Recent Advances and Perspectives on Supported Catalysts for Heterogeneous Hydrogen Production from Ammonia Borane

Two-dimensional molybdenum boride coordinating with ruthenium nanoparticles to boost hydrogen generation from hydrolytic dehydrogenation of ammonia borane

The coordination between carrier and active metal is critical to the catalytic efficiency of ammonia borane (AB) hydrolysis reaction. In the present study, we report a new type of catalytic support based on molybdenum boride (MBene) MoAl1-xB and demonstrate that the effective combination of MoAl1-xB with Ru nanoparticles can realize the significantly enhanced performance for hydrogen generation. Owing to the efficient activation and dissociation of reactants, the optimal Ru/MoAl1-xB catalyst achieves the large turnover frequency of 494 molH2 molRu-1 min-1, high hydrogen generation rate of 119817 mL min-1 gRu-1 and favorable apparent activation energy of 39.2 kJ mol-1 for the catalytic hydrolysis of AB under alkaline-free condition. The isotopic test suggests the cleavage of OH bond in H2O is the rate-determining step for hydrolysis reaction, while the fracture of B-H bond in AB is also well revealed by attenuated total reflectance (ATR)-Fourier transform infrared (FTIR) spectroscopy. Significantly, the flexible on-demand hydrogen generation is achieved by using chemical switches for on-off AB hydrolysis. This study provides a new support platform based on two-dimensional MBene to exploit efficient catalysts to boost AB dehydrogenation.

Rechargeable Zn-H2O hydrolysis battery for hydrogen storage and production

Reactive metals hydrolysis offers significant advantages for hydrogen storage and production. However, the regeneration of common reactive metals (e.g., Mg, Al, etc.) is energy-intensive and produces unwanted byproducts such as CO2 and Cl2. Herein, we employ Zn as a reactive mediator that can be easily regenerated by electrolysis of ZnO in an alkaline solution with a Faradaic efficiency of >99.9 %. H2 is produced in the same electrolyte by constructing a Zn-H2O hydrolysis battery consisting of a Zn anode and a Raney-Ni cathode to unlock the Zn-H2O reaction. The entire two-step water splitting reaction with a net energy efficiency of 70.4 % at 80 °C and 50 mA cm-2. Additionally, the Zn-H2O system can be charged using renewable energy to produce H2 on demand and runs for 600 cycles only sacrificing 3.76 % energy efficiency. DFT calculations reveal that the desorption of H* on Raney-Ni (-0.30 eV) is closer to zero compared with that on Zn (-0.87 eV), indicating a faster desorption of H* at low overpotential. Further, a 24 Ah electrolyzer is demonstrated to produce H2 with a net energy efficiency of 65.5 %, which holds promise for its real application.

Silica Confinement for Stable and Magnetic Co-Cu Alloy Nanoparticles in Nitrogen-Doped Carbon for Enhanced Hydrogen Evolution

Ammonia borane (AB) with 19.6 wt % H2 content is widely considered a safe and efficient medium for H2 storage and release. Co-based nanocatalysts present strong contenders for replacing precious metal-based catalysts in AB hydrolysis due to their high activity and cost-effectiveness. However, precisely adjusting the active centers and surface properties of Co-based nanomaterials to enhance their activity, as well as suppressing the migration and loss of metal atoms to improve their stability, presents many challenges. In this study, mesoporous-silica-confined bimetallic Co-Cu nanoparticles embedded in nitrogen-doped carbon (CoxCu1-x@NC@mSiO2) were synthesized using a facile mSiO2-confined thermal pyrolysis strategy. The obtained product, an optimized Co0.8Cu0.2@NC@mSiO2 catalyst, exhibits enhanced performance with a turnover frequency of 240.9 molH2 ⋅ molmetal ⋅ min-1 for AB hydrolysis at 298 K, surpassing most noble-metal-free catalysts. Moreover, Co0.8Cu0.2@NC@mSiO2 demonstrates magnetic recyclability and extraordinary stability, with a negligible decline of only 0.8 % over 30 cycles of use. This enhanced performance was attributed to the synergistic effect between Co and Cu, as well as silica confinement. This work proposes a promising method for constructing noble-metal-free catalysts for AB hydrolysis.

Cobalt Phosphide-Supported Single-Atom Pt Catalysts for Efficient and Stable Hydrogen Generation from Ammonia Borane Hydrolysis

Ammonia borane (AB) has emerged as a promising chemical hydrogen storage material. The development of efficient, stable, and cost-effective catalysts for AB hydrolysis is the key to achieving hydrogen energy economy. Here, cobalt phosphide (CoP) is used to anchor single-atom Pt species, acting as robust catalysts for hydrogen generation from AB hydrolysis. Thanks to the high Pt utilization and the synergy between CoP and Pt species, the optimized Pt/CoP-100 catalyst exhibits an unprecedented hydrogen generation rate, giving a record turnover frequency (TOF) value of 39911mo l H 2 mo l Pt - 1 mi n - 1 ${\mathrm{mo}}{{{\mathrm{l}}}_{{{{\mathrm{H}}}_{\mathrm{2}}}}}{\mathrm{\ mo}}{{{\mathrm{l}}}_{{\mathrm{Pt}}}}^{{\mathrm{ - 1}}}{\mathrm{\ mi}}{{{\mathrm{n}}}^{{\mathrm{ - 1}}}}$ and turnover number of 2926829mo l H 2 mo l Pt - 1 ${\mathrm{mo}}{{{\mathrm{l}}}_{{{{\mathrm{H}}}_{\mathrm{2}}}}}{\mathrm{\ mo}}{{{\mathrm{l}}}_{{\mathrm{Pt}}}}^{{\mathrm{ - 1}}}$ at room temperature. These metrics surpass those of all existing state-of-the-art supported metal catalysts by an order of magnitude. Density functional theory calculations reveal that the integration of single-atom Pt onto the CoP substrate significantly enhances adsorption and dissociation processes for both water and AB molecules, thereby facilitating hydrogen production from AB hydrolysis. Interestingly, the TOF value is further elevated to 54878mo l H 2 mo l Pt - 1 mi n - 1 ${\mathrm{mo}}{{{\mathrm{l}}}_{{{{\mathrm{H}}}_{\mathrm{2}}}}}{\mathrm{\ mo}}{{{\mathrm{l}}}_{{\mathrm{Pt}}}}^{{\mathrm{ - 1}}}{\mathrm{\ mi}}{{{\mathrm{n}}}^{{\mathrm{ - 1}}}}$ under UV-vis light irradiation, which can be attributed to the efficient separation and mobility of photogenerated carriers at the Pt-CoP interface. The findings underscore the effectiveness of CoP as a support for single-atom metals in hydrogen production, offering insights for designing high-performance catalysts for chemical hydrogen storage.

Insights into the hydrogen generation and catalytic mechanism on Co-based nanocomposites derived from pyrolysis of organic metal precursor

Hydrogen generation from boron hydride is important for the development of hydrogen economy. Cobalt (Co) element has been widely used in the hydrolysis of boron hydride. Pyrolysis is a common method for materials synthesis in catalytic fields. Herein, Co-based nanocomposites derived from the pyrolysis of organic metal precursors and used for hydrolysis of boron hydride are summarized and discussed. The different precursors consisting of MOF, supported, metal, and metal phosphide precursors are summarized. The catalytic mechanism consisting of dissociation mechanism based on oxidative addition-reduction elimination, pre-activation mechanism, SN2 mechanism, four-membered ring mechanism, and acid-base mechanism is intensively discussed. Finally, conclusions and outlooks are conveyed from the design of high-efficiency catalysts, the characterization of catalyst structure, the enhancement of catalytic activities, the investigation of the catalytic mechanism, and the catalytic stability of active structure. This review can provide guidance for designing high-efficiency catalysts and boosting development of hydrogen economy.

Ultrafine Ni-MoOx Nanoparticles Anchored on Nitrogen-Doped Carbon Nanosheets: A Highly Efficient Noble-Metal-Free Catalyst for Ammonia Borane Hydrolysis

The development of low-cost and high-efficiency catalysts for the hydrolytic dehydrogenation of ammonia borane (AB, NH3BH3) is still a challenging technology. Herein, ultrafine MoOx-doped Ni nanoparticles (~3.0 nm) were anchored on g-C3N4@glucose-derived nitrogen-doped carbon nanosheets via a phosphate-mediated method. The strong adsorption of phosphate-mediated nitrogen-doped carbon nanosheets (PNCS) for metal ions is a key factor for the preparation of ultrasmall Ni nanoparticles (NPs). Notably, the alkaline environment formed by the reduction of metal ions removes the phosphate from the PNCS surface to generate P-free (P)NCS so that the phosphate does not participate in the subsequent catalytic reaction. The synthesized Ni-MoOx/(P)NCS catalysts exhibited outstanding catalytic properties for the hydrolysis of AB, with a high turnover frequency (TOF) value of up to 85.7 min-1, comparable to the most efficient noble-metal-free catalysts and commercial Pt/C catalyst ever reported for catalytic hydrogen production from AB hydrolysis. The superior performance of Ni-MoOx/(P)NCS can be ascribed to its well-dispersed ultrafine metal NPs, abundant surface basic sites, and electron-rich nickel species induced by strong electronic interactions between Ni-MoOx and (P)NCS. The strategy of combining multiple modification measures adopted in this study provides new insights into the development of economical and high-efficiency noble-metal-free catalysts for energy catalysis applications.

Regulation of Electronic Structures of the Urchin-Like NiCoP/CoP Nanocatalysts for Fast Hydrogen Evolution

The exploration of stable, efficient, and low-cost catalysts toward ammonia borane hydrolysis is of vital significance for the practical implementation of this hydrogen production technology. Integrating interface engineering and nano-architecture engineering is a favorable strategy to elevate catalytic performance, as it can modify the electronic structure and provide sufficient active sites simultaneously. In this work, urchin-like NiCoP/CoP heterostructures are prepared via a three-step hydrothermal-oxidation-phosphorization synthesis route. It is demonstrated that the original Ni/Co molar ratio and the amount of phosphorus are crucial for adjusting the morphology, enhancing the exposed surface area, facilitating charge transfer, and modulating the adsorption and activation of H2O molecules. Consequently, the optimal Ni1Co2P heterostructure displays remarkable catalytic properties in the hydrolysis of ammonia borane with a turnover frequency (TOF) value of 30.3 molH2 ⋅ min-1 ⋅ molmetal -1, a low apparent activation energy of 25.89 kJ ⋅ mol-1, and good stability. Furthermore, by combining infrared spectroscopy and isotope kinetics experiments, a possible mechanism for the hydrolysis of ammonia borane was proposed.

Co and Co3O4 in the Hydrolysis of Boron-Containing Hydrides: H2O Activation on the Metal and Oxide Active Centers

This work focuses on the comparison of H2 evolution in the hydrolysis of boron-containing hydrides (NaBH4, NH3BH3, and (CH2NH2BH3)2) over the Co metal catalyst and the Co3O4-based catalysts. The Co3O4 catalysts were activated in the reaction medium, and a small amount of CuO was added to activate Co3O4 under the action of weaker reducers (NH3BH3, (CH2NH2BH3)2). The high activity of Co3O4 has been previously associated with its reduced states (nanosized CoBn). The performed DFT modeling shows that activating water on the metal-like surface requires overcoming a higher energy barrier compared to hydride activation. The novelty of this study lies in its focus on understanding the impact of the remaining cobalt oxide phase. The XRD, TPR H2, TEM, Raman, and ATR FTIR confirm the formation of oxygen vacancies in the Co3O4 structure in the reaction medium, which increases the amount of adsorbed water. The kinetic isotopic effect measurements in D2O, as well as DFT modeling, reveal differences in water activation between Co and Co3O4-based catalysts. It can be assumed that the oxide phase serves not only as a precursor and support for the reduced nanosized cobalt active component but also as a key catalyst component that improves water activation.

Exploring Enhanced Hydrolytic Dehydrogenation of Ammonia Borane with Porous Graphene-Supported Platinum Catalysts

Graphene is a good support for immobilizing catalysts, due to its large theoretical specific surface area and high electric conductivity. Solid chemical converted graphene, in a form with multiple layers, decreases the practical specific surface area. Building pores in graphene can increase specific surface area and provide anchor sites for catalysts. In this study, we have prepared porous graphene (PG) via the process of equilibrium precipitation followed by carbothermal reduction of ZnO. During the equilibrium precipitation process, hydrolyzed N,N-dimethylformamide sluggishly generates hydroxyl groups which transform Zn2+ into amorphous ZnO nanodots anchored on reduced graphene oxide. After carbothermal reduction of zinc oxide, micropores are formed in PG. When the Zn2+ feeding amount is 0.12 mmol, the average size of the Pt nanoparticles on PG in the catalyst is 7.25 nm. The resulting Pt/PG exhibited the highest turnover frequency of 511.6 min-1 for ammonia borane hydrolysis, which is 2.43 times that for Pt on graphene without the addition of Zn2+. Therefore, PG treated via equilibrium precipitation and subsequent carbothermal reduction can serve as an effective support for the catalytic hydrolysis of ammonia borane.

Why do Single-Atom Alloys Catalysts Outperform both Single-Atom Catalysts and Nanocatalysts on MXene?

Single-atom alloys (SAAs), combining the advantages of single-atom and nanoparticles (NPs), play an extremely significant role in the field of heterogeneous catalysis. Nevertheless, understanding the catalytic mechanism of SAAs in catalysis reactions remains a challenge compared with single atoms and NPs. Herein, ruthenium-nickel SAAs (RuNiSAAs ) synthesized by embedding atomically dispersed Ru in Ni NPs are anchored on two-dimensional Ti3 C2 Tx MXene. The RuNiSAA-3 -Ti3 C2 Tx catalysts exhibit unprecedented activity for hydrogen evolution from ammonia borane (AB, NH3 BH3 ) hydrolysis with a mass-specific activity (rmass ) value of 333 L min-1  gRu -1 . Theoretical calculations reveal that the anchoring of SAAs on Ti3 C2 Tx optimizes the dissociation of AB and H2 O as well as the binding ability of H* intermediates during AB hydrolysis due to the d-band structural modulation caused by the alloying effect and metal-supports interactions (MSI) compared with single atoms and NPs. This work provides useful design principles for developing and optimizing efficient hydrogen-related catalysts and demonstrates the advantages of SAAs over NPs and single atoms in energy catalysis.

Highly dispersed Pd-based pseudo-single atoms in zeolites for hydrogen generation and pollutant disposal

Atomically dispersed metal catalysts with excellent activity and stability are highly desired in heterogeneous catalysis. Herein, we synthesized zeolite-encaged Pd-based pseudo-single atoms via a facile and energy-efficient ligand-protected direct H2 reduction method. Cs-corrected scanning transmission electron microscopy, extended X-ray absorption, and pair distribution function measurements reveal that the metal species are close to atomic-level dispersion and completely confined within the intersectional channels of silicalite-1 (S-1) zeolite with the MFI framework. The Pd@S-1-H exhibits excellent activity and stability in methane combustion reactions with a complete combustion temperature of 390 °C, and no deactivation is observed even after 100 h on stream. The optimized bimetallic 0.8Pd0.2Ni(OH)2@S-1-H catalyst exhibits an excellent H2 generation rate from FA decomposition without any additives, affording a superhigh turnover frequency up to 9308 h-1 at 333 K, which represents the top activity among all of the best heterogeneous catalysts under similar conditions. Significantly, zeolite-encaged metal catalysts are first used for Cr(vi) reduction coupled with formic acid (FA) dehydrogenation and show a superhigh turnover number of 2980 mol(Cr2O72-) mol(Pd)-1 at 323 K, surpassing all of the previously reported catalysts. This work demonstrates that zeolite-encaged pseudo-single atom catalysts are promising in efficient hydrogen storage and pollutant disposal applications.

Homogenous nickel-catalyzed chemoselective transfer hydrogenation of functionalized nitroarenes with ammonia-borane

Homogeneous Ni-catalyzed highly selective transfer hydrogenation of nitroarenes was successfully established using NH3BH3 as a hydrogen source. A broad range of functional groups were selectively reduced to provide the corresponding anilines in good to high yields. Further, pharmaceutically active compounds can be prepared that would otherwise be challenging to access.

Boosting the Catalytic Performance of NiMoO4 Nanorods in H2 Generation upon NH3BH3 Hydrolysis via a Reduction Process

Although a range of noble metal catalysts, including Ru, Rh, Pd, Pt, and Au, have been developed for efficient H2 generation upon NH3BH3 hydrolysis at room temperature, this is a highly urgent need for exploring earth-abundant metal nanocatalysts for H2 generation upon NH3BH3 hydrolysis. Herein, a NaBH4 reduction strategy was developed to boost the catalytic performance of NiMoO4 nanorods in H2 generation upon NH3BH3 hydrolysis. Indeed, the pristine NiMoO4 nanorods were catalytically inert in NH3BH3 hydrolysis. Significantly, the reduced NiMoO4 nanorods presented excellent catalytic activity in H2 generation upon NH3BH3 hydrolysis, with a turnover frequency (TOF) of 31.2 L(H2)·gcat-1·h-1. Interestingly, the TOF of NH3BH3 hydrolysis over reduced NiMoO4 nanorods significantly increased from 31.2 to 53.6 L(H2)·gcat-1·h-1 under 0.3 M NaOH. The boosting catalytic performance of NiMoO4 nanorods via NaBH4 reduction in H2 generation might be attributed to the higher content of Oads and the formation of nickel boride in the reduced NiMoO4 nanorods. In this work, NH3BH3 hydrolysis over reduced NiMoO4 nanorods was not only used for safe H2 generation but also for its in situ tandem hydrogenation in organic chemistry.

Selective and controlled H2 generation upon additive-free HCOOH dehydrogenation over a Pd/NCS nanocatalyst

Although sodium formate is widely used as a conventional additive to enhance selective H2 evolution from HCOOH dehydrogenation, this leads to a waste of resources and an increase in the cost of H2 production. For this reason, N-doped carbon nanospheres with abundant graphitic C/N have been designed to enrich the electron cloud density of the Pd atom for improving its catalytic activity in H2 generation upon additive-free HCOOH dehydrogenation. Herein, we have synthesized N-doped carbon nanosphere-stabilized Pd nanoparticles (Pd/NCSs) as high-efficiency nano-catalysts, via fixation of Pd nanoparticles onto N-doped carbon nanospheres (NCSs), for selective and controlled H2 generation upon additive-free HCOOH dehydrogenation. Pd/NCS-800 (1640 h-1) provided a 12 times larger TOF than commercial Pd/C (134 h-1) in H2 generation upon additive-free HCOOH dehydrogenation. It seemed that graphitic N/C of NCS-800 enriched the electron cloud density of the Pd atom, which was favorable for the cleavage of C-H bonds in HCOOH dehydrogenation. In addition, the selective H2 evolution from additive-free HCOOH dehydrogenation over Pd/NCS-800 is successfully controlled by adjusting the pH.