Charge transport in polymeric graphitic carbon nitrides is shown to proceed via diffusive hopping of electron and hole polarons with reasonably high mobilities >10(-5) cm(2) V(-1) s(-1). The power-law behavior of the ultrafast luminescence decay exhibits that the predominant transport direction is perpendicular to the graphitic polymer sheets, thus complementing 2D materials like graphene.
A comprehensive investigation of the luminescent properties of carbon nitride polymers, based on tri-s-triazine units, has been conducted. Steady-state temperature-and excitation-power-dependent as well as time-resolved measurements with near-UV excitation (λ = 325 nm and 405 nm) yield strong photoluminescence, covering the visible spectrum. The spectral, thermal, and temporal features of the photoluminescence can be satisfactorily described by the excitation and radiative recombination of molecular excitons, localized at single tri-s-triazine units. The discussed model is in accordance with the recently reported absorption features of carbon nitride polymers. Thus, from the point of view of optical spectroscopy, the material effectively behaves as a monomer.
Based on the arrangement of two-dimensional 'melon', we construct a unit cell for polymeric carbon nitride (PCN) synthesized via thermal polycondensation, whose theoretical diffraction powder pattern includes all major features measured in x-ray diffraction. With the help of this unit cell, we describe the process-temperature-induced crystallographic changes in PCN that occur within a temperature interval between 510 and 610 °C. We also discuss further potential modifications of the unit cell for PCN. It is found that both triazine- and heptazine-based g-C3N4 can only account for minor phases within the investigated synthesis products.
Electrochemical splitting of water to oxygen and hydrogen using earth-abundant first-row transition metal-based catalysts is a promising approach for sustainable energy conversion. Herein, we present a new convenient synthesis of copper nitride (Cu 3 N) that acts as a bifunctional electro(pre)catalyst for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and overall water electrolysis in alkaline media. Strikingly, the electrophoretically deposited Cu 3 N on nickel foam (NF) displayed extremely low overpotentials for both OER and HER, and the overall water splitting cell potential was merely 1.62 V with a remarkable durability of over 10 days. Most notably, the coordinatively unsaturated Cu in Cu 3 N transformed in situ under a reducing environment and in an oxidative environment into a copper-rich shell that serves as the active site over an equally important electrically conductive Cu 3 N core to drive proficient catalysis. To the best of our knowledge, this is the first report on copper nitride for efficient and durable alkaline water electrolysis.
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