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Controllable growth of uniform nanoparticles with specific morphology to obtain high active electrocatalyst is a key common problem in developing efficient energy conversion and storage devices. In this work, a tangerine peel-derived carbon (TPC) supported mixed manganese oxides (MnO x /TPC) was synthesized for oxygen reduction reaction (ORR) through a facile pyrolysis procedure. By making full use of the confinement effect of tangerine peel cells, the MnO x nanoparticles of MnO x /TPC-800 are obtained with a components of Mn(II), Mn(III) and Mn(IV) with cubic morphology of about 15 nm and evenly dispersed on the TPC surface. Electrochemistry measurements show that MnO x /TPC-800 demonstrates excellent ORR performance with a comparable half-wave potential to commercial Pt/C and a high onset potential with a dominant 4e − catalytic process, superior stability, and remarkable immunity to methanol crossover effect in alkaline media. The synergy effect between multi-oxidation states MnO x and TPC of MnO x /TPC-800 is proved to play significant factor for its high ORR performance. This study provides a valuable and rational strategy to construct morphology-controlled metal nanoparticles with unique carbon materials in developing cost-effective catalysts for fuel cells and metal air batteries. [ABSTRACT FROM AUTHOR]

The construction of nonprecious metal catalysts for the oxygen reduction reaction (ORR) is highly desirable but remains as a key challenge for fuel cells and metal–air batteries. Herein, we designed and synthesized novel Fe2P nanoparticles embedded in an N,P co-doped mesoporous carbon catalyst (Fe2P/NPC) through direct pyrolysis of o-methylaniline in the presence of FeCl3·6H2O, H3PO4, silica nanospheres, and hexadecyltrimethyl ammonium bromide (CTAB) micelles. Transmission electron microscopy, Brunauer–Emmett–Teller (BET), X-ray diffraction and X-ray photoelectron spectroscopy measurements demonstrated that the obtained three-dimensional mesoporous Fe2P/NPC catalyst possessed a considerable specific surface area of 785 m2 g−1 with high contents of Fe2P nanoparticles, pyridinic N, and graphitic N species. Electrochemical evaluations showed that the formed Fe2P/NPC exhibited superior ORR performance to Pt/C in terms of a comparable onset potential (−0.01 V vs. Ag/AgCl electrode), about 20 mV higher half-wave potential, excellent stability and remarkable methanol tolerance in alkaline media. The synergistic effect of pyridinic N, graphitic N and Fe2P species together with its three-dimensional porous structure contribute to the impressive ORR performance. This research, most importantly, provides new clues to the rational development of cost-effective FePx-based catalysts for the ORR. [ABSTRACT FROM AUTHOR]

Controlled synthesis of efficient core-shell non-precious metal catalysts for oxygen reduction reaction (ORR) is undoubtedly crucial but challenging for the extensive application of fuel cells and metal-air batteries. Herein, we prepared a core-shell structured Fe/FeC x nanoparticles and porous carbon composited catalyst (Fe/FeC x @NC) via a facile two-step heat treatment strategy. The Fe/FeC x @NC-800 −0.5 prepared with secondary anneal at 800 °C for 0.5 h exhibits superior ORR performance to the commercial Pt/C in terms of comparable onset potential, higher half-wave potential, and outstanding long-term durability in alkaline media. Through combining the physical and electrochemical characterizations of Fe/FeC x @NC- T − t with different anneal temperature and precursors, the outstanding ORR performance of Fe/FeC x @NC-800 − 0.5 is caused by the synergistic effect between Fe/FeC x core and enriched pyridinic N- and graphitic N-doped carbon shell as well as porous carbon with large specific surface area. The structure-activity relationship of core-shell structured Fe–N–C catalysts for ORR provides directions for the development of advanced nonprecious metals catalysts. [ABSTRACT FROM AUTHOR]

Abstract Development of highly active and durable non-precious metal bi-functional electrocatalyst for both oxygen reduction and evolution reaction (ORR and OER) remains a significant challenge. Herein, porous mixed spinel MnCo x O 4 was loaded on the N-doped multi-walled carbon nanotubes (MnCo x O 4 /NCNT) through a facile one-pot hydrothermal method to work as a bi-functional oxygen electrocatalyst. Physical characterizations confirm that the MnCo x O 4 nanoparticles are composed of mixed spinel-type Co 2 MnO 4 and (Co, Mn)[Mn, Co] 2 O 4 with a diameter of 5–10 nm, which are dispersed on NCNT with secondary aggregation and resultant porous structure. Electrochemical measurements show that the MnCo x O 4 /NCNT catalyst exhibits high ORR catalytic activity with a dominant four-electron ORR catalytic pathway, remarkable durability, excellent methanol-tolerance, as well as superior OER catalytic activity with significantly decreased overpotential of 0.479 V in alkaline media. The multiple valence states of Co and Mn ions in MnCo x O 4 coupled with the enlarged specific surface area with the help of NCNT exert crucial roles for the superior catalytic performance for both ORR and OER. Such a bi-functional oxygen electrocatalyst based on mixed spinel MnCo x O 4 provides a new direction for developing low-cost, highly efficient, and robust multiple valence states transition metal-based electrocatalysts for oxygen electrode. Graphical abstract Image 1 Highlights • A porous mixed-spinel MnCo x O 4 /NCNT was prepared by one-pot hydrothermal method. • The MnCo x O 4 /NCNT shows exceptional ORR and OER performance in alkaline media. • Multiple Co, Mn ions valence states and doped N ensure the high oxygen activity. [ABSTRACT FROM AUTHOR]

Exploring cost-effective, high-performance and durable non-precious metal catalysts is of great significance for the acceleration of sluggish oxygen reduction reaction (ORR). Here, we report an intriguing heteroatom-doped graphitized carbon encased Fe species composite by introducing N, S and B sequentially. The experimental approach was designed ingeniously for that the FeCl 3 ·6H 2 O could catalyze thiourea to synthesize N, S co-doped carbon materials which would further react with H 3 BO 3 and NH 3 (emerged at the heat-treatment process) to prepare N, S and B co-doped carbon materials (Fe-N/S/B-C). The Fe-N/S/B-C exhibits an impressive ORR activity for its half-wave potential of −0.1 V, which is 36 mV or 19 mV higher than that of the corresponding single or dual doped counterparts (Fe-N-C or Fe-N/S-C) and 31 mV positive than that of Pt/C catalyst, respectively. Further chronoamperometric measurement and accelerated aging test confirm the excellent electrochemical durability of Fe-N/S/B-C with the stable core–shell structure. The remarkable ORR performance and facile preparation method enable Fe-N/S/B-C as a potential candidate in electrochemical energy devices. [ABSTRACT FROM AUTHOR]

Promoting the oxygen reduction reaction (ORR) catalytic activities of cost-effective catalysts is of great significance for the development of various energy conversion and storage systems. Herein, we describe the preparation of a highly active N- and S-co-doped ketjenblack (Kb) by facile pyrolysis of a mixture of thiourea and Kb in the presence of FeCl3 ⋅6 H2O followed by an acid-leaching process. This novel synthetic approach was rationally designed with the consideration that thiourea could easily introduce both N and S heteroatoms into the carbon matrix by a heat-treatment method by releasing plentiful reactive N- and S-containing gases, which could simultaneously optimize the porous structure of the resultant catalyst. Physical characterization revealed that N and S were homogeneously incorporated into the nanostructure of Kb and formed a hierarchical porous structure with a high specific surface area. The N/S-Kb catalyst showed impressive ORR activity, with an onset potential of 0.08 V at 0.1 mA cm−2, which is 20 mV more positive than that of commercial 20 wt. % Pt/C catalyst. This was coupled with long-term durability and superior methanol tolerance in alkaline media. The improved ORR performance can be mainly ascribed to synergistic contributions of highly efficient active sites arising from high contents of thiophene S and pyridinic N along with the high specific surface area and the favorable mass-transport properties arising from the hierarchical porous structure. The remarkable ORR performance and facile preparation method make the N/S-Kb catalyst a promising substitute for Pt in electrochemical energy devices. [ABSTRACT FROM AUTHOR]