The lack of cost-effective electrocatalysts towards oxygen reduction reaction is hindering the large-scale application of promising energy conversion technologies, such as fuel cells or metal-air batteries. In this context, metal free N and S doped carbon materials have been successfully applied to oxygen reduction reaction (ORR) electrocatalysis. Heteroatom doped biochars, in particular, represent a cost-effective and sustainable replacement to Pt-based electrocatalysts. Herein, we developed several N-doped or N and S co-doped biochars, using shrimp shells as biomass feedstock. Four dopants containing different N/S ratios (N6, SN6, S3N3 and S3N2) were used in order to optimize the ORR performance in alkaline medium. Doping with S3N3 revealed to be more promising, as the resulting electrocatalyst, S3N3-CC, obtained the most positive onset potential (Eonset), higher diffusion limiting current density (jL) and number of electrons transferred per oxygen molecule (nO2) closer to 4. Moreover, this biochar showed excellent stability over 15 h of continuous use. The performance of S3N3-CC was mainly explained by a high content of pyridinic and graphitic N, a high ratio between pyridinic and pyrrolic N, the introduction of thiophenic S and an optimized N/S ratio.

中文翻译：

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用于氧还原反应的高性能无金属 N/S 掺杂生物炭


缺乏用于氧还原反应的具有成本效益的电催化剂阻碍了有前途的能源转换技术的大规模应用，例如燃料电池或金属空气电池。在此背景下，无金属 N 和 S 掺杂碳材料已成功应用于氧还原反应 （ORR） 电催化。特别是杂原子掺杂的生物炭，代表了 Pt 基电催化剂的一种经济高效且可持续的替代品。在此，我们开发了几种 N 掺杂或 N 和 S 共掺杂生物炭，使用虾壳作为生物质原料。使用四种含有不同 N/S 比的掺杂剂 （N6 、 SN6 、 S3N3 和 S3N2） 来优化碱性介质中的 ORR 性能。用 S3N3 掺杂被证明更有前景，因为所得电催化剂 S3N3-CC 获得了最正的起始电位 （Eonset）、更高的扩散极限电流密度 （jL） 和每个氧分子转移的电子数 （nO2） 接近 4。此外，这种生物炭在连续使用 15 小时后表现出优异的稳定性。S3N3-CC 的性能主要归因于吡啶和石墨氮含量高、吡啶和吡咯氮的高比例、噻吩 S 的引入以及优化的 N/S 比。