Novel trifunctional electrocatalyst of nickel foam supported Co2P/NiMoO4 heterostructures for overall water splitting and urea oxidation.

The process of electrocatalytic water splitting for hydrogen generation is significantly limited by sluggish kinetics of the anodic oxygen evolution reaction (OER). The efficiency of H2 electrocatalytic generation can be improved by reducing the anode potential or substituting urea oxidation reaction (UOR) for oxygen evolution process. Here, we report a robust catalyst based on Co2P/NiMoO4 heterojunction arrays supported on nickel foam (NF) for water splitting and urea oxidation. In the hydrogen evolution reaction in alkaline media, the optimized catalyst Co2P/NiMoO4/NF displayed a lower overpotential (169 mV) at a large current density (150 mA cm-2) compared to 20 wt% Pt/C/NF (295 mV@150 mA cm-2). In the OER and UOR, the potentials were as low as 1.45 and 1.34 V. These values surpass (for OER), or compare favorably to (for UOR), the most advanced commercial catalyst RuO2/NF (at 10 mA cm-2). This outstanding performance was attributed to the addition of Co2P, which has a significant effect on the chemical environment and electron structure of NiMoO4, while increasing the number of active sites and promoting charge transfer across the Co2P/NiMoO4 interface. This work proposes a high-performance and cost-effective electrocatalyst for water splitting and urea oxidation.

High temperature induced S vacancies in natural molybdenite for robust electrocatalytic nitrogen reduction.

Defect engineering is an important strategy to regulate electronic structure of electrocatalysts for electrochemical N2 fixation, aiming at improving the electron state density and enhancing the adsorption and activation of inert N2. In this paper, a high-temperature strategy to anneal the natural molybdenite under Ar atmosphere was developed, and the as-obtained molybdenite with S vacancies boosted a high activity for N2 reduction reaction. In 0.1 M HCl, the catalyst annealed at 800 °C exhibits a high Faradic efficiency of 17.9% and a NH3 yield of 23.38 µg h-1 mg-1cat. at -0.35 V versus reversible hydrogen electrode, two times higher than that of the pristine molybdenite. The facile one-step annealing method introduces the defects (e.g., S vacancies) in the surface of the natural molybdenite particles to prepare catalysts for generating ammonia by reducing nitrogen at room temperature under ordinary pressure, promoting the development of low-carbon economic prospect.

Precursor-Engineering Coupled Microwave Molten-Salt Strategy Enhances Photocatalytic Hydrogen Evolution Performance of g-C3 N4 Nanostructures.

A precursor-engineering strategy coupled with a microwave molten-salt process (PE-MWMS) is developed to synthesize graphitic carbon nitride (g-C3 N4 ) with an isotype triazine/heptazine-based g-C3 N4 heterojunction as a photocatalyst for the hydrogen evolution reaction (HER) under visible light illumination. Four hybrid precursor combinations-thiourea/melamine, thiourea/dicyandiamide, urea/melamine, and urea/dicyandiamide-are used to synthesize g-C3 N4 heterojunctions by the PE-MWMS process. Control experiments indicate that the precursor components and microwave treatment have a great effect on the HER performance of the g-C3 N4 samples. Samples synthesized with the optimal molar ratios of thiourea/melamine (2:1), thiourea/dicyandiamide (2:1), urea/melamine (3:1), and urea/dicyandiamide (3:1), exhibit the highest HER rates of 3135, 2519, 2844, and 2565 µmol g-1 h-1 , respectively. The amounts of heptazine and triazine units in the g-C3 N4 samples can be easily adjusted by changing the ratios of the hybrid precursors and play a decisive role in improving the photocatalytic HER activity. Because of the unique composition and microstructure, the efficient separation of electron-hole pairs, the broadened photo-absorption edges, and the narrowed band gaps, the as-obtained triazine/heptazine-based g-C3 N4 nanostructures exhibit promising activity for HER application.