热处理温度对Pt_(3)Co二元金属催化剂氧还原性能影响及泛函密度理论研究

Effect of heat treatment temperature on the Pt_(3)Co binary metal catalysts for oxygen reduced reaction and DFT calculations

制备低成本、高活性、高稳定性的铂(Pt)基氧还原反应(ORR)催化剂是质子交换燃料电池(PEMFC)大规模商业化应用的关键。以钴(Co)等非贵金属与Pt掺杂制备二元合金PtM催化剂不仅可以减少Pt用量,还可以获得高于Pt金属催化剂的ORR催化活性和稳定性。本研究使用浸渍还原法制备碳载铂钴ORR催化剂,通过控制热处理还原温度来控制纳米颗粒的结构、晶相、尺寸等,从而改善催化剂的ORR性能。XRD、TEM和电化学分析结果综合表明,热处理温度对纳米颗粒合金度和平均粒径有显著的影响,平均粒径和合金度随着热处理温度升高而增大。通过控制热处理温度可以获得粒径与合金度之间的最优值从而提高催化剂氧还原活性,实验表明,800℃是低粒径和高合金度的平衡点,在所有制备的催化剂中有最高的质量活性(0.41 A/mg_(Pt))和稳定性。进一步的密度泛函理论(DFT)计算表明高合金度的Pt_(3)Co结构表面可以降低速控步反应势垒,提高ORR活性。

Synthesis of low-cost,high-activity and high-stability Pt-based catalysts is of great importance to the large commercialization of proton exchange membrane fuel cell(PEMFC).Doping non-precious metals such as cobalt(Co)with Pt is attractive due to the reduced depletion of Pt and,more importantly,the enhanced activity on the oxygen reduction reaction(ORR)compared with pure Pt.In this work,carbon-supported platinum-cobalt nanoparticles(NPs)were prepared by the impregnation reduction method for the ORR catalyst.By changing the heat treatment temperature,the structure,the crystal phase and the size of the Pt_(3)Co nanoparticles could be controlled.TEM and XRD characterizations show that larger size NPs with higher alloying degree are obtained at higher temperature.The electrochemical results demonstrate that the Pt_(3)Co NPs at 800℃have the highest mass activity(0.41 A/mg_(Pt))and the best stability among all the samples due to their lower particle size and higher alloying degree.Further Density functional theory(DFT)calculation shows that the surface of the Pt_(3)Co structure with high alloying degree can reduce the rate-determining step barrier and improve the ORR activity.