氧掺杂石墨烯负载的Pt4和Pt3Ni催化氧还原反应的密度泛函理论研究

摘要

The highly efficient alloy electrocatalysts with less content of noble metals for oxygen reduction reac-tion(ORR)should be studied to reduce the cost of fuel cell.In the present density functional theory study,oxygen adsorption and consecutive hydrogenation during ORR process were examined on Pt4 and Pt3Ni tetrahedral clusters supported on O-doped graphene steady.The oxygen is adsorbed and activated in the form of O2 molecule on both sup-ported Pt4 and Pt3Ni clusters,and the interaction of the adsorbed O2 molecule with supported Pt3Ni cluster is stronger.In the first step of hydrogenation,it is more preferable to form co-adsorbed OH* and O* on supported Pt3Ni cluster,with a lower energy of 2.37,eV than that of forming metastable HOO*.Thermodynamic analysis indicates that the dominated ORR route on Pt3Ni-OG is the called "bottom site route" in which OH* adsorbed on bottom Ni.In addition,the introduction of Ni to generate the Pt3Ni alloy can effectively promote the ORR process by reducing re-action energy input for subsquent hydrogenation steps.Further,the calculated results of the free energy of ORR on both catalysts suggest the weak adsorption of OH* on Pt3Ni lead to the formation of H2O* with lower energy in com-parison with that on Pt4.The results indicate that PtNi alloy shows higher ORR activity than Pt,and are meaningful for designing highly efficient ORR electrocatalysts.%为了降低燃料电池的高成本,必须寻找一种既能减小贵金属铂的担载量,又能进一步提高氧还原反应催化活性的新型合金催化剂.基于密度泛函理论,建立了Pt4和Pt3Ni正四面体结构的金属团簇模型,选用氧掺杂石墨烯作为载体,四面体金属团簇以正金字塔形式稳定吸附在缺陷位正上方,在负载的金属团簇上进行氧分子的吸附和连续加氢模拟氧还原反应过程,并进行热力学计算与分析.结果表明,氧在Pt4-OG和Pt3Ni-OG上均以分子形式吸附并被活化,Pt3Ni-OG对氧分子的活化作用更强;第1步加氢反应,在Pt3Ni-OG上形成共吸附的OH*和O*时体系的能量比形成亚稳态的HOO*时低2.37,eV.热力学分析表明,氧还原反应在Pt3Ni-OG上的主要反应路径为底位吸附路径;在Pt金属中引入Ni,使随后在吸附在Pt3Ni-OG上的氧分子上发生的加氢反应所需的能量降低.同时Pt3Ni-OG和Pt4-OG催化氧还原反应的自由能计算结果也表明,Pt3Ni-OG上氧还原反应中间体OH*的吸附作用减弱,进而后续形成H2O*的反应所需的能量降低.这表明PtNi合金的氧还原反应的催化活性较Pt提高.本研究对氧还原反应高效电催化剂的设计具有指导意义.