Amorphous dominated metal hydroxide-organic framework with compositional and structural heterogeneity for enhancing anodic electro-oxidation reactions

Abstract

Inorganic-organic hybrids are promising anode catalysts to realize high activity and stability. Herein, an amorphous-dominated transition metal hydroxide-organic framework (MHOF) with isostructural mixed-linker was successfully synthesized on nickel foam (NF) substrate. The designed IML24-MHOF/NF exhibited remarkable electrocatalytic activity with an ultralow overpotential of 271 mV for oxygen evolution reaction (OER) and a potential of 1.29 V vs. reversible hydrogen electrode for urea oxidation reaction (UOR) at 10 mA·cm−2. Furthermore, the IML24-MHOF/NF||Pt-C cell required only 1.31 V for urea electrolysis at 10 mA·cm−2, which was much smaller than traditional water splitting (1.50 V). When coupled with UOR, the hydrogen yield rate was faster (1.04 mmol·h−1) than with OER (0.32 mmol·h−1) at 1.6 V. The structure characterizations, together with operando monitoring, including operando Raman, Fourier transform infrared, electrochemical impedance spectroscopy, and alcohol molecules probe, revealed that: (1) amorphous IML24-MHOF/NF prefers self-adaptive reconstruction into active intermediate species against the external stimulus; (2) pyridine-3,5-dicarboxylate-incorporation into parent framework reconfigures electronic structure of system, thus mediating the absorption of oxygen-containing reactants during anodic oxidation reactions, such as O* and COO*. This work provides a new approach for boosting the catalytic activity of anodic electro-oxidation reactions by trimming the structure of MHOF-based catalysts.