C_xN_y particles@N-doped porous graphene: a novel cathode catalyst with a remarkable cyclability for Li–O₂ batteries

Abstract

Despite the intrinsic advantages of ultra-high theoretical capacity and energy density of lithium-O2 batteries, there remain several critical issues to be resolved, especially the two concerning poor cyclability and rate capability. In this work, CxNy particles@N-doped porous graphene (CxNy@NPG) with a novel three-dimensional architecture is successfully synthesized via a simple template method and employed as the cathode catalyst of Li-O2 batteries. It is surprisingly found that the as-synthesized CxNy@NPG cathode not only demonstrates a remarkable cycling performance of 200 cycles at 1000 mA g-1 but also an intriguing high-rate capability with 8892 mA h g-1 at 1000 mA g-1, both of which can be attributed to a synergistic effect between the unique 3D porous structure and an effective N-doping. Specifically, it is believed that the unique porous 3D structure will, on one hand, build numerous microchannels, thus facilitating rapid O2 diffusion, and on the other hand, provide sufficient storage space to accommodate adequate discharge products. Indispensably, it is also believed that the N-doped porous graphene enables improved bifunctional catalytic activities towards both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), thus decreasing the discharge/charge overpotential, and reducing undesired side reactions. It is anticipated that the new 3D porous CxNy@NPG provides an inspiring route to design long cycling and high-rate performance cathodes for Li-O2 batteries.

Status Quo on Graphene Electrode Catalysts for Improved Oxygen Reduction and Evolution Reactions in Li-Air Batteries

“…The results are comparable to the commercial Pt noble metal catalysts, and far better than the rGO and reduced holey GO at the relative comparison in the given experimental conditions tested for Li-O 2 batteries [107]. CxNy particles at N-doped 3D porous graphene have also been prepared and demonstrated for successful air cathode with 8892 mA h g −1 at 1000 mA g −1 [108].…”

Application of functionalized graphene in Li–O2 batteries

“…The authors considered that the N doping can offer high adsorption energy towards LiO 2 on graphene, which guaranteed the smooth running of the electrochemical reduction and disproportionation of LiO 2 through surfacebased mechanism; while the weak adsorption of LiO 2 on undoped graphene could result in LiO 2 dissolution and thus form Li 2 O 2 with toroidal morphologies via a solution reaction. In contrast, Zeng et al [74] reported that Li 2 O 2 existed in the form of particles in N-doped graphene and Wu et al [60] also found that the surface of C x N y particles@N-doped porous graphene electrode was suffused with toroidal-shaped Li 2 O 2 discharge products. Therefore, more in-depth studies are needed to determine the effect of N doping on morphological differences.…”

“…Therefore, the NPGAs possessed enhanced ORR and OER kinetics (figures 3(b) and (c)). Wu et al [60] synthesized CxNy @N-doped porous graphene (CxNy@NPG) using urea as nitrogen sources via a sacrificial template method followed by a heat treatment (figure 3(d)). The 3D structure with numerous microchannels and large specific surface areas facilitated O 2 diffusion and accommodation of discharge products (figures 3(e) and (f)).…”

Recent Progress on Catalysts for the Positive Electrode of Aprotic Lithium-Oxygen Batteries †

“…Carbon materials generally possess many merits such as excellent electrical conductivity, good chemical and thermal stability, light weight, high surface area, sufficient resources, and low cost [41,42]. As a result, various carbon materials, including activated carbon [43], carbon paper [44,45], carbon nanotubes (CNT) [46][47][48][49], graphene [42,[50][51][52][53][54], and mesoporous carbon [55][56][57][58], have been used as the positive electrode for Li-O 2 batteries. In this section, various strategies to design high-performance carbon positive-electrode catalysts are discussed, including structural design, heteroatom doping, defect modification, and synergy of the above three strategies.…”