A series of ZIF-derived Fe-N codoped carbon materials with a well-defined morphology, high surface area, tunable sizes and porous nanoframe structure was successfully prepared by synthesizing Fe-doped ZIF-8 through the assembly of Zn ions with 2-methylimidazole in the presence of iron(III) acetylacetonate, followed by pyrolysis at a high temperature and in an Ar atmosphere. The prepared optimum catalyst materials exhibited excellent activity for the oxygen reduction reaction (ORR) and outstanding durability in both acidic and alkaline solutions. We found that Fe doping during the ZIF-8 synthesis stage was crucial to achieve the materials' well-defined morphology, tunable size, good particle dispersion, and high performance. XPS revealed that Fe doping greatly enhanced the fractions of graphitic-N and pyridinic-N and decreased the fraction of oxidized-N. We suggest that the porosity and high surface area of the nanoframe structure originated from the metal-organic frameworks, the high dispersion of Fe in the nanoframe, and the enhanced proportions of active N species, all of which were responsible for the materials' significantly enhanced ORR performance.

A metalorganic gaseous doping approach for constructing nitrogen‐doped carbon polyhedron catalysts embedded with single Fe atoms is reported. The resulting catalysts are characterized using scanning transmission electron microscopy, X‐ray photoelectron spectroscopy, and X‐ray absorption spectroscopy; for the optimal sample, calculated densities of Fe–Nx sites and active N sites reach 1.75812 × 1013 and 1.93693 × 1014 sites cm‐2, respectively. Its oxygen reduction reaction half‐wave potential (0.864 V) is 50 mV higher than that of 20 wt% Pt/C catalyst in an alkaline medium and comparable to the latter (0.78 V vs 0.84 V) in an acidic medium, along with outstanding durability. More importantly, when used as a hydrogen–oxygen polymer electrolyte membrane fuel cell (PEMFC) cathode catalyst with a catalyst loading as low as 1 mg cm‐2 (compared with a conventional loading of 4 mg cm‐2), it exhibits a current density of 1100 mA cm‐2 at 0.6 V and 637 mA cm‐2 at 0.7 V, with a power density of 775 mW cm‐2, or 0.775 kW g–1 of catalyst. In a hydrogen–air PEMFC, current density reaches 650 mA cm‐2 at 0.6 V and 350 mA cm‐2 at 0.7 V, and the maximum power density is 463 mW cm‐2, which makes it a promising candidate for cathode catalyst toward high‐performance PEMFCs.

Atomic Fe-doped hollow carbon nanopolyhedra as efficient ORR catalysts.

The synergy between binary transition metal nitride and nitrogen-doped reduced graphene oxide makes TiCoNx/N-rGO an outstanding ORR catalyst.

It is highly desirable but remains challenging to develop efficient bifunctional electrocatalysts for both the oxygen reduction and oxygen evolution reactions (ORR/OER) in rechargeable metal–air batteries and unitized regenerative fuel cells. Herein, we developed a facile and cost-effective strategy to prepare a cobalt and nitrogen codoped three-dimensional (3D) graphene catalyst through inserting carbon nanospheres into the interlayers of graphene sheets. The catalyst exhibited not only excellent ORR performance but also excellent OER performance, and both were greatly enhanced by the insertion of carbon nanospheres. Its activities for the ORR/OER ranked among the best for doped carbon catalysts thus far reported. Its overall oxygen electrode activity parameter (ΔE) was as low as 0.807 V, which was much lower than that of Pt/C, and made it comparable with the best nonprecious metal based catalysts to date. Furthermore, the catalyst exhibited excellent stability toward ORR and OER, making it a new noble-metal-free bifunctional catalyst for future applications in the fields of alternative energy conversion and storage systems.

Proton exchange membrane fuel cells (PEMFCs) are a highly efficient hydrogen energy conversion technology, which shows great potential in mitigating carbon emissions and the energy crisis. Currently, to accelerate the kinetics of the oxygen reduction reaction (ORR) required for PEMFCs, extensive utilization of expensive and rare platinum‐based catalysts are required at the cathodic side, impeding their large‐scale commercialization. In response to this issue, atomically dispersed metal–nitrogen–carbon (M–N–C) catalysts with cost‐effectiveness, encouraging activity, and unique advantages (e.g., homogeneous activity sites, high atom efficiency, and intrinsic activity) have been widely investigated. Considerable progress in this domain has been witnessed in the past decade. Herein, a comprehensive summary of recent development in atomically dispersed M–N–C catalysts for the ORR under acidic conditions and of their application in the membrane electrode assembly (MEA) of PEM fuel cells, are presented. The ORR mechanisms, composition, and operating principles of PEMFCs are introduced. Thereafter, atomically dispersed M–N–C catalysts towards improved acidic ORR and MEA performance is summarized in detail, and improvement strategies for MEA performance and stability are systematically analyzed. Finally, remaining challenges and significant research directions for design and development of high‐performance atomically dispersed M–N–C catalysts and MEA are discussed.

Both positive and negative interactions among bacteria take place in the environment. We hypothesize that the complexity of the substrate affects the way bacteria interact with greater cooperation in the presence of recalcitrant substrate. We isolated lignocellulolytic bacteria from salt marsh detritus and compared the growth, metabolic activity and enzyme production of pure cultures to those of three-species mixed cultures in lignocellulose and glucose media. Synergistic growth was common in lignocellulose medium containing carboxyl methyl cellulose, xylan and lignin but absent in glucose medium. Bacterial synergism promoted metabolic activity in synergistic mixed cultures but not the maximal growth rate (μ). Bacterial synergism also promoted the production of β-1,4-glucosidase but not the production of cellobiohydrolase or β-1,4-xylosidase. Our results suggest that the chemical complexity of the substrate affects the way bacteria interact. While a complex substrate such as lignocellulose promotes positive interactions and synergistic growth, a labile substrate such as glucose promotes negative interactions and competition. Synergistic interactions among indigenous bacteria are suggested to be important in promoting lignocellulose degradation in the environment.

Efficient, low‐cost catalysts are desirable for the sluggish oxygen reduction reaction (ORR). Herein, UIO‐66‐NH2‐derived multi‐element (Fe, S, N) co‐doped porous carbon catalyst is reported, Fe/N/S‐PC, with an octahedral morphology, a well‐defined mesoporous structure, and highly dispersed doping elements, synthesized by a double‐solvent diffusion‐pyrolysis method (DSDPM). The morphology of the UIO‐66‐NH2 precursor is perfectly inherited by the derived carbon material, resulting in a high surface area, a well‐defined mesoporous structure, and atomic‐level dispersion of the doping elements. Fe/N/S‐PC demonstrates outstanding catalytic activity and durability for the ORR in both alkaline and acidic solutions. In 0.1 m KOH, its half‐potential reaches 0.87 V (vs reversible hydrogen electrode (RHE)), 30 mV more positive than that of a 20 wt% Pt/C catalyst. In 0.1 m HClO4, it reaches 0.785 V (vs RHE), only 65 mV less than that of Pt/C. The catalyst also exhibits excellent performance in acidic hydrogen/oxygen proton exchange membrane fuel cells. A membrane electrode assembly (MEA) with the catalyst as the cathode reaches 700 mA·cm‐2 at 0.6 V and a maximum power density of 553 mW·cm‐2, ranking it among the best MEAs with a nonprecious metal catalyst as the cathode.