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The development of low-cost, highly efficient and stable electrocatalysts for the oxygen evolution reaction (OER) is of great significance for many promising energy storage and conversion applications, including metal–air batteries and water splitting technology. Here we report a layer-structured Ca 0.5 CoO 2 nanofibers composed of interconnected ultrathin nanoplates, synthesized using an electrospinning process. The OER activity of Ca 0.5 CoO 2 can be dramatically improved by iron doping, and the overpotential of Ca 0.5 Co 1− x Fe x O 2 ( x = 0.25) is only 346 mV at a current density of 10 mA cm −2 . The mass activity and intrinsic activity of Ca 0.5 Co 0.75 Fe 0.25 O 2 at 1.6 V are, respectively, ∼18.7 and ∼11.4 times higher than those of Ca 0.5 CoO 2 . Iron doping modifies the electronic structure of Ca 0.5 CoO 2 , resulting in partial oxidation of the surface cobalt and increased amount of highly oxidative species (O 2 2− /O 2 ). Consequently, Ca 0.5 Co 0.75 Fe 0.25 O 2 nanofibers with tuned electronic states have shown great potential as cost-effective and efficient electrocatalysts for OER.

The development of anode materials with high-rate capability is critical to high-power lithium batteries. T-Nb 2 O 5 has been widely reported to exhibit pseudocapacitive behavior and fast lithium storage capability. However, the other polymorphs of Nb 2 O 5 prepared at higher temperatures have the potential to achieve even higher specific capacity and tap density than T-Nb 2 O 5 , offering higher volumetric power and energy density. Here, micrometer-sized H-Nb 2 O 5 with rich Wadsley planar defects (denoted as d-H-Nb 2 O 5 ) is designed for fast lithium storage. The performance of H-Nb 2 O 5 with local rearrangements of [NbO 6 ] octahedra blocks surpasses that of T-Nb 2 O 5 in terms of specific capacity, rate capability, and stability. A wide range variation in the valence of niobium ions upon lithiation was observed for defective H-Nb 2 O 5 via operando X-ray absorption spectroscopy. Operando extended X-ray absorption fine structure and ex situ Raman spectroscopy analyses reveal a large and reversible distortion of the structure in the two-phase region. Computation and ex situ X-ray diffraction analysis reveal that the shear structure expands along major lithium diffusion pathways and contracts in the direction perpendicular tomore »the shear plane. Planar defects relieve strain through perpendicular arrangements of blocks, minimizing volume change and enhancing structural stability. In addition, strong Li adsorption on planar defects enlarges intercalation capacity. Different from nanostructure engineering, our strategy to modify the planar defects in the bulk phase can effectively improve the intrinsic properties. The findings in this work offer new insights into the design of fast Li-ion storage materials in micrometer sizes through defect engineering, and the strategy is applicable to the material discovery for other energy-related applications.« less

Both electronic and ionic conductivities are of high importance to the performance of anode materials for Li-ion batteries. Many large capacity anode materials (such as Ge) do not have sufficiently high electronic and ionic conductivities required for high-rate cycling. Here, we report a novel ternary compound, copper germanium phosphide (CuGe 2 P 3 ), as a high-rate anode. Being synthesized via a facile and scalable mechanochemistry method, CuGe 2 P 3 has a cation-disordered sphalerite structure and offers higher ionic and electronic conductivities and better tolerance to volume change during cycling than Ge, as confirmed by first principles calculations and experimental characterization, including high-resolution synchrotron X-ray diffraction, HRTEM, SAED, XPS and Raman spectroscopy. Furthermore, the results suggest that CuGe 2 P 3 has a reversible Li-storage mechanism of conversion reaction. When composited with graphite by virtue of a two-stage ball-milling process, the yolk–shell structure of the amorphous carbon-coated CuGe 2 P 3 nanocomposite (CuGe 2 P 3 /C@Graphene) delivers a high initial coulombic efficiency (91%), a superior cycling stability (1312 mA h g −1 capacity after 600 cycles at 0.2 A g −1 and 876 mA h g −1 capacity after 1600 cycles at 2 A g −1 ), andmore »an excellent rate capability (386 mA h g −1 capacity at 30 A g −1 ), surpassing most Ge-based anodes reported to date. Moreover, a series of cation-disordered new phases in the Cu(Zn)–Ge–P family with various cation ratios offer similar Li-storage properties, achieving high reversible capacities with high initial coulombic efficiencies and desirable redox chemistry with improved safety.« less

Highly efficient air electrodes are a key component of reversible fuel cells for energy storage and conversion; however, the development of efficient electrodes that are stable against water vapor remains a grand challenge. Here we report an air–electrode, composed of double perovskite material PrBa 0.8 Ca 0.2 Co 2 O 5+δ (PBCC) backbone coated with nanoparticles (NPs) of BaCoO 3−δ (BCO), that exhibits remarkable electrocatalytic activity for oxygen reduction reaction (ORR) while maintaining excellent tolerance to water vapor. When tested in a symmetrical cell exposed to wet air with 3 vol% H 2 O at 750 °C, the electrode shows an area specific resistance of ∼0.03 Ω cm 2 in an extended period of time. The performance enhancement is attributed mainly to the electrocatalytic activity of the BCO NPs dispersed on the surface of the porous PBCC electrode. Moreover, in situ Raman spectroscopy is used to probe reaction intermediates ( e.g. , oxygen species) on electrode surfaces, as the electrochemical properties of the electrodes are characterized under the same conditions. The direct correlation between surface chemistry and electrochemical behavior of an electrode is vital to gaining insight into the mechanisms of the electrocatalytic processes in fuel cells and electrolysers.