Mesoporous MnO_(2)nanosheets for efficient electrocatalytic nitrogen reduction via high spin polarization induced by oxygen vacancy

The electrochemical N_(2)reduction reaction(NRR)represents a green and sustainable route for NH_(3)synthesis under ambient conditions.However,the mechanism of N_(2)activation in the electrocatalytic NRR remains unclear.Herein,we found that the high spin state Mn^(3+)-Mn^(3+)pairs induced by oxygen vacancy in MnO_(2)nanosheets greatly enhance the catalytic activities.The strong electron transfer between d orbital of Mn and orbital of N2 forces the N_(2)to be of radical nature,which activates the hydrogenation process and weakens the N≡N bond.Based on the density functional theory(DFT)calculation results,we precisely designed mesoporous MnO_(2)nanosheets with rich oxygen vacancies via using methyltriphenylphosphonium bromide(MPB)to induce more Mn^(3+)-Mn^(3+)pairs(Mn^(3-3)-MnO_(2)),which can achieve a fairly high ammonia yield of up to 147.2μg·h^(−1)·mgcat−1.at−0.75 V vs.reversible hydrogen electrode(RHE)and a high Faradaic efficiency(FE)of 11%.Furthermore,these mesoporous MnO_(2)nanosheets exhibit the superior durability with negligible changes in both NH3 yield and FE after a consecutive 6-recycle test and the current density electrolyzed over a 24-hour period.Our findings offer an approach to designing highly active transition metal catalysts for electrocatalytic nitrogen reduction.