Graphitic carbon nitride materials (CNs) have emerged as suitable photo- and heterogeneous- catalysts for various reactions thanks to their tunable band gap, suitable energy-band position, high stability under harsh chemical conditions, and low cost. However, the utilization of CN in photoelectrochemical (PEC) and photoelectronic devices is still at an early stage owing to the difficulties in depositing high-quality and homogenous CN layer on substrates, its wide band gap, poor charge-separation efficiency and low electronic conductivity. In this minireview, we discuss the synthetic pathways for the preparation of various structures of CN on substrates, and their underlying photophysical properties and current photoelectrochemical performance. The main challenges for CN incorporation into PEC cell are described, together with possible routes to overcome the standing limitations toward the integration of CN materials in PEC and other photoelectronic devices.

Graphitic carbon nitride (g-CN) has emerged as a promising material for energy-related applications. However, exploitation of g-CN in practical devices is still limited owing to difficulties in fabricating g-CN films with adjustable properties and high surface area. A general and simple pathway is reported to grow highly porous and large-scale g-CN films with controllable chemical and photophysical properties on various substrates using the doctor blade technique. The growth of g-CN films, ascribed to the formation of a supramolecular paste, comprises g-CN monomers in ethylene glycol, which can be cast on different substrates. The g-CN composition, porosity, and optical properties can be tuned by the design of the supramolecular paste, which upon calcination results in a continuous porous g-CN network. The strength of the porous structure is demonstrated by high electrochemically active surface area, excellent dye adsorption and photoelectrochemical and photodegradation properties.

A general synthesis of carbon nitride (CN) films with extended optical absorption, excellent charge separation under illumination, and outstanding performance as a photoanode in water-splitting photoelectrochemical cells is reported. To this end, we introduced a universal method to rapidly grow CN monomers directly from a hot saturated solution on various substrates. Upon calcination, a highly uniform carbon nitride layer with tuned structural and photophysical properties and in intimate contact with the substrate is obtained. Detailed photoelectrochemical and structural studies reveal good photoresponse up to 600 nm, excellent hole extraction efficiency (up to 62%) and strong adhesion of the CN layer to the substrate. The best CN photoanode demonstrates a benchmark-setting photocurrent density of 353 µA cm−2 (51% faradaic efficiency for oxygen), and external quantum yield value above 12% at 450 nm at 1.23 V versus RHE in an alkaline solution, as well as low onset potential and good stability.

A simple method to grow a closely packed carbon nitride (CN) film by the crystallization of CN monomers on a conductive substrate followed by a thermal condensation is reported. The as‐synthesized CN exhibits excellent performance as photoanode material in a photoelectrochemical cell. Detailed (photo)electrochemical and transient absorption measurements indicate excellent charge separation properties, high hole‐extraction efficiency (up to 50 %), a long electron lifetime, and low amount of defect states below the CN conduction band. Consequently, the CN photoanode exhibits a markedly low overpotential of 0.25 V versus reversible hydrogen electrode (RHE), which is comparable with the state‐of‐the‐art metal‐based photoanodes, an impressive photocurrent density of 116 μA cm−2 at 1.23 V versus RHE in an alkaline solution without sacrificial agent, as well as excellent stability over a wide pH range (0–13).