熔盐电脱氧制备高分散纳米结构PtxRE合金催化剂的研究

Pt and rare earth（RE）alloys catalysts have shown the highest electrochemical activity and best stability to oxygen reduction reaction of polymer electrolyte membrane fuel cell. It is urgent to find a feaible way to prepare nanosized PtxRE alloys.Through cooperation with Prof. Qingfeng Li from Technical University of Denmark, electrochemical deoxidation of oxides in molten salts is proposed to prepare PtxRE alloys. First, both hydrolysis of rare earth nitrates and traditional NaBH4 reduction method are applied to prepare highly dispersive and nanosized Pt and rare earth oxides（REyOz）precusor on high specific surface area carbon support（Pt-REyOz/C）.Then PtREyOz/C pallets are made under pressures and used as cathde to prepare PtxRE/C alloys by directly electrochemical deoxidation in chloride molten salts. The research will be focused on the following: (1)the electrochemical deoxidation processes, mechanism and kinetics of PtREyOz/C as well as the formation mechanism of PtxRE alloys,(2)PtxRE alloys morphology,composition and structure as well as the electrochemical catalytic activity and mechanism will be characterized,(3)controllable preparation of PtxRE alloys with different coposition ,morphology and catalytic activity can be reached..Carbon support can effectively prevent the aggregation and growth of nanosized particles of PtxRE alloys, REyOz can be electrochemically deoxidized to form PtxRE alloys on Pt particles. The proposal has exhibited both a feasibility and an original innovation in preparation of nanosized PtxRE alloys.

Pt-稀土（RE）合金催化剂对聚合物燃料电池氧还原反应（ORR）表现出最高的电化学活性和稳定性，急需找到可行的方法制备纳米PtxRE合金。通过与丹麦技术大学李庆峰教授合作，课题拟采用熔盐电化学脱氧方法制备纳米PtxRE合金。采用稀土硝酸盐水解和传统NaBH4还原法，在碳支撑体上制备高度分散的纳米Pt和稀土氧化物（REyOz）前驱体（Pt-REyOz/C），并压制成PtREyOz/C块体。以该块体为阴极，在氯化物熔盐中直接电化学脱氧制备PtxRE/C合金。研究PtREyOz/C电化学脱氧过程、机理和动力学，以及PtxRE合金的形成机理；表征PtxRE合金的形貌、组成、结构以及对ORR的电化学催化性能及机理的影响；实现PtxRE合金组成、形貌和催化性能的可控制备。碳材料能防止PtxRE合金纳米颗粒聚集长大；Pt的存在使REyOz能够电化学脱氧形成合金；研究内容可行，研究思路具有原始创新性。

基于质子交换膜燃料电池（PEMFCs）大规模应用的需求，寻找合适的化学合成策略制备具有优异氧还原反应（ORR）性能的高分散Pt-RE纳米合金催化剂已迫在眉睫。本项目以克级（g）为单位，首次通过熔盐电化学脱氧法成功的合成了一系列高分散、低纳米尺度的碳负载型Pt-Nd/C合金催化剂。通过协调控制稀土氧化物中Nd元素与Pt元素的摩尔比和电解时长，实现了Pt2Nd和Pt5Nd两种不同结构合金的可控制备。与商业JM Pt/C催化剂及其他文献中所制备的Pt-RE合金催化剂相比,两种Pt-Nd/C合金催化剂均表现出优异的催化活性和稳定性。Pt5Nd/C合金催化剂在0.9 V的质量比活性是商业JM Pt/C催化剂的2.9倍。同时，在g-C3N4的辅助下，通过氢还原成功制备了Pt5La纳米合金，研究了Pt5La/C纳米合金的形成过程和机理、优化了制备工艺。g-C3N4有效降低了氢还原温度和合金的颗粒尺寸，提高了纳米合金的电催化活性。Pt5La/C纳米合金催化剂的半波电位（E1/2）分别比商业JM-Pt/C催化剂高出了近27 mV，在0.9 V下其质量比活性是JM-Pt/C催化剂的2.3倍。.本工作解决了高温下合成高分散、低纳米Pt-RE合金的难题，提供了一种低成本、大规模制备适用于PEMFCs阴极ORR的纳米Pt-RE合金催化剂的方法。