Efficient Co and GO co-doped TiO2 catalysts for the electrochemical reduction of nitrate to ammonia

Abstract

Electrocatalytic nitrate (NO₃⁻) reduction to ammonia (NH₃) has emerged as an environmentally friendly method for ammonia production due to its clean, efficient, and sustainable attributes. In this study, we prepared Co-doped TiO₂ materials with graphene oxide (GO), Co–TiO₂/GO, as potential NO₃⁻RR electrocatalysts. Scanning electron microscopy (SEM) images revealed a spherical structure for the catalysts. Following a series of electrochemical tests, our findings indicated that Co-doping significantly enhances the NO₃⁻RR activity of TiO₂. Furthermore, incorporating GO notably diminishes the initial potential of titania-based catalysts, thereby strengthening the NO₃⁻RR performance of TiO₂. The engineered Co–TiO₂/GO exhibits superior NO₃⁻RR electrochemical properties, achieving an NH₃ yield of up to 7.424 mg h⁻¹ cm⁻² and a Faraday efficiency of up to 56.5% at −1.1 V vs. RHE potential. This performance surpasses that of Co–TiO₂, with minimal by-product NO₂⁻ generation. We also conducted tests without the catalyst and in the absence of NO₃⁻ in the electrolyte, confirming that the nitrogen in the synthesized ammonia was not derived from impurities in the catalyst or the electrolyte. Furthermore, Co–TiO₂/GO demonstrated robust stability during eight cycles and 24 hours of continuous testing for the NO₃⁻RR performance. Theoretical calculations suggest that doping TiO₂ with Co and GO can enhance its electronic structure and conductivity, thereby facilitating the electrochemical synthesis of ammonia.