High-electrophilic (SiO)2Nb(OH)(=O) sites confined in silanol defects over Nb-Beta zeolite for efficient cyclic alkene epoxidation reactions.

Dealuminated Beta zeolite has a large amount of silanol defects on its interface, which provides an ideal place for embedding metal species and creating metal active sites in a confined microenvironment. The confined metal sites as well as their surroundings are closely related to the reactant activation and transient state achievement. Hence, unraveling the confined metal sites is of great significance for the catalytic reaction process. Herein, niobium species were incorporated into the silanol defects over dealuminated Beta zeolite with a facile dry impregnation method, co-grinding the niobium precursor with dealuminated Beta zeolite support. The successful incorporation of niobium into the silanol defects for 30Nb-Beta zeolite was verified by DRIFT, 1H MAS NMR, UV-Vis and UV-Raman characterizations. XAS characterization and DFT calculations further disclosed that the confined Nb species existed as (SiO)2Nb(OH)(=O), containing two Si-O-Nb bonds, one Nb=O bond as well as one Nb-OH bond. The synthesized 30Nb-Beta zeolite catalyst displayed a superior cyclohexene conversion of 51.1%, cyclohexene oxide selectivity of 83.1% as well as TOF value of 188.2 h-1 ascribed to the inherent electrophilicity of Nb(V) for confined (SiO)2Nb(OH)(=O) species as well as the low oxygen transfer energy barrier for NbV-OOH species. Furthermore, the prepared 30Nb-Beta zeolite can be effectively employed to other cyclic alkene epoxidation reactions.

Hydrogen Production through Distinctive C-C Cleavage during Acetic Acid Reforming at Low Temperature.

Acetic acid reforming is a green method for sustainable hydrogen production owing to its renewable source from biomass conversion. However, conventional acetic acid reforming would produce various byproducts, including CO, CH4 and so on. Here, we develop a distinctive method for selective hydrogen production from C-C directional cleavage during acetic acid reforming. Completely different from conventional acetic acid reforming process, acetic acid would react with water over organoruthenium catalyst during its C-C cleavage at low temperature, then produce methanol and formic acid (CH3COOH+H2O→CH3OH+HCOOH). Lastly, methanol and formic acid could further decompose into hydrogen and carbon dioxide over organoruthenium selectively. As a result, there is little CO and CH4 produced in the first step of C-C bond cleavage during acetic acid reforming at 100 °C. Hydrogen production rate is up to 26.8 molH2/(h-1*mol-1 Ru) at 150 °C through a tandem catalysis. A mechanism for C-C cleavage of acetic acid is proposed based on intermediate product analysis and density functional theory (DFT) calculation. Firstly, the C-C single bond was transformed into C=C double bond by dropping one H atom to organoruthenium. Then the coming H2O molecule reacted with the C=C bond by an addition reaction, forming methanol and formic acid. This research not only proposes distinctive reaction pathway for hydrogen production from acetic acid reforming, but also provides some inspiration for selective C-C bond cleavage during ethanol reforming.

Nanosized Proton Conductor Array with High Specific Surface Area Improves Fuel Cell Performance at Low Pt Loading.

The use of ordered catalyst layers, based on micro-/nanostructured arrays such as the ordered Nafion array, has demonstrated great potential in reducing catalyst loading and improving fuel cell performance. However, the size (diameter) of the basic unit of the most existing ordered Nafion arrays, such as Nafion pillar or cone, is typically limited to micron or submicron sizes. Such small sizes only provide a limited number of proton transfer channels and a small specific area for catalyst loading. In this work, the ordered Nafion array with a pillar diameter of only 40 nm (D40) was successfully prepared through optimization of the Nafion solvent, thermal annealing temperature, and stripping mode from the anode alumina oxide (AAO) template. The density of D40 is 2.7 × 1010 pillars/cm2, providing an abundance of proton transfer channels. Additionally, D40 has a specific area of up to 51.5 cm2/cm2, which offers a large area for catalyst loading. This, in turn, results in the interface between the catalyst layer and gas diffusion layer becoming closer. Consequently, the peak power densities of the fuel cells are 1.47 (array as anode) and 1.29 W/cm2 (array as cathode), which are 3.3 and 2.9 times of that without array, respectively. The catalyst loading is significantly reduced to 17.6 (array as anode) and 61.0 µg/cm2 (array as cathode). Thus, the nanosized Nafion array has been proven to have high fuel cell performance with low Pt catalyst loading. Moreover, this study also provides guidance for the design of a catalyst layer for water electrolysis and electrosynthesis.

Assembled Organoruthenium(II) for Formaldehyde Decomposition and Hydrogen Production.

Formaldehyde decomposition is not only an attractive method for hydrogen production, but also a potential approach for gaseous formaldehyde removal. In this research, we prepare some assembled organoruthenium through coordination reaction between Ru(p-Cymene)Cl2 and bridge-linking ligands. It is a creative approach for Ru(p-Cymene)Cl2 conversion into heterogeneous particles. The rigidity of bridge-linking ligand enables assembled organoruthenium to have highly ordered crystalline structure, even show clear crystal lattice with spacing of 0.19 nm. XPS shows the N-Ru bond are formed between bridge-linking ligand and Ru(p-Cymene)Cl2 . The assembled organoruthenium has high abundant active sites for formaldehyde decomposition at low temperature. The reaction rate could increase linearly with temperature and formaldehyde concentration, with a TOF of 2420 h-1 at 90 °C. It is promising for gaseous formaldehyde decomposition in wet air or nitrogen. Formaldehyde conversion is up to 95 % over Ru-DAPM is 4,4'-diaminodiphenylmethane at 90 °C in air. Gaseous formaldehyde decomposition is a two-steps process under oxygen-free condition. Firstly, formaldehyde dissolve in water, and be converted into hydrogen and formic acid through formaldehyde-water shift reaction. Then intermediate formic acid will further decompose into hydrogen and carbon dioxide. We also find formaldehyde decomposition is a synergetic catalysis process of oxygen and water in moist air. Oxygen is conducive to formic acid desorption and decomposition on the active sites, so assembled organoruthenium exhibit slightly higher conversion for formaldehyde decomposition in moist air. This work proposes a distinctive method for gaseous formaldehyde decomposition in the air, which is entirely different from formaldehyde photocatalysis or thermocatalysis oxidation.

Photoenzymatic Catalytic Cascade System of a Pyromellitic Diimide/g-C3N4 Heterojunction to Efficiently Regenerate NADH for Highly Selective CO2 Reduction toward Formic Acid.

Photocatalytic reduction of carbon dioxide (CO2) holds great promise for both clean energy and environment protection. However, the low activity and poor selectivity of photocatalysts are the main bottlenecks. Herein, inspired by artificial photosynthesis and taking advantages of high efficiency and specificity of bioenzymes, we marry photo with enzyme to synergistically solve the above problems. A metal-free heterojunction of pyromellitic diimide/g-C3N4 (PDI/CN) with an excellent visible light response (λ < 660 nm) is fabricated for achieving a photoenzymatic catalytic cascade system, which efficiently regenerates nicotinamide adenine dinucleotide (NADH) and selectively reduces CO2 to formic acid (HCOOH). The highest NADH yield of the PDI/CN hybrid achieved is 75%, and the HCOOH generation rate achieved is 1.269 mmol g-1 h-1 with nearly 100% selectivity, which is much higher than those of the reported materials. The excellent photocatalytic performance is attributed to the unique photoenzymatic catalytic cascade system, heterointerface effect, good conductivity, and a wide sunlight response range of the PDI/CN heterojunction. This work provides an efficient strategy and a corresponding photocatalyst for the directional conversion of CO2 to HCOOH.

Low-Temperature Methanol-Water Reforming Over Alcohol Dehydrogenase and Immobilized Ruthenium Complex.

Hydrogen is one of the most promising sustainable energy carriers for its high gravimetric energy density and abundance. Nowadays, hydrogen production and storage are the main constraints for its commercialization. As a current research focus, hydrogen production from methanol-water reforming, especially at low temperature, is particularly important. In this study, a novel reaction path for low-temperature methanol reforming through synergistic catalysis was developed. Alcohol dehydrogenase (ADH) and coenzyme I (nicotinamide adenine dinucleotide, NAD+ ) were employed for methanol catalytic dehydrogenation at low temperature, which could generate formaldehyde and reductive coenzyme I (NADH). Covalent triazine framework-immobilized ruthenium complex (Ru-CTF) was prepared afterwards. On one hand, the catalyst exhibited high activity for the formaldehyde-water shift reaction to generate hydrogen and carbon dioxide. On the other hand, the NADH dehydrogenation was also catalyzed by the Ru-CTF, producing NAD+ and hydrogen. Additionally, the catalyst also showed high biocompatibility with ADH. Through the synergistic effect of the above two main processes, methanol could be converted into hydrogen and carbon dioxide stably at low temperature for more than 96 h. The hydrogen production rate was dependent on the pH of the reaction solution as well as the ADH dosage. A hydrogen production rate of 157 mmol h-1 mol-1 Ru was achieved at the optimum pH (8.1). Additionally, the hydrogen production rate increased linearly with the ADH dosage, reaching 578 mmol h-1 mol-1 Ru when the ADH dosage was 180 U at 35 °C. This research could not only help overcome the difficulties for methanol reforming near room temperature but also give new inspiration for designing new reaction pathways for methanol reforming.

Hydrogen Generation from Catalytic Reforming of Paraformaldehyde and Water by Polymeric Bifunctional Catalysts Comprising Ruthenium and Sulfonic Acid Units.

As a clean and sustainable source of energy, hydrogen shows great potential to be the ultimate energy source in future. In this research, paraformaldehyde is used as hydrogen carrier. Several bifunctional catalysts are prepared for the hydrogen generation from paraformaldehyde. The bifunctional catalysts contain two catalytically active sites. One is a sulfonic acid group for paraformaldehyde hydrolysis, and the other is an organometallic group that catalyzes the hydrogen release from formaldehyde. Bifunctional iridium catalysts and bifunctional rhodium catalysts could only generate traces of hydrogen in the initial phase of paraformaldehyde decomposition. Only the bifunctional ruthenium catalyst shows high activity due to its bifunctional catalytically active sites, thus more than 98.0 % of the initially produced gas contains hydrogen. The initial TOF is 685 h-1 at 363 K when the paraformaldehyde concentration is 20 wt%. A reaction mechanism is proposed for the hydrogen generation from paraformaldehyde in which formaldehyde and formic acid are intermediates Formic acid decomposition is the rate-determining step in the later phase of paraformaldehyde decomposition.

Flexible and Adaptable Fuel Cell Pack with High Energy Density Realized by a Bifunctional Catalyst.

A proton exchange membrane fuel cell (PEMFC) system with a hydrogen generator could have higher energy density than flexible batteries and supercapacitors and is possible to meet the urgent demand of flexible electronics. However, a flexible PEMFC pack is still not available due to the absence of a flexible hydrogen generator. To solve this problem, we successfully invented a flexible and adaptable hydrogen generator, which was realized by a new bifunctional aerogel catalyst with the abilities of both storing and producing hydrogen. The flexible hydrogen generator can produce hydrogen at room temperature when the device is inverting, bending, and rotating. By combining this flexible hydrogen generator and the unique flexible PEMFC stack of our group, we originally made a highly flexible and adaptable fuel cell pack with a high theoretical energy density (up to 722 Wh·kg-1) and current achieved energy density (135.9 Wh·kg-1). Such a PEMFC pack is highly promising to meet the high demand of flexible electronics.

Revealing the Activity Distribution of a Single Nanocatalyst by Locating Single Nanobubbles with Super-Resolution Microscopy.

It is challenging to uncover the catalytic activity at different locations of a single nanocatalyst for gas-generating reactions in real time. This research uses super-resolution microscopy to localize the center of single nanobubbles and reveal the local activity distribution at several to tens of nanometers accuracy. The distances between the centers of the nanobubbles and the center of the nanoplate usually distribute in a certain range from 0 to 500 nm, with the maximum population exhibiting at ∼200 nm. This research also shows that more nanobubbles appear near the tips of the Pd-Ag nanoplate compared with the edges, which indicates higher activity at the tips. In addition, the relationship between the location, lifetime, and turnover rate of the nanobubbles was also carefully studied. This work presents an effective, high-resolution method to localize the activity distribution of nanocatalysts during gas-generating reactions, such as photocatalytic water splitting, dehydrogenation, and electro-oxidation.

Methanol-Water Aqueous-Phase Reforming with the Assistance of Dehydrogenases at Near-Room Temperature.

As an excellent hydrogen-storage medium, methanol has many advantages, such as high hydrogen content (12.6 wt %), low cost, and availability from biomass or photocatalysis. However, conventional methanol-water reforming usually proceeds at high temperatures. In this research, we successfully designed a new effective strategy to generate hydrogen from methanol at near-room temperature. The strategy involved two main processes: CH3 OH→HCOOH→H2 and NADH→HCOOH→H2 . The first process (CH3 OH→HCOOH→H2 ) was performed by an alcohol dehydrogenase (ADH), an aldehyde dehydrogenase (ALDH), and an Ir catalyst. The second procedure (NADH→HCOOH→H2 ) was performed by formate dehydrogenase (FDH) and the Ir catalyst. The Ir catalyst used was a previously reported polymer complex catalyst [Cp*IrCl2 (ppy); Cp*=pentamethylcyclopentadienyl, ppy=polypyrrole] with high catalytic activity for the decomposition of formic acid at room temperature and is compatible with enzymes, coenzymes, and poisoning chemicals. Our results revealed that the optimum hydrogen generation rate could reach up to 17.8 µmol h-1 gcat-1 under weak basic conditions at 30 °C. This will have high impact on hydrogen storage, production, and applications and should also provide new inspiration for hydrogen generation from methanol.

Hydrogen generation from methanol at near-room temperature.

As a promising hydrogen storage medium methanol has many advantages such as a high hydrogen content (12.5 wt%) and low-cost. However, conventional methanol-water reforming methods usually require a high temperature (>200 °C). In this research, we successfully designed an effective strategy to fully convert methanol to hydrogen for at least 1900 min (∼32 h) at near-room temperature. The strategy involves two main procedures, which are CH3OH → HCOOH → H2 and CH3OH → NADH → H2. HCOOH and the reduced form of nicotinamide adenine dinucleotide (NADH) are simultaneously produced through the dehydrogenation of methanol by the cooperation of alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH). Subsequently, HCOOH is converted to H2 by a new iridium polymer complex catalyst and an enzyme mimic is used to convert NADH to H2 and nicotinamide adenine dinucleotide (NAD+). NAD+ can then be reconverted to NADH by repeating the dehydrogenation of methanol. This strategy and the catalysts invented in this research can also be applied to hydrogen production from other small organic molecules (e.g. ethanol) or biomass (e.g. glucose), and thus will have a high impact on hydrogen storage and applications.

Nanobubbles: An Effective Way to Study Gas-Generating Catalysis on a Single Nanoparticle.

Gas-generating catalysis is important to many energy-related research fields, such as photocatalytic water splitting, water electrolysis, etc. The technique of single-nanoparticle catalysis is an effective way to search for highly active nanocatalysts and elucidate the reaction mechanism. However, gas-generating catalysis remains difficult to investigate at the single-nanoparticle level because product gases, such as H2 and O2, are difficult to detect on an individual nanoparticle. Here, we successfully find that nanobubbles can be used to study the gas-generating catalysis, i.e., H2 generation from formic acid dehydrogenation on a single Pd-Ag nanoplate, with a high time resolution (50 ms) via dark-field microscopy. The research reveals that the nanobubble evolution process includes nucleation time and lifetime. The nucleation rate of nanobubbles is proportional to the catalytic activity of a single nanocatalyst. The relationship between the catalytic activity and the nucleation rate is quantitatively described by a mathematical model, which shows that an onset reaction rate (ronset) exists for the generation of nanobubbles on a single Pd-Ag nanoplate. The research also reveals that a Pd-Ag nanoplate with larger size usually has a higher activity. However, some large-sized ones still have low activities, indicating the size of the Pd-Ag nanoplate is not the only key factor for the activity. Notablely, further research shows that Pd content is the key factor for the activity of single Pd-Ag nanoplates with similar size. The methodology and knowledge acquired from this research are also applicable to other important gas-generating catalysis reactions at the single-nanoparticle level.

Flexible and Lightweight Fuel Cell with High Specific Power Density.

Flexible devices have been attracting great attention recently due to their numerous advantages. But the energy densities of current energy sources are still not high enough to support flexible devices for a satisfactory length of time. Although proton exchange membrane fuel cells (PEMFCs) do have a high-energy density, traditional PEMFCs are usually too heavy, rigid, and bulky to be used in flexible devices. In this research, we successfully invented a light and flexible air-breathing PEMFC by using a new design of PEMFC and a flexible composite electrode. The flexible air-breathing PEMFC with 1 × 1 cm2 working area can be as light as 0.065 g and as thin as 0.22 mm. This new PEMFC exhibits an amazing specific volume power density as high as 5190 W L-1, which is much higher than traditional (air-breathing) PEMFCs. Also outstanding is that the flexible PEMFC retains 89.1% of its original performance after being bent 600 times, and it retains its original performance after being dropped five times from a height of 30 m. Moreover, the research has demonstrated that when stacked, the flexible PEMFCs are also useful in mobile applications such as mobile phones. Therefore, our research shows that PEMFCs can be made light, flexible, and suitable for applications in flexible devices. These innovative flexible PEMFCs may also notably advance the progress in the PEMFC field, because flexible PEMFCs can achieve high specific power density with small size, small volume, low weight, and much lower cost; they are also much easier to mass produce.

Hydrogen generation from glucose catalyzed by organoruthenium catalysts under mild conditions.

Concerns about the depletion of fossil fuel reserves and environmental pollution make hydrogen an attractive alternative energy source. Here, we first describe a catalytic reaction system that produces H2 from glucose using a homogeneous catalyst [(p-cymene)Ru(NH3)]Cl2 with the maximum TOF = 719 h-1 at 98 °C and an initial pH = 0.5.

Highly Active Carbon Supported Pd-Ag Nanofacets Catalysts for Hydrogen Production from HCOOH.

Hydrogen is regarded as a future sustainable and clean energy carrier. Formic acid is a safe and sustainable hydrogen storage medium with many advantages, including high hydrogen content, nontoxicity, and low cost. In this work, a series of highly active catalysts for hydrogen production from formic acid are successfully synthesized by controllably depositing Pd onto Ag nanoplates with different Ag nanofacets, such as Ag{111}, Ag{100}, and the nanofacet on hexagonal close packing Ag crystal (Ag{hcp}). Then, the Pd-Ag nanoplate catalysts are supported on Vulcan XC-72 carbon black to prevent the aggregation of the catalysts. The research reveals that the high activity is attributed to the formation of Pd-Ag alloy nanofacets, such as Pd-Ag{111}, Pd-Ag{100}, and Pd-Ag{hcp}. The activity order of these Pd-decorated Ag nanofacets is Pd-Ag{hcp} > Pd-Ag{111} > Pd-Ag{100}. Particularly, the activity of Pd-Ag{hcp} is up to an extremely high value, i.e., TOF{hcp} = 19 000 ± 1630 h(-1) at 90 °C (lower limit value), which is more than 800 times higher than our previous quasi-spherical Pd-Ag alloy nanocatalyst. The initial activity of Pd-Ag{hcp} even reaches (3.13 ± 0.19) × 10(6) h(-1) at 90 °C. This research not only presents highly active catalysts for hydrogen generation but also shows that the facet on the hcp Ag crystal can act as a potentially highly active catalyst.

Massively Screening the Temporal Spectra of Single Nanoparticles to Uncover the Mechanism of Nanosynthesis.

Nanosynthesis is the basis of nanotechnology and its applications. It is necessary to understand the growth mechanism of nanoparticles and the functions of growth factors. An effective way to study the synthesis is at the single nanoparticle level. This study reports a single nanoparticle spectrometer, which is based on a commercial dark-field microscopy and a group of narrowband filters. This spectrometer has many advantages, such as high light transparency (35%-75%), low cost (<$1500), massive screening (≈200 nanoplates at a time), and a high time resolution (<5 s). By using this spectrometer, the galvanic replacement reaction (GRR) is studied on single Ag nanoplates in situ and in real time. The research reveals that GRR on single Ag nanoplates has three different types according to the change of peak wavelength during reaction. Such diverse reaction types can be attributed to the different relative reaction rates of GRR on the faces and edges of Ag nanoplate with different facets. Further research shows that the relative reaction rates of different facets vary a lot under different concentrations of tri-sodium citrate. This research successfully demonstrates that the new single nanoparticle spectrometer can study the growth of single nanoparticles and the effect of growth factors.

Fluorescence enhancement on silver nanoplates at the single- and sub-nanoparticle level.

The fluorescence intensity of a fluorescent molecule can be strongly enhanced when the molecule is near a metal nanoparticle. Hence, fluorescence enhancement has a lot of applications in the fields of biology and medical science. It is necessary to understand the mechanism for such an attractive effect, if we intend to develop better materials to improve the enhancement. In this paper, we directly image the diverse patterns of fluorescence enhancement on single Ag nanoplates by super-resolution microscopy. The research reveals that the edges or tips of the Ag nanoplate usually show a much higher ability of fluorescence enhancement than the mid part. The spatial distribution of fluorescence enhancement strongly depends on the size of the Ag nanoplate as well as the angle between the Ag nanoplate and the incident light. The experimental results above are essentially consistent with the simulated electric field by the theory of localized surface plasmon resonance (LSPR), but some irregularities still exist. We also find that fluorescence enhancement on small Ag nanoplates is mainly due to in-plane dipole plasmon resonance, while the enhancement on large Ag nanoplates is mainly due to in-plane quadrupole plasmon resonance. Furthermore, in-plane quadrupole resonance of large plates has a higher ability to enhance the fluorescence signal than the in-plane dipole plasmon resonance. This research provides many valuable insights into the fluorescence enhancement at the single- and sub-nanoparticle level, and will be very helpful in developing better relevant materials.