Electrocatalytic Nitrate Reduction to Ammonia Using Co <sub>3</sub> O <sub>4</sub> Nanowires Supported on TiO <sub>2</sub> /Ti
Kauan L. Gomes, Manuel E. G. Winkler, Matheus P. Sales, João Batista Souza, Juliano Alves Bonacin, Raphael Nagao
Abstract
High Resolution Image Download MS PowerPoint Slide The electrochemical nitrate reduction reaction (NO 3 RR) offers a sustainable alternative for ammonia synthesis under mild conditions, addressing both nitrate pollution and the energy-intensive nature of the Haber–Bosch process. In this work, Co 3 O 4 nanowires supported on TiO 2 /Ti were synthesized and evaluated for NO 3 RR in an H-type electrochemical cell using Ar-saturated 1.0 mol L –1 NaOH containing 20 mmol L –1 NaNO 3 . After confirming NO 3 RR activity via cyclic voltammetry, 1 h chronoamperometry was performed at potentials ranging from 0 to −0.4 V vs RHE (in 100 mV steps). The catalyst exhibited ammonia production at 0.0 V vs RHE, achieving a maximum faradaic efficiency (FE) of 80.0 ± 5.8% at −0.3 V vs RHE and a maximum yield rate (YR) of 93.3 ± 5.7 μmol h –1 cm –2 at −0.4 V vs RHE. This combination of high FE and low onset potential is rarely achieved in NO 3 RR. The catalyst maintained stable performance over 12 consecutive 1 h chronoamperometric tests. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses before and after electrolysis revealed a significant increase in nanowire diameter (from 97 to 562 nm), no changes in the crystalline structure, and partial reduction of Co 3+ to Co 2+ at the electrocatalyst surface, while preserving the Co 3 O 4 phase. In situ X-ray absorption near edge structure (XANES) further confirmed the stability of the Co 3 O 4 /TiO 2 /Ti under operating conditions. These results provide a basis for future investigations aiming to enhance ammonia yield rate at even lower overpotentials.