One-step synthesis of graphitic carbon-nitride doped with black-red phosphorus as a novel, efficient and free-metal bifunctional catalyst and its application for electrochemical overall water splitting

Abstract

Electrocatalytic water splitting has attracted widespread attention because it is the most efficient and green approach to produce high purity hydrogen as a clean and sustainable energy carrier. In this study, a simple and inexpensive method is introduced to synthesize a black-red phosphorus (BRP)-doped graphitic carbon nitride (g-C₃N₄) composite (BRP-g-C₃N₄). In contrast with g-C₃N₄, BRP-g-C₃N₄ showed excellent electrochemical activity towards water splitting in alkaline media. A carbon paste electrode modified with BRP-g-C₃N₄ (BRP-g-C₃N₄-CPE) exhibited a current density of 10 mA cm⁻² at low overpotentials of 115 mV for the hydrogen evolution reaction (HER) and 430 mV for the oxygen evolution reaction (OER) versus a reversible hydrogen electrode (RHE) in 1.0 M KOH. The obtained Tafel slopes were 73 mV dec⁻¹ for HER with an onset potential of 88 mV and 93 mV dec⁻¹ for OER with an onset potential of 1.63 V versus RHE. BRP-g-C₃N₄-CPE showed excellent stability in 1.0 M KOH solution at the current density of 10 mA cm⁻² for 7 h. Moreover, BRP-g-C₃N₄ was used as a co-modifier, and AgFeO₂, AgO₂ and Fe₂O₃-modified BRP-g-C₃N₄-CPEs were prepared and their electrocatalytic performance towards HER and OER was examined in 1.0 M KOH. The results showed that the application of BRP-g-C₃N₄ as a co-modifier significantly enhanced the performance of the metal oxide-modified carbon paste electrode towards water splitting.