分子组装制备单分散、小尺寸Pt合金负载多级孔碳催化剂

Chemical reduction in a solution system with the assistance of some surface capping agents, is the most typical preparation route for Pt-based alloy nanoparticles loaded carbon materials, by which however it is difficult to tune the elemental compositions of the alloys and to achieve the particles with smaller sizes. Herein, we proposed a “self-assembly of the molecular precursors” route to prepare monodisperse ultrasmall Pt-based alloy nanoparticles loaded on hierarchically porous carbon. In the voids of SiO2 colloidal crystals, amphiphilic block copolymer, resol, and ligands contained metal precursors can be well self-assembled together into micelles, under the strong interactions between hydrophobic chains of block copolymer and metal precursors, and those between hydrophilic chains of block copolymer and resol. During calcination, decomposition of amphiphilic block copolymer would firstly drag the metal precursors to gradually approach and embed into the resol framework. And then when a higher temperature is used to conduct carbonization and metal reduction, the resol framework could protect the embedded metal species from aggregation and size growth, by which monodisperse ultrasmall Pt alloy nanoparticles loaded hierarchically porous carbon can be well produced. Apart from the size decrease, the high temperature directed reduction also allows an exact tuning of the compositions of the Pt alloy catalysts, which could improve their catalytic performances in a range of electrochemical reactions.

Pt合金催化剂在电化学反应中的活性受到颗粒组成和尺寸的影响较大。针对目前溶液体系内化学还原难以对Pt合金的组成进行精确调控、以及合金尺寸无法进一步降低的问题，本申请提出“分子组装制备单分散、小尺寸Pt合金负载多级孔碳催化剂”的研究方案，在SiO2小球立方堆积的大孔模板内，利用两亲性嵌段共聚物的疏水链段、亲水链段分别同有机配合类金属前驱体和碳前驱体酚醛树脂之间强的相互作用，构建三者组装的有序胶束，形成金属前驱体和碳前驱体在分子尺度上的有序组装，再利用焙烧过程中嵌段共聚物和其他小分子的分解挥发，拉动金属原子逐步接近并部分嵌入还未全部碳化的酚醛树脂骨架，通过骨架的限域保护作用避免合金颗粒在更高温度碳化过程中团聚长大，最终形成单分散、小尺寸Pt合金纳米颗粒负载的多级孔碳。该方案除了能够有效降低合金尺寸，所采用的高温还原方法还可以精确调控合金组成，有望实现合金催化剂在电化学反应中催化活性的大幅提升。

基于分子组装策略，本项目制备了一系列单分散超细Pt合金负载多级孔碳催化剂，大幅提升了电催化性能，并探索了催化剂组成、结构对电化学催化活性和稳定性的影响规律和机制。合成了sub-2 nm PtRu合金纳米晶催化剂，揭示了尺寸调控机理和表面活性剂疏水段的分子量高度正相关；制备了sub-3 nm六元、八元、十元高熵Pt合金催化剂，发现颗粒与碳载体之间强的平面接触是材料电化学稳定性高的主要原因；获得了传质通道完全开放、活性位点高度暴露的sub-4 nm PtCo/PtNi合金颗粒负载的空心碳球催化剂，通过将Pt载量提高至33 wt%，有效降低了阴极催化层厚度并大幅提升了传质和燃料电池性能；发展了分子组装联合化学键弱化策略，通过H在Pt、N上的自发强吸附，拉伸弱化Pt-Pt、Fe-N、Ni-N键，降低过程动力学能垒，制备了均匀负载1.55 nm Pt3Fe、1.25 nm Pt3Ni纳米晶的碳纳米管催化剂，以Pt3Ni为阴极的超低Pt燃料电池性能优异；首次制备了sub-1 nm Pt3Co合金催化剂，由其组装的燃料电池在3万圈方波循环后，初始质量活性保持率达91.5%，显著优于DOE 2025标准。这一系列超细合金催化剂有望在能源、催化、环境等领域中发挥重要作用。