Efficient Oxygen Reduction Electrocatalyst Based on Edge-Nitrogen-Rich Graphene Nanoplatelets: Toward a Large-Scale Synthesis

The large-scale synthesis of nitrogen doped graphene (N-graphene) with high oxygen reduction reaction (ORR) performance has received a lot of attention recently. In this work, we have developed a facile and economical procedure for mass production of edge-nitrogen-rich graphene nanoplatelets (ENR-GNPs) by a combined process of ball milling of graphite powder (GP) in the presence of melamine and subsequent heat treatment. It is found that the ball milling process can not only crack and exfoliate pristine GP into edge-expanded nanoplatelets but also mechanically activate GP to generate appropriate locations for N-doping. Analysis results indicate that the doped N atoms mainly locate on the edge of the graphitic matrix, which contains ca. 3.1 at.% nitrogen content and can be well-dispersed in aqueous to form multilayer nanoplatelets. The as-prepared ENR-GNPs electrocatalyst exhibits highly electrocatalytic activity for ORR due to the synergetic effects of edge-N-doping and nanosized platelets. Besides, the stability and methanol tolerance of ENR-GNPs are superior to that of the commercial Pt/C catalyst, which makes the nanoplatelets a promising candidate for fuel cell cathode catalysts. The present approach opens up the possibility for simple and mass production of N-graphene based electrocatalysts in practice

Identifying the Active Site in Nitrogen-Doped Graphene for the VO²⁺/VO₂⁺ Redox Reaction

Nitrogen-doped graphene sheets (NGS), synthesized by annealing graphite oxide (GO) with urea at 700–1050 °C, were studied as positive electrodes in a vanadium redox flow battery. The NGS, in particular annealed at 900 °C, exhibited excellent catalytic performance in terms of electron transfer (ET) resistance (4.74 ± 0.51 and 7.27 ± 0.42 Ω for the anodic process and cathodic process, respectively) and reversibility (Δ<i><i>E</i></i> = 100 mV, <i>I</i>_pa/<i>I</i>_pc = 1.38 at a scan rate of 50 mV s^–1). Detailed research confirms that not the nitrogen doping level but the nitrogen type in the graphene sheets determines the catalytic activity. Among four types of nitrogen species doped into the graphene lattice including pyridinic-N, pyrrolic-N, quaternary nitrogen, and oxidic-N, quaternary nitrogen is verified as a catalytic active center for the [VO]²⁺/[VO₂]⁺ couple reaction. A mechanism is proposed to explain the electrocatalytic performance of NGS for the [VO]²⁺/[VO₂]⁺ couple reaction. The possible formation of a N–V transitional bonding state, which facilitates the ET between the outer electrode and reactant ions, is a key step for its high catalytic activity

A Simple High-Flux Switchable VUV Lamp Based on an Electrodeless Fluorescent Lamp for SPI/PAI Mass Spectrometry

Single-photon ionization (SPI) is a unique soft ionization technique for organic analysis. A convenient high-flux vacuum ultraviolet (VUV) light source is a key precondition for wide application of SPI techniques. In this study, we present a novel VUV lamp by simply modifying an ordinary electrodeless fluorescent lamp. By replacing the glass bulb with a stainless steel bulb and introducing 5% Kr/He (v/v) as the excitation gas, an excellent VUV photon flux over 4.0 × 1014 photons s–1 was obtained. Due to its rapid glow characteristics, the VUV lamp can be switched on and off instantly as required by detection, ensuring the stability and service life of the lamp. To demonstrate the performance of the new lamp, the switchable VUV lamp was coupled with an SPI-mass spectrometer, which could be changed to photoinduced associative ionization (PAI) mode by doping gaseous CH2Cl2 to initiate an associative ionization reaction. Two types of volatile organic compounds sensitive to SPI and PAI, typically benzene series and oxygenated organics, respectively, were selected as samples. The instrument exhibited a high detection sensitivity for the tested compounds. With a measurement time of 11 s, the 3σ limits of detection ranged from 0.33 to 0.75 pptv in SPI mode and from 0.03 to 0.12 pptv in PAI mode. This study provides an extremely simple method to assemble a VUV lamp with many merits, e.g., portability, robustness, durability, low cost, and high flux. The VUV lamp may contribute to the development of SPI-related highly sensitive detection technologies