Ammonia is one of the most important industrial chemicals in the world, known not only as an essential raw material for fertilizer but also as an energy storage medium and carbon-free energy carrier. Currently, the industrial-scale NH3 synthesis relies on the century-old Haber-Bosch process, which requires harsh operating conditions including high temperature (400-500 °C) and high pressure (150-300 atm) using heterogeneous iron-based compounds as catalysts. Such process accounts for 1-2% of the world’s energy supply and causes ca. 1% of total global energy-related CO2 emissions. As an attractive alternative to the Haber-Bosch process, the ambient electrocatalytic nitrogen reduction reaction (NRR), ideally powered by clean/renewable energies (e.g., solar or wind), has attracted great interest during the past few years. However, efficient NRR has proven to be very challenging to achieve up to now. In the past two years, the reduction of nitrate to ammonia has attracted much attention as an attractive process to reduce the negative environmental impact of nitrate by turning it into valuable ammonia. This method has proven to bypass the limitations of the NRR process and is highly competitive with the Haber-Bosch process. In this talk, I will discuss how we can use density functional theory calculations to understand the mechanism of the reaction and guide catalyst design for the reduction of nitrate to ammonia.