Ionic liquid (IL) modified reduced graphene oxide (rGO-IL) nanosheets anchoring manganese oxide (Mn 3 O 4 ) are synthesized via a facile solution-based growth mechanism and applied to a Zn-air battery as an effective electrocatalyst for the oxygen reduction reaction (ORR). In this study, the IL moiety in these composites increases not only the conductivity of the system, but also the electrocatalytic activity compared to pristine rGO, together with the synergic effect of facilitating the ORR with the intrinsic catalytic activity of Mn 3 O 4 . Based on the Koutecky-Levich plot, we suggest that the ORR pathway of these composites is tunable with the relative amount of Mn 3 O 4 nanoparticles supported onto the graphene sheets; for example, the ORR mechanism of the system with a lower Mn 3 O 4 (19.2%) nanoparticle content is similar to a Pt/C electrode, i.e., a one-step, quasi-4-electron transfer, unlike that with a higher Mn 3 O 4 (52.5%) content, which undergoes a classical two-step, 2-electron pathway. We also demonstrate the potential of these hybrid rGO-IL/Mn 3 O 4 nanoparticles as efficient catalysts for the ORR in the Zn-air battery with a maximum peak power density of 120 mW cm À2 ; a higher performance than that from commercial cathode catalysts.

A hybrid electrode consisting of an electric double-layer capacitor of graphene nanosheets and a pseudocapacitor of the conducting polymer polyaniline exhibits a synergistic effect with excellent electrochemical performance for flexible thin film supercapacitors. This hybrid supercapacitor is constructed by a nanoscale blending method of layer-by-layer (LbL) assembly based on the electrostatic interactions between positively charged polyaniline (PANi) and negatively charged graphene oxide (GO) nanosheets. The hybrid electrode provides not only improved electronic conductivity through the intimate contact with the graphene nanosheet, but also enhanced chemical stability during the charge-discharge process. We also investigated the dependence of the electrochemical performance on the various parameters of LbL assembly such as the number of bilayers and the post-thermal and chemical treatments that could affect the degree of reduction of GO and PANi. We found that after thermal treatment, the LbL-assembled thin film of PANi with GO nanosheets exhibited an excellent gravimetric capacitance of 375.2 F g À1 at a discharge current density of 0.5 A g À1 that outperformed many other hybrid supercapacitors reported to date. The hybrid supercapacitor maintained its capacity up to 90.7% over 500 cycles at a high current density of 3.0 A g À1 . This study opens up the possibility for the production of diverse graphene-based hybrid nanocomposites that are promising for future flexible supercapacitors.

A facile approach to the surface modification of spinel LiNi 0.5 Mn 1.5 O 4 (LNMO) cathode active materials for high-voltage lithium ion batteries is demonstrated. This strategy is based on nanoarchitectured polyimide (PI) gel polymer electrolyte (GPE) coating. The PI coating layer successfully wrapped a large area of the LNMO surface via thermal imidization of 4-component (pyromellitic dianhydride/biphenyl dianhydride/phenylenediamine/oxydianiline) polyamic acid. In comparison to conventional metal oxide-based coatings, distinctive features of the unusual PI wrapping layer are the highly continuous surface coverage with nanometre thickness ($10 nm) and the provision of facile ion transport. The nanostructure-tuned PI wrapping layer served as an ionconductive protection skin to suppress the undesired interfacial side reactions, effectively preventing the direct exposure of the LNMO surface to liquid electrolyte. As a result, the PI wrapping layer played a crucial role in improving the high-voltage cell performance and alleviating the interfacial exothermic reaction between charged LNMO and liquid electrolyte. Notably, the superior cycle performance (at 55 C) of the PI-wrapped LNMO (PI-LNMO) was elucidated in great detail by quantitatively analyzing manganese (Mn) dissolution, cell impedance, and chemical composition (specifically, lithium fluoride (LiF)) of byproducts formed on the LNMO surface.

High-theoretical capacity and low working potential make silicon ideal anode for lithium ion batteries. However, the large volume change of silicon upon lithiation/delithiation poses a critical challenge for stable battery operations. Here, we introduce an unprecedented design, which takes advantage of large deformation and ensures the structural stability of the material by developing a two-dimensional silicon nanosheet coated with a thin carbon layer. During electrochemical cycling, this carbon coated silicon nanosheet exhibits unique deformation patterns, featuring accommodation of deformation in the thickness direction upon lithiation, while forming ripples upon delithiation, as demonstrated by in situ transmission electron microscopy observation and chemomechanical simulation. The ripple formation presents a unique mechanism for releasing the cycling induced stress, rendering the electrode much more stable and durable than the uncoated counterparts. This work demonstrates a general principle as how to take the advantage of the large deformation materials for designing high capacity electrode.

Lithium ion movement was accelerated by enlarging the interlayer distance of graphite as well as by polarizing its surface charge. As a result, the rate performances of lithium ion batteries were significantly enhanced.

This study reports a simple method of integrating electroactive gold nanoparticles (Au NPs) with graphene oxide (GO) nanosheet support by layer‐by‐layer (LbL) assembly for the creation of 3‐dimensional electrocatalytic thin films that are active toward methanol oxidation. This approach involves the alternating assembly of two oppositely charged suspensions of Au NPs with GO nanosheets based on electrostatic interactions. The GO nanosheets not only serve as structural components of the multilayer thin film, but also potentially improve the utilization and dispersion of Au NPs by taking advantages of the high catalytic surface area and the electronic conduction of graphene nanosheets. Furthermore, it is found that the electrocatalytic activity of the multilayer thin films of Au NPs with graphene nanosheet is highly tunable with respect to the number of bilayers and thermal treatment, benefiting from the advantageous features of LbL assembly. Because of the highly versatile and tunable properties of LbL assembled thin films coupled with electrocatalytic NPs, we anticipate that the general concept presented here will offer new types of electroactive catalysts for direct methanol fuel cells.

Rapid growth of mobile and even wearable electronics is in pursuit of high-energy-density lithium-ion batteries. One simple and facile way to achieve this goal is the elimination of nonelectroactive components of electrodes such as binders and conductive agents. Here, we present a new concept of monocomponent electrodes comprising solely electroactive materials that are wrapped with an insignificant amount (less than 0.4 wt %) of conducting polymer (PEDOT:PSS or poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate)). The PEDOT:PSS as an ultraskinny surface layer on electroactive materials (LiCoO2 (LCO) powders are chosen as a model system to explore feasibility of this new concept) successfully acts as a kind of binder as well as mixed (both electrically and ionically) conductive film, playing a key role in enabling the monocomponent electrode. The electric conductivity of the monocomponent LCO cathode is controlled by simply varying the PSS content and also the structural conformation (benzoid-favoring coil structure and quinoid-favoring linear or extended coil structure) of PEDOT in the PEDOT:PSS skin. Notably, a substantial increase in the mass-loading density of the LCO cathode is realized with the PEDOT:PSS skin without sacrificing electronic/ionic transport pathways. We envisage that the PEDOT:PSS-skinned electrode strategy opens a scalable and versatile route for making practically meaningful binder-/conductive agent-free (monocomponent) electrodes.

Reactive oxygen species or superoxide (O 2 − ), which damages or ages biological cells, is generated during metabolic pathways using oxygen as an electron acceptor in biological systems. Superoxide dismutase (SOD) protects cells from superoxide-triggered apoptosis by converting superoxide to oxygen and peroxide. Lithium−oxygen battery (LOB) cells have the same aging problems caused by superoxide-triggered side reactions. We transplanted the function of SOD of biological systems into LOB cells. Malonic acid-decorated fullerene (MA-C 60 ) was used as a superoxide disproportionation chemocatalyst mimicking the function of SOD. As expected, MA-C 60 as the superoxide scavenger improved capacity retention along charge/discharge cycles successfully. A LOB cell that failed to provide a meaningful capacity just after several cycles at high current (0.5 mA cm −2 ) with 0.5 mAh cm −2 cutoff survived up to 50 cycles after MA-C 60 was introduced to the electrolyte. Moreover, the SOD-mimetic catalyst increased capacity, e.g., more than a 6-fold increase at 0.2 mA cm −2 . The experimentally observed toroidal morphology of the final discharge product of oxygen reduction (Li 2 O 2 ) and density functional theory calculation confirmed that the solution mechanism of Li 2 O 2 formation, more beneficial than the surface mechanism from the capacity-gain standpoint, was preferred in the presence of MA-C 60 .