形貌可控的铂类贵金属氧还原电催化剂研究进展

Recent Advances on Shape-controlled Pt-based Noble-metal Electrocatalysts for Oxygen Reduction Reaction

金属-空气电池是一类以金属燃料作为负极活性物质,空气中的氧气作为正极活性物质,正负极活性物质反应产生的化学能通过电化学反应而非燃烧反应转化成电能的环境友好型燃料电池。金属-空气电池的成功运行往往依赖于高效的空气电极,氧还原过程作为空气电极的主反应,还原过程中产生的高过电位严重制约着金属-空气电池的大规模应用。目前金属-空气电池阴极普遍使用昂贵的Pt/C氧还原催化剂材料来降低氧还原过程的高过电位,最大程度地减少电池电压以及输出功率的损失。氧还原催化剂材料的研究重点是寻找更高效、廉价的催化剂。目前常见的氧还原催化剂主要包含铂类贵金属、过渡金属氧化物和硫化物以及碳基非金属复合材料,其中铂类贵金属型氧还原催化剂凭借其优异的氧还原催化性能得到广泛关注。随着化学合成手段的不断发展,越来越多的异质结构铂类贵金属型氧还原催化剂被合成,基于各组分之间独特的协同作用,其往往表现出优于单一组分的催化性能,近几年对铂类贵金属型氧还原催化剂的研究主要集中在以下两个方面:(1)探究铂类贵金属催化剂表面元素组成及原子排布与其催化活性之间的关系,例如,研究纯铂纳米晶的晶面指数与其氧还原催化性能之间的关系;(2)设计特殊结构的铂类催化剂来达到优化氧还原催化剂催化活性和降低材料生产成本的目的,例如,在廉价核材料上通过异质外延生长的方式沉积铂壳层,可大大提升铂原子的催化效率。本文归纳了形貌可控的铂类贵金属氧还原催化剂的研究进展,分别对规则多面体型纯铂及铂类合金纳米晶,特殊结构铂类合金纳米晶氧还原催化剂进行了详细介绍。此外,为了更好地理解氧还原的催化机制,本文就氧还原过程的动力学与热力学原理进行了简单总结。由于铂类贵金属氧还原催化剂的形貌对其氧还原活性影响很大,为了更好地说明催化剂形貌的设计与合成原理,本文还补充说明了纳米晶体的生长机制。最后,简要总结了铂类贵金属型氧还原催化剂未来的研究重点。

Metal-air batteries are pertained to an environment-friendly fuel cell with metal fuel as active substance for cathode and oxygen in air as active substance for anode,which directly convert chemical energy of fuel and oxidant into electric energy via electrochemical reaction rather than combustion reactions.The successful operation of metal-air batteries highly relies on efficient air-electrode,the high overpotential generated during the oxygen reduction has seriously restricted their widespread application.To cure the above problem,the air-electrode generally utilizes noble-metal Pt/C electrocatalyst to trigger the oxygen reduction reaction(ORR)as close to the reversible conditions as possible(i.e.with an overpotential as close to zero as possible).Searching for more efficient and low-cost electrocatalysts for ORR is presently an urgent task of study.Common oxygen reduction catalysts mainly include Pt-based noble metals,transition metal oxides and sulfides,and carbon-based composites,etc.Among them,Pt-based noble-metal electrocatalysts are the state-of-the-art electrocatalysts for ORR.The continuous development of chemical synthesis methods contribute to the prosperity of research in Pt-based noble-metal electrocatalysts with heterogeneous structures,which exhibit excellent catalytic activity due to the synergistic effect.Currently researches on Pt-based noble-metal electrocatalysts mainly revolve round the following two aspects.Ⅰ.Explore the relationship between catalytic activity and elemental composition or atomic arrangement of Pt-based noble-metal electrocatalysts,for instance,the mechanistic basis of the interaction of the Miller indices of Pt single namocrystal and its catalytic activity.Ⅱ.Design unique structure to optimize catalytic activity and reduce the costs for Pt-based noble-metal electrocatalysts.For example,depositing a thin Pt-based shell on an inexpensive core can remarkably ameliorate the catalytic efficiency of Pt atoms.This review aims to summarize the recent advances in shape-controlled Pt-based noble-metal electrocatalysts for ORR,with a particular concern over Pt polyhedra,Pt alloys polyhedra,and Pt-based catalysts with unique structure.Furthermore,the thermodynamics and kinetics of ORR are expounds,aiming at providing a better understanding of catalytic mechanism of oxygen reduction.As is known to all,the morphology of Pt-based noble-metal electrocatalysts exert a serious influence on their activity,therefore,the growth mechanisms of noble-metal nanocrystals are illustrated as well for better explaining the principles of morphology design and synthesis.Eventually,the future development direction of Pt-based noble-metal oxygen reduction catalysts is prospected.