A Linear Mn₃ Molecular Cluster as a Bifunctional Electrocatalyst for Overall Water Splitting

In this research article, a cluster material [Mn3L2(μ2-OAc)2] (1) with linear MnII···MnII···MnII motif in which two peripheral Mn centers are five-coordinated and the central Mn center is six-coordinated has been explored as an excellent OER and HER molecular electrocatalyst (H2L = 2,2'-(propane-1,3-diylbis(azaneylylidene))bis(ethan-1-yl-1-ylidene)diphenol); (OAc═CH3CO2-). The organic framework H2L is so flexible, and the preference toward linear assembly is so high, that this cluster is readily accomplished by a synthetic approach that uses H2L and Mn(OAc)2·4H2O as the building blocks. Characterizations of 1 have been performed by molar conductance, microanalysis, FTIR, UV-vis, FESEM, TGA, PXRD, and SCXRD analyses. The crystal structure of 1 contains two crystallographically equivalent [MnIIL] species interconnected by a central MnII ion via the four μ2-phenoxide and two μ2-acetate bridges. Measurement of electrical properties of 1 reveals an interesting current-voltage feature of the aluminum/1 two-terminal device structure. Cluster 1 shows outstanding activity when working as both an OER and HER electrocatalyst, with overpotential values of 324 and 130 mV, respectively, at a current density of 10 mA/cm2. DFT computational studies reveal mechanistic insight into the OER and HER processes, suggesting that the MnII-Ophenoxide-MnII linkage is the active site for the formation of molecular oxygen and hydrogen.