A synergetic effect of K, Ti and F together on improving the reversible hydrogen storage properties of NaAlH(4) is found by intruding K(2)TiF(6) as catalyst precursor. Around 4.4 wt% of hydrogen can be released from the NaAlH(4)-0.025 K(2)TiF(6) sample within 40 min at 140 °C.
Lithium borohydride (LiBH4), with a high hydrogen capacity of 18.5 wt %, is an ideal candidate for hydrogen storage; however, it suffers from high thermal stability, low kinetics, and poor reversibility. Nanoconfinement is an effective strategy to tackle these problems, but a main drawback of nanoconfined systems is the low loading fraction of LiBH4, which leads to a low theoretical hydrogen capacity of the systems. It is thus highly desired to design scaffolds with high porosity and a reasonable pore structure for achieving high loading of LiBH4. In this work, porous hollow carbon nanospheres (PHCNSs) with uniform size, high specific surface area, large pore volume, and reasonable pore structure are delicately designed and controllably synthesized as the scaffold for confining LiBH4. The as-prepared PHCNSs can accommodate up to 70 wt % LiBH4, while the system still shows a low dehydrogenation temperature of ca. 200 °C and releases rapidly 8.1 wt % H2 at 350 °C within 25 min. Such a high loading of LiBH4 and high dehydrogenation capacity at a low temperature have never been reported to date based on our knowledge of carbon-based nanoconfined LiBH4 systems. Moreover, the system with 60 wt % LiBH4 shows favorable reversibility and rapid hydrogenation under moderate conditions. The morphology and structure evolutions of the confined systems during cycling are investigated, and the mechanism of the improved hydrogen storage property is proposed. The present work provides further insight into rationally utilizing porous carbon scaffolds with a well-designed structure to improve the hydrogen storage performance of LiBH4.
Abstract The electrochemical conversion reaction, usually featured by multiple redox processes and high specific capacity, holds great promise in developing high‐energy rechargeable battery technologies. However, the complete structural change accompanied by spontaneous atomic migration and volume variation during the charge/discharge cycle leads to electrode disintegration and performance degradation, therefore severely restricting the application of conventional conversion‐type electrodes. Herein, latticed‐confined conversion chemistry is proposed, where the “intercalation‐like” redox behavior is realized on the electrode with a “conversion‐like” high capacity. By delicately formulating the high‐entropy compounds, the pristine crystal structure can be preserved by the inert lattice framework, thus enabling an ultra‐high initial Coulombic efficiency of 92.5% and a long cycling lifespan over a thousand cycles after the quasistatic charge–discharge cycle. This lattice‐confined conversion chemistry unfolds a ubiquitous insight into the localized redox reaction and sheds light on developing high‐performance electrodes toward next‐generation high‐energy rechargeable batteries.
Abstract Developing non‐platinum group metal (non‐PGM) electrocatalysts for the hydrogen oxidation reaction (HOR) represents the efforts towards the more economical use of hydrogen fuel cells and hydrogen energy, which has attracted tremendous attention recently. However, non‐PGM electrocatalysts for the HOR are still in their early development stages as compared with the significant advances in those for the oxygen reduction reaction and hydrogen evolution reaction. Herein, this paper summarizes the recent progresses and highlights the key challenges for the rational design of non‐PGM electrocatalysts, aiming to promote the development of non‐PGM HOR electrocatalysts. Fundamental understandings of the HOR mechanism are firstly reviewed, where theoretical interpretations on the low HOR kinetics in alkaline media, including the hydrogen binding energy theory, the bifunctional mechanism, and the water molecule reorganization, are particularly discussed. Subsequently, progresses of typical non‐PGM HOR electrocatalysts in acid and alkaline media are summarized separately. For the HOR under alkaline conditions, the superiorities and challenges of Ni‐based catalysts are discussed with a particular focus as they are the most promising non‐PGM electrocatalysts. Finally, this paper highlights the challenges and provide perspectives on the future development directions of non‐PGM HOR electrocatalysts.
In an era dominated by electronic equipment, the development of high-efficiency electromagnetic wave (EMW) absorbers is of great significance in solving electromagnetic (EM) pollution. Micro/Nanostructural engineering for optimizing EMW absorption performance depends on the design of vacancy, defect, and heterogeneous interface, which remains a considerable challenge in adjusting the micro and macro-interface effects. In this work, S atoms are incorporated into a dielectric-magnetic complementary system (Fe3O4/Fe7S8@C) to arouse the polarization effect of vacancies, defects, and non-uniform interfaces, thus tremendously boosting the EM energy attenuation capacity. Besides, the carbon shell provides more propagation paths for the dissipation of EMWs, and dielectric-magnetic synergy improves impedance matching. Eventually, in comparison with Fe2O3 and Fe3O4@C composites, interface-engineered Fe3O4/Fe7S8@C acquires a much better EM wave absorption performance. Its minimum reflection loss value reaches as much as -56.2 dB with a thickness of only 1.6 mm, and the corresponding effective absorption bandwidth (EAB) is up to 4.5 GHz. This unique hydrangea-like layered structure provides space to facilitate non-uniform coupling between the layers and has strong anisotropy to enhance the magnetic response. The high density of magnetic flux in the nanosheets builds a three-dimensional magnetic coupling network, which is supported by Off-axis electron holography. Besides, the radar cross section from HFSS simulation further confirms that S-doping can favor the best synergy between dielectric and magnetic losses, facilitating the composite to achieve a more optimal impedance matching and improve the absorption capacity. In conclusion, this work presents new ideas for the design of excellent absorbing materials.
Overcoming the sluggish kinetics of alkaline hydrogen oxidation reaction (HOR) is challenging but is of critical importance for practical anion exchange membrane fuel cells. Herein, abundant and efficient interfacial active sites are created on ruthenium (Ru) nanoparticles by anchoring atomically isolated chromium coordinated with hydroxyl clusters (Cr1(OH)x) for accelerated alkaline HOR. This catalyst system delivers 50-fold enhanced HOR activity with excellent durability and CO anti-poisoning ability via switching the active sites from Ru surface to Cr1(OH)x-Ru interface. Fundamentally different from the conventional mechanism merely focusing on surface metal sites, the isolated Cr1(OH)x could provide unique oxygen species for accelerating hydrogen or CO spillover from Ru to Cr1(OH)x. Furthermore, the original oxygen species from Cr1(OH)x are confirmed to participate in hydrogen oxidation and H2O formation. The incorporation of such atomically isolated metal hydroxide clusters in heterostructured catalysts opens up new opportunities for rationally designing advanced electrocatalysts for HOR and other complex electrochemical reactions. This work also highlights the importance of size effect of co-catalysts, which should also be paid substantial attention to in the catalysis field.
The specific capacity of Li- and Mn-rich layered oxide (LMROs) cathodes can be enhanced by the oxidation of lattice oxygen at high voltages. Nevertheless, an irreversible oxygen loss emerges with cycling, which triggers interlocking surface/interface issues and results in the fast deterioration of cycling performance. Herein, we prepare a surface modified LMRO electrode by one step doctor-blade casting and introducing a benzoquinone species DBBQ redox couple. The electrochemical test shows that the DBBQ-modified electrode has a high reversible capacity (>320 mAh g–1) and excellent rate performance, while the cyclic stability has been significantly improved as well. The capacity retention reaches as high as 93.3% after 500 cycles at 1 C. Mechanism analysis shows that DBBQ can not only play a redox couple in LMROs which achieves the adsorption and reduction of surface oxygen gas but also significantly enhance anionic redox in the bulk, thus realizing extraordinary capacity.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)