Deciphering the cluster-to-spinel transformation pathway of CoMn₂ precursors toward efficient bifunctional...

The role of spinel oxides and their electrocatalytic mechanisms have been extensively investigated. Nevertheless, their precise synthesis and the underlying mechanisms of their formation and evolution remain inadequately explored. Herein, we introduce an o-vanillin-1,3-propanediamine Schiff-base CoMn₂ molecular cluster, [CoMn₂(L1)₂Cl₂] (L1 = C₁₉H₂₀N₂O₄), as a precursor to produce CoMn₂O₄/MOₓ@NC (M = Co, Mn) through one-step pyrolysis. The decomposition pathway can be represented as follows: [CoMn₂(L1)₂Cl₂] → CoMn₂O₄/MO_x + C_xH_y, H₂, C, HCl, CH₃OH → CoMn₂O₄/MOₓ@NC. We not only designed a CoMn₂ molecular-cluster precursor whose Co/Mn ratio is consistent with the stoichiometric composition of spinel CoMn₂O₄, but also found that the (311) crystal plane of the resulting CoMn₂O₄ forms a strong synergistic interaction with the carbon layer, thereby promoting the generation of catalytic active sites. The CoMn₂O₄/MO_x@NC synthesized from molecular clusters as precursors also exhibit excellent electrocatalytic performance. Electrochemical measurements show that the catalyst affords oxygen evolution reaction (OER)/hydrogen evolution reaction (HER) overpotential of 255/91 mV, respectively, to deliver 10 mA cm^-2. Theoretical calculations further reveal that the N-doped carbon layer induces interfacial charge redistribution in CoMn₂O₄-based oxide domains and tailors the binding energies of crucial OER and HER intermediates. This method of synthesizing spinel oxides based on molecular cluster precursors provides an efficient and precise synthesis strategy for the field of electrocatalysis.