Single-Atom Engineered Poly(Heptazine Imide) Photocathodes for Efficient Alkaline Hydrogen Evolution

Fonseca Reis I, Diab GA, Nenaniya S, Da Silva MAR, Shah H, Da Silva GMGD, Lopes CW, Isaacs M, Hutzler A, Teixeira IF, Jiménez Calvo P (2026)

Publication Status: Submitted

Publication Type: Unpublished / Preprint

Future Publication Type: Journal article

Publication year: 2026

DOI: 10.26434/chemrxiv.10001991/v1

Abstract

The development of sustainable photoelectrocatalysts for the hydrogen evolution reaction (HER) is key for advancing solar-to-X energy conversion technologies. Ionic crystalline poly(heptazine imides) (PHI) emerges as a versatile platform owing to their facile synthesis, high chemical stability, and tunable electronic structure under visible-light irradiation. Herein, Fe, Cu, and Co transition metals are incorporated into PHI via cation-exchange strategy, acting as co-catalytic centers that enhance charge separation photoelectrochemically. Photoelectrochemical tests reveal that metal-modified PHIs outperform pristine NaPHI for alkaline HER upon blue-light activation, with CoPHI showing the highest 2 activity. CoPHI displays a current densities at voltages vs RHE of ≈ −60 mA cm-2 at −0.76 V (or −5 A mg-1 at ≈ −0.72 V), with a favorable onset potential (≈ 0.55 V), a low Tafel slope (53 mV dec-1), reduced charge-transfer resistance (≈ 120 Ω), and an enhanced photocurrent response (≈ 9 μA cm-2). Advanced spectroscopic and microscopic analyses reveal that atomically dispersed Co sites operate as Co 2+ centers, facilitating interfacial charge transfer, due to their lower electronegativity and favorable electronic coupling with the PHI framework. These findings suggest CoPHI as an efficient carbon-based proof-of concept platform for single-atom-engineered photoelectrodes in alkaline HER.

Authors with CRIS profile

Involved external institutions

Universidade Federal do Paraná (UFPR) Brazil (BR) Universidade Federal de São Carlos (UFSCar) / Federal University of São Carlos Brazil (BR) Rutherford Appleton Laboratory United Kingdom (GB) Helmholtz-Institut Erlangen-Nürnberg für Erneuerbare Energien (HI-ERN) Germany (DE)

How to cite

APA:

Fonseca Reis, I., Diab, G.A., Nenaniya, S., Da Silva, M.A.R., Shah, H., Da Silva, G.M.G.D.,... Jiménez Calvo, P. (2026). Single-Atom Engineered Poly(Heptazine Imide) Photocathodes for Efficient Alkaline Hydrogen Evolution. (Unpublished, Submitted).

MLA:

Fonseca Reis, Izadora, et al. Single-Atom Engineered Poly(Heptazine Imide) Photocathodes for Efficient Alkaline Hydrogen Evolution. Unpublished, Submitted. 2026.

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