A sandwich-type catalytic composite reassembled with a birnessite layer and metalloporphyrin as a water oxidation catalyst.

High purity birnessite was synthesized and exfoliated into a negatively charged monolayer structure. A positively charged 5, 10, 15, 20-tetrakis (4-aminophenyl) manganese porphyrin (MnTAPP) was synthesized. Driven by the electrostatic force and the coordination effect of the amino nitrogen on the manganese ion in birnessite, the single-layer birnessite was reassembled with MnTAPP, forming a new sandwich-type catalytic composite MnTAPP@bir. The structure and chemical properties of the composite were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and Brunauer-Emmett analysis (BET). Electrocatalytic studies showed that the MnTAPP@bir exhibited an overpotential for water oxidation of 450 mV (at 10 mA cm) and a Tafel slope of 121.5 mV dec compared to birnessite with 700 mV (at 10 mA cm) and 230 mV dec. Impedance spectroscopy results suggested that the charge transfer resistivity of MnTAPP@bir was significantly lower than that of birnessite, suggesting that MnTAPP in the interlayer increased the conductivity of birnessite. Through a chronoamperometry test, the new material also showed excellent stability within 4000 s.