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

Abstract

Polymeric carbon nitride is a promising photoanode material for water‐splitting and organic transformation‐based photochemical cells. Despite achieving significant progress in performance, these materials still exhibit low photoactivity compared to inorganic photoanodic materials because of a moderate visible light response, poor charge separation, and slow oxidation kinetics. Here, the synthesis of a sodium‐ and boron‐doped carbon nitride layer with excellent activity as a photoanode in a water‐splitting photoelectrochemical cell is reported. The new synthesis consists of the direct growth of carbon nitride (CN) monomers from a hot precursor solution, enabling control over the monomer‐to‐dopant ratio, thus determining the final CN properties. The introduction of Na and B as dopants results in a dense CN layer with a packed morphology, better charge separation thanks to the in situ formation of an electron density gradient, and an extended visible light response up to 550 nm. The optimized photoanode exhibits state‐of‐the‐art performance: photocurrent densities with and without a hole scavenger of about 1.5 and 0.9 mA cm−2 at 1.23 V versus reversible hydrogen electrode (RHE), and maximal external quantum efficiencies of 56% and 24%, respectively, alongside an onset potential of 0.3 V.

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

“…The pyrolisis of a crystallized molecular film on a transparent electrode offers a quick and straightforward appraoch to prepare photoelectrodes with tuneable composition [129] . The crystallization on substrates is challenging and the presence of a nucleation centre (such as fluorine doped tin oxide, commonly employed in photo‐electrochemistry) may lead to a fast precipitaion of unordered or polycrystalline mixtures rather than coordination complexes with a long‐range order.…”

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

“…and bi- or multielemental 2D materials (e.g., transition metal sulfides and oxides, hexagonal boron nitride, MXenes, etc. ). − Among those, carbon nitrides (CNs) are constituted by layers of heterocyclic C–N units cross-linked by nitrogen bonds stacked in a graphitic fashion, with an ideal carbon-to-nitrogen ratio of 0.75. , Since their rediscovery in the early 2000s, CNs have been thoroughly investigated for a wide range of applications particularly in energy conversion, such as metal-free photocatalysts and (photo)­electrocatalysts and more. − However, in most cases, these applications involve the use of CNs as bulk materials, making them impractical for use as optical materials, as membranes for selective separation, and in interfacial modification for battery electrodes, requiring the development of homogeneous thin film coatings over large surfaces. − Furthermore, several different structures of CNs have been reported experimentally both based on heptazine units (i.e., tri-s-triazine, C 6 N 7 ), such as melon, poly­(heptazine imide)­s, heptazine-based graphitic carbon nitride, and triazine (C 3 N 3 ) units, such as poly­(triazine imide)­s and triazine-based graphitic carbon nitride . The latter in particular has recently gained interest, as it provides a structure with significantly smaller repeating units, implying smaller in-plane trigonal voids.…”

NC Meets CN: Porous Photoanodes with Polymeric Carbon Nitride/ZnSe Nanocrystal Heterojunctions for Photoelectrochemical Applications

“…Converting solar energy into fuels (e.g., hydrogen) via photoelectrochemical cells (PECs) is a promising route toward sustainable energy supply. − At the heart of a PEC device lies a light-harvesting semiconductor (SC), which, under solar illumination, transforms the absorbed photons into excited charge carriers (electrons and holes). ,− Such PEC photoelectrodes require cheap and abundant materials, manifesting in efficient solar-to-fuel conversion and high stability. Thus far, research in this field has focused mainly on inorganic SCs such as metal-oxides, -oxynitrides, -sulfides, etc.…”