Synthesis of spinel type 2D Co3O4 nanodiscs using gallic acid for electrochemical NH3 formation by N2 reduction

Abstract

The production of ammonia through electrochemical nitrogen reduction reaction (ENRR) has garnered significant interest as a potential method of artificial nitrogen fixation in ambient conditions. This study reports an environmentally friendly synthesis of pristine Co3O4 nanodiscs (NDs) as a catalyst to effectuate electrochemical nitrogen reduction to ammonia. The absorption spectra of Co3O4 NDs revealed two peaks at 435 and 735 nm, indicative of O2− to Co2+/Co3+ charge transfer. The particles exhibited a distinct propensity for the growth along the (311) direction with induced oxygen vacancies which resulted from the release of NOx from the decomposition of precursor in the calcination step. The diameter and thickness of Co3O4 NDs were determined to be 240 and 35.5 nm, respectively. Faradaic efficiency of NH3 production of 2.6% was achieved with a yield rate of 8.8 µg h−1 mgcat.−1 at −1.25 V (vs. Ag/AgCl). Co3O4 NDs/TCP electrode showed six times higher Faradaic efficiency (FE) for ENRR compared to the bare TCP electrode. However, prolong electrolysis could result a reduction in FE due to sacrifice of active Co(III) sites due to the formation of Co(OH)2. Co2+ in tetrahedral sites easily bond with the N≡N, whereas Co3+ in octahedral sites facilitate the electron transfer for ENRR.