Combining transition metal oxide catalysts with conductive carbonaceous material is a feasible way to improve the conductivity. However, the electrocatalytic performance is usually not distinctly improved because the interfacial resistance between metal oxides and carbon is still large and thereby hinders the charge transport in catalysis. Herein, the conductive interface between poorly conductive NiO nanoparticles and semi-conductive carbon nitride (CN) is constructed. The NiO/CN exhibits much-enhanced oxygen evolution reaction (OER) performance than corresponding NiO and CN in electrolytes of KOH solution and phosphate buffer saline, which is also remarkably superior over NiO/C, commercial RuO 2 , and mostly reported NiO-based catalysts. X-ray photoelectron spectroscopy and extended X-ray absorption fine structure spectrum reveal that a metallic Ni-N bond is formed between NiO and CN. Density functional theory calculations suggest that NiO and CN linked by a Ni-N bond possess a low Gibbs energy for OER intermediate adsorptions, which not only improves the transfer of charge but also promotes the transmission of mass in OER. The metal-nitrogen bonded conductive and highly active interface pervasively exists between CN and other transition metal oxides including Co 3 O 4 , CuO, and Fe 2 O 3 , making it promising as an inexpensive catalyst for efficient water splitting.

Ni2P2O7-based composites grown on conductive substrate can efficiently promote the electrical transport during the electrochemical reactions in supercapacitors. However, Ni2P2O7 nanoarrays are easily peeled off from the substrate upon repeated electrochemical reaction. Herein, Ni2P2O7 nanoarrays grown on Ni foam with surficially decorated C3N4 thin nanosheets are achieved by a hydrothermal and in situ calcination strategy. The decorated C3N4 nanosheet network on the surface fully covers both Ni2P2O7 and Ni foam and efficiently prevents Ni2P2O7 nanoarrays from peeling off during the charge and discharge cycles. The optimized composites exhibit high pseudocapacitance and greatly enhanced cycling stability. The assembled asymmetric supercapacitor shows favorable specific capacitance and stability as energy storage devices. Such a strategy for fabricating C3N4-modified Ni2P2O7 nanoarrays is feasible and efficient, and can be therefore extended for constructing other electrodes with high capacitance and excellent stability.

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Although various cobalt-sulfide-based materials have been reported for the hydrogen evolution reaction, only a few have achieved high activity in both acid and alkaline electrolytes due to the inherent poor conductivity and low active sites. In this work, a heterojunction of cobalt sulfide and Mo 2 N is designed for efficient hydrogen evolution reactions in both acid and alkaline electrolytes. X-ray photoelectron spectroscopy reveals that Mo−S bonds are formed at the interface between Mo 2 N and CoS 2 , which result in the fabricated Mo 2 N/CoS 2 materials exhibiting a considerably enhanced hydrogen evolution reaction activity than the corresponding Mo 2 N, CoS 2 , and most reported Mo-and Co-based catalysts in electrolytes of H 2 SO 4 and KOH solutions. Density functional theory calculations suggest that the redistribution of charges occurs at the heterointerface. In addition, the interfacial active sites possess a considerably lower hydrogen adsorption Gibbs free energy than those atoms that are far away from the interface, which is beneficial to the process of hydrogen evolution reaction. This study provides a feasible strategy for designing hetero-based electrocatalysts with a tuned highly active interface.

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