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To reduce the cost of fuel cell oxygen reduction reaction catalysts, the gels of polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO) triblock copolymer (F127) and Fe(NO3)3·9H2O, formed in ethanol-hexane mixture by sol–gel method, were pyrolyzed to prepare the iron-doped carbon-based ORR catalysts. Among all the prepared samples, the Fe2-C, pyrolyzed at 800 ℃ with 0.6 mmol content of Fe(NO3)3·9H2O, possessed highly graphitized structures (ID/IG = 0.632), the highest specific surface area (251.3 m2/g) and the best electrochemical performance. Its onset potential and half-wave potential were 0.85 V vs. RHE and 0.71 V vs. RHE in 0.1 M KOH solution, respectively. Meanwhile, Fe2-C also had better stability and methanol tolerance than commercial 20% Pt/C. The results provided a convenient and low-cost method for preparing more efficient ORR catalysts for anion exchange membrane fuel cells. [ABSTRACT FROM AUTHOR]

Methanol steam reforming (MSR) is considered as an effective way to provide on-line hydrogen production technology for fuel cell applications, and perovskite catalyst is considered as an efficient and potential catalyst for this technology. A series of La1-xMxCo0.5Ni0.5O3 perovskite catalysts doped with yttrium(Y) and cerium(Ce) at A site were prepared by sol-gel method. The catalysts were characterized by SEM, EDS, BET, XPS and XRD techniques. The results of XRD, SEM and BET show that the main phase of the catalyst is perovskite when a small amount of Y or Ce is doped. However, with the increase of Y and Ce doping levels, some other new phases appeared. The appearance of the new phase of yttrium oxide promotes the richer pore structure of the catalyst, increases the pore volume and pore diameter, and enhances the active catalytic sites. More importantly, it also promotes the increase of the specific surface area, allowing the active component particles to maintain a very uniform dispersion state, effectively preventing the aggregation of active components and improving the catalytic activity. From the XPS results of Y-doped catalyst with x of 0.9, Y-O bonds belonging to Y2O3 can be observed, the presence of yttrium carbonate species can promote the formation of oxygen vacancies, thereby accelerating the catalytic reaction and enhancing the catalytic performance. After multiple cycles of start-stop stability experiments, the results showed that the CO selectivity of the gas product was 1.8% and remained unchanged without significant fluctuations. The novel yttrium-doped catalyst with x of 0.9 developed in this study is a potential catalyst which can directly provide hydrogen-rich source for HT-PEMFCs applications. Highlights: Y and Ce doped La1-xMxCo0.5Ni0.5O3 catalyst is applied to produce enriched H2 for HT-PEMFCs at first time. Excessive Y doping produces yttrium carbonate species which can promote the formation of oxygen vacancies, and enhancing the catalytic performance. Proper doping of Y and Ce at A site is beneficial to reduce the CO selectivity of the catalyst at low temperature. Catalyst developed in this study have can directly provide hydrogen-rich source for HT-PEMFCs applications. [ABSTRACT FROM AUTHOR]

Fe–N–C materials have emerged as promising alternatives to precious metals for oxygen reduction reaction/oxygen evolution reaction (ORR/OER). In this study, a strategy is presented to investigate the influence of different chemical states of iron species in Fe–N–C materials on their electrocatalytic performance. Three Fe–N–C catalysts, containing either zero-valent Fe or Fe3O4 nanoparticles, are synthesized using acid pickling, high-speed centrifugation and ultrasound-assisted hydrothermal methods, respectively. The findings manifest that the chemical state of iron significantly affects the electrocatalytic activity of Fe–NX active sites, namely zero-valent Fe enhancing Fe–NX activity while Fe3O4 weakening its activity. Notably, the Fe@FeNC catalyst containing only zero-valent iron, demonstrates the only 0.621 V potential difference between the ORR half-wave potential and the OER potential at 10 mA cm−2. Furthermore, the rechargeable Zn–air battery assembled with Fe@FeNC as the air cathode exhibits a remarkable peak power density of 179.0 mW cm−2, excellent cycling stability over 210 h (with a cycle frequency of one every 10 min), and the minimal voltage gap of 0.710 V. These results reveal the significance of different chemical states of metal-based nanoparticles in Fe–NX activity of Fe–N–C catalysts and offer insights into the rational design of electrocatalysts with exceptional activity and versatile applications. [ABSTRACT FROM AUTHOR]

The NiMn2O4/graphene oxide (GO) nanocomposite material was in situ grown on the surface of a nickel foam 3D skeleton by combining the solvent method with the microwave-assisted hydrothermal method and annealing; then, its performance was investigated as a superior supercapacitor electrode material. When nickel foam was soaked in GO aqueous or treated in nickel ion and manganese ion solution by the microwave-assisted hydrothermal method and annealing, gauze GO film or flower-spherical NiMn2O4 was formed on the nickel foam surface. If the two processes were combined in a different order, the final products on the nickel surface had a remarkably different morphology and phase structure. When GO film was first formed, the final products on the nickel surface were the composite of NiO and Mn3O4, while NiMn2O4/GO nanocomposite material can be obtained if NiMn2O4 was first formed (immersed in 2.5 mg/L GO solution). In a 6M KOH solution, the specific capacitance of the latter reached 700 F/g at 1 A/g which was superior to that of the former (only 35 F/g). However, the latter's specific capacitance was still inferior to that of in-situ grown NiMn2O4 on nickel foam (802 F/g). Though the gauze-formed GO film, almost covering the preformed flower-spherical NiMn2O4, can also contribute a certain specific capacitance, it also restricted the electrolyte diffusion and contact with NiMn2O4, accounting for the performance decrease of the NiMn2O4/GO nanocomposite. A convenient method was raised to fabricate the nanocomposite of carbon and double metal oxides. [ABSTRACT FROM AUTHOR]

A structured carambola-like CoWO4 was fast prepared by a microwave-assisted hydrothermal method with the help of urea and NH4F. Physical characterization indicated that the as-obtained CoWO4 displayed a large specific surface area, high dispersion and self-selected orientation of crystal growth. Further electrochemical tests presented a high specific capacity of 492.0 C ⋅ g − 1 at 1 A ⋅ g − 1 , low internal resistance and excellent cycle stability as 137.3% capacity maintenance after 8000 cycles at 20 A ⋅ g − 1 . These excellent electrochemical properties for the as-obtained material indicate that CoWO4 has great potential as hybrid supercapacitor electrode materials. This work also provides a new and effective solution for regulating the morphology of CoWO4-based hybrid supercapacitor materials to further improve the electrochemical performance. [ABSTRACT FROM AUTHOR]

Fe-Cr-based soft magnetic alloy (SMA) monolayer coatings with high saturation magnetization (Ms) above 1.3 T were deposited onto AISI 1010 substrate by co-axial powder feeding plasma transferred arc (PTA) welding, using FeCrBSi self-fluxing powders Fe313, which have a similar chemical composition to AISI 430 ferritic stainless steel (FSS). The effect of welding parameters on the phase assemblage, microstructure, hardness and magnetic performance of the coatings was investigated. The results show that the coating's maximum width and the welding surplus height increased with the rise in welding heat input and powder distribution density, respectively. The coating's Ms increased sharply, but its coercivity (Hc) decreased with the growth in the substrate dilution ratio. The coating's Hc increased whereas its Ms decreased with the increment in welding heat input. The as-welded coating C3 with optimum magnetic performance had a dendrites–eutectics composite structure, where the columnar or equiaxed sorbitic pearlite dendritic cores surrounded by network-like eutectics α(Fe,Cr) + (Fe1−xCrx)2B were the main contents. Moreover, (Fe,Cr)7C3 and CrB had also been detected, and they were mainly distributed in the interdendritic regions. The body-centered cubic (b.c.c.) α(Fe,Cr) multi-element solid solution contributes to a high Ms of 1.61 T, and the borides (Fe1−xCrx)2B and CrB as well as (Fe,Cr)7C3 and other carbides cause a high Hc of 58.6 Oe and hardness HV0.3 of 4.90 ± 0.06 GPa, much higher than that of AISI 430 FSS (HV < 1.8 GPa). The current work verifies the feasibility of fabricating Ni- and Co-free FeCrBSi SMA coatings with high Ms and high hardness via PTA welding, and since the feedstock powders have chemical composition similar to AISI 430 FSS, the work may bring about novel applications for AISI 430 FSS in particular cases where the considerable wear-resistant performance as well as superior soft magnetic and anti-corrosive properties are required. [ABSTRACT FROM AUTHOR]