Doped graphene supercapacitors

Heteroatom-doped graphitic frameworks have received great attention in energy research, since doping endows graphitic structures with a wide spectrum of properties, especially critical for electrochemical supercapacitors, which tend to complement or compete with the current lithium-ion battery technology/devices. This article reviews the latest developments in the chemical modification/doping strategies of graphene and highlights the versatility of such heteroatom-doped graphitic structures. Their role as supercapacitor electrodes is discussed in detail. This review is specifically focused on the concept of material synthesis, techniques for electrode fabrication and metrics of performance, predominantly covering the last four years. Challenges and insights into the future research and perspectives on the development of novel electrode architectures for electrochemical supercapacitors based on doped graphene are also discussed. © 2015 IOP Publishing Ltdclose0

Surface controlled generation of reactive radicals from persulfate by carbocatalysis on nanodiamonds

Production of radicals by metal-free catalysis is expected to offer a promising oxidative reaction for remediation of emerging contaminants. In this study, novel metal-free activation of persulfate (PS) on annealed nanodiamonds (ANDs) was investigated, which demonstrated superior performances in decomposition of various pollutants to conventional metal-based catalysis. Comprehensive investigations on the effects of reaction parameters, such as solution pH, reaction temperature, initial phenol concentration, catalyst loading, PS usage, the presence of chlorine ions and humic acid, on phenol degradation were carried out. In addition, nanodiamond (ND) material optimization and reusability were also studied. Electron paramagnetic resonance (EPR) and selective organic degradation unraveled that the PS/AND system may produce both hydroxyl radicals (·OH) and sulfate radicals (SO4 · -), initialized from oxidizing water molecules on the nanodiamond surface. The carbocatalysts served as an excellent electron tunnel to facilitate the charge transfer from water or hydroxide ions to PS, and the oxidized intermediates may play a crucial role in PS activation. Electrochemical analyses in PS oxidant solution and oxygen reduction reaction (ORR) were carried out to understand OO bond activation by the metal-free catalysis. This study provides an environmentally benign and highly efficient oxidative reaction system with reactive radicals along with insights into the metal-free PS activation process

Synthesis of supported nickel nanoparticles via a nonthermal plasma approach and its application in CO2 reforming of methane

A microwave plasma treatment was applied to obtain not only a desired strong metal-support interaction but also well-dispersed nickel nanoparticles supported on ceria. The catalytic properties of these supported nanoparticles were tested in CO reforming of methane. The plasma-treated Ni/CeO catalysts showed enhanced turnover frequencies (TOFs), normalized by Ni on the surface, as compared with the thermally calcined samples. The Ni/CeO treated under plasma with low Ni loading gave an enhanced TOF of 9.5 s (700 °C, 50% CH and 50% CO, and 1 atm) as compared with the thermally calcined catalyst (8.7 s). Increasing the Ni loading on the plasma-treated Ni/CeO catalysts gave an improved TOF (10.4 s) which was stable with time, while the TOF was observed to drop by a factor of 2 relative to the optimal TOF on the thermally calcined catalyst after 5 h. For the plasma-treated samples, concurrent treatment of both the uncalcined ceria support and the loaded metal precursor generated strong metal-support interaction and formation of well-dispersed Ni particles, resulting in a superior and stable TOF with time. In the case of thermally calcined catalysts, the weak metal-support interaction and the agglomeration of Ni clusters together with the migration of the Ni particles into the ceria support hindered the accessibility of active nickel sites, resulting in deactivation of the materials during reaction. Moreover, high-resolution transmission electron microscopy, high-angle annular dark-field scanning transmission electron microscopy, H temperature-programmed reduction, and X-ray photoelectron spectroscopy yielded a clear picture of the impact of microwave plasma treatment on the nickel particle size, shape, distribution, and interaction with the ceria support