Synergistically boosting the anchoring effect and catalytic activity of MXenes as bifunctional electrocatalysts for sodium-sulfur batteries by single-atom catalyst engineering.

MXene based sulfur hosts have attracted enormous attention in room temperature sodium-sulfur (RT Na-S) batteries due to their strong affinity towards soluble sodium polysulfides (NaPSs). However, their electrocatalytic performance needs further improvement. Here, a series of single non-noble transition metal (TM = Fe, Co, Ni, and Cu) atoms anchored on Ti2CS2 (TM@Ti2CS2) were proposed as bifunctional sulfur hosts for Na-S batteries. The results testify that the introduction of TMs dramatically enhanced the chemical interaction between sulfur-containing species and Ti2CS2, which is attributed to the co-formation of TM-S and Na-S covalent bonds. Importantly, compared with pristine Ti2CS2, the sulfur reduction reaction (SRR) is thermodynamically more favorable on TM@Ti2CS2. In addition, the incorporation of Fe, Co, and Ni atoms is also conducive to promoting the dissociation of Na2S. The density of states (DOS) results suggest that TM@Ti2CS2 maintains metallic conductivity during the whole charge and discharge process. Overall, constructing single atom catalysts is an effective strategy to further improve the electrochemical performance of MXene based sulfur hosts for Na-S batteries.

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.

Covalent surface modification of bifunctional two-dimensional metal carbide MXenes as sulfur hosts for sodium-sulfur batteries.

Room temperature sodium-sulfur (RT Na-S) batteries show extraordinary potential in large-scale energy storage. MXenes have been demonstrated to be promising sulfur hosts for Na-S batteries, and their surface functional groups play a pivotal role in their performance. However, the effect of different surface functional groups of MXenes on their anchoring effect and catalytic performance has not been systematically investigated. Herein, density functional theory (DFT) calculations were employed to explore the various electrochemical performances of a series of Ti2CTx (T = O, S, N, F, Cl, and Br) MXenes as sulfur hosts for Na-S batteries. We find that surface functional groups significantly affect the structural properties of MXenes as well as their electrochemical performance. Ti2CO2, Ti2CS2, and Ti2CN2 exhibit prominent affinity toward soluble sodium polysulfides. Moreover, they display excellent catalytic activity toward the sulfur reduction reaction and the decomposition reaction of Na2S. Finally, during the whole discharge process, Ti2CO2, Ti2CS2, and Ti2CN2 always maintain their metallic conductivity, which could improve the rate capability of Na-S batteries. Overall, Ti2CO2, Ti2CS2, and Ti2CN2 are proposed as promising bifunctional sulfur hosts for Na-S batteries, and our results may also provide insights for modulating the performance of MXenes in other applications.

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.

Product Control and Insight into Conversion of C6 Aldose Toward C2, C4 and C6 Alditols in One-Pot Retro-Aldol Condensation and Hydrogenation Processes.

Alcohols have a wide range of applicability, and their functions vary with the carbon numbers. C6 and C4 alditols are alternative of sweetener, as well as significant pharmaceutical and chemical intermediates, which are mainly obtained through the fermentation of microorganism currently. Similarly, as a bulk chemical, C2 alditol plays a decisive role in chemical synthesis. However, among them, few works have been focused on the chemical production of C4 alditol yet due to its difficult accumulation. In this paper, under a static and semi-flowing procedure, we have achieved the product control during the conversion of C6 aldose toward C6 alditol, C4 alditol and C2 alditol, respectively. About C4 alditol yield of 20 % and C4 plus C6 alditols yield of 60 % are acquired in the one-pot conversion via a cascade retro-aldol condensation and hydrogenation process. Furthermore, in the semi-flowing condition, the yield of ethylene glycol is up to 73 % thanks to its low instantaneous concentration.

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.

Ultrathin dodecyl-sulfate-intercalated Mg-Al layered double hydroxide nanosheets with high adsorption capability for dye pollution.

A high-performance dye adsorbent of ultrathin dodecyl-sulfate (DS-) intercalated Mg-Al layered double hydroxide nanosheets (DI-LDH Ns) were controllably synthesized by a simple one-step surfactant-assisted hydrothermal method. The unique intercalated structure with week interlayer interaction and high accessible surface of DI-LDH Ns provide efficient adsorption of methyl orange (MO), leading to its superior performance with much higher uptake capability (846.6 mg/g at 298 K) and less adsorbing equilibrium time (5 min) than those of ultrathin DS--surface-modified Mg-Al-LDH nanosheets (DM-LDH Ns, 327.4 mg/g at 298 K, 120 min) and original Mg-Al-LDH (O-LDH, 208.2 mg/g at 298 K, 120 min). The composition and structure of these LDHs were investigated by systematic physicochemical characterization, such as XRD, TEM, FT-IR, BET and TGA. The adsorption behavior of DI-LDH Ns follows the Langmuir isotherm equation. A plausible mechanism is proposed to explain the adsorption process of such DI-LDH Ns, in which the synergistic contributions of surface and interlayer adsorption between DI-LDH Ns and MO play an important role. This study puts forward a new thought for the development of high-performance LDH adsorbents with an ultrathin intercalated structure for the efficient and rapid removal of dyes.

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.

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.

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.