Core–Shell-Structured Low-Platinum Electrocatalysts for Fuel Cell Applications

Pt-based catalysts are the most efficient catalysts for low-temperature fuel cells. However, commercialization is impeded by prohibitively high costs and scarcity. One of the most effective strategies to reduce Pt loading is to deposit a monolayer or a few layers of Pt over other metal cores to form core–shell-structured electrocatalysts. In core–shell-structured electrocatalysts, the compositions of the core can be divided into five classes: single-precious metallic cores represented by Pd, Ru, and Au; single-non-precious metallic cores represented by Cu, Ni, Co, and Fe; alloy cores containing 3d, 4d or 5d metals; and carbide and nitride cores. Of these, researchers have found that carbide and nitride cores can yield tremendous advantages over alloy cores in terms of cost and promotional activities of Pt shells. In addition, desirable shells with reasonable thicknesses and compositions have been recognized to play a dominant role in electrocatalytic performances. And recently, researchers have also found that the catalytic activity of core–shell-structured catalysts is dependent on the binding energy of the adsorbents, which is determined by the d-band center of Pt. The shifting of this d-band center in turn is mainly affected by strain and electronic effects, which can be adjusted by adjusting core compositions and shell thicknesses of catalysts. In the development of these core–shell structures, optimal synthesis methods are of primary concern because they directly determine the practical application potential of the resulting electrocatalysts. And in this article, the principles behind core–shell-structured low-Pt electrocatalysts and the developmental progresses of various synthesis methods along with the traits of each type of core and its effects on Pt shell catalytic activities are discussed. In addition, perspectives on this type of catalyst are discussed and future research directions are proposed.