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 (Ru_x Cu_x /rGO) are fabricated and used for the direct reduction of NO₃ ^- to NH₃ . It is found that the Ru₁ Cu₁₀ /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 Ru₁ Cu₁₀ /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.