Ultralow overpotential nitrate reduction to ammonia via a three-step relay mechanism

Ammonia plays a substantial role in agriculture and the next generation of carbon-free energy supply. Electrocatalytic nitrate reduction to NH3 is attractive for nitrate removal and NH3 production under ambient conditions. However, the energy efficiency is limited by the high reaction overpotential. Here we propose a three-step relay mechanism composed of a spontaneous redox reaction, electrochemical reduction and electrocatalytic reduction to overcome this issue. RuxCoy alloys were designed and adopted as model catalysts. Ru15Co85 exhibits an onset potential of +0.4 V versus reversible hydrogen electrode, and an energy efficiency of 42 +/- 2%. The high performance results in a low production cost of US$0.49 +/- 0.02 per kilogram of ammonia. The high nitrate reduction performances on Ru15Fe85 and Ru15Ni85 also highlight the promising potential of the relay mechanism.