Tuning graphitic carbon nitride (g-C3N4) electrocatalysts for efficient oxygen evolution reaction (OER)

Abstract

Nowadays, energy conversion and storage technologies are essential research topics due to the necessity of more sustainable processes. Specifically, water splitting is highly affected by slow kinetics and limited knowledge of the oxygen evolution reaction (OER). This work envisages the preparation of graphitic carbon nitride (g-C3N4) electrocatalysts for efficient OER by a facile one-pot method. The impact of the preparation temperature (450–650 °C) of g-C3N4 was assessed for the first time on water splitting processes and explained by different characterisation techniques. The unique crystal structure, surface chemistry, and electronic properties of the material prepared at 550 °C lead to a remarkable OER efficiency, with an overpotential of 355 mV at 10 mA cm−2 and a Tafel slope of 46.8 mVdec−1. Interestingly, three major differences were observed when comparing the material prepared at 550 °C with those obtained at other temperatures: the reduced structural distortion, the superior composition in oxygen and the presence of terminal functional groups. Also, compared to other metal-free g-C3N4 electrocatalysts reported in the literature, we achieved lower Tafel slope values without additional post-treatments or co-catalysts. Hence, for the first time a metal-free catalyst defeats benchmark IrO2. The prepared electrodes were stable for up to 45 h, even when increasing the applied current density to 100 mA cm−2 for 15 h. Thus, this work provides a simple route for the fabrication of highly-efficient and long-lasting electrocatalysts for a remarkable OER performance.