Photocatalytic Hydrogen Production with Crystalline Carbon Nitrides

Photocatalytic hydrogen production harnesses solar irradiation to drive water splitting via semiconductor materials, offering a sustainable route to clean fuel. Crystalline carbon nitrides—defined by ordered networks of triazine or heptazine units—combine visible-light absorption with high thermal and chemical resilience and an earth-abundant composition. Well-defined structures such as poly(triazine imide) and poly(heptazine imide) exhibit superior charge transport and reduced electron–hole recombination relative to amorphous analogues. Synthetic approaches, including salt-melt and ionothermal methods, allow precise control over crystallinity, interlayer spacing and surface functionality, thereby tuning band gaps and extending carrier lifetimes. The strategic deposition of noble-metal or transition-metal co-catalysts facilitates rapid electron transfer to protons, achieving high hydrogen evolution rates under visible light. These advances advance the design of scalable, low-cost photocatalytic systems that address global energy demands and carbon-neutral targets. Ongoing efforts concentrate on interfacial engineering, heterojunction design and defect control to further boost quantum efficiencies and operational stability.

Research from Nature Portfolio

Recent studies have elucidated dynamic charge-migration pathways in phase-engineered carbon nitride homojunctions. A crystalline triazine–heptazine assembly was used to probe an S-scheme mechanism: under illumination, photogenerated electrons migrate selectively between the two phases, while holes remain spatially separated. In situ surface photoemission measurements, supported by theoretical modelling, confirmed a reversible electron-transfer trajectory that enhances charge separation and suppresses unwanted recombination. This heterostructure delivered markedly improved activity for solar-driven CO₂ photoreduction, demonstrating the potential of tailored phase interfaces to elevate the performance of photocatalytic processes.

Photocatalytic Hydrogen Production with Crystalline Carbon Nitrides publication trend

The graph below shows the total number of articles in photocatalytic hydrogen production with crystalline carbon nitrides across all publications each year (not limited to Nature Index journals).

Technical terms

Photocatalysis: Acceleration of a photochemical reaction by a semiconductor upon light absorption.

Band gap: Energy interval between the valence and conduction bands of a semiconductor that determines the onset of light absorption.

Poly(triazine imide) (PTI): A crystalline carbon nitride formed by triazine rings linked through imide bridges.

Poly(heptazine imide) (PHI): A crystalline carbon nitride comprising heptazine cores and imide linkages, often featuring ionic pores.

S-scheme heterojunction: A junction between two semiconductor phases that drives stepwise carrier transfer to enhance charge separation and redox potential.

Co-catalyst: A secondary catalytic species, typically metal nanoparticles, that promotes efficient charge transfer and lowers reaction barriers in photocatalytic systems.

References

1. Salt‐melt synthesis of poly(heptazine imide) in binary alkali metal bromides for enhanced visible‐light photocatalytic hydrogen production. Interdisciplinary Materials (2024).
2. Understanding the unique S-scheme charge migration in triazine/heptazine crystalline carbon nitride homojunction. Nature Communications (2023).
3. Photocatalytic overall water splitting by conjugated semiconductors with crystalline poly(triazine imide) frameworks. Chemical Science (2017).
4. Interfacial Engineering for Improved Photocatalysis in a Charge Storing 2D Carbon Nitride: Melamine Functionalized Poly(heptazine imide). Advanced Energy Materials (2020).