Explore the vast range of titles available.

The development of crystalline porous materials with high chemical stability is of paramount importance for their practical application. Here, we report the synthesis of polyarylether-based covalent organic frameworks (PAE-COFs) with high crystallinity, porosity and chemical stability, including towards water, owing to the inert nature of their polyarylether-based building blocks. The PAE-COFs are synthesized through nucleophilic aromatic substitution reactions between ortho -difluoro benzene and catechol building units, which form ether linkages. The resulting materials are shown to be stable against harsh chemical environments including boiling water, strong acids and bases, and oxidation and reduction conditions. Their stability surpasses the performance of other known crystalline porous materials such as zeolites, metal–organic frameworks and covalent organic frameworks. We also demonstrate the post-synthetic functionalization of these materials with carboxyl or amino functional groups. The functionalized PAE-COFs combine porosity, high stability and recyclability. A preliminary application of these materials is demonstrated with the removal of antibiotics from water over a wide pH range. The development of porous, crystalline materials with high chemical stability is crucial for their practical uses. Now, polyarylether-based covalent organic frameworks (PAE-COFs) have been synthesized that show high crystallinity and porosity, as well as good stability against harsh chemical environments including boiling water and strong acids and bases.

The development of cost-effective hydroxide exchange membrane fuel cells is limited by the lack of high-performance and low-cost anode hydrogen oxidation reaction catalysts. Here we report a Pt-free catalyst Ru 7 Ni 3 /C, which exhibits excellent hydrogen oxidation reaction activity in both rotating disk electrode and membrane electrode assembly measurements. The hydrogen oxidation reaction mass activity and specific activity of Ru 7 Ni 3 /C, as measured in rotating disk experiments, is about 21 and 25 times that of Pt/C, and 3 and 5 times that of PtRu/C, respectively. The hydroxide exchange membrane fuel cell with Ru 7 Ni 3 /C anode can deliver a high peak power density of 2.03 W cm −2 in H 2 /O 2 and 1.23 W cm −2 in H 2 /air (CO 2 -free) at 95 °C, surpassing that using PtRu/C anode catalyst, and good durability with less than 5% voltage loss over 100 h of operation. The weakened hydrogen binding of Ru by alloying with Ni and enhanced water adsorption by the presence of surface Ni oxides lead to the high hydrogen oxidation reaction activity of Ru 7 Ni 3 /C. By using the Ru 7 Ni 3 /C catalyst, the anode cost can be reduced by 85% of the current state-of-the-art PtRu/C, making it highly promising in economical hydroxide exchange membrane fuel cells. Development of hydroxide exchange membrane fuel cells (HEMFCs) requires high-performance and low-cost catalysts for hydrogen oxidation reaction at the anode. Here the authors report Ru 7 Ni 3 /C as anode catalysts, delivering high power density and good durability in alkaline media for HEMFCs.

This Perspective establishes catalyst activity targets for hydroxide exchange membrane fuel cells and discusses advantages and research needs of this technology. Fuel cells are the zero-emission automotive power source that best preserves the advantages of gasoline automobiles: low upfront cost, long driving range and fast refuelling. To make fuel-cell cars a reality, the US Department of Energy has set a fuel cell system cost target of US$30 kW −1 in the long-term, which equates to US$2,400 per vehicle, excluding several major powertrain components (in comparison, a basic, but complete, internal combustion engine system costs approximately US$3,000). To date, most research for automotive applications has focused on proton exchange membrane fuel cells (PEMFCs), because these systems have demonstrated the highest power density. Recently, however, an alternative technology, hydroxide exchange membrane fuel cells (HEMFCs), has gained significant attention, because of the possibility to use stable platinum-group-metal-free catalysts, with inherent, long-term cost advantages. In this Perspective, we discuss the cost profile of PEMFCs and the advantages offered by HEMFCs. In particular, we discuss catalyst development needs for HEMFCs and set catalyst activity targets to achieve performance parity with state-of-the-art automotive PEMFCs. Meeting these targets requires careful optimization of nanostructures to pack high surface areas into a small volume, while maintaining high area-specific activity and favourable pore-transport properties.

The mechanism of pH-dependent hydrogen oxidation and evolution kinetics is still a matter of significant debate. To make progress, we study the Volmer step kinetics on platinum (111) using classical molecular dynamics simulations with an embedded Anderson-Newns Hamiltonian for the redox process and constant potential electrodes. We investigate how negative electrode electrostatic potential affects Volmer step kinetics. We find that the redox solvent reorganization energy is insensitive to changes in interfacial field strength. The negatively charged surface attracts adsorbed H as well as H + , increasing hydrogen binding energy, but also trapping H + in the double layer. While more negative electrostatic potential in the double layer accelerates the oxidation charge transfer, it becomes difficult for the proton to move to the bulk. Conversely, reduction becomes more difficult because the transition state occurs farther from equilibrium solvation polarization. Our results help to clarify how the charged surface plays a role in hydrogen electrocatalysis kinetics. Excess free charges on electrode surfaces drive changes in hydrogen electrocatalysis kinetics. Here, the authors show how redox solvent reorganization energy is insensitive to interfacial electric field strength; instead, the charged surface directly modulates proton electrochemical potential.

The development of a low-cost, high-performance platinum-group-metal-free hydroxide exchange membrane fuel cell is hindered by the lack of a hydrogen oxidation reaction catalyst at the anode. Here we report that a composite catalyst, nickel nanoparticles supported on nitrogen-doped carbon nanotubes, has hydrogen oxidation activity similar to platinum-group metals in alkaline electrolyte. Although nitrogen-doped carbon nanotubes are a very poor hydrogen oxidation catalyst, as a support, it increases the catalytic performance of nickel nanoparticles by a factor of 33 (mass activity) or 21 (exchange current density) relative to unsupported nickel nanoparticles. Density functional theory calculations indicate that the nitrogen-doped support stabilizes the nanoparticle against reconstruction, while nitrogen located at the edge of the nanoparticle tunes local adsorption sites by affecting the d -orbitals of nickel. Owing to its high activity and low cost, our catalyst shows significant potential for use in low-cost, high-performance fuel cells. Cheap and efficient hydrogen oxidation catalysts are needed for low cost hydroxide exchange membrane fuel cells. Here, the authors report that nickel nanoparticles supported on nitrogen doped carbon nanotubes have hydrogen oxidation activity similar to platinum-group-metals in alkaline electrolyte.

Ion exchange membranes are widely used to selectively transport ions in various electrochemical devices. Hydroxide exchange membranes (HEMs) are promising to couple with lower cost platinum-free electrocatalysts used in alkaline conditions, but are not stable enough in strong alkaline solutions. Herein, we present a Cu2+-crosslinked chitosan (chitosan-Cu) material as a stable and high-performance HEM. The Cu2+ ions are coordinated with the amino and hydroxyl groups of chitosan to crosslink the chitosan chains, forming hexagonal nanochannels (~1 nm in diameter) that can accommodate water diffusion and facilitate fast ion transport, with a high hydroxide conductivity of 67 mS cm−1 at room temperature. The Cu2+ coordination also enhances the mechanical strength of the membrane, reduces its permeability and, most importantly, improves its stability in alkaline solution (only 5% conductivity loss at 80 °C after 1,000 h). These advantages make chitosan-Cu an outstanding HEM, which we demonstrate in a direct methanol fuel cell that exhibits a high power density of 305 mW cm−2. The design principle of the chitosan-Cu HEM, in which ion transport channels are generated in the polymer through metal-crosslinking of polar functional groups, could inspire the synthesis of many ion exchange membranes for ion transport, ion sieving, ion filtration and more.A Cu2+-crosslinked chitosan material with unique 1 nm hexagonal nanochannels is synthesized and applied as a high-performance and alkaline-stable hydroxide exchange membrane.

One promising approach to reduce the cost of fuel cell systems is to develop hydroxide exchange membrane fuel cells (HEMFCs), which open up the possibility of platinum-group-metal-free catalysts and low-cost bipolar plates. However, scalable alkaline polyelectrolytes (hydroxide exchange membranes and hydroxide exchange ionomers), a key component of HEMFCs, with desired properties are currently unavailable, which presents a major barrier to the development of HEMFCs. Here we show hydroxide exchange membranes and hydroxide exchange ionomers based on poly(aryl piperidinium) (PAP) that simultaneously possess adequate ionic conductivity, chemical stability, mechanical robustness, gas separation and selective solubility. These properties originate from the combination of the piperidinium cation and the rigid ether-bond-free aryl backbone. A low-Pt membrane electrode assembly with a Ag-based cathode using PAP materials showed an excellent peak power density of 920 mW cm −2 and operated stably at a constant current density of 500 mA cm −2 for 300 h with H 2 /CO 2 -free air at 95 °C. A key challenge for hydroxide exchange membrane fuel cells is the development of membranes with both high ionic conductivity and mechanical strength. Here the authors report a high-performance family of poly(aryl piperidinium) membranes enabling promising durability and power density.

Hydroxide exchange membrane fuel cells (HEMFCs) have the advantages of using cost-effective materials, but hindered by the sluggish anodic hydrogen oxidation reaction (HOR) kinetics. Here, we report an atomically dispersed Ir on Mo 2 C nanoparticles supported on carbon (Ir SA -Mo 2 C/C) as highly active and stable HOR catalysts. The specific exchange current density of Ir SA -Mo 2 C/C is 4.1 mA cm −2 ECSA , which is 10 times that of Ir/C. Negligible decay is observed after 30,000-cycle accelerated stability test. Theoretical calculations suggest the high HOR activity is attributed to the unique Mo 2 C substrate, which makes the Ir sites with optimized H binding and also provides enhanced OH binding sites. By using a low loading (0.05 mg Ir cm −2 ) of Ir SA -Mo 2 C/C as anode, the fabricated HEMFC can deliver a high peak power density of 1.64 W cm −2 . This work illustrates that atomically dispersed precious metal on carbides may be a promising strategy for high performance HEMFCs. High-performance hydroxide exchange membrane fuel cells rely on the anode loading of platinum-group metals. Here, the authors report a highly active hydrogen oxidation electrocatalyst which contains atomically dispersed Ir on Mo2C nanoparticles supported on a carbon substrate.

Rural livelihood transition towards non-agriculturalization, non-grainization and even anti-urbanization has become a thorny social problem that undermines farmland resources and worldwide food security. Based on a simulation survey, this study explored the risk preferences and the livelihood transition mechanisms of typical farmers in the hilly and mountainous region. The results indicated that: (1) 76.86% of rural households exhibited risk aversion tendencies, with 60.67% being highly risk-averse. The ranking of risk aversion among the three typical farmers is consistent with asset abundance, with non-agriculture oriented households > semi-farmer and semi-labour households > vocational farmer households. (2) The non-grainization of vocational farmer households is significantly and positively correlated with the family labour force, land management area, and housing assets, yet negatively correlated with risk preferences. Compared to traditional grain cultivation, non-grainization in the hilly and mountainous region possesses lower risks and higher profitability for vocational farmer households. (3) The total non-agriculturalization of semi-farmer and semi-labour households correlates negatively with land management area but positively with family income. (4) Anti-urbanization and returning hometowns for farming are still regarded as a livelihood fallback by the non-agriculture oriented households, but excessive gift expenditure has become a heavy burden in rural society. Therefore, practical and systematical countermeasures are proposed in this research to guide sustainable livelihood transition.

Alzheimer’s disease (AD) is the most common neurodegenerative disease. However, effective drugs for this disease have not yet been developed. The analysis of big data indicated that childhood herpes virus infection may be associated with the incidence of AD, suggesting that anti-herpetic drugs, such as acyclovir, may have preventive and suppressive effects in AD therapy. Moreover, short-term use of dexamethasone (DXMT), a clinical used synthetic corticosteroid, could effectively inhibit AD-related neuroinflammation. In this study, we have found that the combination of acyclovir and DXMT, but not acyclovir or DXMT alone, could protect against AD causing β-amyloid (Aβ) oligomer-induced spatial cognitive impairments. Moreover, acyclovir and DXMT could prevent Aβ oligomer-induced over-activation of microglia and astrocytes, and over-expression of pro-inflammatory cytokines, indicating that anti-AD effects of drug combination might be at least partially via neuroinflammation inhibition and immunomodulation. Furthermore, Aβ oligomer-induced decrease of PSD-95 and increase of pTau expression was prevented by the combination of acyclovir and DXMT, suggesting the involvement of synaptic protective effects of the drug combination. Taken together, our studies indicated that the combination of acyclovir and DXMT might be an alternative therapy for the treatment of AD.