The development of efficient non-platinum group metal (non-PGM) catalysts for oxygen reduction reaction (ORR) is of paramount importance for clean and sustainable energy storage and conversion devices. The major bottleneck in developing Fe-N-C materials as the leading non-PGM catalysts lies in the poor understanding of the nature of active sites and reaction mechanisms. Herein, we report a scalable metal organic framework-derived Fe-N-C catalyst with high ORR activity demonstrated in practical H 2 /air fuel cells, and an unprecedented turnover frequency (TOF) in acid in rotating disk electrode. By characterizing the catalyst under both ex situ and operando conditions using combined microscopic and spectroscopic techniques, we show that the structures of active sites under ex situ and working conditions are drastically different. Resultantly, the active site proposed here, a non-planar ferrous Fe-N 4 moiety embedded in distorted carbon matrix characterized by a high Fe 2+/3+ redox potential, is in contrast with those proposed hitherto derived from ex situ characterizations. This site reversibly switches to an in-plane ferric Fe-N 4 moiety poisoned by oxygen adsorbates during the redox transition, with the population of active sites controlled by the Fe 2+/3+ redox potential. The unprecedented TOF of the active site is correlated to its near-optimal Fe 2+/3+ redox potential, and essentially originated from its favorable biomimetic dynamic nature that balances the site-blocking effect and O 2 dissociation. The porous and disordered carbon matrix of the catalyst plays pivotal roles for its measured high ORR activity by hosting high population of reactant-accessible active sites. 50In situ characterizations reveal that the biomimetic dynamic nature of the Fe-N-C active site with a near-optimal Fe 2+/3+ redox potential formed upon pyrolysis accounts for its high ORR activity by balancing the site-blocking effect and O 2 dissociation.

This review is specifically focused on the progress in the cathodes for non-aqueous Li–air batteries in the terms of the materials, structure and fabrication.

This comprehensive review gives a picture about the state-of-the-art progress of HT-PEMFCs, and the challenges, strategies and rules to design, evaluate and promote the performance of HT-PEMFCs.

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Chitosan modification can turn many solids, such as local clays and soils, into highly effective flocculants in removing harmful cyanobacterial blooms in freshwaters. AbstractAfter sepiolite was modified with Fe 3C to increase its surface charge, the initial algal removal rate increased significantly, but its Q 8 h was not improved substantially at clay loadings below 0.1 g/L. Modification on netting and bridging properties of clays by either chitosan or polyacrylamide (PAM) dramatically increased flocculation (Q 8 h ) of MA cells in freshwaters. Algal removal efficiencies of different solids, including Type III clays, local soils and sediments, were all improved to a similar level of O90% at a total loading of 0.011 g/L (contained 0.001 g/L chitosan) after they were modified with chitosan, making the idea of clearing up algal blooms using local soils/sediments possible. The mechanism of netting and bridging was confirmed to be the most important factor in improving the removal efficiency of cells, whereas clays also played important roles in the sedimentation of the floc.

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Inspired by the water-collecting mechanism of the Stenocara beetle's back structure, we prepared a superhydrophilic bumps-superhydrophobic/superoleophilic stainless steel mesh (SBS-SSM) filter via a facile and environmentally friendly method. Specifically, hydrophilic silica microparticles are assembled on the as-cleaned stainless steel mesh surface, followed by further spin-coating with a fluoropolymer/SiO nanoparticle solution. On the special surface of SBS-SSM, attributed to the steep surface energy gradient, the superhydrophilic bumps (hydrophilic silica microparticles) are able to capture emulsified water droplets and collect water from the emulsion even when their size is smaller than the pore size of the stainless steel mesh. The oil portion of the water-in-oil emulsion therefore permeates through pores of the superhydrophobic/superoleophilic mesh coating freely and gets purified. We demonstrated an oil recovery purity up to 99.95 wt % for surfactant-stabilized water-in-oil emulsions on the biomimetic SBS-SSM filter, which is superior to that of the traditional superhydrophobic/superoleophilic stainless steel mesh (S-SSM) filter lacking the superhydrophilic bump structure. Together with a facile and environmentally friendly coating strategy, this tool shows great application potential for water-in-oil emulsion separation and oil purification.

A novel catalyst, Co-PPy-TsOH/C, for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs) was prepared by pyrolyzing cobalt salt and p-toluenesulfonic acid (TsOH)-doped polypyrrole-modified carbon support in an inert atmosphere. The characteristics and electrocatalytic activities of Co-PPy-TsOH/C were analyzed with various techniques, including Raman spectroscopy, elemental analysis, rotating ring disk electrode analysis, and a single H(2)-O(2) PEMFC, and compared with those of undoped catalyst Co-PPy/C. The results showed that doping TsOH introduces larger N and S contents in Co-PPy-TsOH/C, leading to much better electrocatalytic performance for ORR than Co-PPy/C, and that Co-PPy-TsOH/C is more likely to follow a four-electron-transfer reaction to reduce oxygen directly to H(2)O. The performance of PEMFCs with Co-PPy-TsOH/C as cathode catalyst is better than that with Co-PPy/C, and the resulting maximum output power density of 203 mW cm(-2) is a substantial improvement over the best values reported in the literature with Co-PPy/C-based cathode catalyst. This implies that doping TsOH is a valuable method to improve the catalytic activity of Co-PPy/C and that Co-PPy-TsOH/C is a promising cathode catalyst for PEMFCs. The function and mechanism of doping have also been analyzed and the configurations of PPy-TsOH/C and Co-PPy-TsOH/C proposed.