Catalysis has been crucial in advancing and commercializing energy conversion technologies. It is essential to identify abundant, active, and stable materials to enable the reliable and cost-efficient use of catalysts in renewable technologies, such as fuel cells (FCs) and electrolyzers. Suitable candidates, such as nonprecious metals, can be found in first-row transition metals, where materials such as bimetallics, metal oxides, and metal nitrides can be readily synthesized. Recently, these materials have exhibited high activity toward the oxygen reduction (ORR) and oxygen evolution (OER) reactions in alkaline media, which, in turn, were related to promising performance in FCs and electrolyzers. However, most of these studies have not gone beyond half-cell reactions. In this study, we explored the synthesis of a metal nitride, Ni₃FeN, and its application as an electrocatalyst for ORR and OER. We developed procedures for the synthesis of Ni₃FeN nanocrystals with different carbon loadings using a one-step ammonolysis route. We show that the pristine structure of the material encompasses a nitride core and an oxide shell with a thickness of a few nanometers. However, the bulk electronic structure is mainly dominated by the Ni₃FeN phase. The nitride exhibited an impressive and stable ORR performance in 1 M KOH favoring the 4 e^– pathway. The material exhibited a slight decrease in E_1/2 of 10 mV (from 0.85 to 0.84 V vs RHE) during a prolonged (100 K) accelerated stress test (AST). The AST degradation at ORR potentials indicates that the catalyst aggregates into larger nanoparticles, forming a Ni@NiFeOx structure. After tests at OER potentials, the catalyst breaks into smaller nanoparticles and mainly favors the NiFeOx structure. MEA testing of the Ni₃FeN ORR catalyst in a hydrogen-fueled alkaline exchange membrane fuel cell (AEMFC) yielded a peak power density of ca. 700 mW/cm²; among the highest reported for nitride and NiFe-based materials. We believe that this work could enable the use of NiFe-based materials as viable, inexpensive alternatives for fuel cell applications.

中文翻译：

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高性能 Ni-Fe 氮化物燃料电池和电解槽电催化剂的表面调制见解


催化在推进能源转换技术并实现商业化方面发挥着关键作用。必须确定丰富、活性和稳定的材料，以便在燃料电池 （FC） 和电解槽等可再生能源技术中可靠且经济高效地使用催化剂。合适的候选材料，如非贵金属，可以在第一排过渡金属中找到，其中双金属、金属氧化物和金属氮化物等材料可以很容易地合成。最近，这些材料在碱性介质中表现出对氧还原 （ORR） 和析氧 （OER） 反应的高活性，这反过来又与 FCs 和电解槽中的良好性能有关。然而，这些研究中的大多数并没有超越半电池反应。在这项研究中，我们探索了金属氮化物 Ni₃FeN 的合成，以及它作为 ORR 和 OER 电催化剂的应用。我们开发了使用一步氨解路线合成具有不同碳负载量的 Ni₃FeN 纳米晶体的程序。我们表明，该材料的原始结构包括一个氮化物核和一个厚度为几纳米的氧化物壳。然而，本体电子结构主要以 Ni₃FeN 相为主。氮化物在 1 M KOH 中表现出令人印象深刻且稳定的 ORR 性能，有利于 4 e^– 途径。在长时间 （100 K） 加速应力测试 （AST） 期间，该材料的 E_1/2 略有降低 10 mV（从 0.85 V 到 0.84 V vs RHE）。ORR 电位处的 AST 降解表明催化剂聚集成更大的纳米颗粒，形成Ni@NiFeOx结构。 在 OER 电位测试后，催化剂分解成更小的纳米颗粒，主要有利于 NiFeOx 结构。氢燃料碱换膜燃料电池 （AEMFC） 中 Ni₃FeN ORR 催化剂的 MEA 测试产生约 700 mW/cm² 的峰值功率密度;氮化物和 NiFe 基材料报告的最高水平之一。我们相信，这项工作可以使 NiFe 基材料成为燃料电池应用的可行、廉价的替代品。