Unveiling the promotion of accelerated water dissociation kinetics on the hydrogen evolution catalysis of NiMoO_(4) nanorods

Nickel molybdate(NiMoO_(4))attracts superior hydrogen desorption behavior but noticeably poor for efficiently driving the hydrogen evolution reaction(HER)in alkaline media due to the sluggish water dissociation step.Herein,we successfully accelerate the water dissociation kinetics of NiMoO_(4)for prominent HER catalytic properties via simultaneous in situ interfacial engineering with molybdenum dioxide(MoO_(2))and doping with phosphorus(P).The as-synthesized P-doped NiMoO_(4)/MoO_(2)heterostructure nanorods exhibit outstanding HER performance with an extraordinary low overpotential of-23 m V at a current density of 10 m A cm^(-2),which is highly comparable to the performance of the state-of-art Pt/C coated on nickel foam(NF)catalyst.The density functional theory(DFT)analysis reveals the enhanced performance is attributed to the formation of MoO_(2)during the in situ epitaxial growth that substantially reduces the energy barrier of the Volmer pathway,and the introduction of P that provides efficient hydrogen desorption of Ni MoO_(2).This present work creates valuable insight into the utilization of interfacial and doping systems for hydrogen evolution catalysis and beyond.

Ice-Shielding Models for Self-Preservation of Gas Hydrates

The self-preservation of methane hydrate is a key process in its engineering applications because the hydrate can survive for a significant period under atmospheric pressure and moderate temperature. Some experiments have predicted that the shielding ice formed on the hydrate surface after initial dissociation of the hydrate plays an important role in the self-preservation effect. We propose ice-shielding models of gas hydrates to investigate the dissociation rates quantitatively, including the self-preservation process, at temperatures below the ice-melting point and at atmospheric pressure. Three general models are constructed for two temperature ranges The rate-determining process for the lower temperature range is hydrate dissociation, and those for the higher range are gas diffusion through ice or hydrate layers, which depend on the thickness of the shielding-ice layer. Our models suggest that the extent of self-preservation depends on temperature, original hydrate size, and guest substances, which can explain the experimental results.

Methane hydrate stability in the presence of water-soluble hydroxyalkyl cellulose

The effect of low-dosage water-soluble hydroxyethyl cellulose （approximate MW～90,000 and 250,000） as a member of hydroxyalkyl cellulosic polymer group on methane hydrate stability was investigated by monitoring hydrate dissociation at pressures greater than atmospheric pressure in a closed vessel. In particular, the influence of molecular weight and mass concentration of hydroxyethyl cellulose （HEC） was studied with respect to hydrate formation and dissociation. Methane hydrate formation was performed at 2℃ and at a pressure greater than 100 bar. Afterwards, hydrate dissociation was initiated by step heating from -10℃ at a mild pressure of 13 bar to 3℃, 0℃ and 2℃. With respect to the results obtained for methane hydrate formation/dissociation and the amount of gas uptake, we concluded that HEC 90,000 at 5000 ppm is suitable for long-term gas storage and transportation under a mild pressure of 13 bar and at temperatures below the freezing point.