Efficient electrochemical water oxidation mediated by different substituted manganese-salophen complexes

Abstract

• The electrocatalytic role of different substituted Mn II salophen complexes was investigated for water oxidation. • It was revealed that the studied complexes show excellent activity for OER. • The overpotential for the OER was in the range of 345–420 mV. • It was speculated that the O O bond formation occurs by oxidizing the active center of Mn complexes. • The Mn II complexes catalyzed the OER as real electrocatalysts. Developing robust and efficient water oxidation catalysts is an essential challenge in water splitting. In this work, the electrocatalytic behavior of the modified carbon paste electrodes with different substituted Mn II salophen complexes, MnL 1 -MnL 3 , (H 2 L 1 = N,N′-bis(salicylidene)-1,2-diaminobenzene, H 2 L 2 = N,N′-bis(salicylidene)-4-bromo-1,2-diaminobenzene and H 2 L 3 = N,N′-bis(2-hydroxy-3-methoxybenzilidine)-1,2-diaminobenzene) was evaluated for water oxidation by electrochemical methods. All three complexes were found highly effective, stable, and robust catalysts for water oxidation. Electrochemical experiments, Field emission-scanning electron microscope (SEM), energy-dispersive X-ray (EDX), and powder X-ray diffraction (PXRD) analyses indicated that the studied Mn II salophen complexes are molecular catalysts for water oxidation in origin. Cyclic voltammetry experiments in different pHs displayed that the O O bond formation probably occurs by oxidizing the active center of Mn II complexes through proton-coupled electron transfer (PCET). The results showed that the nature of the substituent on the salophen ligand could not affect the stability of the complexes under applied electrochemical conditions. It was found that Mn oxide nanostructures obtained by the thermal decomposition of MnL 1 can also effectively catalyze the reaction, but in comparison with MnL 1 , they have lower activity.