筛选电催化硝酸根还原制氨的MXene基单原子催化剂

Screening MXene-based single-atom catalysts for selective nitrate-to-ammonia electroreduction

电催化硝酸根还原制氨是调节全球氮循环和合成氨的一种很有前景的方法.当前实现高效硝酸根还原制氨(NRA)的关键问题是开发具有高活性、选择性和稳定性的催化剂.本文通过把过渡金属(TM:3d=Sc-Zn,4d=Y-Cd,5d=La-Hg)锚定在二维材料Ti_(3)C_(2)O_(2)MXene(Ti_(3)C_(2)O_(2)-TM)上,筛选出新的NRA单原子催化剂.本工作采用密度泛函理论进行理论计算,发现Ti_(3)C_(2)O_(2)上的表面O官能团对TM具有较高的锚定能力,同时材料拥有良好的抗溶解稳定性.此外,锚定的TM与硝酸根之间强的p-d耦合作用使NO_(3)-易于活化.锚定TM在费米能级处有较高的不饱和d轨道,具有良好的稳定性和NO_(3)-活化能力.基于此,本文筛选出10种前线分子轨道在d5附近的Ti_(3)C_(2)O_(2)-TMs(TM=Cr,Mn,Fe,Tc,Ru,W,Re,Os,Ir,Pt),并且最有利的反应路径是持续的脱氧加氢:NO_(3)-→*NO_(3)→*NO_(2)→)*NO→*N→*NH→*NH_(2)→*NH_(3)→NH_(3)(g).本工作认为Ti_(3)C_(2)O_(2)-CrSA、Ti_(3)C_(2)O_(2)-ReSA和Ti_(3)C_(2)O_(2)-OsSA这3种具有低NRA过电位的Ti_(3)C_(2)O_(2)-TM是优异的NRA催化剂.这些发现为设计低能耗、低碳排放的先进氨合成路线提供了新策略.

Electrocatalytic nitrate reduction to ammonia(NRA)is a promising way to regulate the global nitrogen cycle and synthesize ammonia.The key factor to achieve efficient NRA is to develop desired catalysts with high activity,selectivity and stability.Herein,a new family of single-atom catalysts(SACs)for NRA are screened by anchoring transition metal(TM:3d=Sc-Zn,4d=Y-Cd,5d=La-Hg)atoms on two-dimensional Ti_(3)C_(2)O_(2)MXene(Ti_(3)C_(2)O_(2)-TM).Using density functional theory calculations,the surface O functional group on Ti_(3)C_(2)O_(2)is found to deliver high anchoring ability for TM,resulting in excellent anti-dissolution stability.Besides,strong p-d coupling between the anchored TM and the nitrate facilitates nitrate activation.Ten Ti_(3)C_(2)O_(2)-TMs with orbitals around d5(TM=Cr,Mn,Fe,Tc,Ru,W,Re,Os,Ir,and Pt)are first screened out based on the relatively high unsaturated anchored TM d orbitals at Fermi level to achieve good stability and nitrate activation.The most favorable reaction pathway is determined being the continuous deoxygenation,followed by hydrogenation:NO_(3)−→*NO_(3)→*NO_(2)→*NO→*N→*NH→*NH_(2)→*NH_(3)→NH_(3)(g).Three Ti_(3)C_(2)O_(2)-TMs including Ti_(3)C_(2)O_(2)-CrSA,Ti_(3)C_(2)O_(2)-ReSA,and Ti_(3)C_(2)O_(2)-OsSA with low overpotentials are regarded as the outstanding catalysts for NRA.These findings could open up new strategies for an advanced ammonia synthesis route with low energy consumption and low carbon emission.