Tuning the Electronic and Molecular Structures of Bioinspired Heterodinuclear NiFe Catalyst for Enhanced Catalytic H₂...

With the aim of enhancing the HER activity of the previously described bioinspired [NiFe]-hydrogenase complex [L^N2S2Ni^IIFe^IICp-(CO)]⁺ (LNiFe, with L^N2S2 = 2,2'-(2,2'-bipyridine-6,6'-diyl)-bis-(1,1'-diphenylethanethiolate) and Cp = cyclopentadienyl), the electronic structure of the L^N2S2 site has been fine-tuned. In L ^OMe NiFe, the bipyridine (Bpy) unit was substituted with methoxy electron-donating groups, while in L ^Phen NiFe, the Bpy unit was replaced with the 1,10-phenanthroline backbone. These complexes were fully characterized, and their HER activity was investigated. A mechanistic study was conducted by using IR and EPR spectroscopies combined with density functional theory (DFT) calculations. Both complexes act as efficient electrocatalysts to produce H₂, following an ECEC mechanism, starting from the monoreduced species. L ^OMe NiFe exhibits the fastest kinetics among the series (K _obs = 1.6 × 10⁴ s^-1), attributed to its higher ΔpK _a value for the protonation step of the two-electron reduced species, [L ^OMe NiFe] ^- . In contrast, L ^Phen NiFe exhibits the lowest overpotential, with a cathodic shift of 150 mV. This improved performance is attributed to the fact that the phenanthroline backbone is more easily reduced with respect to a bipyridine unit.