Photocatalytic Water Splitting Using Carbon Nitride Materials

Carbon nitride materials, in particular polymeric graphitic carbon nitride (g-C3N4), have emerged as promising photocatalysts for the solar-driven splitting of water into hydrogen and oxygen. The layered conjugated structure of g-C3N4 endows it with visible-light absorption up to about 460 nm, chemical stability in aqueous environments and tunable electronic properties. Upon illumination, g-C3N4 absorbs photons to generate electron–hole pairs; the photogenerated electrons reduce protons to produce hydrogen at suitable cocatalyst sites, while holes oxidise water to oxygen. However, overall efficiency is often limited by rapid charge carrier recombination, sluggish surface redox kinetics and narrow spectral response. Recent strategies to overcome these limitations have included structural and defect engineering to prolong charge separation lifetimes; construction of heterojunctions with complementary semiconductors to enhance charge extraction; cocatalyst deposition to lower activation barriers for hydrogen and oxygen evolution; and direct growth of uniform thin films on conductive substrates to improve electrical conductivity and light harvesting. These developments have advanced g-C3N4–based systems towards practical solar-to-fuel conversion, demonstrating stable performance, faradaic efficiencies above 50 % and hydrogen evolution rates that approach benchmarks for overall water splitting without sacrificial agents. The global significance of this research lies in its potential to provide a clean, sustainable source of molecular hydrogen as an energy carrier and feedstock, thereby contributing to the decarbonisation of the energy sector.

Research from Nature Portfolio

A universal method for direct growth of carbon nitride monomers onto diverse substrates has recently led to highly uniform thin films with extended optical absorption up to 600 nm, enhanced hole extraction efficiencies of up to 62 % and strong adhesion to conductive supports. These photoanodes achieve photocurrent densities above 350 µA cm−2 for water oxidation at 1.23 V versus RHE, with more than 12 % external quantum efficiency at 450 nm and over 50 % faradaic efficiency for oxygen evolution. The rapid solution-based growth and tuned photophysical properties of these films address key challenges of charge separation and film–substrate interfacing in photoelectrochemical water splitting.

Photocatalytic Water Splitting Using Carbon Nitride Materials publication trend

The graph below shows the total number of articles in photocatalytic water splitting using carbon nitride materials across all publications each year (not limited to Nature Index journals).

Technical terms

Photocatalytic Water Splitting: A light-driven process in which a semiconductor catalyst absorbs photons to drive redox reactions that split water into hydrogen and oxygen.

Graphitic Carbon Nitride (g-C3N4): A polymeric, metal-free semiconductor composed of carbon and nitrogen, notable for its visible-light absorption and chemical stability.

Photoanode: The electrode at which water oxidation occurs under illumination in a photoelectrochemical cell.

Cocatalyst: A material, often a metal or metal oxide, deposited on a photocatalyst to lower the activation energy of hydrogen or oxygen evolution reactions.

Heterojunction: An interface formed between two different semiconductors that promotes charge separation by aligning their energy bands.

References

1. Direct growth of uniform carbon nitride layers with extended optical absorption towards efficient water-splitting photoanodes. Nature Communications (2020).
2. g-C 3 N 4 Photocatalysts: Utilizing Electron–Hole Pairs for Boosted Redox Capability in Water Splitting. Energy Material Advances (2023).
3. Promoting intramolecular charge transfer of graphitic carbon nitride by donor–acceptor modulation for visible‐light photocatalytic H2 evolution. Interdisciplinary Materials (2022).
4. Overall water splitting by Pt/g-C 3 N 4 photocatalysts without using sacrificial agents. Chemical Science (2016).