Ultra-low overpotential and high rate capability in Li–O2 batteries through surface atom arrangement of PdCu nanocatalysts (original) (raw)

PdCu bimetallic nanoparticles (NPs) having mixed disordered facecentered cubic (fcc) and ordered body-centered cubic (B2-type) phases enhance the kinetics of oxygen reduction/evolution reaction by significant reduction of overpotentials, which leads to the superb round-trip efficiency of $80%. In addition, the PdCu catalyst demonstrates a remarkable cyclic enhancement in stability and an outstanding rate capability even at a high current density of 5000 mA g carbon À1. Our first-principles calculations demonstrate that the low overpotentials of the PdCu catalyst are strongly correlated with the weak LiO 2 adsorption strength, caused by electron transfer from Cu to the top-layer Pd atoms on the surface. Recently, Li-O 2 batteries have emerged as promising technology for electric vehicles and energy storage systems due to their high theoretical energy density (gravimetric energy density). The energy density of Li-ion batteries is between 100 and 200 W h kg À1 , which is far from the target of matching the practical energy density of gasoline (1700 W h kg À1). However, Li-O 2 batteries are predicted to be an alternative fuel because their theoretical energy density is as high as 11 680 W h kg À1. 1,2 At present, there are many obstacles limiting practical applications of Li-O 2 batteries, including poor power capability, 3,4 short cycle life, 5 and low energy efficiency 6 mainly caused by their sluggish kinetics. Apparently, to improve these kinetics, a rational design of electrocatalysts toward improving oxygen reduction reaction (ORR, during discharge) or oxygen evolution reaction (OER, during charging) must be devised. Numerous researchers have investigated various materials, including porous carbons, metal oxides, and metals, for use as the ORR and/or OER catalysts. 7 Among them, noble metal-based catalysts are known to have higher discharge voltages than those of metal oxides. 8 In particular, bimetallic catalysts that consist of two distinct noble metals exhibit enhanced catalytic reactivity due to their ensemble, ligand, and geometric effects. 9 Shao-Horn et al. 10 reported that bifunctional catalysts containing Au, which is highly active in the ORR, and Pt, which is highly active in the OER, demonstrated an enhanced round-trip efficiency. We note, however, that other electrochemical properties important for practical applications, such as discharge rate capability and cycle performance, still remain to be improved. Moreover, the studies on catalysts which can simultaneously improve cycle life and power capability, as well as round-trip efficiency, have been seldom reported. The atomic arrangement of such bimetallic catalysts exerts a signicant inuence on reaction activity. Sun et al. 11 found that the catalytic activity of FePt nanoparticles (NPs) depends on