Cube-shaped metal-nitrogen–carbon derived from metal-ammonia complex-impregnated metal-organic framework for highly efficient oxygen reduction reaction

The non-platinum metal-nitrogen-carbon (M-NC) system is a class of highly active oxygen reduction reaction (ORR) electrocatalysts that are well known and widely used in fuel cell applications. Herein, one simple synthesizing method of efficient M-NC electrocatalysts is proposed by the direct pyrolysis of a pretreated core-shell structure of ZnO@ZIF-8 containing metal-ammonia complex (MAC, [M(NH3)x]n+) from the polydisperse self-sacrificing MOF-5 cubes. The as-pyrolyzed M-NC (M = Co, Ag, Cu, and Ni) electrocatalysts showcase high electrocatalytic ORR activity in an alkaline medium. Among them, Co-NC catalyst exhibits an excellent ORR performance where its E1/2 = 0.80 V, JL = 5.88 mA cm−2, as well as Tafel slope of 67.0 mV dec−1 are close to commercial Pt/C and Ag-NC, better than the other two catalysts of Cu-NC and Ni-NC. Impressively, zinc-O2 batteries assembled with M-NC materials exhibit the better discharge performance, and have great potential in the practical energy conversion and storage. The experimental demonstration of metal-based nanoparticles and active M-N sites in the carbonaceous matrix can be efficiently used to promote the ORR activity, which is derived from a synergistic contribution of its particular hollow structure, large specific surface area, rich M-N active sites, and high degree of graphitization. This attractive preparation approach provides us a powerful contribution to the construction of high-performance carbon-based ORR electrocatalysts.

非铂金属 - 氮 - 碳（M - NC）体系是一类高活性的氧还原反应（ORR）电催化剂，在燃料电池应用中广为人知且被广泛使用。在此，我们提出了一种高效M - NC电催化剂的简单合成方法，即通过对来自多分散自牺牲MOF - 5立方体的含金属 - 氨络合物（MAC，[M(NH3)x]n +）的ZnO@ZIF - 8核 - 壳结构进行预处理后直接热解。所得到的热解M - NC（M = Co、Ag、Cu和Ni）电催化剂在碱性介质中展现出高的电催化ORR活性。其中，Co - NC催化剂表现出优异的ORR性能，其半波电位E1/2 = 0.80 V，极限电流密度JL = 5.88 mA cm−2，以及塔菲尔斜率为67.0 mV dec−1，接近商业Pt/C和Ag - NC，优于Cu - NC和Ni - NC这两种催化剂。令人印象深刻的是，用M - NC材料组装的锌 - 氧电池表现出更好的放电性能，在实际的能量转换和存储方面具有巨大潜力。实验证明，碳质基体中的金属基纳米粒子和活性M - N位点可有效用于提高ORR活性，这源于其特殊的中空结构、大比表面积、丰富的M - N活性位点以及高度石墨化的协同作用。这种有吸引力的制备方法为构建高性能碳基ORR电催化剂做出了有力贡献。