Boron and Sodium Doping of Polymeric Carbon Nitride Photoanodes for Photoelectrochemical Water Splitting

Unravelling the Photoelectrochemical Water Splitting of Nanometer-Thick Carbon Nitride Layer

Matching the thickness of the graphitic carbon nitride (CN) nanolayer with the charge diffusion length is expected to compensate for the poor intrinsic conductivity and charge recombination in CN for photoelectrochemical cells (PEC). Herein, the compact CN nanolayer with tunable thickness is in situ coated on carbon fibers. The compact packing along with good contact with the substrate improves the electron transport and alleviates the charge recombination. The PEC investigation shows CN nanolayer of 93 nm-thick yields an optimum photocurrent of 116 µA cm-2 at 1.23 V versus RHE, comparable to most micrometer-thick CN layers, with a low onset potential of 0.2 V in 1 m KOH under 1 sun illumination. This optimum performance suggests the electron diffusion length matches with the thickness of the CN nanolayer. Further deposition of NiFe-layered double hydroxide enhanced the surface water oxidation kinetics, delivering an improved photocurrent of 210 µA cm-2 with IPCE of 12.8% at 400 nm. The CN nanolayer also shows extended potential in PEC organic synthesis. This work experimentally reveals the PEC behavior of the nanometer-thick CN layer, providing new insights into CN in the application of energy and environment-related fields.

Triazine-Based Graphitic Carbon Nitride Thin Film as a Homogeneous Interphase for Lithium Storage

Triazine-based graphitic carbon nitride is a semiconductor material constituted of cross-linked triazine units, which differs from widely reported heptazine-based carbon nitrides. Its triazine-based structure gives rise to significantly different physical chemical properties from the latter. However, it is still a great challenge to experimentally synthesize this material. Here, we propose a synthesis strategy via vapor-metal interfacial condensation on a planar copper substrate to realize homogeneous growth of triazine-based graphitic carbon nitride films over large surfaces. The triazine-based motifs are clearly shown in transmission electron microscopy with high in-plane crystallinity. An AB-stacking arrangement of the layers is orientationlly parallel to the substrate surface. Eventually, the as-prepared films show dense electrochemical lithium deposition attributed to homogeneous charge transport within this thin film interphase, making it a promising solution for energy storage.

Bio-Inspired Supramolecular Self-Assembled Carbon Nitride Nanostructures for Photocatalytic Water Splitting

Fast production of hydrogen and oxygen in large amounts at an economic rate is the need of the hour to cater to the needs of the most awaited hydrogen energy, a futuristic renewable energy solution. Production of hydrogen through simple water splitting via visible light photocatalytic approach using sunlight is considered as one of the most promising and sustainable approaches for generating clean fuels. For this purpose, a variety of catalytic techniques and novel catalysts have been investigated. Among these catalysts, carbon nitride is presently deemed as one of the best candidates for the visible light photocatalysis due to its unique molecular structure and adequate visible-range bandgap. Its bandgap can be further engineered by structural and morphological manipulation or by doping/hybridization. Among numerous synthetic approaches for carbon nitrides, supramolecular self-assembly is one of the recently developed elegant bottom-up strategies as it is bio-inspired and provides a facile and eco-friendly route to synthesize high surface area carbon nitride with superior morphological features and other semiconducting and catalytic properties. The current review article broadly covers supramolecular self-assembly synthesis of carbon nitride nanostructures and their photocatalytic water-splitting applications and provides a comprehensive outlook on future directions.

Carbon Nitrides from Supramolecular Crystals: From Single Atoms to Heterojunctions and Advanced Photoelectrodes

Carbon nitride materials (CN) have become one of the most studied photocatalysts within the last 15 years. While CN absorbs visible light, its low porosity and fast electron-hole recombination hinder its photoelectric performance and have motivated the research in the modification of its physical and chemical properties (such as energy band structure, porosity, or chemical composition) by different means. In this Concept we review the utilization of supramolecular crystals as CN precursors to tailor its properties. We elaborate on the features needed in a supramolecular crystal to serve as CN precursor, we delve on the influence of metal-free crystals in the morphology and porosity of the resulting materials and then discuss the formation of single atoms and heterojunctions when employing a metal-organic crystal. We finally discuss the performance of CN photoanodes derived from crystals and highlight the current standing challenges in the field.