Floating Seawater Splitting Device Based on NiFeCrMo Metal Hydroxide Electrocatalyst and Perovskite/Silicon Tandem Solar Cells.

Photovoltaic hydrogen production from seawater is of great significance. Challenges of solar-driven seawater electrolysis, for example, competing among chlorine evolution reactions, chloride corrosion, and catalyst poisoning, seriously restrict the development of this technology. In this paper, we report a two-dimensional nanosheet quaternary metal hydroxide catalyst composed of Ni, Fe, Cr, and Mo elements. By in situ electrochemical activation, a partial Mo element was leached and morphologically transformed in the catalyst. The higher metal valence states and many O vacancies were obtained, providing excellent catalytic activity and corrosion resistance in overall alkaline seawater electrolysis operating at an industrial-required current density of 500 mA cm-2 over 1000 h under 1.82 V low voltages at room temperature. The floating solar seawater splitting device shows a 20.61 ± 0.77% efficiency of solar energy to hydrogen (STH). This work demonstrates the development of efficient solar seawater electrolysis devices and potentially promotes research on clean energy conversion.

Efficient and stable noble-metal-free catalyst for acidic water oxidation.

Developing non-noble catalysts with superior activity and durability for oxygen evolution reaction (OER) in acidic media is paramount for hydrogen production from water. Still, challenges remain due to the inadequate activity and stability of the OER catalyst. Here, we report a cost-effective and stable manganese oxybromide (Mn7.5O10Br3) catalyst exhibiting an excellent OER activity in acidic electrolytes, with an overpotential of as low as 295 ± 5 mV at a current density of 10 mA cm-2. Mn7.5O10Br3 maintains good stability under operating conditions for at least 500 h. In situ Raman spectroscopy, X ray absorption near edge spectroscopy, and density functional theory calculations confirm that a self-oxidized surface with enhanced electronic transmission capacity forms on Mn7.5O10Br3 and is responsible for both the high catalytic activity and long-term stability during catalysis. The development of Mn7.5O10Br3 as an OER catalyst provides crucial insights into the design of non-noble metal electrocatalysts for water oxidation.

Molecular Recognition of Hydrophilic Molecules in Water by Combining the Hydrophobic Effect with Hydrogen Bonding.

During the last half a century, great achievements have been made in molecular recognition in parallel with the invention of numerous synthetic receptors. However, the selective recognition of hydrophilic molecules in water remains a generally accepted challenge in supramolecular chemistry but is commonplace in nature. In an earlier Communication [ Huang et al. J. Am. Chem. Soc. 2016 , 138 , 14550 ], we reported a pair of endo-functionalized molecular tubes that surprisingly prefer highly hydrophilic molecules over hydrophobic molecules of a similar size and shape. The hydrophobic effect and hydrogen bonding were proposed to be responsible, but their exact roles were not fully elucidated. In this Article, we present a thorough study on the binding behavior of these molecular tubes toward 44 hydrophilic molecules in water. Principal component analysis reveals that the binding strength is weakly correlated to the hydrophobicity, volume, surface area, and dipole moment of guests. Furthermore, molecular dynamics simulations show the hydrophobic effect through releasing the poorly hydrogen-bonded cavity water contributes to the binding of all the hydrophilic molecules, while hydrogen bonding differentiates these molecules and is thus the key to achieve a high selectivity toward certain hydrophilic molecules over other molecules with a similar size and shape. Therefore, a good guest for these molecular tubes should meet the following criteria: the hydrogen-bonding sites should be complementary, and the molecular volume should be large enough to expel all the cavity water but not too large to cause steric hindrance. This rule of thumb may also be used to design a selective receptor for certain hydrophilic molecules. Following these guidelines, a "best-fit" guest was found for the syn-configured molecular tube with a binding constant as high as 106 M-1.

Regioselective Synthesis of Methylene-Bridged Naphthalene Oligomers and Their Host-Guest Chemistry.

In this research, we report the regioselective synthesis of methylene-bridged naphthalene oligomers from 2,6-dialkoxyl naphthanene and paraformaldehyde by using p-TsOH as the catalyst and CH2Cl2 as the solvent. The structures were characterized by NMR spectroscopy and X-ray crystallography. Their host-guest chemistry with organic cations was studied, and optimal naphthalene numbers in the oligomers were revealed for different guests. In addition, the reason for the unsuccessful synthesis of methylene-bridged naphthalene macrocycles was discussed.