Exploring the Electronic Influence of β‐Br Substitutions in CuTPP on Electrochemical Overall Water Splitting in Alkaline Medium

Abstract

AbstractBeta substitution has a marked influence on the electronic environment of porphyrin ring atoms and the structure of the substituted porphyrin. In this work, we explore the influence of the bromo (Br) substitution at the β‐positions of copper tetraphenylporphyrin (CuTPP) and its consequent influence on the electrocatalytic alkaline overall water splitting. The β‐Br substitution is expected to exercise a strong influence on the electronic environment of central Cu through the electronic effects of Br. The overall influence of electronic effects is seen to lead to the net increase in the electron density of the central Cu (observed from XPS shifts) which is ultimately reflected in their different HER and OER performance in the alkaline medium. We observe the HER overpotentials (for 10 mA cm−2) of 697 mV, 760 mV, 838 mV, and 883 mV for the unsubstituted, bisubstituted, tetrasubstituted, and octasubstituted [Cu(TPP)]. The OER performance on the contrary depicts the reverse order with the overpotentials of 1118 mV, 827 mV, 637 mV, and 420 mV respectively for unsubstituted, bisubstituted, tetrasubstituted, and octasubstituted [Cu(TPP)]. The observed shifts in the catalytic performance can directly be attributed to increasing charge density on the central metal Cu2+ with the increase in the number of Br groups which in turn has opposite consequences for HER and OER performance.