Alloying of Cu with Ru Enabling the Relay Catalysis for Reduction of Nitrate to Ammonia

Abstract

Involving eight electron transfer process and multiple intermediates of nitrate (NO3−) reduction reaction leads to a sluggish kinetic and low Faradaic efficiency, therefore, it is essential to get an insight into the reaction mechanism to develop highly efficient electrocatalyst. Herein, a series of reduced-graphene-oxide-supported RuCu alloy catalysts (RuxCux/rGO) are fabricated and used for the direct reduction of NO3− to NH3. It is found that the Ru1Cu10/rGO shows the ammonia formation rate of 0.38 mmol cm−2 h−1 (loading 1 mg cm−2) and the ammonia Faradaic efficiency of 98% under an ultralow potential of −0.05 V versus Reversible Hydrogen Electode (RHE), which is comparable to Ru catalyst. The highly efficient activity of Ru1Cu10/rGO can be attributed to the synergetic effect between Ru and Cu sites via a relay catalysis, in which the Cu shows the exclusively efficient activity for the reduction of NO3− to NO2− and Ru exhibits the superior activity for NO2− to NH3. In addition, the doping of Ru into Cu tunes the d-band center of alloy and effectively modulates the adsorption energy of the NO3− and NO2−, which promotes the direct reduction of NO3− to NH3. This synergetic electrocatalysis strategy opens a new avenue for developing highly efficient multifunctional catalysts.