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Modulating Surface Redox Reactions and Solvated Electron Emission on Boron-Doped Diamond by (Photo)electrochemistry

Arsène Chemin1,2,*, Louis Godeffroy1, Marin Rusu1, Michael Drisch3, Maik Finze3, Peter Knittel4, Anke Krueger5, and Tristan Petit1

  • *Contact author: arsene.chemin@univ-lyon1.fr
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PRX Energy 4, 033011 – Published 28 August, 2025

DOI: https://doi.org/10.1103/zhcb-13pn

Abstract

The interplay between photochemical and electrochemical reactions fundamentally influences charge transfer processes at solid-liquid interfaces. Nevertheless, chemical processes at semiconductor surfaces triggered by light excitation under an applied potential remain poorly explored. This work deciphers the synergistic effect of potential and light excitation on boron-doped diamond electrodes in producing either surface redox reactions or emission of solvated electrons in water. The effect of diamond surface termination on electron affinity, band bending, and charge extraction is identified in a photoelectrochemical cell. While photocurrent is observed for excitation as low as 3.5 eV, we show that it is induced mostly by surface redox reactions, whereas solvated electrons are detected only for excitation above the band gap (5.47 eV). Solvated electrons are generated irrespective of band bending, which affects only the emission yield. Depending on the surface band bending, photoreduction of the hydroxylated surface groups and photooxidation of the C—H surface groups can be induced by direct photoexcitation in the range of 4.2–4.8 eV. The surface of the diamond can be electrochemically reduced when the Fermi level of the oxidized surface decreases below the H+/H2 redox potential. On the other hand, the hydrogenated surface oxidizes spontaneously for potentials at which the Fermi level drops below the occupied C---H surface states, depending on both the pH and the electron affinity of the surface. This work provides insights into (photo)redox processes on diamond materials, which may find applications in photoelectrochemical solar fuel generation or energy storage.

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Photoelectrochemistry using renewable solar energy will play an essential role in the energy transition to a decarbonized society. There is an urgent need to develop sustainable electrodes with excellent stability, photoactivity, and selectivity. Due to rapidly decreasing fabrication costs and scalable synthesis, synthetic boron-doped diamond is attracting interest for this purpose. Boron-doped diamond is a promising metal-free electrode material for electrochemical reactions under harsh conditions, such as water decontamination, due to its wide potential window and exceptional stability. Diamond also serves as a source of solvated electrons when excited by UV light, catalyzing the chemical reduction of CO2 and N2 molecules. Understanding the complex interactions at the interface between diamond and the electrolyte upon photoexcitation and potential variation is crucial for designing competitive diamond materials with excellent performance for future photochemical applications.

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PRX Energy 4, 033011– Published 28 August, 2025
  • Received 17 March 2025
  • Revised 6 June 2025
  • Accepted 1 August 2025
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