Metal–organic frameworks (MOFs) have attracted intensive attention for high-performance supercapacitors owing to their large specific surface area and tunable pore structure. Herein, ultrathin NiCo-MOF nanosheets are fabricated by a facile ultrasonication at room temperature and employed as a supercapacitor electrode material. The unique nanosheet-like structure of NiCo-MOF provides more electroactive sites and a shorter pathway for electron transfer and electrolyte diffusion, resulting in excellent electrochemical performance with a high specific capacitance of 1202.1 F g–1 at 1 A g–1. In addition, an asymmetric supercapacitor of NiCo-MOF//activated carbon was assembled in 2 M KOH electrolyte. It delivers an energy density of 49.4 W h kg–1 at a power density of 562.5 W h kg–1 in a voltage window of 1.5 V. The results demonstrate a new method to fabricate ultrathin MOF nanosheets for high-performance supercapacitor electrode materials.

Density functional calculations show that the “magic” structures of titanium carbide nanoparticles display an unexpected high reactivity toward CO, NH3, and H2O when compared to the bulk TiC(001) surface. In spite of the large C/Ti ratio in Ti8C12, our results show that the bulk surface is much more tightly bonded than the nanocluster, and thus the nanocluster has a much higher chemical activity.

The temperature and pressure dependence of the rate constant of the methyl−methyl recombination reaction with He bath gas has been studied using time-resolved time-of-flight mass spectrometry. Methyl radicals were produced by the 193 nm laser photolysis of acetone. In the observed temperature (300−700 K) and pressure (0.6−10 Torr) range, the rate constant exhibits a negative temperature dependence and falloff behavior typical for recombination reactions. The integrity of the measurements has been validated by determining the recombination rate constant with Ar (1 Torr) as the bath gas at room temperature and by analyzing the yield of the reaction product, ethane. In addition, rate constants were calculated theoretically using variable reaction coordinate transition state theory in a manner that improves upon the previous treatment of Wagner and Wardlaw by incorporating high-level ab initio results. The calculated high-pressure rate constant can be expressed as (T) = 7.42 × 10-11 (T/298 K)-0.69 e-88K/ T cm3 molecule-1 s-1. With reasonable downward energy transfer parameters, the experimentally observed pressure dependence of the rate constants for Ar, He, and H2 bath gases were reproduced very well using master equation analysis. Troe's equation, describing the T and P dependence of the recombination rate constant, was fit to a set of data for He as bath gas comprised of rate constants from this work and taken from the literature. With k ∞(T) set to be the high-pressure limit rate constant calculated here, the other remaining parameters can be given by k 0(T) = 1.17 × 10-25 (T/298 K)-3.75 e-494 K/ T cm6 molecule-2 s-1 and F cent(T) = e- T /570K.

Chemical energy conversion/storage through water splitting for hydrogen production has been recognized as the ideal solution to the transient nature of renewable energy sources. Solid polymer electrolyte (SPE) water electrolysis is one of the most practical ways to produce pure H2. Electrocatalysts are key materials in the SPE water electrolysis. At the anode side, electrode materials catalyzing the oxygen evolution reaction (OER) require specific properties. Among the reported materials, only iridium presents high activity and is more stable. In this Minireview, an application overview of single iridium metal and its oxide catalysts—binary, ternary, and multicomponent catalysts of iridium oxides and supported composite catalysts—for the OER in SPE water electrolysis is presented. Two main strategies to improve the activity of an electrocatalyst system, namely, increasing the number of active sites and the intrinsic activity of each active site, are reviewed with detailed examples. The challenges and perspectives in this field are also discussed.

The microscopic reaction mechanism for the water adsorption/dissociation processes on the R-Al 2 O 3 (0001) surface was calculated using density functional theory with the all-electron triple numerical polarized basis sets. Both unit-cell and 2 Â 2 supercell slab models were employed to investigate the coverage-dependent hydroxylation of the surface. Geometries of the molecular adsorbed intermediates, transition states, and the hydroxylated products were fully optimized, and the energetic reaction routes were clarified. The hydroxylation occurs predominantly via the low-barrier 1,4-hydrogen migration path, and the 1,2-dissociation path is competitive. The 1,2hydroxylated surface is more preferable thermodynamically in the consideration of reaction exothermicity. It was found that the in-plane hydrogen atoms can roam between the surface oxygen atoms, resulting in isomerization between the 1,2-and 1,4-hydroxylated products. Calculations for the multiple layer adsorption confirm that the hydroxylated surface is relatively inert to further hydroxylation by water. Further added water molecules prefer to form multilayered hexagonal ice-like arrangements through a hydrogen-bonding network. The electric field might not play a significant role in either surface reconstruction or the hydroxylation process until it exceeds 10 8 V/m. The present theoretical work is useful to gain some new insights on the ice accumulation of high-voltage power lines under high humidity and supercooled environment.