Isomorphous Heterometallic Mn/Zn/Co-CPs as Robust Photoelectrocatalysts for Water Oxidation: Structural and Performance Insights

Abstract

The cooperative effects between different metal centers play a crucial role in photoelectrocatalytic applications. Therefore, the design and synthesis of heterometallic coordination polymers (CPs) have become a significant research direction. Herein, we report the solvothermal synthesis and characterization of three novel isomorphous heterometallic CPs, namely {[M¹M²(H₂O)₆(DODDA)]·4H₂O}_n (SNUT-42-MnZn, M¹M² = MnZn; SNUT-42-CoZn, M¹M² = CoZn; SNUT-42-CoMn, M¹M² = CoMn), based on the tetracarboxylic ligand H₄(DODDA) (1-(3,5-dicarboxyphenyl)-4-oxo-1,4-dihydropyridazine-3,5-dicarboxylic acid). Single-crystal X-ray diffraction analysis indicates that all three compounds adopt identical crystal structures, characterized by a distinctive one-dimensional ladder-type double-chain framework. The photoelectrocatalytic performance varied significantly among the three compounds, as evidenced by their oxygen evolution reaction (OER) activities—SNUT-42-CoMn exhibiting the lowest overpotential (η = 107 mV at 10 mA cm⁻²) and the smallest Tafel slope (135.41 mV dec⁻¹) within the series, suggesting favorable reaction kinetics among the prepared catalysts. Mott-Schottky analysis confirms n-type semiconductor behavior with bandgap energies of 2.34 eV, 2.35 eV, and 2.41 eV correlating with photocurrent densities of 1.26, 1.42, and 1.71 mA cm⁻² achieved at 1.23 V vs. RHE, respectively. Thermal gravimetric analysis highlights stability up to 300°C, with dehydration mass losses matching theoretical values. The synergistic interplay between redox-active metal pairs enhances carrier separation, as evidenced by PL quenching and EIS data, positioning these materials as robust candidates for solar-driven water oxidation.