Although the use of transition metals as bifunctional catalysts for zinc–air batteries (ZABs) has obvious economic advantages, their performance in ZABs still fails to meet expectations due to the uncontrollable loading caused by the rapid nucleation rate of transition metals. In this study, controllable loading of an Fe/Co alloy on heteroatom-doped hollow graphene spheres (FeCo@NGHS) was realized via the regulation of small molecules. Sodium citrate, which served as a metal complexing agent and reaction buffer, effectively suppressed the excessive loading of Fe/Co alloy particles and facilitated the formation of Fe(Co)N_x active sites. Melamine, which served as a precursor for doping N atoms, provided anchor points for the loading of Fe/Co alloy particles and participated in the generation of Fe(Co)N_x. The fabricated catalyst had active sites with different chemical structures, such as pyridine-N, graphite-N, Fe(Co)N_x and Fe/Co alloy particles, all of which benefit the improvement of the oxygen reduction reaction/oxygen evolution reaction (ORR/OER) performance. Results showed that the fabricated FeCo@NGHS, which possesses the appropriate amount of Fe/Co alloy particles combined with the highest amount of formed Fe(Co)N_x active sites, exhibited the best ORR/OER bifunctional catalytic performance in alkaline electrolytes and excellent electrocatalytic stability. The ORR onset potential and half-wave potential were 0.961 V and 0.846 V (vs. RHE), respectively. The OER could achieve a low overpotential level of 391 mV at a current density of 10 mA cm⁻². Furthermore, the rechargeable liquid ZAB and flexible all-solid-state (ASS) ZAB assembled by FeCo@NGHS exhibited higher discharge power density and longer charge–discharge cycle performance. FeCo@NGHS-based air cathodes exhibited outstanding performance in flexible ASS–ZABs, showing high open circuit voltage (1.45 V) and peak power density (74.06 mW cm⁻²). Thus, in clean energy storage and conversion technologies, a new synthetic strategy for constructing excellent bifunctional oxygen electrocatalysts is proposed in this work.

中文翻译：

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通过调节可充电锌空气电池的小分子，实现 Fe/Co 合金在杂原子掺杂空心石墨烯球上的可控负载


尽管使用过渡金属作为锌-空气电池 （ZABs） 的双功能催化剂具有明显的经济优势，但由于过渡金属的快速成核速率导致负载不可控，它们在 ZABs 中的性能仍然未能达到预期。在本研究中，通过小分子的调节实现了 Fe/Co 合金在杂原子掺杂空心石墨烯球 （FeCo@NGHS） 上的可控负载。柠檬酸钠作为金属络合剂和反应缓冲液，有效抑制了 Fe/Co 合金颗粒的过度负载，促进了 Fe（Co）N_x 活性位点的形成。三聚氰胺作为掺杂 N 原子的前驱体，为 Fe/Co 合金颗粒的负载提供了锚点，并参与了 Fe（Co）N_x 的产生。所制备的催化剂具有不同化学结构的活性位点，如吡啶-N、石墨-N、Fe（Co）N_x 和 Fe/Co 合金颗粒，这些都有利于氧还原反应/析氧反应 （ORR/OER） 性能的提高。结果表明，制备的FeCo@NGHS具有适量的 Fe/Co 合金颗粒和最大量的形成 Fe（Co）N_x 活性位点，在碱性电解质中表现出最佳的 ORR/OER 双功能催化性能和优异的电催化稳定性。ORR 起始电位和半波电位分别为 0.961 V 和 0.846 V （vs. RHE）。OER 可以在 391 mA ^cm-10 的电流密度下实现 2 mV 的低过电位水平。 此外，由 FeCo@NGHS 组装的可充电液体 ZAB 和柔性全固态 （ASS） ZAB 表现出更高的放电功率密度和更长的充放电循环性能。FeCo@NGHS基空气阴极在柔性 ASS-ZAB 中表现出出色的性能，表现出高开路电压 （1.45 V） 和峰值功率密度 （74.06 mW ^cm-2）。因此，在清洁能源储存和转换技术中，本工作提出了一种构建优良双功能氧电催化剂的新型合成策略。