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N-doped carbon materials are considered as one of the most promising alternatives for oxygen reduction reaction (ORR). However, they are usually limited due to their low porosity and low active N content. Here, we use adenine as a nitrogen-doped carbon (NC) precursor and the NaCl and ZnCl2 mixed molten salt as a template, and show that the pore structure of carbon materials can be controlled by adjusting the pyrolysis temperature, facilitating the exposure of active sites and improving the graphite-N content. Experiments showed that SZ-NC-900 (where S represents sodium chloride, Z represents zinc chloride) had a hierarchical porous structure (specific surface area was 2710.58 m2 g−1) and high N-doping content (8.93%). Therefore, it exhibited comparable ORR activity in alkaline medium (half wave potential was 0.856 V versus reversible hydrogen electrode). After 5000 cycles, the half-wave potential of SZ-NC-900 shifted only 1.4 mV compared with Pt/C (53 mV). In addition, the zinc–air battery (ZAB) prepared with SZ-NC-900 as the catalyst was superior to the Pt/C-based ZAB, further proving its application value. [ABSTRACT FROM AUTHOR]

Fe2O3/reduced graphene oxide (Fe2O3/rGO) composite anode materials have been successfully synthesized by a polyvinylpyrrolidone (PVP)-assisted homogeneous precipitation method. The size of Fe2O3nanoparticles on the surface of rGO sheets was less than 35 nm. Fe2O3nanoparticles and rGO sheets formed a network structure. Electrochemical properties were evaluated in two-electrode cells vs. metallic lithium. The Fe2O3/rGO composite exhibited excellent electrochemical lithium storage performances. The first discharge/charge capacities were 1600/1053 mA h g−1at a current density of 100 mA g−1, and the coulomb efficiencies was 65.8%. The reversible specific capacity remained 893 mA h g−1and the capacity retention was 84.8% after 100 cycles. [ABSTRACT FROM AUTHOR]

[Display omitted] • A Zn 5 (OH) 6 (CO 3) 2 -assisted pyrolysis strategy is proposed to prepare a coupled catalyst. • Fe nanoparticles can optimize electronic structures and d-band center of Fe center. • Fe-FeN-C exhibits eminent ORR activity with a E 1/2 of 0.921 V in alkaline media. • The Zn-air batteries deliver high power density and long-cycle life for 408 h. Fe single-atom catalysts still suffer from unsatisfactory intrinsic activity and durability for oxygen reduction reaction (ORR). Herein, the coexisting Fe single atoms and nanoparticles on hierarchically porous carbon (denoted as Fe-FeN-C) are prepared via a Zn 5 (OH) 6 (CO 3) 2 -assisted pyrolysis strategy. Theoretical calculation reveals that the Fe nanoparticles can optimize the electronic structures and d-band center of Fe active center, hence reducing the reaction energy barrier for enhancing intrinsic activity. The Zn 5 (OH) 6 (CO 3) 2 self-sacrificial template not only can promote the formation of Fe single atoms, but also contributes to the construction of microporous/mesoporous/macroporous structures. Therefore, the obtained Fe-FeN-C exhibits impressive ORR activity with a half-wave potential of 0.921 V, which far exceeds Pt/C. With Fe-FeN-C as the cathode catalyst, the assembled Zn-air batteries delivered a maximum power density of 206 mW cm−2 and a long-cycle life over 400 h. [ABSTRACT FROM AUTHOR]

Solvent environment engineering is developed to synthesize ZIF-derived hierarchically porous cubic Fe N C(C) catalysts with densely Fe-N x sites. [Display omitted] • The Fe-N x site density of ZIF-derived Fe N C is controlled by changing the solvent. • The Fe N C(C) synthesized in water has a high single Fe atom loading (0.6 at%). • The catalyst displays satisfactory ORR activity under alkaline/acidic environment. • The catalyst presents nice performance in liquid and solid-state Zn-air batteries. Zeolitic imidazole framework (ZIF)-derived iron–nitrogen-carbon (Fe N C) materials are expected to be high-efficiency catalysts for oxygen reduction reaction (ORR). However, increasing the density of active sites while avoiding metal accumulation still faces significant challenges. Herein, solvent environment engineering is used to synthesize the Fe N C containing dense Fe-N x moieties by adjusting the solvent during the ZIF precursor synthesis process. Compared with methanol and water/methanol, the aqueous media can provide a more moderate Fe content for the ZIF precursor, which facilitates the construction of high-density Fe-N x sites and prevent the appearance of iron-based nanoparticles during pyrolysis. Therefore, the Fe N C(C) nanocubes synthesized in an aqueous media have the highest single atom Fe loading (0.6 at%) among the prepared samples, which presents excellent oxygen reduction properties and durability under alkaline and acidic conditions. The advantage of Fe N C(C) is proven in Zn-air batteries, with outstanding performance and long-term stability. [ABSTRACT FROM AUTHOR]

SnO2/graphene composite with superior cycle performance and high reversible capacity was prepared by a one-step microwave-hydrothermal method using a microwave reaction system. The SnO2/graphene composite was characterized by X-ray diffraction, thermogravimetric analysis, Fourier-transform infrared spectroscopy, Raman spectroscopy, scanning electron microscope, X-ray photoelectron spectroscopy, transmission electron microscopy and high resolution transmission electron microscopy. The size of SnO2 grains deposited on graphene sheets is less than 3.5 nm. The SnO2/graphene composite exhibits high capacity and excellent electrochemical performance in lithium-ion batteries. The first discharge and charge capacities at a current density of 100 mA g−1 are 2213 and 1402 mA h g−1 with coulomb efficiencies of 63.35%. The discharge specific capacities remains 1359, 1228, 1090 and 1005 mA h g−1 after 100 cycles at current densities of 100, 300, 500 and 700 mA g−1, respectively. Even at a high current density of 1000 mA g−1, the first discharge and charge capacities are 1502 and 876 mA h g−1, and the discharge specific capacities remains 1057 and 677 mA h g−1 after 420 and 1000 cycles, respectively. The SnO2/graphene composite demonstrates a stable cycle performance and high reversible capacity for lithium storage. [ABSTRACT FROM AUTHOR]

[Display omitted] • HP-Fe-N-C/2 exhibits eminent ORR activity and stability in alkaline and acidic media. • The Zn-air battery shows high power density and superior cyclability for 1342 h. • The power density of HP-Fe-N-C/2-based PEM fuel cell is up to 0.66 W cm−2. Atomically dispersed Fe-N-C catalysts are a promising alternative to platinum group metal (PGM) catalysts for oxygen reduction reaction (ORR). However, attaining efficient ORR activity and superior stability in Fe-N-C catalysts is still crucial yet challenging. Herein, we report a rational SiO 2 -mediated two-step pyrolysis strategy for stabilizing densely exposed Fe-N 4 active sites on hierarchically porous carbon (HP-Fe-N-C/2). Benefiting from the high density of accessible Fe-N 4 sites and the high graphitization degree of carbon support, the obtained HP-Fe-N-C/2 catalyst demonstrates outstanding activity and stability for ORR in both alkaline and acidic media. When used as the cathode catalyst, the assembled Zn-air battery shows a high peak power density of 217 mW cm−2 and ultra-long cycling stability for 1342 h without noticeable degradation. As a PGM-free cathode in proton exchange membrane fuel cells, it delivers a maximum output power density of 0.66 W cm−2. [ABSTRACT FROM AUTHOR]

Nanoparticles of the bimetallic alloy CoNi wrapped in nitrogen-doped graphite-like carbon shells and dispersed on nitrogen-doped graphite-like carbon sheets (CoxNi1−x@NC) were synthesized by calcining CoNi metal–organic frameworks that were prepared through a facile solvothermal reaction using various raw-material molar ratios Co:Ni and CoNi:ethylenedinitrilotetraacetic acid. After depositing CoxNi1−x@NC for use as a counter electrode film in dye-sensitized solar cells, it was found that the electrocatalytic activity of the CoxNi1−x@NC counter electrode towards triiodide reduction could be optimized by simply tuning the molar ratios (Co:Ni and CoNi:ethylenedinitrilotetraacetic acid) appropriately during CoxNi1−x@NC synthesis. Cells that utilized a CoxNi1−x@NC counter electrode exhibited strong chemical-composition-dependent photovoltaic performance. Under optimal conditions, the CoxNi1−x@NC counter electrode presented an impressive energy conversion efficiency of 3.58%, suggesting that it is a highly promising counter electrode for application in dye-sensitized solar cells. This counter electrode has the advantages that it is considerably less expensive than a Pt counter electrode and that it provides the basis for the design and preparation of other inexpensive and efficient counter electrodes to replace Pt. [ABSTRACT FROM AUTHOR]

Nitrogen-doped graphene (N-G) is considered as a promising catalyst for the oxygen reduction reaction (ORR). However, the contributions of pyridinic N, pyrrolic N and graphitic N in N-G for the ORR catalytic activity are controversial. In this work, the contents of pyridinic N, pyrrolic N and graphitic N in N-G were transformed by annealing at different temperatures. It is found that the total N content in N-G is not the critical factor to determine the ORR activity. An increase in the annealing temperature can enhance the content of graphitic N in N-G, causing an improved catalytic ORR activity, which confirms that graphitic N is the active component. Moreover, the enriched graphitic N in the N-G-1000 catalyst shows a half-wave potential (E1/2) of 0.862 V, 29 mV higher than that of the commercial Pt/C catalyst (0.833 V), which is one of the best reported for ORR metal-free catalysts. [ABSTRACT FROM AUTHOR]

Atomically dispersed iron-nitrogen-carbon catalysts offer great potential in oxygen reduction reaction (ORR), yet the poor exposure and low density of Fe-N x sites causes relatively low ORR activity. Herein, a zinc-assisted MgO template strategy is reported to construct porous carbon-supported Fe-N 4 sites (Fe-N-C). Iron atoms surrounded by zinc species are converted to abundant Fe-N 4 sites rather than Fe containing nanoparticles. Meanwhile, both the zinc species and the MgO template can effectively produce porous structure so as to increase the utilization of Fe-N 4 sites. Fe-N-C achieves superior ORR performance and stability in alkaline medium. Theoretical calculations manifest that Fe-N 4 sites can narrow the energy barrier for ORR. Moreover, finite element simulation exhibits the porous framework in Fe-N-C could significantly accelerate the diffusion of O 2. Therefore, Fe-N-C provides a high peak power density and superior discharge ability toward Zn-air batteries. [Display omitted] • Atomically dispersed Fe-N-C are prepared by zinc-assisted template strategy. • High density of Fe-N x and hierarchical porosity boost oxygen reduction reaction. • The porous framework of Fe-N-C could significantly accelerate the diffusion of O 2. • The catalyst exhibits an excellent performance in Zn-air batteries. [ABSTRACT FROM AUTHOR]

The reasonable design of porous structures is important but usually overlooked for nonprecious metal ORR catalysts. In this study, a facile dual melt-salt-mediated templating method is developed to prepare a Fe-N-C catalyst with tailored porous framework. The ZnCl 2 and NaCl are employed to construct abundant micropores and promote the transformation of partial micropores to mesopores, respectively, reasonably forming a 3D hierarchically porous framework. The catalyst demonstrates a satisfactory surface area (1605 m2/g), promoting mass transport and exposure of FeN 4 sites. Interestingly, the dual melt-salt templates avoid rapid loss of nitrogen during pyrolysis, thus enhancing Fe-N 4 active center density. Therefore, the obtained Fe-N-C material presents outstanding ORR performance in both alkaline and acid media, as well as good stability. The advances of this catalyst are further proved in liquid and solid-state Zn-air battery, with nice discharge stability and high peak power densities. The dual melt-salt-mediated templating strategy is developed to prepare the hierarchically porous Fe-N-C catalyst incorporated with abundant Fe-N x site. [Display omitted] • 3D hierarchically porous structure is engineered using ZnCl 2 and NaCl as templates. • The protective molten salts can sharply increase the Fe-Nx active site density. • The catalyst presents outstanding ORR activity under alkaline/acidic electrolytes. • The catalyst exhibits superior performance in practical Zn-air batteries. [ABSTRACT FROM AUTHOR]

[Display omitted] • A porous carbon was prepared from Microcystis aeruginosa and polypropylene. • Polypropylene enhanced the pore structure of porous carbon. • Porous carbon exhibited a high S BET (2140 m2/g) and abundant functional groups. • Porous carbon exhibited a high methylene blue adsorption capacity (667 mg/g). Porous carbon obtained by co-pyrolysis of plastic and biomass has received a lot of attention due to its excellent adsorption properties, and the pore structure plays an essential role in adsorption performance, however, the pore structure is still not well understood. Herein, we synthesized cyanobacteria-based porous carbon derived from cyanobacteria and polypropylene plastic by one-step method. CPC-800–30% exhibited a high BET surface area (2140 m2/g), pore volume up to 1.44 cm3/g. PP not only improved the pore structure of porous carbon, but also enriched the types of functional groups, such as O–H, N–H, C=O, and –CH, due to dehydroxylation or amino group decreased, resulting in the hydrogen radicals increased, hence PP had positive effect for biomass during co-pyrolysis. Meanwhile, CPC-800–30% showed excellent methylene blue (MB) adsorption capacity (667 mg/g). This work provided a new strategy for enhancing porous carbon structure via using PP as additive. [ABSTRACT FROM AUTHOR]

[Display omitted] • GHNCNs_Urea was designed by introducing nitrogen source, increasing pore structures. • The GHNCNs_Urea electrocatalyst exhibited outstanding ORR activity. • The excellent ORR activity was attributed to ultra-high SSA and large pore volume. • The Zn-air battery exhibited a high peak power density and a long-term stability. When designing carbon-based electrocatalysts as Pt-free catalysts for the oxygen reduction reaction (ORR), pore structures is crucial, in addition to creating active sites. Here, N-doped carbon nanosheets were rationally designed by tactfully introducing nitrogen source into the carbonization process, which could increase the density of pore structures and effective active sites. Owing to the ultra-high specific surface area (2127 m2 g−1), large pore volume (5.77 cm3 g−1), and bimodal-pore structure (micropores and mesopores), the optimized catalyst exhibited an excellent ORR activity (a half-wave potential of 0.86 V), as well as outstanding durability and methanol tolerance in alkaline medium. Moreover, it provided excellent stability and high peak power density when used as ORR catalyst in Zn-air battery, exceeding that driven by Pt/C catalyst. This work brings a feasible and universal strategy for fabricating metal-free ORR catalysts. [ABSTRACT FROM AUTHOR]