The exploring of catalysts with high‐efficiency and low‐cost for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is one of the key issues for many renewable energy systems including fuel cells, metal–air batteries, and water splitting. Despite several decades pursuing, bifunctional oxygen catalysts with high catalytic performance at low‐cost, especially the one that could be easily scaled up for mass production are still missing and highly desired. Herein, a hybrid catalyst with NiCo alloy nanoparticles decorated on N‐doped carbon nanofibers is synthesized by a facile electrospinning method and postcalcination treatment. The hybrid catalyst NiCo@N‐C 2 exhibits outstanding ORR and OER catalytic performances, which is even surprisingly superior to the commercial Pt/C and RuO2 catalysts, respectively. The synergetic effects between alloy nanoparticles and the N‐doped carbon fiber are considered as the main contributions for the excellent catalytic activities, which include decreasing the intrinsic and charge transfer resistances, increasing CC, graphitic‐N/pyridinic‐N contents in the hybrid catalyst. This work opens up a new way to fabricate high‐efficient, low‐cost oxygen catalysts with high production.

We have investigated the impact of electrocatalyst loading on rotating ring-disk electrode ͑RRDE͒ experiments for the oxygen reduction reaction on Fe-N-C catalysts ͑ORR͒ in acid medium. In particular, the fraction of H 2 O 2 produced as a function of catalyst loading was studied. A dramatic increase in H 2 O 2 release was observed as the catalyst loading was decreased. For the same non-noble metal catalyst ͑NNMC͒, the fraction of produced H 2 O 2 varied between less than 5% and greater than 95%, depending on the catalyst loading. These observations suggest that oxygen reduction occurs stepwise, via H 2 O 2 , and if the catalyst is sparsely loaded, the produced H 2 O 2 cannot be efficiently reduced to H 2 O before it escapes. These studies have important implications for fundamental studies of ORR on NNMCs.Polymer electrolyte membrane fuel cells are currently under intensive research because they are a clean energy conversion device. 1 Electrocatalysts which have high activity for oxygen reduction and show stability in acidic environments are highly desired, because a significant fraction ͑70%͒ of voltage loss in a fuel cell originates at the cathode where oxygen reduction occurs. 2,3 Besides being active and stable, the electrocatalysts must meet other requirements, including immunity against poisoning; ease of preparation; affordable cost, and minimum release of H 2 O 2 . The latter is a particularly important attribute because H 2 O 2 is known to decompose into highly reactive intermediates that initiate a chain oxidation, starting with the carboxylic groups that then propagate within the Nafion membrane. This membrane breakdown results in the release of F − ions in the effluent water. There are extensive reports on the role of H 2 O 2 , OH radicals, and the degradation of Nafion membranes in the literature. 4-6 Furthermore, reduction of oxygen to H 2 O 2 is a twoelectron reaction, thus producing smaller electric current per available oxygen molecule. Thus, minimum production of H 2 O 2 and a complete, four-electron reduction of oxygen are highly preferred.Although there are reports of detecting H 2 O 2 produced at the electrocatalyst in real operating fuel cells, 7 the best known method to measure the H 2 O 2 yield is still that of the rotating-ring disk electrode ͑RRDE͒. By fixing the potential ͓1.2-1.5 V vs a reversible hydrogen electrode ͑RHE͔͒ of the ring during cathodic or anodic sweeps of the disk potential, free H 2 O 2 , generated at the disk and passing near the ring by convection, is oxidized and produces a current. By comparing this current to the current produced at the central disk electrode, the percentage of O 2 molecules that are reduced to H 2 O 2 can be calculated. Paulus and Schmidt et al. explain the RRDE method applied to carbon-supported oxygen reduction reaction ͑ORR͒ electrocatalysts in detail. 8,9 Although there is extensive literature on RRDE measurements of ORR activity for Pt-based and non-noble metal catalysts ͑NNMCs͒, 10-13 there have been very few reports of the impact of the cat...

A lithium ion battery electrode is a composite of active material, polymeric binder, and conductive carbon additive(s). Cooperation among the different components plays a subtle and important role in determining the physical and electrochemical properties of the electrode. In this study, the physical and electrochemical properties of a Li-Ni 0.8 Co 0.15 Al 0.05 O 2 cathode were investigated as a function of the electrode compositions. The electrode conductivity, porosity, specific capacity, first Coulombic efficiency, and rate capability were found significantly affected by the polyvinylidene difluoride (PVDF)-to-acetylene black (AB) ratio and the total inactive material amount. The electronic conductivity of the laminate does not so much decide the rate performance of the electrode as it is generally believed. The rate capability of the electrode is enhanced by an increase in the total inactive material content at a PVDF/AB ratio of 5:4, whereas it is deteriorated by increasing the total inactive material content at PVDF/AB ratios of 5:1 and 5:2. At a PVDF/AB ratio of 5:3, the rate performance is not considerably affected by the inactive material content. The result is explained by the competition between the ion-blocking effect of PVDF binder and the electronic conducting effect of the AB additive. A long-term cycling experiment shows the mechanical integrity of the laminate is important for the durability of the composite electrode.

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