Mo-doped one-dimensional needle-like Ni_(3)S_(2) as bifunctional electrocatalyst for efficient alkaline hydrogen evolution and overall-water-splitting

Hydrogen energy plays an important role in clean energy system and is considered the core energy source for future technological development owing to its lightweight nature,high calorific value,and clean combustion products.The electrocatalytic conversion of water into hydrogen is considered a highly promising method.An electrocatalyst is indispensable in the electrocatalytic process,and finding an efficient electrocatalyst is essential.However,the current commercial electrocatalysts(such as Pt/C and Ru)are expensive;therefore,there is a need to find an inexpensive and efficient electrocatalyst with high stability,corrosion resistance,and high electrocatalytic efficiency.In this study,we developed a cost-effective bifunctional electrocatalyst by incorporating molybdenum into nickel sulfide(Ni_(3)S_(2))and subsequently tailoring its structure to achieve a one-dimensional(1D)needle-like configuration.The hydrogen production efficiency of nickel sulfide was improved by changing the ratio of Mo doping.By analyzing the electrochemical performance of different Mo-doped catalysts,we found that the Ni_(3)S_(2)-Mo-0.1 electrocatalyst exhibited the best electrocatalytic effect in 1 M KOH;at a current density of 10 mA cm^(-2),it exhibited overpotentials of 120 and 279 mV for hydrogen evolution reaction(HER)and oxygen evolution reaction(OER),respectively;at a higher current density of 100 mA cm^(-2),the HER and OER overpotentials were 396 and 495 mV,respectively.Furthermore,this electrocatalyst can be used in a two-electrode water-splitting system.Finally,we thoroughly investigated the mechanism of the overall water splitting of this electrocatalyst,providing valuable insights for future hydrogen production via overall-water-splitting.

Microstructure investigation of dynamic recrystallization in hard machining:From thermodynamic irreversibility perspective

The drastically changed thermal,mechanical,and chemical energies within the machined surface layer during hard machining tend to initiate microstructural alteration.In this paper,attention is paid to the introduction of thermodynamic potential to unravel the mechanism of microstructure evolution.First,the thermodynamic potential-based model expressed by the Helmholtz free energy was proposed for predicting the microstructure changes of serrated chip and the machined surface layer.Second,the proposed model was implemented into a validated finite element simulation model for cutting operation as a user-defined subroutine.In addition,the predicted irreversible thermodynamic state change in the deformation zones associated with grain size,which was reduced to less than 1 mm from the initial size of 1.5 mm on the machined surface,was provided for an in-depth explanation.The good consistency between the simulated results and experimental data validated the efficacy of the developed model.This research helps to provide further insight into the microstructure alteration during metal cutting.