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

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.