NiCo₂S₄@graphene as a Bifunctional Electrocatalyst for Oxygen Reduction and Evolution Reactions

Here, the hybrid of NiCo₂S₄ nanoparticles grown on graphene in situ is first described as an effective bifunctional nonprecious electrocatalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in the alkaline medium. NiCo₂S₄@N/S-rGO was synthesized by a one-pot solvothermal strategy using Co­(OAc)₂, Ni­(OAc)₂, thiourea, and graphene oxide as precursors and ethylene glycol as the dispersing agent; simultaneously, traces of nitrogen and sulfur were double-doped into the reduced graphene oxide (rGO) in the forms of pyrrolic-N, pyridinic-N, and thiophenic-S, which are often desirable for metal-free ORR catalysts. In comparison with commercial Pt/C catalyst, NiCo₂S₄@N/S-rGO shows less reduction activity, much better durability, and superior methanol tolerance toward ORR in 0.1 M KOH; it reveals higher activity toward OER in both KOH electrolyte and phosphate buffer at pH 7.0. NiCo₂S₄@graphene demonstrated excellent overall bicatalytic performance, and importantly, it suggests a novel kind of promising nonprecious bifunctional catalyst in the related renewable energy devices

Direct Synthesis of Nitrogen-Doped Carbon Nanosheets with High Surface Area and Excellent Oxygen Reduction Performance

Graphene-like nitrogen-doped carbon nanosheets (NCN) have become a fascinating carbon-based material for advanced energy storage and conversion devices, but its easy, cheap, and environmentally friendly synthesis is still a grand challenge. Herein we directly synthesized porous NCN material via the facile pyrolysis of chitosan and urea without the requirement of any catalyst or post-treatment. As-prepared material exhibits a very large BET surface area of ∼1510 m² g^–1 and a high ratio of graphitic/pyridinic nitrogen structure (2.69 at. % graphitic N and 1.20 at. % pyridinic N). Moreover, compared to a commercial Pt/C catalyst, NCN displays excellent electrocatalytic activity, better long-term stability, and methanol tolerance ability toward the oxygen reduction reaction, indicating a promising metal-free alternative to Pt-based cathode catalysts in alkaline fuel cells. This scalable fabrication method supplies a low-cost, high-efficiency metal-free oxygen reduction electrocatalyst and also suggests an economic and sustainable route from biomass-based molecules to value-added nanocarbon materials

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

Salt-Induced Phase Separation to Synthesize Ordered Mesoporous Carbon by pH-Controlled Self-Assembly

Self-assemly of block copolymers (BCPs) and phenolic resin (PR) is an important method to prepare ordered mesoporous polymers (OMPs) and carbon materials (OMCs). In the process, phase separation of the BCP–PR composite is a critical step which is, however, time-consuming in aqueous solution. Here we report, for the first time, a new salt-induced phase separation strategy to achieve this goal. Triblock copolymer F127 and phenol-formaldehyde resin (PF) are used as the template and precursor, respectively, and sodium chloride (NaCl) is applied to induce the coagulation and phase separation of the F127–PF composite which is transformed to be OMC at high temperature. It is found that the maintenance of the ordered mesostructure is highly dependent on the pH of the F127–PF solution under NaCl interference. A hypothetical mechanism is proposed to explain the role of pH in the formation of ordered mesostructure when salt is introduced into the self-assembly system. The effects of pH, salt concentration, and varied salts on the structures and properties of the as-prepared OMCs are investigated in detail. The new salt-induced phase separation strategy can synthesize OMC facilely and can provide a new insight into understanding the process of preparing ordered mesoporous materials by self-assembly more deeply

Effect of siLDH-A on the expression of LDH-A in GC cell line MGC-803.

<p>In the LDH-A-siRNA expressing cells, expression of LDH-A protein assayed by western blot was hardly detectable(a); Significant down-regulation of LDH-A at the mRNA level was detected after siLDH-A infection(b).</p

Immunohistochemical staining of LDH-A in gastric samples.

<p>LDH-A was expressed in the cytoplasm of NNM and carcinomas: <b>a</b> LDH-A positivity was observed in the cytoplasm of NNM, <b>b</b> LDH-A was detected in the cytoplasm of differentiated gastric carcinoma, <b>c</b> and in the poorly-differentiated gastric carcinoma.</p

Expression of LDH-A in NNM and cancerous tissues.

<p>Expression of LDH-A in NNM and cancerous tissues.</p

Relationship between LDH-A expression and clinico-pathologic features of GC.

<p>Relationship between LDH-A expression and clinico-pathologic features of GC.</p

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

Univariate and multivariate analysis for overall survival after surgery using cox RR relative risk.

<p>Univariate and multivariate analysis for overall survival after surgery using cox RR relative risk.</p