Hydride Transfer Limits Hydrogen Evolution Efficiency With Zn Porphyrin Photocatalysts
Ouissam El Bakouri1, Simon T Clausing2, Lluís Blancafort1
1Institut De Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona, Girona, Spain.
Chemistry, an Asian Journal
|March 7, 2026
Summary
Computational study reveals an electron-proton-electron-hydride (EPEH) cycle for photocatalytic hydrogen evolution using Zn-based catalysts. This mechanism highlights challenges in hydride transfer efficiency for improved solar fuel production.
Area of Science:
- Computational chemistry
- Photocatalysis
- Hydrogen evolution
Background:
- Zn-based metalloporphyrins (ZnP) are potential catalysts for hydrogen evolution.
- The active species is a Zn chlorin (ZnC), formed via photohydrogenation of ZnP.
Purpose of the Study:
- To elucidate the photocatalytic hydrogen evolution mechanism using ZnP and water.
- To identify key intermediates and rate-limiting steps in the catalytic cycle.
Main Methods:
- Density Functional Theory (DFT) calculations were employed.
- Investigated the electron-proton-electron-hydride (EPEH) photocatalytic cycle.
Main Results:
- The EPEH cycle involves sequential photoreduction and protonation steps, forming a ZnCHP4- intermediate.
- Increased aromaticity of porphyrin rings facilitates photoreduction.
- Hydride transfer from ZnCH- is thermodynamically feasible but kinetically hindered by loss of aromaticity.
Conclusions:
- The study clarifies the mechanism of hydrogen generation by Zn-based catalysts.
- Identified loss of aromaticity during hydride transfer as a key factor limiting catalytic efficiency.
- Findings offer insights for designing improved porphyrin-based photo- and electrocatalysts for hydrogen production.
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