Electronic Structure and Charge‑Transfer Mechanisms in Ionic Poly(Heptazine Imide) Photoanodes for Alcohol Oxidation

Weidong Xu^a^,^b, Andrea Rogolino^c, Carolina Pulignani^c, Milos Dubajic^a^,^b, Filip Podjaski^d, Linfeng Pan^e, Erwin Reisner^c, Samuel Stranks^a^,^b

^aDepartment of Chemical Engineering and Biotechnology, University of Cambridge, CB3 0AS, UK

^bCavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK

^cYusuf Hamied Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK

^dDepartment of Chemistry, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, UK

^eFrontiers Science Center for Transformative Molecules, Shanghai Jiao Tong University, Shanghai 200240, China

Proceedings of MATSUS Spring 2026 Conference (MATSUSSpring26)

E4 Photo-assisted chemical reactions: materials, characterization and mechanisms

Barcelona, Spain, 2026 March 23rd - 27th

Organizers: Josep Albero Sancho and Diego Mateo Mateo

Poster, Weidong Xu, 964
Publication date: 15th December 2025

Polymeric carbon nitrides have emerged as promising metal-free semiconductors for solar-driven organic transformations. While conventional graphitic carbon nitride (g-C₃N₄), such as melon, has been extensively investigated as a heterogeneous photocatalyst, its implementation as a stable and efficient photoanode remains limited by low intrinsic conductivity, pronounced charge trapping, and sluggish interfacial charge-transfer kinetics. In contrast, poly(heptazine imide) (PHI), particularly cyanamide-functionalized PHI (^NCNCN_x), represents an ionic carbon nitride framework characterized by enhanced structural order, efficient charge separation, and long-lived photogenerated carriers. Despite its superior photoelectrochemical performance in selective organic oxidation, the fundamental origins of its activity remain insufficiently understood.[1]

This work advances the mechanistic understanding of ^NCNCN_x photoanodes for photoelectrochemical alcohol oxidation through direct comparison with g-C₃N₄. We (i) elucidate the electronic structure and band energetics at the electrode–electrolyte interface under operando conditions; (ii) identify the nature and localization of photogenerated holes in ^NCNCN_x; (iii) quantify interfacial charge-transfer kinetics during different alcohol oxidations; and (iv) correlate film morphology with charge transport properties in functional photoanodes.

By integrating time‑resolved spectroscopy, operando and spatially resolved photoluminescence spectroscopy, electrochemical analysis, powder X‑ray diffraction, and total‑scattering structural characterization, this study reveals how electronic structure and morphology collectively govern PEC organic oxidation. The results establish a unified structure–property–function framework that distinguishes ionic PHI from covalent g‑C₃N₄ and provide design principles for next‑generation carbon nitride photoanodes for selective solar‑driven organic synthesis.

References:

[1] Pulignani, C., Mesa, C. A., Hillman, S. A., Uekert, T., Giménez, S., Durrant, J. R., & Reisner, E. Rational design of carbon nitride photoelectrodes with high activity toward organic oxidations. Angewandte Chemie, 2022, 134, e202211587.

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