金属氮碳化合物M-N-C多功能“界面限域催化”研究

The transition metal encapsulated in nitrogen-doped graphene core-shell catalysts have the similar bifunctional electrocatalytic performance as Pt for hydrogen evolution reaction and oxygen reduction reaction, and the transition-nitrogen-carbon species (M-N-C) located in the outer graphene shell is the active center. It’s important to study the interfacial confinement effect of M-N-C for the scientific significance. The project aims to use Prussian blue complex as a single precursor, synthesize M-N-C complexes through the high temperature carbonization process. By controlling the composition and structure of the precursor, the morphology, crystal form and surface electron structure of M-N-C were controlled. The electrocatalytic hydrogen evolution and oxygen reduction activities of M-N-C will be systematically studied. Then M-N-C was applied in metal-air batteries such as zinc-air batteries and Al-air batteries to improve the power density and stability. In our design, we will focus on the synergistic effect of bimetal or polymetal on the catalytic performance; the effect of heterogeneous nonmetallic elements B, S, P, F on the catalytic properties after doping in M-N-C structure; the effect of transition metal on the growth of amorphous carbon and the regulation of the density and distribution for the active center M-N-C in amorphous carbon. Through the above-mentioned control of the structure and composition for M-N-C species, it will be a novel method to develop alternative multifunctional catalysts for Pt.

氮掺杂石墨烯包覆过渡金属核壳催化剂具备跟Pt类似的析氢和氧还原双功能催化效果，限域于石墨烯壳层中M-N-C是其催化的活性中心，研究M-N-C的“界面限域催化”具有重要的科学意义。本项目拟以普鲁士蓝类配合物作为单一前驱物，通过高温固相反应制备过渡金属氮碳化合物M-N-C，通过控制前驱物组成、结构来调控M-N-C形貌、晶型和表面电子结构，进而系统地研究M-N-C对电催化析氢和氧还原电催化性能，然后将其应用于锌空电池、铝空电池等金属-空气电池中，以提高金属空气电池的功率密度和工作稳定性。在M-N-C材料的设计上，我们将重点研究双金属或者多金属对催化性能的协同作用效果；同类异质非金属元素B、S、P、F等对M-N-C掺杂后催化性能的影响；研究金属元素对于无定性碳生长的影响以及无定型碳对于活性中心M-N-C密度和分布的调控。通过对M-N-C结构和组成的调控，为发展可替代Pt的多功能催化剂提供新的思路。

本项目采用液相沉淀法合成普鲁士蓝类配合物，进一步控制高温固相碳化反应来调控金属氮碳化合物M-N-C的结构、形貌、晶型等。通过对M-N-C催化剂的双金属调控和非金属元素掺杂，我们系统优化了其析氢反应、氧还原反应、析氧反应等多功能电催化性能。其中CoMn@NG-acid在1 M KOH和0.5 M H2SO4溶液中，10 mA/cm2电流密度下的过电位均在200 mV~220 mV，且侧面验证了在石墨烯壳层上CoMn-N-C化合物的“界面限域催化”机制。通过对CoMn@NG进行P掺杂得到CoMn-P@NG，在1 M KOH和0.5 M H2SO4溶液中达到10 mA/cm2电流密度时，CoMn-P@NG的过电位分别为164 mV和140 mV，获得更加优异的析氢催化性能。此外，FeNi/HNC在1 M KOH溶液中10 mA/cm2电流密度下的析氧过电位只有250 mV，且氧还原半波电位只有0.87 V，其析氧和氧还原活性非常接近贵金属Pt/C和Ir/C催化剂。我们将FeNi/HNC应用在可充放电锌空电池正极，在放电情况下，该催化剂表现出310 mW/cm2的最高功率密度，放电电压为1.0 V时电流密度为215 mA/cm2，在充放电测试中，10 mA/cm2充放电的状态下表现出较高的电压效率（64.7%）和远高于贵金属Pt/C+Ir/C的可充电稳定性。最后，我们通过对活性中性进行SCN−的毒化测试，结果表明其活性中心为石墨烯壳层上的FeNi-N-C化合物，而并非来自于FeNi合金内核。区别于传统的“限域催化”，石墨烯壳层上FeNi-N-C的“界面限域催化”是其优异析氧和氧还原双功能催化性能的关键。M-N-C具备类贵金属的电子结构特征，表现出优异的多功能催化性能，为发展可替代贵金属的高效、稳定和廉价多功能催化剂提供了一种可行的新思路。