ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Water reduction on the spinel NiFe_0.4Mn_1.6O₄ upon visible light illumination

M. Trari, G. Rekhila, and K. Cherifi

Laboratory of Storage and Valorization of Renewable Energies, Faculty of Chemistry (USTHB), Algiers, Algeria

E-mail: mtrari@usthb.dz

Received: 21 August 2025  Accepted: 12 November 2025

Abstract:

NiFe_0.4Mn_1.6O₄ synthetized by sol–gel route is successfully exploited for the Hydrogen Evolution Reaction (HER) under visible light illumination. The oxide crystallizes in a spinel structure with a crystallite size of 51 nm, smaller than that observed by transmission electron microscopy (TEM, 460 nm), indicating an agglomeration process. p-type conduction is indicating by the positive thermoelectric power (S_300K =  + 130 µV K⁻¹), with an activation energy of 290 meV. The direct band gap (E_g = 1.04 eV), comes from the lifting of degeneracy of the 3d orbital of (Fe, MnO₆) octahedra is obtained from the diffuse reflectance, ideal for the exploitation of the solar spectrum. The “Capacitance –Potentiel” characteristic yields a hole concentration (N_A) of 0.28 × 10¹⁶ cm⁻³ and a flat band potential (E_fb) of − 0.04 V_SCE. The correlation between physical and electrochemical properties predict the feasibility of NiFe_0.4Mn_1.6O₄ for HER from an energy diagram. The conduction band (− 0.79 VSCE) is cathodically positioned relative to the H₂O/H₂ couple (~ − 0.46 VSCE), thus allowing HER under visible irradiation. The optimization of NiFe_0.4Mn_1.6O₄ dose, pH and S₂O₃²⁻ concentration has been undertaken, giving a maximal H₂ volume of 70 µmol and an evolution rate of 7.9 µmol g⁻¹ min⁻¹.

Keywords: NiFe0.4Mn1.6O4; Water reduction; Transport Properties; Photo electrochemical; Hydrogen; Visible light

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-025-04510-w

Chemical Papers 80 (3) 2189–2197 (2026)