Integration of morphology and electronic structure modulation on cobalt phosphide nanosheets to boost photocatalytic hydrogen evolution from ammonia borane hydrolysis

The controllable and safe hydrogen storage technologies are widely recognized as the main bottleneck for the accomplishment of sustainable hydrogen energy.Ammonia borane(AB)has regarded as a competitive candidate for chemical hydrogen storage.However,developing efficient yet high-performance catalysts towards hydrogen evolution from AB hydrolysis remains an enormous challenge.Herein,cobalt phosphide nanosheets are synthesized by a facile salt-assisted along with low-temperature phosphidation strategy for simultaneously modulating its morphology and electronic structure,and function as hydrogen evolution photocatalysts.Impressively,the Co_(2)P nanosheets display extraordinary performance with a record high turnover frequency of 44.9 min^(-1),outperforming most of the noble-metal-free catalysts reported to date.This remarkable performance is attributed to its desired nanosheets structure,featuring with high specific surface area,abundant exposed active sites,and short charge diffusion paths.Our findings provide a novel strategy for regulating metal phosphides with desired phase structure and morphology for energy-related applications and beyond.

Anomalous metastable hcp Ni nanocatalyst induced by non-metal N doping enables promoted ammonia borane dehydrogenation

Developing high-performing non-noble transition metal catalysts for H_(2) evolution from chemical hydrogen storage materials is of great significance for the hydrogen economy system, yet challenging. Herein,we present for the first time that anomalous metastable hexagonal close-packed Ni nanoparticles induced by heteroatom N doping encapsulated in carbon(N-hcp-Ni/C) can exhibit admirable catalytic performance for ammonia borane(AB) dehydrogenation, prominently outperforming conventional fcc Ni counterpart with similar morphology and favorably presenting the state-of-the-art level.Comprehensive experimental and theoretical studies unravel that unusual hcp phase engineering of Ni together with N doping could induce charge redistribution and modulate electronic structure, thereby facilitating H_(2)O adsorption and expediting H_(2)O dissociation(rate-determining step). As a result, AB dehydrogenation can be substantially boosted with the assistance of N-hcp-Ni/C. Our proposed strategy highlights that unconventional crystal phase engineering coupled with non-metal heteroatom doping is a promising avenue to construct advanced transition metal catalysts for future renewable energy technologies.

Ammonia borane-enabled hydrogen transfer processes:Insights into catalytic strategies and mechanisms

Transfer hydrogenation(TH) with in situ generated hydrogen donor is of great importance in reduction reactions, and an alternative strategy to traditional hydrogenation processes involving pressurized molecular hydrogen. Ammonia borane(NH3BH3, AB) is a promising material of hydrogen storage, and it has attracted much attention in reductive organic transformations owing to its high activity, good atom economy, nontoxicity, sustainability, and ease of transport and storage. This review focuses on summarizing the recent progress of AB-mediated TH reactions of diverse substrates including nitro compounds, nitriles, imines, alkenes, alkynes, carbonyl compounds(ketones and aldehydes), carbon dioxide,and N-and O-heterocycles. Syntheses protocols(metal-containing and metal-free), the effect of reaction parameters, product distribution, and variation of reactivity are surveyed, and the mechanism of each reaction involving the action mode of AB as well as structure-activity relationships is discussed in detail. Finally, perspectives are presented to highlight the challenges and opportunities for AB-enabled TH reactions of unsaturated compounds.

A step‐growth strategy to grow vertical porous aromatic framework nanosheets on graphene oxide:Hybrid material‐confined Co for ammonia borane methanolysis

The rational synthesis of a two-dimensional(2D)porous aromatic framework(PAF)with a controllable growth direction remains a challenge to overcome the limitation of traditional stacked 2D materials.Herein,a step-growth strategy is developed to fabricate a vertically oriented nitrogen-rich porous aromatic framework on graphene oxide(V-PAF-GO)using monolayer benzidine-functionalized GO(BZ-GO)as a molecular pillar.Then,the confined Co nanoparticle(NP)catalysts are synthesized by encapsulating ultra-small Co into the slit pores of V-PAF-GO.Due to the high nitrogen content,large specific surface area,and adequate slit pores,the optimized vertical nanocomposites V-PAF-GO provide abundant anchoring sites for metal NPs,leading to ultrafine Co NPs(1.4 nm).The resultant Co/V-PAF-GO catalyst shows an extraordinary catalytic activity for ammonia borane(AB)methanolysis,yielding a turnover frequency value of 47.6 min−1 at 25°C,comparable to the most effective non-noble-metal catalysts ever reported for AB methanolysis.Experimental and density functional theory studies demonstrate that the electron-donating effect of N species of PAF positively corresponds to the low barrier in methanol molecule activation,and the cleavage of the O–H bond in CH3OH has been proven to be the rate-determining step for AB methanolysis.This work presents a versatile step-growth strategy to prepare a vertically oriented PAF on GO to solve the stacking problem of 2D materials,which will be used to fabricate other novel 2D or 2D–2D materials with controllable orientation for various applications.

Interface electron collaborative migration of Co–Co3O4/carbon dots:Boosting the hydrolytic dehydrogenation of ammonia borane

Ammonia borane(AB)is an excellent candidate for the chemical storage of hydrogen.However,its practical utilization for hydrogen production is hindered by the need for expensive noble-metal-based catalysts.Herein,we report Co-Co3O4 nanoparticles(NPs)facilely deposited on carbon dots(CDs)as a highly efficient,robust,and noble-metal-free catalyst for the hydrolysis of AB.The incorporation of the multiinterfaces between Co,Co3O4 NPs,and CDs endows this hybrid material with excellent catalytic activity(rB=6816 mLH2 min^-1 gCo^-1)exceeding that of previous non-noble-metal NP systems and even that of some noble-metal NP systems.A further mechanistic study suggests that these interfacial interactions can affect the electronic structures of interfacial atoms and provide abundant adsorption sites for AB and water molecules,resulting in a low energy barrier for the activation of reactive molecules and thus substantial improvement of the catalytic rate.

Carbon dots-confined CoP-CoO nanoheterostructure with strong interfacial synergy triggered the robust hydrogen evolution from ammonia borane

Ammonia borane(NH_(3)BH_(3),AB) is promising for chemical hydrogen sto rage;however,current systems for rapid hydrogen production are limited by the expensive noble metal catalysts required for AB hydrolysis.Here we report the design and synthesis of a highly efficient and robust non-noble-metal catalyst for the hydrolysis of AB at 298 K(TOF=89.56 molH_(2) min^(-1) molCo^(-1)).Experiments and density functional theory calculations were performed to explore the catalyst’s hybrid nanoparticle heterostructure and its catalytic mechanism.The catalyst comprised nitrogen-doped carbon dots confining CoO and CoP,and exhibited strong interface-induced synergistic catalysis for AB hydrolysis that effectively decreased the energy barriers for the dissociation of both AB and water molecules.The co-doping of N and P introduced numerous defects,and further regulated the reactivity of the carbon layers.The heterogeneous interface design technique presented here provides a new strategy for developing efficient and inexpensive non-noblemetal catalysts that may be applicable in other fields related to energy catalysis.

Co-CoO_x supported onto TiO_(2) coated with carbon as a catalyst for efficient and stable hydrogen generation from ammonia borane

Ammonia borane(AB) can be catalytically hydrolyzed to provide hydrogen at room temperature due to its high potentaial for hydrogen storage. Non-precious metal heterogeneous catalysts have broad application in the field of energy catalysis. In this article, catalysts precursor is obtained from Co-Ti-resorcinol-formaldehyde resin by sol–gel method. Co/TiO_(2)@N-C(CTC) catalyst is prepared by calcining the precursor under high temperature conditions in nitrogen atmosphere. Co-CoO_x/TiO_(2)@N-C(COTC) is generated by the controllable oxidation reaction of CTC. The catalyst can effectively promote the release of hydrogen during the hydrolytic dehydrogenation of AB. High hydrogen generation at a specific rate of 5905 m L min^(-1) g_(Co)^(-1) is achieved at room temperature. The catalyst retains its 85% initial catalytic activity even for its fifth time use in AB hydrolysis. The synergistic effect among Co, Co_(3)O_(4) and TiO_(2) promotes the rate limiting step with dissociation and activation of water molecules by reducing its activation energy. The applied method in this study promotes the development of non-precious metals in catalysis for utilization in clean energy sources.

Core-shell structured nanospheres with mesoporous silica shell and Ni core as a stable catalyst for hydrolytic dehydrogenation of ammonia borane

Core-shell structured nanospheres with mesoporous silica shell and Ni core(denoted as Ni@meso-SiO2) are prepared through a three-step process. Monodispersed Ni precursors are first prepared, and then coated with mesoporous SiO2. Final Ni@meso-SiO2spheres are obtained after calcination. The products are characterized by X-ray powder diffraction, transmission electron microscopy and N2adsorption-desorption methods. These spheres have a high surface area and are well dispersed in water, showing a high catalytic activity with a TOF value of 18.5,and outstanding stability in hydrolytic dehydrogenation of ammonia borane at room temperature.

Convenient Asymmetric Borane Reduction of Ketones Catalyzed by Simple Amino Alcohols and Corresponding Amino Acids

An asymmetric borane reduction of prochiral ketones catalyzed by simple amino alcohols and corresponding amino acids was examined to give alcohols with e.e. value up to 92% .

EFFECTS OF RATE OF ADDITION AND TENIPERATURE ON THE ENANTIOSELECTIVITY IN BORANE REDUCTION OF KETONES CATALYZED BY CHIRAL OXAZABOROLIDINE

The exoellent enantioselectivity with o. p. >99% in asymmetrio borane reduction of acetophenone catalyzed by (4S, 5R ) 4, 5-diphenyi-1. 3. 2-oxazaborolidine has been achieved via the important modincation of the reaction conditions.

Asymmetric Reduction of Aromatic Ketones Catalyzed by Using (αs,4s)-2-Dichloromethyl-4,5-Dihydro-α-(4-Nitrophenyl)-4- Oxazolemethanol-Borane Complex

Chiral oxazoborolidine borane complex was prepared from (αs, 4s)-2-dichloromethyl-4, 5-dihydro-α-(4-nitrophenyl)-4-oxazolemethanol with Borane in THF. The borane modified by chiral oxazoborolidine enantioselectively reduced aromatic ketones to second-alcohol with about 95%yield and medium optical yields. In the end of article, results are discussed and reduction mechanism is shown which proves the resulting major isomers fit very well.

Polymer Film Supported Bimetallic Au–Ag Catalysts for Electrocatalytic Oxidation of Ammonia Borane in Alkaline Media

Ammonia borane is widely used in most areas including fuel cell applications.The present paper describes electrochemical behavior of ammonia borane in alkaline media on the poly(p-aminophenol) film modified with Au and Ag bimetallic nanoparticles.The glassy carbon electrode was firstly covered with polymeric film electrochemically and then,Au,Ag,and Au–Ag nanoparticles were deposited on the polymeric film,respectively.The surface morphology and chemical composition of these electrodes were examined by scanning electron microscopy,transmission electron microscopy,electrochemical impedance spectroscopy,X-ray diffraction,and X-ray photoelectron spectroscopy.It was found that alloyed Au–Ag bimetallic nanoparticles are formed.Electrochemical measurements indicate that the developed electrode modified by Au–Ag bimetallic nanoparticles exhibit the highest electrocatalytic activity for ammonia borane oxidation in alkaline media.The rotating disk electrode voltammetry demonstrates that the developed electrode can catalyze almost six-electron oxidation pathway of ammonia borane.Our results may be attractive for anode materials of ammonia borane fuel cells under alkaline conditions.

Two-Dimensional Borane with ‘Banana' Bonds and Dirac-Like Ring

Designing new two-dimensional （2D） semiconductors with novel topological characters is highly desirable for further material innovation. We propose a theoretical design of a stable 2D inorganic material, namely, borane, which is jointly stabilized by traditional B B localized and unique B-H-B delocalized chemical bonds. In borane, the bonding natures along different directions are distinguishing, which lead to huge differences in mechanical strengths of 142.73 and 97.47N/m for a and b directions, respectively. In a unit cell, each hydrogen atom binds to two boron atoms forming a three-center-two-electron （3c-2e） bridge bond B H B. This can be considered as an extension of diborane molecules from OD to 2D. The collaboration of localized and delocalized chemical bonds endows borane with high structural stability, as indicated by its favorable cohesive energy, high mechanical strength, absence of imaginary modes in the phonon spectrum, and moderate melting point. Remarkably, borane has a fascinating electronic property featured with a Dirae-like ring in the electronic band structure. The unique bonding nature and electronic property in borane would attract intensive interests in both theory and experiment.

Selective synthesis of the B_(11)H_(14)^(-) and B_(12)H_(12)^(2-) borane derivatives and the general mechanisms of the B-H bond condensation

Polyhedral boranes are a class of well-known boron molecular clusters with unique physical and chemical properties,and great efforts have been made in the past decades to find more effective synthetic methods.However,the established synthetic methods suffer from low efficiency and low selectivity because the mechanism of the B-H bond condensation reaction,critical for the synthesis of the polyhedral boranes,is not well understood.Here we report highly selective and efficient synthetic methods of the salts of the tetradecahydridoundecaborate(1-)(B_(11)H^(-)_(14)) and dodecahydrido-dodecaborates(2-)(B_(12)H_(12)^(2-)) anions by employing commercially available and inexpensive starting materials.Both theoretical and experimental investigations are carried out to elucidate the reaction mechanisms.We have found that the nature of the B-H bond condensation is the dihydrogen bonding interaction in which the positively charged hydrogens(bridged hydrogens) play a crucial role.The current study has not only led to more effective and selective synthetic methods for B_(11)H^(-)_(14) and B_(12)H_(12)^(2-) but also unveiled the nature of the B-H bond condensation and the general formation mechanisms of polyhedral boranes.This finding will facilitate the development of more effective synthetic methods for polyhedral boranes and spur their wide application.

A metal-free coordination–insertion ring-opening polymerization of tetrahydrofuran by the central metalloid bis(pentafluorophenyl)(phenoxy)borane

A new strategy for the metal-free coordination–insertion ring-opening polymerization of tetrahydrofuran by the central metalloid Boron has been first identified.Bis(pentafluorophenyl)(phenoxy)borane was used as a catalyst for the polymerization reaction system.And polytetrahydrofuran with high molecular weight and narrow molecular weight distribution could be obtained.The proposed mechanism was studied by MALDI-TOF,ESI-MS and O-18 isotope labeling analyses as a metal-free coordination insertion mechanism.

Asymmetric Hydrogenation of Phenanthridines with Chiral Boranes

The asymmetric hydrogenation of N-heteroarenes provides an efficient method for the synthesis of optically active cyclic secondary amines.In this paper,we described an asymmetric hydrogenation of phenanthridines using a chiral mono-alkene-derived borane.A variety of dihydrophenanthridines were furnished in high yields with up to 93%ee.The current catalytic system was very sensitive for the steric hindrance of phenanthridines.Bulky substituents at one phenyl group of phenanthridines were required to obtain the high enantioselectivity.But large substituents on the carbon of the C=N bonds would diminish the reactivity sharply.

Constructing ultrafine monodispersed Co_(2)P/(0.59-Cu_(3)P)on Cu doped CoZn-ZIF derived porous N-doped carbon for highly efficient dehydrogenation of ammonia borane

Rational construction of highly dispersed,small size,low cost catalysts for release of hydrogen from ammonia borane(AB)is regarded as a prospective approach for promoting the development of upcoming hydrogen economy.However,the high price and scarcity of precious metal catalysts impose restrictions on their large-scale application.To this end,with the aid of a Cu doped CoZn-zeolitic imidazolate frameworks(ZIFs)template strategy,we successfully construct ultrafine monodispersed Co_(2)P/(0.59-Cu_(3)P)on CoZn-ZIF derived porous N-doped carbon(Co_(2)P/(0.59-Cu_(3)P)-NC)as an efficient non-noble-metal catalyst.Specifically,Co and Cu atoms can be geometrically separated to high degree due to the presence of Zn in the CuCoZn-ZIF precursor,evaporation of Zn during pyrolysis can generate porous structure with the framework well maintained.The results show that porous Co_(2)P/(0.59-Cu_(3)P)-NC bimetallic phosphide exhibits large specific surface area,hierarchical pore structure,well-exposed active sites.Based on the kinetics analyses and ion effects,the catalyst has achieved an unprecedentedly high total turnover frequency(TOF)of 798 mol·molcat^(−1)·min^(−1)in 0.4 M NaOH solution at 298 K,which surpasses all the ever-reported transition-metal phosphides catalysts for hydrogen generation from AB.Experiments and theoretical studies confirm that the highly porous structure of the support,the ultrafine and high dispersion of nanoparticles,the N/P doping and their synergistic effects(e.g.,M-P,M-N,N-C,M-M',M-support)jointly induce strong electron transfer,which can reduce the reaction energy barrier and enhance their interaction with AB,thus correspondingly obtaining excellent catalytic performance.The mechanism and strategy presented in this work pave an avenue for the design of non-noble metal catalyst for hydrogen energy system.

Y_(2)O_(3)-functionalized graphene-immobilized Ni–Pt nanoparticles for enhanced hydrous hydrazine and hydrazine borane dehydrogenation

Developing efficient and highly selective catalyst to promote hydrogen generation from hydrous hydrazine(N_(2)H_(4)·H_(2)O) and hydrazine borane(N_(2)H_(4)BH_(3))remains a challenging issue for fuel cell-based hydrogen economy.In this work,ultrafine and well-dispersed bimetallic NiPt nanoparticles(3.4 nm) were successfully immobilized on Y_(2)O_(3)-functionalized graphene(Y_(2)O_(3)/rGO) without any surfactant by a simple liquid impregnation approach.It is firstly found that integration of graphene and Y_(2)O_(3) not only can facilitate the formation of ultrafine NiPt nanoparticles(NPs),but also can effectively modulate the electronic structure of NiPt NPs,thereby boosting the catalytic performance.Compared with NiPt/Y_(2)O_(3) and NiPt/rGO,the NiPt/Y_(2)O_(3)/rGO nanocomposites(NCs) show remarkable enhanced catalytic efficiency for hydrogen production from N_(2)H_(4)-H_(2)O.In particular,the optimized Ni_(0.6)Pt_(0.4/)Y_(2)O_(3)/rGO NCs display the best catalytic efficiency and 100% H_(2) selectivity for N_(2)H_(4)-H_(2)O dehydrogenation,providing a turnover frequency(TOF) of2182 h^(-1) at 323 K,which is among the highest values ever reported.Moreover,the Ni_(0.6)Pt_(0.4)/Y_(2)O_(3)/rGO NCs also exhibit an excellent catalytic performance(TOF=3191 h^(-1)) and 100% H_(2) selectively for N_(2)H_(4)BH_(3)dehydrogenation at 323 K.The outstanding catalytic results obtained provide more possibilities for the potential applications of N_(2)H_(4)·H_(2)O and N_(2)H_(4)BH_(3) as promising chemical hydrogen storage materials.

A review on hydrogen production from ammonia borane:Experimental and theoretical studies

Ammonia borane(NHsBH3,AB)is an ideal raw material of hydrogen production with higher hydrogen storage capacity.In this paper,the catalytic processes of AB dehydrogenation were described from different ways,including thermal dehydrogenation,hydrolysis,methanolysis,photocatalysis and photopiezoelectric synergy catalysis with experimental research and theoretical calculations.Catalyst models include bulk materials,two-dimensional materials,nanocluster particles and single/diatomic structures.Among them,the proportion of H2 released is different,and the reaction conditions are also different,which are suitable for different application scenarios.Through this review,we could have a preliminary comprehensive understanding of AB dehydrogenation reaction.

Facile Synthesis of Polycarbonate Diol via Copolymerization of CO_(2) and Cyclohexene Oxide Catalysed by a Combination of One-Component Phosphonium Borane Lewis Pair and Water

Well-defined polycarbonate diol was successfully synthesized through a strategy using a combination of organocatalyst and water.Such strategy was less developed in organocatalyzed polymerization and frequently regarded as side reactions.Herein,one-component phosphonium borane Lewis pairs PB1-PB8 were successfully applied in the copolymerization of CO_(2) and cyclohexene oxide(CHO)to generate poly(CHO-alt-CO_(2))carbonate(PCHC).Parameters of linker length and counter anion effects on the catalyst activity were investigated.It was found that Lewis pair PB3 served as a dual initiator and catalyst in the copolymerization of CHO and CO_(2) with or without the presence of water.In contrast,Lewis pair PB8 can serve as a true catalyst for the preparation of well-definedα,ω-hydroxyl PCHC diols.This was achieved by introducing a labile CF3COO group as counter anion through anion exchange reaction while water molecules acted as chain transfer agents.The function of trifluoroacetate group in the polymerization process was investigated in detail and possible mechanism was proposed.Upon changing the amount of water and catalyst loading,PCHC diols with varied molecular weight(1.5 kg/mol to 7.5 kg/mol),low dispersities(D<1.2)and carbonate content(>99%)could be easily obtained.The low molecular weight PCHC diol was used as a bifunctional macroinitiator for the ring-opening polymerization of L-lactide(LLA)to afford ABA triblock copolymer in one-pot synthesis.