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

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 MnII salophen complexes, MnL1-MnL3, (H2L1 = N,N'-bis(salicylidene)-1,2-diaminobenzene, H2L2 = N,N0-bis(salicylidene)-4-bromo-1,2-diaminobenzene and H2L3 = 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 OAO 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 MnL1 can also effectively catalyze the reaction, but in comparison with MnL1, they have lower activity.