Interfacial Electronic Modulation of Mo5 N6 /Ni3 S2 Heterojunction Array Boosts Electrocatalytic Alkaline Overall Water Splitting.

Bifunctional electrocatalysts with excellent activity and durability are highly desirable for alkaline overall water splitting, yet remain a significant challenge. In this contribution, palm-like Mo5 N6 /Ni3 S2 heterojunction arrays anchored in conductive Ni foam (denoted as Mo5 N6 -Ni3 S2 HNPs/NF) are developed. Benefiting from the optimized electronic structure configuration, hierarchical branched structure and abundant heterogeneous interfaces, the as-synthesized Mo5 N6 -Ni3 S2 HNPs/NF electrode exhibits remarkably stable bifunctional electrocatalytic activity in 1 m KOH solution. It only requires ultralow overpotentials of 59 and 190 mV to deliver a current density of 10 mA cm-2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 1 m KOH solution, respectively. Importantly, the overall water splitting electrolyzer assembled by Mo5 N6 -Ni3 S2 HNPs/NF exhibits an exceptionally low cell voltage (1.48 V@10 mA cm-2 ) and outstanding durability, surpassing most of the reported Ni-based bifunctional materials. Density functional theory (DFT) further confirms the heterostructure can optimize the Gibbs free energies of H and O-containing intermediates (OH, O, OOH) during HER and OER processes, thereby accelerating the catalytic kinetics of electrochemical water splitting. The findings provide a new design strategy toward low-cost and excellent catalysts for overall water splitting.

Phase-Engineered Robust Cocatalyst of NiFe Bicarbonate with Pt Dopant for Enhanced Photocatalytic Water Splitting.

Exploring efficient cocatalysts capable of accelerating surface catalytic reaction is of great significance for the development of solar-driven hydrogen production. Herein, on the basis of NiFe hydroxide, we developed a series of Pt doped NiFe-based cocatalysts to promote the photocatalytic hydrogen production of graphitic carbon nitride (g-C3 N4 ). We find that the Pt doping can trigger phase reconstruction of NiFe hydroxide and lead to the formation of NiFe bicarbonate, which displays higher catalytic activity toward hydrogen evolution reaction (HER). The Pt doped NiFe bicarbonate modified g-C3 N4 shows excellent photocatalytic activity with H2 evolution rate up to 100 µmol/h, which is more than 300 times that of pristine g-C3 N4 . The experimental and calculation results demonstrate that the greatly improved photocatalytic HER activity of g-C3 N4 is not only due to the efficient carrier separation, but also attributed to the accelerated HER kinetics. Our work may provide guidance for designing novel and superior photocatalysts.

Polymeric structure optimization of g-C3N4 by using confined argon-assisted highly-ionized ammonia plasma for improved photocatalytic activity.

The optimization of the polymeric structure and the modulation of surface amino groups in graphitic carbon nitride (g-CN) are critical but challenging in improving the photoelectric and photocatalytic performances of this polymer semiconductor. Ammonia plasma treatment may provide a fast and useful approach to optimize g-CN materials yet is seriously restricted by the low ionization ability of ammonia. Herein, a confined fast and environmental-friendly ammonia plasma method based on argon-assisted high ionization of NH3 was developed for efficient modification of raw g-CN. Compared with the weakly-ionized pure ammonia plasma which can only introduce amino group onto the surface g-CN, the argon-assisted highly-ionized ammonia plasma treatment obviously contributes to the comprehensively polymeric structure optimization of g-CN, and thus plays a key role in enhancing its light-harvesting and decelerating the recombination of the photogenerated charge carriers. As a result, the argon-assisted highly-ionized ammonia plasma-treated g-CN-Ar+NH3 outperformed the raw g-CN by a 2.5-fold higher photocatalytic reduction of hexavalent chromium and a remarkable 3.8-fold higher photocatalytic H2 evolution activity (up to 957.8 µmol·h-1·g-1) under visible light irradiation. Our findings suggest the great prospects of this novel highly-ionized ammonia plasma treatment method in the controllable modification of semiconductors and polymers.

ZnO nanorod arrays grown on g-C3N4 micro-sheets for enhanced visible light photocatalytic H2 evolution.

The designed synthesis of noble-metal-free photocatalysts with hierarchical heteroassemblies in a facile, mild and eco-friendly way becomes more and more important, because we can explore the novel properties and applications of novel heterostructures via this method. Herein we report a two-step aqueous strategy for novel hierarchical heterostructures of ZnO nanorod (NR) arrays grown on graphitic carbon nitride (g-C3N4). The novel g-C3N4/ZnO NR heterostructures that integrate g-C3N4 and ZnO NR via high-quality g-C3N4-ZnO heterojunctions have beneficial properties such as high specific surface area (SSA), open spatial architecture, good electronic conductivity, and effective charge transfer interfaces, and are promising in many related areas such as water splitting, solar cells, etc. As a noble-metal-free and visible-light-responsive photocatalytic material, a typical g-C3N4/ZnO NR photocatalytic system exhibits enhanced photocatalytic activity toward H2 evolution, almost 3.5 times higher than that of pure g-C3N4. The superior photocatalytic property can be ascribed to the synergistic effect of the unique g-C3N4/ZnO NR heterostructures.