An 'active site anchoring' strategy for the preparation of PBO fiber derived carbon catalyst towards an efficient oxygen reduction reaction and zinc-air batteries.

In order to promote the wide application of clean energy-fuel cells, it is urgent to develop transition metal-based high-efficiency oxygen reduction reaction (ORR) catalytic materials with a low cost and available rich raw material resources to replace the currently used precious metal platinum-based catalytic materials. Herein, a novel 'active-site-anchoring' strategy was developed to synthesize highly-activated carbon-based ORR catalysts. Firstly, poly(p-phenylene benzobisoxazole) (PBO) fiber with a stable chemical structure was selected as the main precursor, and iron was complexed on its surface, and then poly-dopamine (PDA) was coated on the surface of PBO-Fe to form a PBO-Fe-PDA composite structure. Therefore, carbon-based catalyst PBO-Fe-PDA-900 with abundant Fe2O3 active sites was prepared by anchoring iron sites by PDA after pyrolysis. As a result, the PBO-Fe-PDA-900 catalyst displayed a 30 mV higher half-wave potential (0.86 V) than that of a commercial Pt/C electrocatalyst. Finally, PBO-Fe-PDA-900 was used as a cathode material for zinc-air batteries, showing a high peak power density superior to Pt/C. This work offers new prospects for the design of efficient, non-precious metal-based materials in zinc-air batteries.

A facile strategy to prepare FeNx decorated PtFe intermetallic with excellent acidic oxygen reduction reaction activity and stability.

The construction of low-Pt-content intermetallic on carbon supports has been verified as a promising method to promote the activity of the oxygen reduction reaction (ORR). In this study, we have developed a simple and effective strategy to obtain a well-designed CNT-PtFe-PPy precursor. This precursor contains modulated Pt- and Fe-based content dispersed in polypyrrole (PPy) chain segments, which are in-situ generated on the templates of carbon nanotubes (CNTs). Subsequent pyrolysis of the CNT-PtFe-PPy precursor produces a CNT-PtFe@FeNC catalyst, which contains both Fe-Nx and PtFe intermetallic active sites. Due to the highly efficient dispersion of active species, the CNT-PtFe@FeNC electrocatalyst displays a 9.5 times higher specific activity (SA) and 8.5 times higher mass activity (MA) than those of a commercial Pt/C catalyst in a 0.1 M HClO4 solution. Additionally, these results, combined with excellent durability (the SA and MA maintained 94 % and 91 % of initial activity after a 10-k cycle accelerated durability test), represent among the best performance achieved so far for Pt-based ORR electrocatalysts. Furthermore, density functional theory (DFT) calculations revealed that the presence of Fe-N4 species reduces the adsorption energy between the PtFe intermetallic compound and OH*, accelerating the ORR process.

Conversion of rice husk biomass into electrocatalyst for oxygen reduction reaction in Zn-air battery: Effect of self-doped Si on performance.

An outstanding oxygen reduction reaction (ORR) electrocatalyst is firstly developed deriving from sustainable rice husk (RH) biomass. Benefiting from self-doped Si in RH, the higher proportion of pyridine N, graphite N and expecially Fe-Nx as well as thiophene S contents were produced in Si-Fe/S/N-RH3 in comparison with those of Si-free Fe/S/N-RH3. Consequently, the half-wave potential of 0.89 V and the onset potential of 0.96 V are achieved for Si-Fe/S/N-RH3, outperforming the benchmark electrocatalyst Pt/C and other Fe-based electrocatalysts reported in alkaline media. Furthermore, it is found that the exisentence of self-doped Si can improve the graphitization degree of the catalyst, leading to the long-term stability (larger than 85% retention after 40000 s) and prominent methanol tolerance for Si-Fe/S/N-RH3. In addition, Si-Fe/S/N-RH3 shows a power density of 86.2 mW cm-2 and excellent durability in Zn-air battery. The work highlights the potential to develop sustainable and cost-effective ORR electrocatalysts from waste biomass as the substitute for precious metal catalysts.

The cobalt carbide/bimetallic CoFe phosphide dispersed on carbon nanospheres as advanced bifunctional electrocatalysts for the ORR, OER, and rechargeable Zn-air batteries.

It is very important, but also challenging to produce high-activity, high durability and affordable non-noble-metal-bifunctional-electrocatalysts for sustainable energy application. Here, one-pot synthesized iron covalent porphyrin polymers (FePor-CPP), with carefully placed Fe, N atoms, a regular porous structure, Co3[Co(CN)6]2 and NaH2PO2 precursors were carbonized into N,P-doped carbon nanospheres with the active species of both bimetallic CoFe phosphides and CoCx nanoparticles (denoted as CoCx/(Co0.55Fe1.945)2P@C). By employing the CoCx/(Co0.55Fe1.945)2P@C as oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrode catalysts, superior catalytic activity is achieved with E1/2 of 0.84 V for ORR, and overpotential of 0.39 V at 10 mA cm-2 for OER in an alkaline medium, respectively. Furthermore, CoCx/(Co0.55Fe1.945)2P@C as air electrode for rechargeable Zn-air battery shows power density as high as 131 mW cm-2 and charge-discharge cycle stability, and this suggests the potential application of CoCx/(Co0.55Fe1.945)2P@C in energy transformation systems. The high electrocatalytic performances are revealed to originate from the change of electronic structure of bimetallic (Co0.55Fe1.945)2P via introducing P into the Co0.55Fe1.945 alloy, resulting in a decreased energy gap of CoCx/(Co0.55Fe1.945)2P@C relative to that of CoCx/Co0.55Fe1.945@C. This work proposes a versatile strategy to develop multifunctional non-precious catalysts for this kind of energy-related electrocatalytic reactions.

Electrocatalytic oxygen reduction by a Co/Co3O4@N-doped carbon composite material derived from the pyrolysis of ZIF-67/poplar flowers.

Catalysts used for the oxygen reduction reaction (ORR) are crucial to fuel cells. However, the development of novel catalysts possessing high activity at a low cost is very challenging. Recently, extensive research has indicated that nitrogen-doped carbon materials, which include nonprecious metals as well as metal-based oxides, can be used as excellent candidates for the ORR. Here, Co/Co3O4@N-doped carbon (NC) with a low cost and highly stable performance is utilized as an ORR electrocatalyst through the pyrolysis of an easily prepared physical mixture containing a cobalt-based zeolite imidazolate framework (ZIF-67 precursor) and biomass materials from poplar flowers. Compared with the pure ZIF-derived counterpart (Co@NC) and PL-bio-C, the as-synthesized electrocatalysts show significantly enhanced ORR activities. The essential roles of doped atoms (ZIF-67 precursor) in improving the ORR activities are discussed. Depending mainly on the formation of Co-Co3O4 active sites and abundant nitrogen-containing groups, the resulting Co/Co3O4@NC catalyst exhibits good electroactivity (onset and half-wave potentials: E onset = 0.94 V and E 1/2 = 0.85 V, respectively, and a small Tafel slope of 90 mV dec-1) compared to Co@NC and PL-bio-C and follows the 4-electron pathway with good stability and methanol resistance. The results of this study provide a reference for exploring cobalt-based N-doped biomass carbon for energy conversion and storage applications.

Micelles of Mesoporous Silica with Inserted Iron Complexes as a Platform for Constructing Efficient Electrocatalysts for Oxygen Reduction.

Iron, N-codoped carbon materials (Fe-N-C) are promising electrocatalysts toward oxygen reduction reactions due to their high atom utilization efficiency and intrinsic activity. Nanostructuring of the Fe-N-C materials, such as introducing porosity into the carbon structure, would be conducive to further increasing the exposure of active sites as well as improving the mass transfer. Herein, we explore the potential of iron complex-functionalized micelles of mesoporous SiO2 as a platform for constructing porous Fe-N-C materials. The classical three-dimensional MCM-48 was selected as a proof-of-concept example, which was utilized as the hard template, and cetyltrimethylammonium bromide micelles inside it played the role of the main carbon source. Fe-Nx sites were derived from Fe-1,10-phenanthroline complexes in the micelles introduced by in situ incorporation of 1,10-phenanthroline and post Fe2+ insertion in an aqueous solution. After thermal annealing in a nitrogen atmosphere and subsequent removal of the MCM-48 framework, a carbon material that possesses porous structural features with uniformly dispersed Fe-Nx sites (MPC@PhFe) was obtained, which shows superior ORR activity in a 0.1 M KOH solution and great potential for Zn-air battery applications as well. This work demonstrates the feasibility as well as the effectiveness of turning micelles of mesoporous SiO2 into porous carbon structures and might offer a universal strategy for manufacturing carbon materials for future application in energy storage and conversion.

An Activatable Triplet Sensitizer Based on Triplet Electron Transfer and Its Application for Triplet-Triplet Annihilation Upconversion.

Activatable triplet photosensitization refers to a photosentization process which can be turned on/off easily by external stimulus. Activatable triplet photosensitizations are normally achieved by interfering with the singlet excited state before the intersystem cross process (ISC), i.e., the formation process of triplet states of sensitizer. To achieve novel activatable triplet photosensitization, a disulfide-bridged porphyrin zinc(II) dyad (ZnPor-S-S-ZnPor) is prepared. Although fast ISC can be conducted in this dyad, an extremely low efficiency is obtained when employing this dyad as a triplet donor in triplet-triplet annihilation upconversion (TTA-UC) for sensitizing perylene. This is because of the presence of electron transfer from the triplet state of the porphyrin zinc(II) unit to the disulfide bond, which quickly quenches the triplet state of the porphyrin zinc(II) unit. This electron transfer process can be stopped by the cleavage of the disulfide bond in the presence of thiol, and TTA-UC efficiency can be enhanced significantly. Our result demonstrates for the first time that the disulfide bond can act as not only an easy cleavage linker but also a triplet electron acceptor. Furthermore, quenching the triplet states of sensitizer by triplet electron transfer provides an alternative protocol for designing activatable triplet sensitizers except controlling the singlet excited state before the ISC process.

Pickering Emulsion Formation of Paraffin Wax in an Ethanol-Water Mixture Stabilized by Primary Polymer Particles and Wax Microspheres Thereof.

Stable dispersions of paraffin wax droplets and their nano- and microspheres have broad applications. Despite intensive efforts, the production of uniform wax spheres remains a challenge. For their preparation, abundant surfactants and other additives are commonly used to stabilize the dispersions. These additives are hardly removable and entrain often adverse consequence in many applications, particularly in biological and medical applications, where microspheres with absolutely clean surface are preferred. We report here a novel process to prepare stable dispersion of wax droplets in a water-ethanol mixture with a narrow size distribution by simply shaking without any surfactants. The process is featured by using primary polymer particles (PPs) of poly(dodecene-trihydroxymethylpropane triacrylate) as a Pickering stabilizer. PPs were prepared by precipitation polymerization without any surfactant and stabilizer. By rapidly cooling the wax emulsion, solid wax spheres with good uniformity were obtained. Their size, between 50 and 480 µm, was easily adjustable by changing the shaking rate, number of PPs, and particularly the size of PPs. The morphology of the wax spheres was examined by SEM, which showed that they were covered by a layer of PPs. The formation mechanism of the microspheres was also discussed on the basis of the adsorption energy of PPs on wax spheres, estimated from the corresponding contact angle of the solvent toward the PPs and the wax. This paper presents a novel pathway for the preparation of wax microspheres with only polymer particles without the need for any other additives.