Search

Abstract: Low‐cost and high‐activity electrocatalysts for the oxygen reduction reaction (ORR) are necessary for the development of fuel cells and metal‐air batteries. Manganese oxide would be a good candidate because of its low cost, abundant supply, and environmental benignity if not for its relatively low activity compared with noble metals. To improve the ORR activity of manganese oxide, we developed a sulfurization process to create pores in 2 D manganese oxide nanosheets. The nanoporous MnO2 nanosheets (np‐MnO2‐ns) prepared as such contain 7 nm pores in the nanosheets and their half‐wave potential (0.73 V) is 40 mV more positive than that of pore‐free MnO2 nanosheets (0.69 V). The higher ORR activity of np‐MnO2‐ns may be attributed to the combination of a large surface area and the presence of high‐ORR‐activity Mn3+/4+ sites. The np‐MnO2‐ns also showed an enhanced oxygen evolution reaction activity and delivered a good performance in rechargeable Zn‐air batteries. [ABSTRACT FROM AUTHOR]

The C3 selectivity of carbon-supported Au nanoparticles for glycerol electro-oxidation was significantly enhanced by the interaction of Au with electro-deposited Cu species. Notably, the C3 selectivity of supported Au nanoparticles doubled after 90 min of Cu electro-deposition at +0.015 V. This result was obtained if glycerol electro-oxidation was performed at +0.1 V for 2 h. The most selective catalysts contained an Au+ species that was generated by an interaction between Au and electro-deposited Cu2O. The presence of Au+ increased the selectivity to glycerate and tartronate and suppressed C−C bond cleavage to glycolate and formate simultaneously. [ABSTRACT FROM AUTHOR]

Although transition-metal oxides are common non-platinum group metal catalysts for the industrially important oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), the performance gap between transition-metal oxides and platinum group metal catalysts is still substantial and there is a continuing need to search for alternatives. In this study, transition-metal (Mn, Fe, Co, and Ni) phosphates prepared by a solution chemistry method under ambient conditions are found to display interesting electrocatalytic properties for the ORR and OER in alkaline solution. Among them, manganese phosphate is more active than most state-of-the-art manganese oxides for the ORR, and nickel phosphate is as active as the best Ni-based catalysts for the OER. Hence these phosphates can be used as tandem catalysts for rechargeable metal-air batteries in which both the ORR and OER take place. The good performance may be attributed to the stabilization of the catalytic centers by the phosphate framework. This study establishes phosphates as yet another class of highly active low-cost non-platinum group metal alternatives for oxygen electrocatalysis in alkaline solution. [ABSTRACT FROM AUTHOR]

With new chemistry and advantageous configuration, the lithium-oxygen (Li-O2) battery promises a much higher specific energy than traditional lithium-ion batteries. The limited understanding on the complicated battery reactions therein, however, has become a major bottleneck of its development for applications requiring a high energy efficiency and long cycle-life. Herein, in a confined potential window with negligible electrolyte degradation, we studied the rechargeability of Li-O2 cathodes with pre-filled well-defined discharge products of Li2O2, Li2CO3, LiOH, or their combinations. Our results suggest Li2CO3 as the most difficult species to be electrochemically decomposed among the three lithium compounds, whereas the presence of LiOH notably increases the initial charge potential. The clearly visible difference in the charge behavior and cycling stability of these artificially 'discharged' electrodes provides a guideline for the development of future high-performance Li-O2 batteries. [ABSTRACT FROM AUTHOR]

Nanoscale Li-rich Li1.2Mn0.54Ni0.13Co0.13O2 material is synthesized by a co-precipitation combined freeze drying (CP-FD) method, and compared with a conventional co-precipitation method combined vacuum drying (CP-VD). With the combination of X-ray diffraction (XRD) and scanning electron microscopy (SEM), it is found that the sample from CP-FD method consists of a pure phase with good crystallinity and small, homogenous particles (100-300 nm) with uniform particle size distribution. Inductively coupled plasma spectroscopy (ICP) shows that the sample has a stoichiometric ratio of n(Li): n(Mn): n(Ni): n(Co)=9:4:1:1; and its Brunauer-Emmett-Teller (BET) specific surface area is 5.749 m2 g−1. This sample achieves excellent electrochemical properties: its initial discharge capacities are 298.9 mAh g−1 at 0.1 C (20 mA g−1), 246.1 mAh g−1 at 0.5 C, 215.8 mAh g−1 at 1 C, and 154.2 mAh g−1 at 5 C (5 C charge and 5 C discharge), as well as good cycling performance. In addition, the Li+ chemical diffusion coefficient of Li1.2Mn0.54Ni0.13Co0.13O2 material prepared by the CP-FD method is 4.59×10−11 cm2 s−1, which is higher than that of the Li1.2Mn0.54Ni0.13Co0.13O2 material prepared by CP-VD. This phenomenon illustrates the potential for Li1.2Mn0.54Ni0.13Co0.13O2 with good rate performance synthesized by CP-FD method. [ABSTRACT FROM AUTHOR]

Manganese oxide is grown directly on carbon paper through a simple immersion process, and used as a catalyst-modified air cathode for rechargeable zinc-air batteries. The manganese oxide is distributed evenly within the porous carbon paper, which promotes a rapid three-phase reaction and high utilization of the active materials. Zinc-air batteries with the manganese oxide catalyst directly grown on the carbon paper exhibit improved performance compared with zinc-air batteries fabricated by using manganese oxide powder catalyst coated on carbon paper. The directly grown catalyst reduces the contact resistance and enhances the discharge/charge profile of the zinc-air batteries. Zinc-air batteries with the directly grown catalyst show a discharge voltage of 1.2 V at a current density of 15 mA cm−2 and deliver a power density as high as 108 mW cm−2 at an applied current of 168 mA cm−2. Furthermore, good cycling stability for up to 500 cycles is achievable during continuous discharge-charge tests without the need to replace the zinc anode or replenish the electrolyte; this outperforms most currently available bifunctional catalysts for rechargeable zinc-air batteries. This study illustrates a promising platform to enhance the cycle life of rechargeable metal-air batteries. [ABSTRACT FROM AUTHOR]

Porous microspherical Li4Ti5O12 aggregates (LTO-PSA) can be successfully prepared by using porous spherical TiO2 as a titanium source and lithium acetate as a lithium source followed by calcinations. The synthesized LTO-PSA possess outstanding morphology, with nanosized, porous, and spherical distributions, that allow good electrochemical performances, including high reversible capacity, good cycling stability, and impressive rate capacity, to be achieved. The specific capacity of the LTO-PSA at 30 C is as high as 141 mAhg-1, whereas that of normal Li4Ti5O12 powders prepared by a sol-gel method can only achieve 100 mAhg-1. This improved rate performance can be ascribed to small Li4Ti5O12 nanocrystallites, a three-dimensional mesoporous structure, and enhanced ionic conductivity. [ABSTRACT FROM AUTHOR]

Highlights: [•] The effect of calcium incorporation in strontium molybdate is investigated. [•] Metallic molybdenum ex-solution is observed under SOFCs’ operating condition. [•] Molybdenum ex-solution is demonstrated to be reversible. [•] Molybdenum ex-solution enhances the electrochemical performance. [ABSTRACT FROM AUTHOR]