Enhanced oxygen reduction and evolution by in situ decoration of hematite nanoparticles on carbon nanotube cathodes for high-capacity nonaqueous lithium–oxygen batteries

Abstract

Lithium-oxygen (Li-O 2 ) batteries are considered to be the next generation energy storage technology due to their extremely high theoretical energy density and the simplicity of the battery cells. However, a large energy density can be obtained only with a slow discharge-charge rate, and quickly decreases upon cycling. These drawbacks can be attributed to the large overpotential and sluggish kinetics of the oxygen reduction and evolution reactions. To overcome the current problems, recent research has focused on developing catalysts made of inexpensive metal oxides and carbonaceous materials in addition to precious metals, but the role of non-precious metal catalysts in the battery performance is still largely unexplored. Here we present kinetic studies and comparative evaluation of enhanced oxygen reduction and evolution reactions with carbon nanotube (CNT) arrays containing in situ decorated a-Fe 2 O 3 nanoparticles as both a binder-free catalyst and a cathode for nonaqueous Li-O 2 batteries. Our Fe 2 O 3 -decorated CNTs greatly helped to form Li 2 O involving the four-electron reduction pathway in addition to Li 2 O 2 commonly formed via the one/two-electron reduction pathway, and thereby delivered a very large capacity of 26.5 A h g À1 at the 1 st discharge and a relatively long cycling performance (48 cycles with a capacity limit of 1.5 A h g À1 ). Unique and branch-like nanocrystalline Li 2 O and Li 2 O 2 after discharge would have lowered the overpotential for the oxygen evolution reaction. Our detailed compositional and morphological studies will be of great help to further improve the cycling performance as well as develop better non-precious metal catalysts and electrodes for Li-O 2 batteries.

Paramecium‐Like Iron Oxide Nanotubes as a Cost‐Efficient Catalyst for Nonaqueous Lithium‐Oxygen Batteries

“…[56] After full discharge at 500 mA g À1 ,t he surfaces of the three cathodes are coveredb yadisc-like solid product (Figure 5d-f), which is consistent with the Li 2 O 2 morphology reported previously. [11,20,21,23,32,40,47,57,58] In detail, the solid products arem ade up of split layers with rough boundaries, but the size of every particlei sd ifferentf or the three cathodes.F or the SP cathode,t he average size of the Li 2 O 2 particles is the largestw ith ad iametero fa pproximately 800-900 nm, whereas for the FNT/SP cathode,t he diameter of the Li 2 O 2 particles is approximately 400-500 nm. Thes maller discharge product arises mainly from the uniform distribution of oxygen and electrolyte with the help of the FNTs in the cathode,a nd thus there are abundant active sites for the discharge product deposition at the same time.T he morphologies of the three cathodes after charging are presented in Figure 5g-i.…”

“….Ah igh-capacity nonaqueousL i-O 2 battery with enhanced oxygenr eductiona nd evolution utilizing ac atalyst prepared by the in situ decoration of hematite nanoparticles on CNTs was presented by Jeee tal. [47] Their battery delivered av ery high capacity of 26.5 Ah g À1 in the first cycle andarelatively good cycling performance (48 cyclesw ith ac apacity limit of 1.5 Ah g À1 ). Wu et al [23] synthesized Fe 2 O 3 nanoparticles supported on Vulcan XC-72 carbon as acatalyst for the OER and obtained an onaqueous Li-O 2 battery with an excellent cycling stability ( % 50 cycles with ac apacity of 500 mAh g À1 ).…”

One-step synthesis of nitrogen-iron coordinated carbon nanotube catalysts for oxygen reduction reaction

“…4b). [5,35,36] The peak shift of the surface Fe 3+ in Fe-A/P-CNT toward a lower binding energy also indicate the stronger coordination of iron with pyridinic nitrogen. [6,35,36] RDE tests of Fe-A/P-CNT at different rotational speeds were performed (Fig.…”

“…5b). The Koutecky-Levich plots [5,37] were obtained by using −1 = −1 + −1 −1/2 and = 0.62 2/3 −1/6 , where −1 is kinetic limiting current density, ω is the rotational speed, n is the number of electrons transferred, F is the Faraday constant (F = 96,500 C mol -1 ), C is the bulk concentration of O2 (C = 1.2×10 -6 mol cm -3 in 0.1 M KOH), D…”

“…Oxygen reduction reaction (ORR) is a key reaction occurred in many electrochemical cells such as fuel cells and metal-oxygen batteries. [1][2][3][4][5][6] Sluggish ORR typically necessitates precious metal based catalysts whose high prices have been major challenges for commercial applications. [1,[7][8][9] Over the past several years, various non-precious metal based nanomaterials have been suggested to reduce the cost of the catalysts, but these catalysts involve complicated synthesis processes, significantly increasing the manufacturing cost.…”