Electrocatalytic oxidation of water using self-assembled copper(ii) tetraaza macrocyclic complexes on a 4-(pyridine-4′-amido)benzene grafted gold electrode

Abstract

The oxidation of water is the most crucial step in electrochemical water splitting and artificial photosynthesis. To ease the water oxidation process, the development of stable, robust, and efficient catalysts is needed that can operate under mild conditions. Here we present the heterogenization of a Cu-based molecule [Cu(MC)](ClO₄)₂ (where MC = 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetra-azacyclotetradeca-4,11-diene) by immobilizing it on a 4-(pyridine-4′-amido)benzene (L) layer modified gold electrode and explore its activity for the electrocatalytic oxidation of water in neutral phosphate buffer solution. The modified electrode was characterized using FE-SEM, EDX, ATR-FTIR, SERS, CV, and EIS techniques. The newly developed surface-bound complex [Cu(MC)]-L-Au can catalyze the oxygen evolution reaction (OER) exceptionally well with an onset overpotential of 227 mV (J = 1.0 mA cm⁻²), an overpotential ∼284 mV at J = 1.32 mA cm⁻² and a low Tafel slope of 48 mV decade⁻¹. Furthermore, the Cu-based heterogeneous electrocatalyst has no observable decomposition during an 8-hour period of controlled potential electrolysis and displayed a substantial and stable current for O₂ evolution with a faradaic efficiency of >85%.