Iron carbide encapsulated in graphitic layers has recently been recognized as an active oxygen reduction reaction (ORR) catalyst made of earth-abundant elements. Here, the ORR activity of graphene (G) and N-doped graphene (NG) supported on Fe₃C(010) and Fe(110) is studied computationally by means of density functional theory calculations. The calculations show higher activity of the Fe₃C-supported model system than the Fe-supported one, as well as the importance of N-doping in achieving high ORR activity, in agreement with experimental observations. We find the most active sites on a single N-doped graphitic layer placed on the Fe₃C surface. Like in the case of unsupported NG, the reaction on the Fe₃C/NG model interface proceeds at the atomic oxygen coverage between 0.5 < θ_O < 1.0. The charge on O adsorbate caused by the presence of support is found to correlate with the oxygen binding strength. In the case of the Fe/NG system, this results in a surface poisoning by oxygen. On the basis of these findings, we propose that a heterostructure consisting of a NG overlayer and a support with stronger electron-donating properties than Fe₃C and weaker than Fe may approach or even exceed the ORR activity of the Pt(111) surface.

中文翻译：

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DFT研究碳包覆铁和碳化铁的氧还原反应

封装在石墨层中的碳化铁最近被认为是由富含地球的元素制成的活性氧还原反应（ORR）催化剂。在此，通过密度泛函理论计算，研究了负载在Fe ₃ C（010）和Fe（110）上的石墨烯（G）和N掺杂石墨烯（NG）的ORR活性。计算结果表明，Fe ₃ C支撑的模型系统比Fe支撑的模型系统具有更高的活性，并且N掺杂在实现高ORR活性方面的重要性与实验观察一致。我们在放置在Fe ₃ C表面的单个N掺杂石墨层上发现了最活跃的位点。像在不支持NG的情况下一样，对Fe ₃的反应在0.5 <θ之间的原子氧覆盖率C / NG模型接口前进_Ò <1.0。发现由载体的存在引起的O吸附物上的电荷与氧结合强度相关。在Fe / NG系统的情况下，这会导致表面被氧气中毒。基于这些发现，我们提出由NG覆盖层和具有比Fe ₃ C强的给电子性但比Fe弱的支持体组成的异质结构可能接近甚至超过Pt（111）表面的ORR活性。