Exploring Group Interaction Patterns of Meso-Substituted Porphyrinoids on the Alkaline Electrochemical Water Splitting

In this article, we explore the impact of chloro (-Cl), methyl (-Me), and methoxy (-OMe) functional groups at the meso-position of copper-derived tetraphenylporphyrin (CuTPP) on water-splitting half-reactions. The nature of meso-substituents significantly alters the electron density of the central Cu atom and also influences the electron density in the porphyrin ring backbone. Cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS) were employed to analyze the electron density in the substituted porphyrin system. The observed electron density dynamics correlate with variations in catalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance in an alkaline medium. For HER, we observe overpotentials of 505, 608, 698, and 730 mV for CuTMeOPP, CuTMePP, CuTPP, and CuTClPP, respectively (for a standard current density of 10 mA cm –2 ). Conversely, for the OER, the overpotentials are 800, 1025, 1105, and 1168 mV for CuTClPP, CuTPP, CuTMePP, and CuTMeOPP, respectively. The substituents’ electronic effects on the central Cu atom drive these performance shifts, demonstrating opposite trends for the HER and the OER.