Bo Nan

Highly durable organic electrode for sodium-ion batteries via a stabilized α-C radical intermediate.

It is a challenge to prepare organic electrodes for sodium-ion batteries with long cycle life and high capacity. The highly reactive radical intermediates generated during the sodiation/desodiation process could be a critical issue because of undesired side reactions. Here we present durable electrodes with a stabilized α-C radical intermediate. Through the resonance effect as well as steric effects, the excessive reactivity of the unpaired electron is successfully suppressed, thus developing an electrode with stable cycling for over 2,000 cycles with 96.8% capacity retention. In addition, the α-radical demonstrates reversible transformation between three states: C=C; α-C·radical; and α-C− anion. Such transformation provides additional Na+ storage equal to more than 0.83 Na+ insertion per α-C radical for the electrodes. The strategy of intermediate radical stabilization could be enlightening in the design of organic electrodes with enhanced cycling life and energy storage capability.

Bimetallic organic frameworks derived CuNi/carbon nanocomposites as efficient electrocatalysts for oxygen reduction reaction

Catalysts of oxygen reduction reaction (ORR) play key roles in renewable energy technologies such as metal-air batteries and fuel cells. Despite tremendous efforts, highly active catalysts with low cost remain elusive. This work used metal-organic frameworks to synthesize non-precious bimetallic carbon nanocomposites as efficient ORR catalysts. Although carbon-based Cu and Ni are good candidates, the hybrid nanocomposites take advantage of both metals to improve catalytic activity. The resulting molar ratio of Cu/Ni in the nanocomposites can be finely controlled by tuning the recipe of the precursors. Nanocomposites with a series of molar ratios were produced, and they exhibited much better ORR catalytic performance than their monometallic counterparts in terms of limited current density, onset potential and half-wave potential. In addition, their extraordinary stability in alkaline is superior to that of commercially-available Pt-based materials, which adds to the appeal of the bimetallic carbon nanocomposites as ORR catalysts. Their improved performance can be attributed to the synergetic effects of Cu and Ni, and the enhancement of the carbon matrix.摘要氧还原催化剂在金属空气电池和燃料电池的可再生能源技术中起至关重要的作用. 尽管该方面研究已有很多, 高活性低成本的催化剂的开发仍然十分困难. 本文以金属有机骨架为前驱体, 成功合成出非贵金属铜镍双金属碳基纳米复合物并作为高效的氧还原催化剂. 单金属复合物Cu/C和Ni/C皆具有较好的氧还原催化作用, 铜镍双金属复合物进一步综合了二者优点从而提升了催化性能. 本文所合成的铜镍双金属复合物中的金属比例可通过调整前驱体中的原料配比来准确控制, 所得的一系列金属比例的铜镍双金属碳基纳米复合物在极限电流密度、起始电位和半波电位三个方面都超过了单金属复合物. 此外, 铜镍双金属碳基纳米复合物在碱性环境中具有良好的稳定性且超过了目前最好的氧还原催化材料铂, 大大加强了其作为氧还原催化剂的优势. 铜镍双金属碳基纳米复合物优越的电化学催化性能归功于金属铜和镍以及碳材料基底的协同作用.

MoC ultrafine nanoparticles confined in porous graphitic carbon as extremely stable anode materials for lithium- and sodium-ion batteries

Molybdenum carbide (MoC)/graphitic carbon nanocomposites are synthesized using a green and facile method. Well-crystallized MoC ultrafine nanoparticles (<5 nm diameter) are formed in situ inside the pores of a highly conductive graphitic carbon matrix. The resulting MoC/graphitic carbon nanocomposites exhibit very promising electrochemical performance when evaluated as anodes in LIBs and SIBs, because the synergistic effects of the small MoC nanoparticles provide fast and efficient transport and porous graphitic carbon can prevent continual rupturing as well as enhance conductivity. Meanwhile, this novel material has potential for broad application in rechargeable batteries, maintaining a reversible capacity of 742 mA h g−1 after 50 cycles at 200 mA g−1 for LIBs and a discharge capacity of 250 mA h g−1 after 50 cycles at 50 mA g−1 for SIBs. Furthermore, the required Mo can be recovered from wastewater, which gives this method an added environmental benefit and in return satisfy the current demand for sustainable development.

Facile synthesis of ultrathin MoS2/C nanosheets for use in sodium-ion batteries

We present a clean and simple method for the synthesis of MoS2/C hybrids. Commercial ion-exchange resins are used to absorb aqueous molybdate, followed by annealing with sulfur powder in an inert atmosphere. Even ultrathin MoS2 nanosheets with enlarged interlayers (0.63 nm) are homogeneously wrapped by mesoporous graphitic carbon. When evaluated as anodes for sodium-ion batteries, the MoS2/C nanocomposite exhibits good electrochemical performance. The first discharge/charge capacities at current density 50 mA g−1 are 784.3 and 590.0 mA h g−1, respectively, with initial coulombic efficiency of approximately 75%. It exhibits superior rate capabilities, with specific discharge capacities of 513.1, 467.3, 437.1, 399.2, 361.8, and 302.7 mA h g−1 at current densities of 50, 100, 200, 500, 1000, and 2000 mA g−1, respectively. This superior electrochemical performance is mainly due to the synergistic effect between the uniformly-distributed, ultrathin MoS2 nanosheets and the highly graphitized carbon. This not only mitigates mechanical stress during repeated cycling, but also provides good conductivity.

Low-Cost and Novel Si-Based Gel for Li-Ion Batteries

Si-based nanostructure composites have been intensively investigated as anode materials for next-generation lithium-ion batteries because of their ultra-high-energy storage capacity. However, it is still a great challenge to fabricate a perfect structure satisfying all the requirements of good electrical conductivity, robust matrix for buffering large volume expansion, and intact linkage of Si particles upon long-term cycling. Here, we report a novel design of Si-based multicomponent three-dimensional (3D) networks in which the Si core is capped with phytic acid shell layers through a facile high-energy ball-milling method. By mixing the functional Si with graphene oxide and functionalized carbon nanotube, we successfully obtained a homogeneous and conductive rigid silicon-based gel through complexation. Interestingly, this Si-based gel with a fancy 3D cross-linking structure could be writable and printable. In particular, this Si-based gel composite delivers a moderate specific capacity of 2711 mA h g-1 at a current density of 420 mA g-1 and retained a competitive discharge capacity of more than 800.00 mA h g-1 at the current density of 420 mA g-1 after 700 cycles. We provide a new method to fabricate durable Si-based anode material for next-generation high-performance lithium-ion batteries.

Edge Defect Engineering of Nitrogen-Doped Carbon for Oxygen Electrocatalysts in Zn–Air Batteries

Metal-free bifunctional oxygen electrocatalysts are extremely critical to the advanced energy conversion devices, such as high energy metal-air batteries. Effective tuning of edge defects and electronic density on carbon materials via simple methods is especially attractive. In this work, a facile alkali activation method has been proposed to prepare carbon with large specific surface area and optimized porosity. In addition, subsequent nitrogen-doping leads to high pyridinic-N and graphitic-N contents and abundant edge defects, further enhancing electrochemical activities. Theoretical modeling via first-principles calculations has been conducted to correlate the electrocatalytic activities with their fundamental chemical structure of N doping and edge defect engineering. The metal-free product (NKCNPs-900) shows a high half-wave potential of 0.79 V (ORR). Furthermore, the assembled Zn-air batteries display excellent performance among carbon-based metal-free oxygen electrocatalysts, such as large peak power density up to 131.4 mW cm-2, energy density as high as 889.0 W h kg-1 at 4.5 mA cm-2, and remarkable discharge-charge cycles up to 575 times. Preliminarily, the rechargeable nonaqueous Li-air batteries were also investigated. Therefore, our work provides a low-cost, metal-free, and high-performance bifunctional carbon-based electrocatalyst for metal-air batteries.