catalyzed by Rh/g-C3N4 under mild conditions

Developing effective catalysts for hydrogen evolution from hydrolysis of ammonia borane (AB) is of great significance considering the useful applications of hydrogen. Herein, graphitic carbon nitride (g-C₃N₄) prepared through the simply pyrolysis of urea was employed as a support for Rh nanoparticles (NPs) stabilization. The in-situ generated Rh NPs supported on g-C₃N₄ with an average size of 3.1 nm were investigated as catalysts for hydrogen generation from the hydrolysis of AB under mild conditions. The Rh/g-C₃N₄ catalyst exhibits a high turnover frequency of 969 mol H₂· (min·mol_Rh)^?1 and a low activation energy of 24.2 kJ/mol. The results of the kinetic studies show that the catalytic hydrolysis of AB over the Rh/g-C₃N₄ catalyst is a zero-order reaction with the AB concentration and a first-order reaction with the Rh concentration. This work demonstrates that g-C₃N₄ is a useful support to design and synthesis of effective Rh-based catalyst for hydrogen-based applications.     

Smart construction of oxidized-Ti3C2TX stabilized Rh nanoparticles for remarkable improving the catalytic performance for ammonia borane hydrolysis

Supported Rh nanoparticle (NP) catalysts have been widespread investigated for hydrogen production from ammonia borane (AB) hydrolysis. However, it is still challenging to develop an efficient strategy to improve the catalytic performances of supported Rh NP catalysts considering the high-cost and limited reserve of Rh. To overcome this limitation, we propose a facile but effective method to significantly improve the catalytic performance of Rh NPs by using oxidized-Ti₃C₂T_x (o-Ti₃C₂T_x) as a NP support. The systematic investigation results suggest that well distributed and ultrasmall Rh NPs with a diameter of 2.60 nm are successfully loaded on the o-Ti₃C₂T_x surface, which can be used as excellent catalysts for hydrogen release from AB hydrolysis. The corresponding turnover frequency (TOF) of 2021 min⁻¹ and activation energy of 18.7 kJ/mol are achieved, which are superior to that of Rh NPs supported on a fresh Ti₃C₂T_x support and most of previous reported Rh NP catalysts. Additionally, the reusability test shows that Rh/o-Ti₃C₂T_x can maintain 53% of the initial catalytic activity after the fifth run. This study opens a new avenue to adjust the catalytic activity of metal NP catalysts for use in field of catalytic applications.     

Carbon-supported small Rh nanoparticles prepared with sodium citrate: Toward high catalytic activity for hydrogen evolution from ammonia borane hydrolysis

Hydrogen generation from the hydrolysis of ammonia borane (AB) over heterogeneous catalysts is essential for practical applications. Herein, efficient hydrogen evolution from AB hydrolysis over the carbon-supported Rh nanoparticles synthesized with sodium citrate (Rh/C-SC) was achieved at 25 °C. The turnover frequency value of Rh/C-SC was 336 mol H₂ (mol_Rh min)^?1, whereas that of Rh/C catalyst only yielded a value of 134 mol H₂ (mol_Rh min)^?1. The improvement of the catalytic performance of Rh/C-SC catalyst could be attributed to the small Rh particles with highly active surface areas, which were prepared by using sodium citrate as the stabilizing agent. This result indicates that sodium citrate can be applied as a useful stabilizing agent for synthesizing active metal nanoparticles, thus highly promoting the practical application of AB system for fuel cells.     

Anchoring and space-confinement effects to synthesize ultrasmall Pd nanoparticles for efficient ammonia borane hydrolysis

Hydrogen production from ammonia borane (AB) hydrolysis catalyzed by efficient heterogenous catalysts is regarded as a compelling strategy to meet the increasing requirement for clean energy. Palladium (Pd) nanoparticle (NP)-based catalysts have stimulated intensive attention for AB hydrolysis, while their catalytic performances still need to be significantly improved. By exploiting sodium hydroxide and three-dimensional (3D) architecture of interconnected porous carbon nanosheets (IPCNs) as a NP carrier, a simple yet efficient strategy is developed to synthesize uniformly distributed ligand-free Pd NPs (2.17 nm in diameter) for hydrogen generation from AB hydrolysis. The particle size and spatial dispersion control of Pd NPs on the IPCNs surface supply an abundance of surface-active sites and thus remarkable improve the catalytic performance for AB hydrolysis to hydrogen evolution. Specifically, the achieved Pd/IPCNs reveals an extremely high catalytic activity with a turnover frequency (TOF) of 122.8 min⁻¹ toward AB hydrolysis, which is higher than that of many reported Pd-based catalysts. This simple, straightforward and efficient method is of significant importance for preparing metal NP catalysts with high catalytic activities for catalytic applications.     

Spatially localized fabrication of uniform Rh nanoclusters on nanosheet-assembled hierarchical carbon architectures as excellent electrocatalysts for boosting alkaline hydrogen evolution

Construction of homogenously distributed and ultrafine Rh nanoclusters (NCs) anchored on suitable support with low loading toward hydrogen evolution reaction (HER) is paramount but remains challenging. Here, we developed a space confinement-assisted strategy for the construction of highly dispersed and ultrasmall Rh NCs supported on 3D nanosheet-assembled hierarchical carbon architectures (NHCAs) as advanced electrocatalysts for alkaline HER. Benefiting from the abundant and ultrasmall micro/mesopores of NHCAs, uniformly dispersed Rh NCs with diameters of 1.83 nm were embedded in NHCAs without the aid of surface capping agents. The resultant Rh NCs/NHCAs exhibited excellent electrochemical HER activity with low overpotentials of 7 and 48 mV at 10 and 100 mA cm⁻² current densities in basic solution, respectively, superior than most of the previous developed electrocatalysts. The surface-clean and ultrafine Rh NCs with high dispersity on the NHCAs surface could provide abundant surface-active sites and resulted in the high performance of Rh NCs/NHCAs for HER. The present study may offer a novel yet convenient pathway to synthesize highly dispersed and catalytically active supported noble metal electrocatalyst for catalytic applications.     

Promoted hydrogen generation from ammonia borane aqueous solution using cobalt–molybdenum–boron/nickel foam catalyst

Ammonia borane (AB) is an intriguing molecular crystal with extremely high hydrogen density. In the present study, by using a modified electroless plating method, we prepare a robust supported cobalt–molybdenum–boron (Co–Mo–B)/nickel (Ni) foam catalyst that can effectively promote the hydrogen release from AB aqueous solution at ambient temperatures. The catalytic activity of the catalyst towards the hydrolysis reaction of AB can be further improved by appropriate calcination treatment. In an effort to understand the effect of calcination treatment on the catalytic activity of the catalyst, combined structural/phase analyses of the series of catalyst samples have been carried out. Using the catalyst that is calcined at optimized condition, a detailed study of the catalytic hydrolysis kinetics of AB is carried out. It is found that the hydrolysis of AB in the presence of Co–Mo–B/Ni foam catalyst follows first-order kinetics with respect to AB concentration and catalyst amount, respectively. The apparent activation energy of the catalyzed hydrolysis reaction is determined to be 44.3 kJ mol⁻¹, which compares favorably with the literature results for using other non-noble transition metal catalysts.     

CuO–NiO/Co3O4 hybrid nanoplates as highly active catalyst for ammonia borane hydrolysis

Dehydrogenation of hydrogen-rich chemicals, such as ammonia borane (AB), is a promising way to produce hydrogen for mobile fuel cell power systems. However, the practical application has been impeded due to the high cost and scarcity of the catalysts. Herein, a low-cost and high-performing core-shell structured CuO–NiO/Co₃O₄ hybrid nanoplate catalytic material has been developed for the hydrolysis of AB. The obtained hybrid catalyst exhibits a high catalytic activity towards the hydrolysis of AB with a turnover frequency (TOF) of 79.1 mol_H2 mol cat⁻¹ min⁻¹. The apparent activation energy of AB hydrolysis on CuO–NiO/Co₃O₄ is calculated to be 23.7 kJ.mol⁻¹. The synergistic effect between CuO–NiO and Co₃O₄ plays an important role in the improvement of the catalytic performance. The development of this high-performing and low-cost CuO–NiO/Co₃O₄ hybrid catalytic material can make practical applications of AB hydrolysis at large-scale possible.     

Facile construction of composition-tuned ruthenium-nickel nanoparticles on g-C3N4 for enhanced hydrolysis of ammonia borane without base additives

Developing high-efficiency and low-cost catalysts for hydrogen evolution from hydrolysis of ammonia borane (AB) is significant and critical for the exploitation and utilization of hydrogen energy. Herein, the in-situ fabrication of well-dispersed and small bimetallic RuNi alloy nanoparticles (NPs) with tuned compositions and concomitant hydrolysis of AB are successfully achieved by using graphitic carbon nitride (g-C₃N₄) as a NP support without additional stabilizing ligands. The optimized Ru₁Ni_7.5/g-C₃N₄ catalyst exhibits an excellent catalytic activity with a high turnover frequency of 901 min^?1 and an activation energy of 28.46 kJ mol^?1 without any base additives, overtaking the activities of many previously reported catalysts for AB hydrolysis. The kinetic studies indicate that the AB hydrolysis over Ru₁Ni_7.5/g-C₃N₄ is first-order and zero-order reactions with respect to the catalyst and AB concentrations, respectively. Ru₁Ni_7.5/g-C₃N₄ has a good recyclability with 46% of the initial catalytic activity retained even after five runs. The high performance of Ru₁Ni_7.5/g-C₃N₄ should be assigned to the small-sized alloy NPs with abundant accessible active sites and the synergistic effect between the composition-tuned Ru–Ni bimetals. This work highlights a potentially powerful and simple strategy for preparing highly active bimetallic alloy catalysts for AB hydrolysis to generate hydrogen.     

Enhanced catalytic performance of CuNi bimetallic nanoparticles for hydrogen evolution from ammonia borane hydrolysis

Ammonia borane (AB, NH₃BH₃) hydrolysis is an effective way to safely generate hydrogen. However, a suitable catalyst is indispensable because the hydrolytic reaction cannot take place kinetically at room temperature. In this work, CuNi alloy nanoparticles are immobilized on porous graphitic carbon nitride (g-C₃N₄) with a facile adsorption-chemical reduction method. Benefiting from the hierarchical porous structure of the support, the interesting alloy effect of Cu and Ni, as well as the synergistic effect between g-C₃N₄ and the CuNi alloys, the optimal Cu_0·7Ni_0.3/g-C₃N₄ catalyst displays excellent catalytic performance in AB hydrolysis, such as high turnover frequency (2.08 min⁻¹, at 303 K), low apparent activation energy (23.58 kJ mol⁻¹), and satisfactory durability. The results verify that the optimal catalyst has particular potential in hydrogen energy utilization due to the advantages such as the facile preparation procedure, low cost and excellent catalytic behavior.     

Nanosizing ammonia borane with nickel – An all-solid and all-in-one approach for H2 generation by hydrolysis

Ammonia borane NH₃BH₃ (AB) and nickel (Ni) have been considered together as an all-solid and all-in-one material for H₂ generation by hydrolysis at 20–50 °C. Our novel approach, denoted Ni/AB, consists of AB nanoparticles within a Ni matrix. Upon contact with water, Ni/AB readily hydrolyzes and liberates H₂ with a turnover frequency of 13.8 mol(H₂) mol_Ni^?1 min^?1 at 43.3 °C. The apparent activation energy, determined over the temperature range 23.5–50.4 °C, is low, with 19.5 ± 4.1 kJ mol^?1. These results imply that such a Ni matrix embedding AB acts as an effective catalyst. Beyond the catalytic performance, this is the first report of the successful utilization of an all-solid and all-in-one approach for the hydrolysis of AB, and the work brings unique perspectives for one-shot catalytic systems.     

Noble-metal-free Co@Co2P/N-doped carbon nanotube polyhedron as an efficient catalyst for hydrogen generation from ammonia borane

Developing an efficient catalyst for hydrogen (H₂) generation from hydrolysis of ammonia borane (AB) to significantly improve the activity for the hydrogen generation from AB is important for its practical application. Herein, we report a novel hybrid nanostructure composed of uniformly dispersed Co@Co₂P core-shell nanoparticles (NPs) embedded in N-doped carbon nanotube polyhedron (Co@Co₂P/N–CNP) through a carbonization-phosphidation strategy derived from ZIF-67. Benefiting from the electronic effect of P doping, high dispersibility and strong interfacial interaction between Co@Co₂P and N-CNTs, the Co@Co₂P/N–CNP catalyst exhibits excellent catalytic performance towards the hydrolysis of AB for hydrogen generation, affording a high TOF value of 18.4 mol H₂ mol metal^?1 min^?1 at the first cycle. This work provides a promising lead for the design of efficient heterogeneous catalysts towards convenient H₂ generation from hydrogen-rich substrates in the close future.     

Boron nitride supported NiCoP nanoparticles as noble metal-free catalyst for highly efficient hydrogen generation from ammonia borane

Herein, ternary metal phosphides NiCoP nanoparticles supported on porous hexagonal boron nitride (h-BN) was fabricated via hydrothermal-phosphorization strategy. The as-prepared Ni_0.8Co_1.2P@h-BN exhibited excellent catalytic performance for the hydrogen generation from ammonia borane (AB) hydrolysis, with an initial turnover frequency of 86.5 mol(H₂) mol(Ni_0.8Co_1.2P) ⁻¹ min⁻¹ at 298 K. The experimental outcome can be attributed to the synergistic effect between Ni, Co and P, as well as the strong metal-support interaction between NiCoP and h-BN. This study presents a new paradigm for supporting transition metal phosphides, and provides a new avenue to develop high performance and low cost non noble metal catalysts for hydrolysis of AB.