OH scavenging pyridinic N for facile oxygen reduction reaction on free Pt surface.

Compared to hydrogen oxidation reaction, oxygen reduction reaction (ORR) is a sluggish reaction in the proton exchange membrane fuel cell. Many studies have focused on the development of complex synthesis methods for new catalysts. In this study, we introduce a simple catalyst layer preparation method using an additive based on physical mixing for facile ORR in acid media. N-doped carbon containing mainly pyridinic N was used as the additive in the Pt or PtCo catalyst layer. The adjacent pyridinic N near the Pt catalyst works as a Lewis base and removes hydroxyl ions from Pt, thus leading to the simultaneous suppression of Pt oxidation. Based on electrochemical and spectroscopic analyses, we found that pyridinic N reacts with hydroxyl ions and is oxidized. Consequently, Pt catalyst without Pt oxide species exhibited higher ORR activity than pristine Pt or PtCo catalyst.

Improved Redox Reaction of Lithium Polysulfides on the Interfacial Boundary of Polar CoC2 O4 as a Polysulfide Catenator for a High-Capacity Lithium-Sulfur Battery.

Invited for this month's cover is the group of Jaeyoung Lee at the Gwangju Institute of Science and Technology. The cover shows how the cobalt oxalates faced on the conductive carbon can act as an electrocatalyst to facilitate the redox reaction of lithium polysulfide at the cathode interface in lithium-sulfur batteries. The facilitated electrochemical redox reaction of lithium polysulfides was proved by a series of catenation reactions formed on the interfacial boundary area. The electrochemical performance was enhanced in terms of the specific capacity and long-term cycle performance from the facilitated electrochemical activity. The Full Paper itself is available at 10.1002/cssc.202002140.

Improved Redox Reaction of Lithium Polysulfides on the Interfacial Boundary of Polar CoC2 O4 as a Polysulfide Catenator for a High-Capacity Lithium-Sulfur Battery.

The performance of cobalt oxalate as an electrocatalyst in a lithium-sulfur battery (LSB) is improved owing to the suitable adsorbent properties of sulfur. The adsorption mechanism is elucidated by UV/Vis spectroscopy and surface analysis through X-ray photoelectron spectroscopy. Li2 S6 is converted into thiosulfate and polythionate by a catenation reaction on the interfacial boundary of CoC2 O4 contacted with carbon. Following this, the active polythionate and short-chained liquid lithium polysulfides (LiPS) bound to the cobalt surface are further reduced as CoC2 O4 reduces the overpotential to facilitate the LiPS redox reaction, leading to high specific capacity, lower self-discharge rate, and stable long-term cycling performance.

Electrochemical Properties of High Nickel Content Li(Ni0.7Co0.2Mn0.1)O2 with an Alumina Thin-Coating Layer as a Cathode Material for Lithium Ion Batteries.

The cathode material, high Nickel content Ni0.7Co0.2Mn0.1 (NCM), was synthesized by coprecipitation with NH4OH used as a complexing agent. The prepared materials are made in the formation of spherical particles of Li(Ni0.7Co0.2Mn0.1)O2 of several micrometers in diameter. Al2O3 was coated by an impregnation method and its content was gradually increased to 1, 2 and 5 wt%. As a result, 1 wt% coated Al2O3 compared to pristine NCM exhibited 82% and 80% retention rates at 5 C and 1 wt% Al2O3 coated NCM recovery at 0.2 C after 5 C showed 100%. In addition, capacity retention of 1 wt% NCM+Al gently decreased in 100 cycle life characteristics, and capacity retention of 95% or more was confirmed.

Effective Electrochemical Activation of Oleate-Residue-Fouled Pt Nanoparticle Catalysts for Methanol and Formic Acid Oxidation.

Platinum plays a crucial role in the field of basic electrochemistry, regeneration energy, and so on. Pt nanomaterials with well-controlled size and shape could be easily obtained from metal-oleate complexes. However, these nanoparticles (NPs) were electrochemically inactive because of the attached organic residue. This work has been reported as a robust method to remove the residues from the surface of Pt nanoparticle catalysts by the electrochemical treatment in alkaline media. After the electrochemical activation, the Pt nanoparticle catalysts show good catalytic behavior toward the electrochemical oxidation of methanol and formic acid.

Scalable Synthesis of Few-Layer MoS2 Incorporated into Hierarchical Porous Carbon Nanosheets for High-Performance Li- and Na-Ion Battery Anodes.

It is still a challenging task to develop a facile and scalable process to synthesize porous hybrid materials with high electrochemical performance. Herein, a scalable strategy is developed for the synthesis of few-layer MoS2 incorporated into hierarchical porous carbon (MHPC) nanosheet composites as anode materials for both Li- (LIB) and Na-ion battery (SIB). An inexpensive oleylamine (OA) is introduced to not only serve as a hinder the stacking of MoS2 nanosheets but also to provide a conductive carbon, allowing large scale production. In addition, a SiO2 template is adopted to direct the growth of both carbon and MoS2 nanosheets, resulting in the formation of hierarchical porous structures with interconnected networks. Due to these unique features, the as-obtained MHPC shows substantial reversible capacity and very long cycling performance when used as an anode material for LIBs and SIBs, even at high current density. Indeed, this material delivers reversible capacities of 732 and 280 mA h g(-1) after 300 cycles at 1 A g(-1) in LIBs and SIBs, respectively. The results suggest that these MHPC composites also have tremendous potential for applications in other fields.

Facile synthesis of one-dimensional iron-oxide/carbon hybrid nanostructures as electrocatalysts for oxygen reduction reaction in alkaline media.

One-dimensional iron-oxide/carbon hybrid nano tubular structures were synthesized via anodic aluminium oxide (AAO) template method. Highly unform iron oxide nanoparticles and carbon structures were formed simultaneously on the wall surface of the AAO template from an iron-oleate precursor by solventless thermal decomposition method. The 1D iron-oxide/carbon nanostructures were obtained after removing the AAO template. The typical size of the iron oxide nanoparticles was - 6 nm, and the nanoparticles had a crystalline structure of maghemite (γ-Fe2O3), which was determined from the HRTEM and X-ray diffraction (XRD). This nanocrystalline spinel structure could provide more active sites for oxygen reduction reaction (ORR) catalysis due to the higher specific surface area and numerous defects. As an ORR catalyst, the hybrid nanotubes showed higher limiting mass activity (8.8 A/g) and a more positive onset potential (-0.241 V, vs. Hg/HgCl) than iron oxide nanoparticles in alkaline media. This electrocatalytic activity of the nanocomposites is mainly attributed to the synergetic effects of the iron oxide nanoparticles and carbon matrix in the one-dimensional nanostructure.

A chemically activated graphene-encapsulated LiFePO4 composite for high-performance lithium ion batteries.

A composite of modified graphene and LiFePO4 has been developed to improve the speed of charging-discharging and the cycling stability of lithium ion batteries using LiFePO4 as a cathode material. Chemically activated graphene (CA-graphene) has been successfully synthesized via activation by KOH. The as-prepared CA-graphene was mixed with LiFePO4 to prepare the composite. Microscopic observation and nitrogen sorption analysis have revealed the surface morphologies of CA-graphene and the CA-graphene/LiFePO4 composite. Electrochemical properties have also been investigated after assembling coin cells with the CA-graphene/LiFePO4 composite as a cathode active material. Interestingly, the CA-graphene/LiFePO4 composite has exhibited better electrochemical properties than the conventional graphene/LiFePO4 composite as well as bare LiFePO4, including exceptional speed of charging-discharging and excellent cycle stability. That is because the CA-graphene in the composite provides abundant porous channels for the diffusion of lithium ions. Moreover, it acts as a conducting network for easy charge transfer and as a divider, preventing the aggregation of LiFePO4 particles. Owing to these properties of CA-graphene, LiFePO4 could demonstrate enhanced and stably long-lasting electrochemical performance.

Uniform graphene quantum dots patterned from self-assembled silica nanodots.

Graphene dots precisely controlled in size are interesting in nanoelectronics due to their quantum optical and electrical properties. However, most graphene quantum dot (GQD) research so far has been performed based on flake-type graphene reduced from graphene oxides. Consequently, it is extremely difficult to isolate the size effect of GQDs from the measured optical properties. Here, we report the size-controlled fabrication of uniform GQDs using self-assembled block copolymer (BCP) as an etch mask on graphene films grown by chemical vapor deposition (CVD). Electron microscope images show that as-prepared GQDs are composed of mono- or bilayer graphene with diameters of 10 and 20 nm, corresponding to the size of BCP nanospheres. In the measured photoluminescence (PL) spectra, the emission peak of the GQDs on the SiO(2) substrate is shown to be at ∼395 nm. The fabrication of GQDs was supported by the analysis of the Raman spectra and the observation of PL spectra after each fabrication step. Additionally, oxygen content in the GQDs is rationally controlled by additional air plasma treatment, which reveals the effect of oxygen content to the PL property.

Particle size control of Pd/C for improved electrocatalytic activity in a formic acid oxidation.

Carbon-supported Pd electrocatalyst is prepared by an improved aqueous impregnation method applying a reducing agent of HCHO and an acidic sedimentation promoter of HCl. We investigate the effect of a solution pH on the zeta potential of both Pd particles and carbon support. The opposite sign of zeta potential results in uniform dispersion of Pd on carbon surface without aggregation problem. TEM analysis shows that optimal solution pH of 4.27 adjusted by NaOH provides a mean particle diameter of 3.2 nm with narrow size distribution. Cyclic voltammograms indicate that home-made Pd/C catalyst exhibits significantly higher electrochemical active surface area and better stability compared with commercial 40 wt.% Pd/C in a formic acid oxidation.

Electrochemical detection of dopamine in the presence of ascorbic acid using graphene modified electrodes.

Dopamine plays a significant role in the function of human metabolism. It is important to develop sensitive sensor for the determination of dopamine without the interference by ascorbic acid. This paper reports the synthesis of graphene using a modified Hummer's method and its application for the electrochemical detection of dopamine. Electrochemical measurements were performed at glassy carbon electrode modified with graphene via drop-casting method. Cyclic voltammogram of ferri/ferrocyanide redox couple at graphene modified electrode showed an increased current intensity compared with glassy carbon electrode and graphite modified electrode. The decrease of charge transfer resistance was also analyzed by electrochemical impedance spectroscopy. The capacity of graphene modified electrode for selective detection of dopamine was confirmed in a sufficient amount of ascorbic acid (1 mM). The observed linear range for the determination of dopamine concentration was from 4 microM to 100 microM. The detection limit was estimated to be 2.64 microM.