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Summary: Hollow cobalt nitrogen‐doped carbon (H‐CoNC) is suggested for use in the membraneless hydrogen peroxide fuel cell (HPFC) and enzymatic biofuel cell (EBC) as anodic catalyst boosting hydrogen peroxide oxidation reaction (HPOR). For fabricating H‐CoNCs, a facile spray pyrolysis‐assisted process is used, and such produced H‐CoNCs show a porous and hollow‐shell structure, while they include a large amount of isolated Co atoms and coordinate bonds with Co and nitrogen (CoN4). This structure promotes mass transfer to the active site and excellent catalytic activity for HPOR. With these benefits of H‐CoNCs, the current density of the bioanode consisting of H‐CoNC, carbon nanotube, and glucose oxidase (H‐CoNC/CNT/GOx) observed at 0.3 V under 150 mM glucose is 315.5 μA cm−2, which is 2.1 times higher than that of a conventionally synthesized catalyst using Co‐doped carbon nanoparticles (CoNC‐NPs) (CoNC‐NPs/CNT/GOx, 146.2 μA cm−2). With this superior catalytic activity for HPOR, maximum power density (MPD) of membraneless EBC using H‐CoNC/CNT/GOx is 33.8 ± 4.52 μW cm−2, which is 52% higher than that of CoNP‐NPs/CNT/GOx. In addition, a membraneless HPFC using H‐CoNC/CNT demonstrates 4.87 times higher MPD (231.3 ± 11.3 μW cm−2) than that using CoNC‐NPs/CNT, proving that H‐CoNC improves the performance of fuel cells by its excellent catalytic activity. [ABSTRACT FROM AUTHOR]

Summary: Platinum‐free electrocatalysts for oxygen–reduction reactions in acidic medium are challenging as the cathode of PEMFC. Here, we synthesized core‐shell‐type leaf‐shaped CoFe‐NC (L‐CoFe‐NC) catalysts using 2D ZIFs as cores and 3D ZIFs as shells. The amounts of Co and Fe were carefully controlled to obtain highly dispersed CoFe‐doped carbon. This strategy made it easy to tune the catalyst while maintaining the advantages of the 2D structures. The prepared L‐CoFe‐NC showed a half‐wave potential (E1/2) of 0.77 V and an onset potential (Eonset) of 0.88 V in 0.5 M H2SO4. In addition, the results confirmed high durability even after 10 000 tests while retaining excellent performance. This outstanding stability was achieved owing to the high dispersion of Co and Fe in the 2D carbon frame. Furthermore, PEMFC was evaluated using an MEA containing L‐CoFe‐NC catalysts as a cathode. [ABSTRACT FROM AUTHOR]

Primary Li-SO2 batteries offer a high energy density in a wide operating temperature range with exceptionally long shelf life and have thus been frequently used in military and aerospace applications. Although these batteries have never been demonstrated as a rechargeable system, herein, we show that the reversible formation of Li2S2O4, the major discharge product of Li-SO2 battery, is possible with a remarkably smaller charging polarization than that of a Li-O2 battery without the use of catalysts. The rechargeable Li-SO2 battery can deliver approximately 5400 mAh g−1 at 3.1 V, which is slightly higher than the performance of a Li-O2 battery. In addition, the Li-SO2 battery can be operated with the aid of a redox mediator, exhibiting an overall polarization of less than 0.3 V, which results in one of the highest energy efficiencies achieved for Li-gas battery systems. [ABSTRACT FROM AUTHOR]

The lithium-oxygen battery has the potential to deliver extremely high energy densities; however, the practical use of Li-O2 batteries has been restricted because of their poor cyclability and low energy efficiency. In this work, we report a novel Li-O2 battery with high reversibility and good energy efficiency using a soluble catalyst combined with a hierarchical nanoporous air electrode. Through the porous three-dimensional network of the air electrode, not only lithium ions and oxygen but also soluble catalysts can be rapidly transported, enabling ultra-efficient electrode reactions and significantly enhanced catalytic activity. The novel Li-O2 battery, combining an ideal air electrode and a soluble catalyst, can deliver a high reversible capacity (1000 mAh g−1) up to 900 cycles with reduced polarization (about 0.25 V). [ABSTRACT FROM AUTHOR]

Abstract: Soybean oil was pyrolyzed with various catalysts in a fixed-bed reactor under nitrogen flow at 420 and 450°C. The H-ZSM5 catalysts (molar ratio SiO2/Al2O3 =28, 40, and 180) and 2wt% (Ga, Al or Cu) impregnated MCM41 catalysts were used in order to investigate the effect of catalysts during the pyrolysis process. The gas products in all experiments were mainly methane, ethane and propylene. The liquid products in the presence of H-ZSM5 catalysts were mainly aromatic components while those with metal/MCM41 catalysts were a mixture of alkanes, alkenes, alkadienes, aromatic and carboxylic acids. The highest coke yield of 4.4wt% was obtained with Ga/MCM41 catalyst at the pyrolysis temperature of 420°C. The effect of catalysts on product yield and composition was systematically investigated. [Copyright &y& Elsevier]

[Display omitted] • M–N–C catalyst with Single-atoms (Fe, Co) and Co nanoparticles were synthesized. • Optimizing PPy concentration enhanced the active site for ORR in alkaline media. • The prepared catalyst showed excellent ORR performance, stability, and durability. • The prepared catalyst based-zinc-air batteries achieved high performance. Non-platinum electrocatalyst development for improving the oxygen reduction reaction (ORR) is critical in electrochemical energy conversion applications such as zinc-air batteries (ZABs). Herein, we developed dual Fe-Co single atoms and Co nanoparticles embedded N-doped hollow carbon (Fe-Co/N-HCS-x) catalysts via the carbonization of polypyrrole (PPy)@zeolitic imidazolate framework (ZIF) core–shell particles, with various PPy concentrations. PPy serves as a secondary nitrogen source that enhances nitrogen amount and promotes metal dispersion to increase active sites density. The Fe-Co/N-HCS-x catalysts with optimized PPy concentration control demonstrated improved ORR performance in alkaline media, with a half-wave potential (E 1/2) of 0.921 V and an onset potential (E onset) of 1.019 V. Fe-Co/N-HCS-x also exhibited high ZABs performance, with a power density of 244.6 mW cm−2 and an operating time of more than 100 h. Our research contributes to the development of optimized active sites for ORR, which can be applied to new electrochemical storage and conversion systems. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR), one of the key reactions for fuel cells and zinc-air batteries, should be improved for higher performance. Herein, we fabricated hollow Fe, Co, and nitrogen co-doped carbon (H-FeCo-NC) catalyst, which was prepared by carbonization of core-shell particles made of polypyrrole (PPy)-coated polystyrene (PS) spheres as cores and (Zn, Co) bimetallic-zeolitic imidazolate frameworks (ZnCoBZIFs) as shells. PPy was used as a nitrogen and a carbon source. The H-FeCo-NC catalyst had a high surface area of 324.08 m2 g−1 with uniformly distributed Fe and Co species, and excellent ORR performance with the half-wave potential of 0.888 V vs. reversible hydrogen electrode in alkaline media. Furthermore, the H-FeCo-NC catalyst demonstrated exceptional stability, durability, and tolerance to methanol crossover. • Hollow Fe, Co, and N-doped carbon was prepared using polypyrrole and MOFs. • Polypyrrole served as the source of carbon and nitrogen. • Hollow FeCo-NC catalyst showed high surface area with high metal dispersion. • The ORR activity, stability, and durability of the H-FeCo-NC catalyst were excellent. [ABSTRACT FROM AUTHOR]

Governing the fundamental reaction in lithium–oxygen batteries is vital to realizing their potentially high energy density. Here, novel oxygen reduction reaction (ORR) catalysts capable of mediating the lithium and oxygen reaction within a solution‐driven discharge, which promotes the solution‐phase formation of lithium peroxide (Li2O2), are reported, thus enhancing the discharge capacity. The new catalysts are derived from mimicking the biological redox mediation in the electron transport chain in Escherichia coli, where vitamin K2 mediates the oxidation of flavin mononucleotide and the reduction of cytochrome b in the cell membrane. The redox potential of vitamin K2 is demonstrated to coincide with the suitable ORR potential range of lithium–oxygen batteries in aprotic solvent, thereby enabling its successful functioning as a redox mediator (RM) triggering the solution‐based discharge. The use of vitamin K2 prevents the growth of film‐like Li2O2 even in an ether‐based electrolyte, which has been reported to induce surface‐driven discharge and early passivation of the electrode, thus boosting the discharge capacity by ≈30 times. The similarity of the redox mediation in the biological cell and lithium–oxygen "cell" inspires the exploration of redox active bio‐organic compounds for potential high‐performance RMs toward achieving high specific energies for lithium–oxygen batteries. A new redox mediator (RM), vitamin K2, for oxygen reduction reaction of lithium–oxygen batteries is developed, which is enabled by the inspiration from biological respiration system. Vitamin K2 surprisingly enhances the discharge capacity of lithium–oxygen cell by converting the reaction pathway of oxygen reduction. Successeful utilization of vitamin K2 shows validity of exploiting biological knowledge to discover high‐performance RM. [ABSTRACT FROM AUTHOR]

We report the synthesis and characterization, reaction kinetics, and deactivation mechanism of a series of catalysts with metallic nickel (Ni) and molybdenum carbide (Mo 2 C) particles supported on zeolite Y (Ni-Mo 2 C/FAU) in methane steam reforming (MSR) reaction at 850 °C. Despite a low Ni loading of 2.4 wt%, MSR on Ni-Mo 2 C/FAU exhibits high activity and stability, yet deactivation of Ni-FAU is significant. Further investigations elucidate that the catalyst deactivation is caused by Ni particle sintering via Ostwald ripening instead of coking, and steam induces hydroxylated Ni surface that accelerates sintering. Moreover, Mo 2 C boosts the activity and stability of Ni on zeolite Y by enhancing CH 4 activation rather than activating H 2 O. The interplays among Mo 2 C and Ni particles dynamically balance the carbon formation and consumption rates, and inhibit Ni sintering. This study demonstrates that high MSR activity and stability can be achieved on transition metal carbide – Ni catalysts with systematically tuned compositional, structural, and interfacial factors. [Display omitted] • Sintering and coking are the deactivation mechanisms of Ni- and Mo 2 C-FAU in MSR. • The synergy between Ni and Mo 2 C increased both activity and stability in MSR. • Mo 2 C enhanced CH 4 activation, shown by its 4 times higher CH 4 decomposition rate. • Mo 2 C has excellent thermal stability and is still highly dispersed after reaction. • The real active sites are Mo 2 C decorated Ni species as shown in TEM-EDX. [ABSTRACT FROM AUTHOR]

Herein, we report a series of Platinum (Pt) phase loading on the highly porous channels of the metal-organic framework (MOF) introduces open Lewis acid sites through a defective-effect, which are crucial for selective hydrodeoxygenation (HDO) process of anisole. Thereby, UiO-66 (University of Oslo) based-supports were synthesized by a microwave-assisted solvothermal method using isophthalic acid (IPA) as a mixed linker at different concentrations. The total amount of acid sites in the defective UiO-66 samples was 1.5–2.5 times higher than that of pristine UiO-66, with the corresponding linker deficiency increasing to 1.94 as the concentration of the mixed linker was increased to 30% in the starting material. Consequently, the 3Pt/defective UiO-66 catalysts achieved better catalytic performance for the anisole HDO process, with a turn-over frequency (TOF) value of the Pt site being 2–3 times higher than that of the pristine 3Pt/UiO-66. Notably, the reaction pathway shifted from producing cyclohexane to producing benzene through the demethoxylation of anisole. This resulted in an increase in the TOF value based on the benzene yield by over 10 times as the defective linker content increased from 0 to 20%. The catalytic stability was also investigated using a series of Pt/defective UiO-66 catalysts. • Pt/defective-UiO66 catalysts were synthesized by the microwave-solvothermal method. • TOF Pt over Pt/defective-UiO66 catalysts were 2–3 times higher than that of Pt/UiO-66. • Demethoxylation of anisole to benzene production is predominant to hydrogenation. • HDO conversion was maintained above 80% after 8 h reaction with 3Pt/UiO-66-20def catalyst. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pt/UiO66-xNH 2 catalysts were synthesized by the microwave-solvothermal method. • TOF Pt over Pt/UiO66-NH 2 catalysts were 1.8–3.2 times higher than that of Pt/UiO-66. • Transferring from DCOx to HDO reaction, confirmed by increase in C 18 /C 17 ratio. • Showing a good catalytic stability for coke deposition during HDO reaction. With the aim of developing more efficient catalysts based on MOF materials for biomass upgrading through the hydrodeoxygenation, a novel Pt/UiO-66-based catalyst was first designed by introducing amino groups, together with creating mixing-linker defect using 5-amino-isophthalic acid as a mixed linker, were successfully synthesized with a microwave-solvothermal method. XPS and CO-chemisorption measurements revealed that the presence of amino groups significantly enhance the reducibility of the PtCl 6 2- and PtCl 4 2- phases to the Pt0 phase. As a result, the catalytic performance of these catalysts in the HDO of oleic acid was enhanced, as demonstrated by the 1.8–3.2-fold higher turnover frequency compared to the original Pt/UiO-66 catalyst. Interestingly, the presence of amino-defective linker facilitated the transition from decarbonylation to the hydrodeoxygenation reaction, as confirmed by the significant increase in C 18 /C 17 ratio. Importantly, the modified catalysts were shown to possess a good catalytic stability, thus preventing coke deposition on the UiO-66 structure. [ABSTRACT FROM AUTHOR]

In this study, Ni/γ-Al 2 O 3 and Fe/activated carbon (AC) catalysts were prepared by an incipient impregnation method and then utilized for hydrodeoxygenation (HDO) of guaiacol (GUA). The AC used in the process was derived from bamboo through steam activation. The effects of the calcination temperature, metal loading, and phosphorus addition on the HDO of GUA were systematically investigated. At 300 °C and atmospheric pressure, 91.52% of GUA was successfully transformed into cresol and 1,2-dimethoxybenzene in liquid phase using 10 wt% of the Fe/AC catalyst, which was calcined at 550 °C. Under the same reaction conditions, utilizing 10 wt% of the Ni/ γ -Al 2 O 3 catalyst, which was calcined at 450 °C, resulted in 96.88% GUA conversion, producing 13.03% of cresol, 58.98% of 1,2-dimethoxybenzene, and 27.99% of 3-methyl guaiacol. Additionally, the reaction pathways of the GUA HDO were proposed based on the obtained product distributions. [Display omitted] • Effect of metal loading and calcination temperature on γ-Al 2 O 3 and AC support was investigated for guaiacol HDO. • 10 wt% Ni/γ-Al 2 O 3 catalyst calcined at 450 °C resulted in the highest GUA conversion of 96.88%. • Phosphorus addition to Ni/γ-Al 2 O 3 and Fe/AC affected product distributions. • Reaction pathways of guaiacol HDO were proposed based on liquid products. [ABSTRACT FROM AUTHOR]

[Display omitted] • MOF-PPy composites were synthesized in a one-pot reaction. • The CoFe-NC-PPy with single-atom of Fe and Co was successfully synthesized. • PPy served as secondary nitrogen sources for enhanced ORR activity. • The CoFe-NC-PPy showed excellent ORR activity and durability in alkaline media. • The AEMFC performance with CoFe-NC-PPy exhibited remarkable efficiency. Metal-nitrogen-doped carbon (M−N−C) catalysts have emerged as highly active noble-metal-free catalysts for oxygen reduction reactions (ORR) in anion-exchange membrane fuel cells (AEMFCs). However, the performance of existing M−N−C catalysts is limited by the inaccessibility of internal M−N x active sites and loss of nitrogen doping after the carbonization process. Here, a single-atom Co, Fe and N-doped porous carbon catalyst (CoFe-NC-PPy) were constructed using a complex of metal–organic frameworks (MOFs) and polypyrrole (PPy). As a new approach, we synthesized MOF and PPy composites by combining in situ MOF synthesis and pyrrole polymerization in a one-pot reaction. Through pyrolysis, the PPy and MOF composites demonstrated an enhanced specific surface area, a high active-site density, and a high concentration of nitrogen species in the M−N−C catalyst. These contributed to a superior ORR performance (E 1/2 of 0.915 V) and high durability in alkaline media. Additionally, the CoFe-NC-PPy material studied in an AEMFC enabled high performance with a current density of 550 mA cm−2 at 0.6 V and a peak power density of 352 mW cm−2. This study suggests potential in combining polymers and MOFs in the synthesis of ORR catalysts for fuel cells. [ABSTRACT FROM AUTHOR]

In this study, spherical mixed oxides of Al 2 O 3 and TiO 2 supported molybdenum (Mo) catalysts, Mo/Al 2 O 3 −TiO 2 , were successfully prepared using a novel approach combining sol-gel and spray pyrolysis (SP) methods. First, both boehmite sol and titania sol were prepared by a sol-gel process, and then molybdate salt was dispersed in the sol mixture with the assistance of citric acid, followed by spray pyrolysis of the mixed precursor solution. Structural analyses of prepared catalysts showed that the dispersion of active sites was affected by the TiO 2 concentration in the Al 2 O 3 −TiO 2 mixed oxide support. The catalytic activities of reduced catalysts were investigated for hydrodeoxygenation (HDO) of palmitic acid, which is the main component of microalgae–derived biocrude. The results show that the Mo/Al 2 O 3 –TiO 2 catalysts exhibited excellent catalytic performance for the HDO of palmitic acid. [ABSTRACT FROM AUTHOR]

Fe-N-C catalysts are promising alternatives to the platinum-group catalysts for use in oxygen reduction reactions of proton exchange membrane fuel cells. However, Fe-N-C catalysts suffer from poor durability, compared to non-precious metal catalysts, because of their accelerated demetallation by the Fenton reaction. In this study, we report the synthesis of a melamine-encapsulated Co-ZnO-C composite as a precursor and template for zeolite-imidazole-frameworks (ZIF-8). This approach allows formation of Co-N-C for constructing unique structures at meso- and macropore scales, while maintaining microporosity. Density functional theory analysis confirms the superior stability of the Co-N-C catalyst over other M-N-C catalysts (M = Fe, Ni, Cr, and Mn). Furthermore, it reveals that a closed interaction between the Co-N 4 moiety and organic adducts enhances oxophilicity, which prefers a 4-electron ORR activity. The Co-NC catalyst with a developed pore structure shows remarkable durability (6.7% performance degradation for 100 h) and full cell performance in H 2 /O 2 under 1 bar of backpressure (723 mW/cm2 of maximum power density). Consequently, the unique structure of the synthesized catalyst successfully translates to the computationally-established ORR activity in the half-cell; superior durability is seen in the real device operation and stability analysis. This work is expected to support next-generation fuel cell development. [Display omitted] • Melamine encapsulated Co-ZnO-C was prepared as precursor and template for atomic-cluster and porous Co-N-C catalyst. • ma-Co-NC exhibited excellent proton exchange membrane fuel cell performance and stability. • This approach allows formation of M-N-C for constructing unique structures at meso- and macropore scales, while maintaining microporosity. [ABSTRACT FROM AUTHOR]

Abstract: This study investigated the control of hydroxyl groups, one of key factors determining the surface properties of silica particles synthesized by the sol-precipitation of tetraethyl orthosilicate (TEOS). Thus, a thermal gravity analysis (TGA) was used to facilitate quantitative measurements of the hydroxyl groups on the silica particles, while BET and FT-IR were used to analyze the specific surface area and functional silane groups on the silica particles, respectively. In the sol-precipitation process, silanes that include various hydroxyl groups are formed as intermediates based on the hydrolysis and condensation of TEOS. Thus, NH3, as a basic catalyst initiating the nucleophilic substitution of TEOS, was found to accelerate the hydrolysis and increase the hydroxyl group content on the silica particles. Plus, the hydroxyl group content was also increased when increasing the concentrations of TEOS and water as the hydrolysis reactants. However, the hydroxyl group content was reduced when increasing the temperature, due to the promotion of condensation. Based on the weight loss of the particles according to the thermal analysis, the hydroxyl group content on the silica particles varied from 5.6–42.7OH/nm2 under the above reaction conditions. [Copyright &y& Elsevier]

Abstract: In this work, the activity values of Cu/Al2O3-, Fe/Al2O3- and Cu/Fe/Al2O3-composite granule catalysts prepared by a combination of Yoldas-process and oil-drop method were studied in an attempt to find some suitable catalysts for the decomposition of sulfur trioxide as the oxygen-generating reaction in the thermo-chemical water splitting process. The SO3 decomposition was performed in the temperature range of 750–950°C at a space velocity of 72,000mL/gcat.h in a fixed bed reactor. The catalytic activity of Cu/Fe/Al2O3-composite granule catalyst was better than that of Cu/Al2O3- and Fe/Al2O3-composite granule catalysts. The composite of Cu and Fe in the alumina granules increased the catalytic activity and found the optimum ratio of [Cu]/[Fe]=1/2 with [Cu]+[Fe]=0.125M. [Copyright &y& Elsevier]