熔盐电解氧化铁/碳混合固态阴极制备碳化铁包覆结构纳米铁的基础研究

Interaction between iron and carbon species is a classical proposition in metallurgy, which also forms scientific grounds for high-benefit metallurgy. In our preliminary study, metallic Fe nanoparticles were successfully prepared via electrolysis of the solid hybrid between iron oxide and graphite in molten salts, in which minor iron carbide generated on the surface of metallic Fe nanoparticles effectively retards agglomeration of Fe nanoparticles. It is speculated that such an unusual phenomenon might be due to the coupling result between electro-reduction of iron oxides and in-situ formation of iron carbide. Based on the preliminary results, by introducing the microstructure and composition controlling experiences between Fe3C and Fe in iron and steel industry to the molten salt electrolysis process, this project aims at production of Fe3C-coated metallic Fe nanoparticles (Fe@Fe3C) via electrolysis of the solid hybrid between iron oxide and graphite in molten salt. To deep understand the synergy process of multi-phase reactions, the following contents are investigated: (1) structure and composition design of the carbon-containing iron oxide solid cathode; (2) the electrode reaction mechanism for the Fe@Fe3C structure formation; (3) the structure-function relationship for the prepared Fe@Fe3C nano-functional materials. Correspondingly, the results reveal the particle size evolution process, illustrate the iron carbide shell formation mechanism including the regulating rules, and finally uncover the relationship between the surface structure and functional characteristics. Hopefully, the present study contributes to lay a theoretical foundation and provide basic data for metallic nanoparticles preparation by molten salt electrolysis.

铁碳物种的相互作用是冶金过程中的经典问题，且是实现冶金增值化的科学基础。申请人在前期预研中，通过熔盐电解氧化铁/石墨混合固态阴极制备了纳米级金属铁，且表面生成的少量碳化铁可使产物粒径显著降低。申请人推测这一特异现象可能是氧化铁电化学还原-铁碳化合反应协同耦合的结果。本项目拟在此基础上，将钢铁材料金属热处理过程碳化铁-铁物相间的微观组织调控这一经典问题引入熔盐电解体系，提出直接熔盐电解氧化铁/碳混合固态阴极制备碳化铁包覆的纳米铁功能材料，围绕电解过程铁、碳物种的多反应协同耦合及界面成分微结构调控这一科学问题，拟通过研究固态阴极成分-结构设计、碳化铁包覆铁结构形成的电极反应机制及调控、产物界面微结构与催化性能构效关系，探明金属铁粒径演变规律，揭示碳化铁包覆层生长机制及调控措施，阐明界面结构与催化活性的作用机理，为发展高活性铁基催化剂的熔盐材料高效制备技术提供科学基础。

熔盐电解固态氧化物是一种新型的电化学冶金技术，其中蕴含很多特殊的固-固反应界面现象。例如，在固相氧化物电解转化为固态金属单质过程，由于热烧结严重，电解产物均为微米级海绵态金属，而当掺入非金属元素如碳时，部分微米级海绵态金属会转变为相应的纳米级碳化物。这表明碳化物具有抑制固态产物烧结团聚的作用，巧妙利用这一特殊界面现象有望为高附加值功能金属材料的短程制备提供新方法。.本项目以金属铁氧化物为对象，通过在其固态氧化物电解过程引入非金属元素碳，构建金属-碳-氧电解体系以诱发表界面碳化过程，实现产物的结构纳米化、成分碳复合化，提高熔盐电解产物的成分微结构可控性，拓展电解产物的功能属性。重要结果如下:. 1) 以Fe2O3为固态阴极，以包覆的有机物为碳源，通过电解条件优化及电解质成分的选型，实现了Fe-O-C转化为碳包覆纳米铁-碳化铁（Fe/Fe3C@C）的复合纳米材料。采用热力学计算、气体在线监测及不同条件下产物成分演变规律，发现了电解-热解耦合作用机制。. 2) 发现了产物的多功能应用属于。产物特殊的微结构及成分特征赋予其优异的电化学析氢性能（在0.5 M H2SO4体系10 mA cm-2的过电位为147 mV，塔菲尔斜率仅78 mV dec-1。在1 M KOH碱性条件下，上述数值为153 mV及91 mV dec-1。）及显著的固硫能力（用于锂硫电池固硫电极时，经1C充放电370圈后容量保持在620 mAh g-1）。另外，产物具备优异的降解甲基蓝等水体污染物的能力。. 上述研究结果不仅高附加值功能金属基材料的短程制备提供了新方法，同时也为熔盐电解过程产物的成分-形貌微结构调控提供了新策略，另外也为温室气体CO2的熔盐捕获-高值转化提供了新思路。