Nitride or Oxynitride? Elucidating the Composition–Activity Relationships in Molybdenum Nitride Electrocatalysts for the Oxygen Reduction Reaction,Chemistry of Materials

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Nitride or Oxynitride? Elucidating the Composition–Activity Relationships in Molybdenum Nitride Electrocatalysts for the Oxygen Reduction Reaction
Chemistry of Materials ( IF 7.2 ) Pub Date : 2020-03-25 , DOI: 10.1021/acs.chemmater.9b05212
Melissa E. Kreider _{1,

2} , Michaela Burke Stevens _{1,

2} , Yunhzi Liu ₃ , Anjli M. Patel _{1,

2} , Michael J. Statt _{1,

2} , Brenna M. Gibbons _{2,

3} , Alessandro Gallo _{2,

4} , Micha Ben-Naim _{1,

2} , Apurva Mehta _{4,

5} , Ryan C. Davis _{4,

5} , Anton V. Ievlev ₆ , Jens K. Nørskov ₇ , Robert Sinclair ₃ , Laurie A. King ₈ , Thomas F. Jaramillo _{1,

2}

Affiliation

Molybdenum nitride (Mo–N) catalysts have shown promising activity and stability for the oxygen reduction reaction (ORR) in acid. However, the effect of oxygen (O) incorporation (from synthesis, catalysis, or exposure to air) on their activity remains elusive. Here, we use reactive sputtering to synthesize three compositions of thin-film catalysts and use extensive materials characterization to investigate the depth-dependent structure and incorporated O. We show that the as-deposited Mo–N films are highly oxidized both at the surface (>30% O) and in the bulk (3–21% O) and that the ORR performance is strongly correlated with the bulk structure and composition. Activity for 4e^– ORR is highest for compositions with the highest N/O and N/Mo ratio. Furthermore, H₂O₂ production for the films with moderate O content is comparable to or higher than the most H₂O₂-selective nonprecious metal catalysts in acidic electrolyte, on a moles per mass or surface area of catalyst basis. Density functional theory provides insight into the energetics of O incorporation and vacancy formation, and we hypothesize that activity trends with O/N ratios can be traced to the varying crystallite phases and their interactions with ORR adsorbates. This work demonstrates the prevalence and significance of O in metal nitride electrocatalysts and motivates further investigation into the role of O in other nonprecious metal materials.

中文翻译：

氮化物或氧氮化物？阐明用于还原氧反应的氮化钼电催化剂的组成-活性关系

氮化钼（Mo–N）催化剂对酸中的氧还原反应（ORR）具有良好的活性和稳定性。但是，氧（O）掺入（通过合成，催化或暴露于空气中）对其活性的影响仍然难以捉摸。在这里，我们使用反应溅射法合成了三种组成的薄膜催化剂，并使用广泛的材料表征研究了深度依赖的结构并结合了O。我们证明了沉积的Mo–N膜在表面都被高度氧化（ > 30％O）和大部分（3–21％O），并且ORR性能与整体结构和组成密切相关。N / O和N / Mo比最高的组合物的4e ^- ORR活性最高。此外，H ₂ O ₂在催化剂的每质量或表面积的摩尔数基础上，具有适度O含量的薄膜的产量可与酸性电解质中大多数H ₂ O ₂选择性非贵金属催化剂相比或更高。密度泛函理论提供了关于O结合和空位形成的能量学的见解，并且我们假设具有O / N比的活性趋势可以追溯到变化的微晶相及其与ORR吸附物的相互作用。这项工作证明了O在金属氮化物电催化剂中的普遍性和意义，并促使人们进一步研究O在其他非贵金属材料中的作用。

更新日期：2020-04-23

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