A growth-temperature-mediated two-step chemical vapor deposition strategy is designed to synthesize MoS /WS and WS /MoS stacks on Au foils. Predominantly A-A stacked MoS /WS and A-B stacked WS /MoS are selectively achieved and confirmed. Relative enhancements or reductions in photocatalytic activities of MoS /WS or WS /MoS are observed under illumination, because the type-II band alignment enables directional electron flow from electrode to active site.

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Development of earth-abundant, efficient, and stable electrocatalysts for hydrogen evolution reactions (HER) in alkaline or even neutral pH electrolyte is very important for hydrogen production from water splitting. Construction of bimetal phosphides via tuning the bonding strength to hydrogen and increasing effective active sites through nanostructuring and surface engineering should lead to high HER activity. Here, ternary NiCoP nanowires (NWs) decorated by homogeneous nanoparticles have been obtained on Ni foam for a highly efficient HER property via long-term cyclic voltammetric (CV) sweeping. The electron density transfer between the positively charged Ni and Co and negatively charged P atoms, one-dimensional electron transfer channel of the NWs, and abundant active sites supplied by the nanoparticles and NWs endow the catalyst with low overpotentials of 43 and 118 mV to achieve the respective current densities of 10 and 100 mA cm together with long durability for at least 33 h in 1 M KOH. A cycled anodic dissolution-redeposition mechanism is disclosed for the formation of the NiCoP nanoparticles during the CV sweeping process. Such a surface roughening method is found to be adaptable to enhance the HER property of other phosphides, including NiP nanoplates/NF, NiCoP nanoparticles/NF, and CoP NW/NF.

Active catalysts for nitrogen fixation (N2-fixation) have been widely pursued through constant efforts for industrial applications. Here, we report a family of catalysts, MXenes (M2X: M = Mo, Ta, Ti, and W; X = C and N), for application in N2-fixation based on density functional theory calculations. We find that the catalytic performance of MXenes strongly depends on the reaction energy in each reaction step. More exothermic steps lead to higher catalytic performance in the course of N2-fixation. We show that the reaction energy in N2-fixation is strongly affected by the charge transfer: (1) if N atoms gain more electrons in a step, the reaction is exothermic with a larger reaction energy; (2) if N atoms lose electrons in a step, the reaction is endothermic in general. We further show that Mo2C and W2C are highly active for N2-fixation due to their exothermic reactions and strong charge transfer, which may be applicable in the chemical-engineering industry.

Hydrogen has attracted extensive attention due to its versatile applications in various fields. As the starting step, hydrogen production has been being a critical technique for the practical applications of...