Supramolecular Modulation of Molecular Conformation of Metal Porphyrins toward Remarkably Enhanced Multipurpose Electrocatalysis and Ultrahigh-Performance Zinc-Air Batteries

Modulating the intrinsic catalytic activity of molecular catalysts to improve electrocatalytic performance is significant but challenging. Herein, a simple yet effective strategy to induce molecular flattening of Co (III) meso-tetra (N-methyl-4-pyridyl) porphyrine (Co-TMPyP) by supramolecular assembly with chemically converted graphene (CCG) via synergistic electrostatic and pi-pi interactions is reported. This unique variation in molecular conformation leads to a shortened Co-N coordination bond and enhanced electron transfer from the porphyrin macrocycle to the metal ion, thereby optimizing the electronic structure of the catalytic active center in Co-TMPyP molecule. Thus, the flattened Co-TMPyP on CCG (Co-TMPyP/CCG) demonstrates remarkable electrocatalytic performance for the oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), and oxygen evolution reaction (OER) simultaneously as a tri-functional molecular catalyst for the first time with a high half-wave potential of 0.824 V for ORR and a low overpotential for HER (320 mV) and OER (379 mV) at 10 mA cm(-2), respectively, not only much better than the pristine Co-TMPyP but also among the best results of molecular catalysts in each aspect of ORR, OER, and HER achieved thus far. As a practical demonstration, the Co-TMPyP/CCG catalyst is used to assemble a rechargeable Zn-air battery, which shows the highest specific capacity (793 mAh g(-1)) and power density (225.4 mW cm(-2)) among all molecular catalyst-based Zn-air batteries ever reported.

Automated summary

The study demonstrates a simple yet effective strategy to induce molecular flattening of Co-TMPyP, enhancing its catalytic activity for ORR, HER, and OER. The flattened Co-TMPyP/CCG molecule shows remarkable electrocatalytic performance, achieving high half-wave potential for ORR and low overpotential for HER and OER. Its application in a rechargeable Zn-air battery shows the highest specific capacity and power density among all molecular catalyst-based Zn-air batteries reported so far.