Bridging heterogeneous and homogeneous catalysts by ultrathin metal-polyphthalocyanine-based nanosheets from electron-coupled transalkylation delamination

Abstract

Homogeneous and heterogeneous materials are attractive electrochemical reaction catalysts, specifically metal-nitrogen-carbon (M-Nx-C) organic-based molecular materials are emerged as the most promising candidates. However, efficiently producing M-Nx-C organic-based nanosheets for solving the poor activity of bulk-phase catalysts remains a significant challenge. Herein, we put forward a first concept of semi-homogeneous molecular catalysts, through producing 2D metal-polyphthalocyanine (M-PPc) nanosheet with the superiority of hetero/homogeneous via an electrochemical delamination to achieve bridging from hetero to homogeneous. Multi-step ex-situ characterizations and theoretical simulations reveal a novel mechanism of electrochemical stripping, named as electron-coupled transalkylation, where occurs transalkylation, site-to-site transalkylation, and hydrocarbon evolution reactions accompanied by the transformation of intermediates from B-Ni1.0Fe0.3 PPc, (TBA+)x·B-Ni1.0Fe0.3 PPc, x*(C4H9)x·B-Ni1.0Fe0.3 PPc, to final product of Ni1.0Fe0.3 PPc NSs, realizing the eventual delamination. The semi-homogeneous Ni1.0Fe0.3 PPc NSs delivers a lower overpotential of 269 mV to reach 10 mA cm-2 than benchmark RuO2 and maintains superior stability for oxygen evolution. DFT calculations unveil that the NiN4 double sites of Ni1.0Fe0.3 PPc NSs acted as real catalytic centres not only reduce the energy barrier of reaction process, but also accelerate adsorption of intermediates and desorption of oxygen molecules, thus boosting the oxygen evolution kinetics.