Molecular engineering of Fe-MIL-53 electrocatalyst for effective oxygen evolution reaction

Homogeneous molecular catalysts have obtained considerable attention in electrocatalytic fields owing to the easily accessible catalytic sites and well-defined structure. However, they are generally regarded as less practical application compared to heterogeneous catalysts due to the challenge to integrate molecular catalysts onto electrodes and poor durability. Here, the heterogenization of homogeneous Ni-based molecular catalyst with the definite coordination configuration of NiN2Cl2 is achieved by covalently grafting it into the framework of solid Fe-MIL-53-NH2 on the basis of the imine condensation reaction, which effectively integrates the advantages of homogeneous and heterogeneous catalysis. Electrochemical results of oxygen evolution reaction (OER) indicate that the overpotential at 10 mA cm-2 in NiN2Cl2@Fe-MIL-53 (287 mV) is obviously lower than that of parent Fe-MIL-53-NH2 (466 mV). This significantly improved OER activity in NiN2Cl2@Fe-MIL-53 confirms that the Ni-based molecular catalyst is the key active sites. The kinetic analysis reveals that the Eapp in Ni-based molecular catalyst (31.6 kJ/mol) is obviously lower than that in NiN2Cl2@Fe-MIL-53 (60.3 kJ/mol), proving that incorporating Ni-based molecular catalyst can regulate the rate-determining step and thus improve the OER activity. This work provides a novel covalent grafting strategy for molecular engineering of metal-organic-framework (MOF) and demonstrates their huge potential in electrocatalytic fields.

Automated summary

This study successfully achieves the heterogenization of homogeneous Ni-based molecular catalyst with the solid Fe-MIL-53-NH2 framework by covalently grafting, effectively integrating the advantages of homogeneous and heterogeneous catalysis. Electrochemical results indicate that the overpotential in NiN2Cl2@Fe-MIL-53 for the oxygen evolution reaction (OER) is significantly lower than that in Fe-MIL-53-NH2, confirming the key active sites of the Ni-based molecular catalyst. Kinetic analysis shows that the Eapp in the Ni-based molecular catalyst is much lower than that in NiN2Cl2@Fe-MIL-53, demonstrating the improved OER activity by regulating the rate-determining step with the incorporation of the Ni-based molecular catalyst.