Interface Anchoring of Cobalt Porphyrin on a Conductive Metal Organic Framework Platform for Water Electrolysis

We report the synthesis, characterization, and electrochemical analysis of a heterogeneous composite featuring cobalt(II) meso-tetrakis(4-carboxyphenyl)porphyrin (CoTcPP, 1) and zinc 2,3,6,7,10,11-hexahydroxytriphenylene-based (ZnHHTP, 2) metal organic framework (MOF), denoted CoTcPP@ZnHHTP (3). The resulting composite 3 has cobalt porphyrin as the electroactive site, while the ZnHHTP substrate serves as a highly conductive support providing adsorption sites for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), such as H_⁺ and OH^-. FT-IR spectra of the composite display characteristic bands from both precursors with shifts in aromatic C=C and carboxylate stretching modes and perturbation of the O-H region, consistent with secondary interactions between CoTcPP and the ZnHHTP framework. The XRD reveals that 3 has both crystalline diffraction peaks attributed to the ZnHHTP phase, and a new peak assigned to the cobalt porphyrin. Additionally, the EDX of 2 shows the absence of cobalt, while composite 3 displays a clear cobalt signal, indicating incorporation of CoTcPP onto the ZnHHTP. Composite 3 demonstrates bifunctional electrocatalytic activity, with overpotentials at j₁₀ mA cm^-2 (η₁₀) of 340 mV for the OER and 362 mV for the HER. Notably, the HER η₁₀ decreases to 146 mV when the composite is employed as both the anode and cathode. The material also shows a Tafel slope of 55 mV dec^-1 for OER, comparable to benchmark catalysts. It is stable for over 14 h, with a Faradaic efficiency of 98%. The composite achieves TOF of 1.8 s^-1 for OER and 6.2 s^-1 for HER, along with corresponding TON of 90,000 and 314,000, respectively.