Topology Engineering Promoting Electron Transfer in Phthalocyanine-Based Polymer Electrocatalysts for Oxygen Reduction

Abstract

Exploring bifunctional catalysts that display both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities is crucial in clean energy conversion technologies such as zinc–air batteries. Transition metal phthalocyanine-based polymer electrocatalysts have been demonstrated as efficient molecular electrocatalysts. In particular, through careful selection of connectivity, the topology and electron transfer routes can be optimized. For the first time, we systematically engineered aldehyde monomers exhibiting different connectivities (2-, 3-, and 4-connect) by reacting them with heterometal tetra-amino phthalocyanines (MTAPcs, M = Fe/Co), thus tailoring the topological structure of polymer catalysts. Notably, Fe-/Co-TPDA-PP featuring a tetratopic monomer performs outstandingly in both ORR and OER, with a half-wave potential (E_1/2) of 0.882 V and a potential at a current density of 10 mA cm^–2 (E_j=10) reaching 1.583 V. Through careful analysis of band structure and electron state with XPS, UV–vis, and UPS, the exceptional performance originates from the increased delocalization of electrons in the tetratopic TPDA ligand, coupled with a lower work function and a narrower band gap. These findings are strongly correlated with electron transfer kinetics studies employing EIS and classical redox probes, where the electron transfer resistance follows the order: 4-connect < 3-connect < 2-connect. Moreover, the application of Fe-/Co-TPDA-PP in rechargeable zinc–air battery has demonstrated superior catalytic performance, enduring stability. By meticulously controlling the topological structure of the ligands, this study significantly optimizes electron transport efficiency, opening perspectives and strategies for the design and performance optimization of molecular electrocatalysts.