Fuel cells are clean, sustainable energy conversion devices for power generation, and they most commonly use platinum as the electrocatalyst.[1] However, Pt-based catalysts suffer from very limited reserves, high cost, and inactivation by CO poisoning; these are major obstacles that fuel cells have to overcome for commercialization. [1][2][3][4][5][6] Thus, exploring nonprecious metal or even metal-free catalysts to rival platinum in activity and durability is absolutely crucial, with a potentially revolutionary impact on fuel-cell technologies. Very recently, metal-free PEDOT [6] and nitrogen-doped carbon nanotubes (NCNTs) [7,8] have shown a striking electrocatalytic performance for the oxygen reduction reaction (ORR). These breakthroughs have activated an exciting field for exploring the advanced metal-free electrocatalysts and understanding the related mechanism.As one of the most important carbon nanostructures, carbon-based nanotubes have been widely studied as the support of electrocatalysts for fuel cells in recent years. [9][10][11][12] Recent progress involving doping carbon nanotubes (CNTs) with electron-rich nitrogen to transform CNTs into superb metal-free electrocatalysts for the ORR [7,8] has motivated our curiosity to examine the corresponding performance of its counterpart by doping CNTs with electron-deficient boron. Intuitively, the adsorption of O 2 on boron dopant should be quite easy owing to the large difference of electronegativity between boron and oxygen, which is the precondition for the subsequent O 2 dissociation. In this study, BCNTs with tunable boron content of 0-2.24 atom % were synthesized. The ORR onset and peak potentials shift positively and the current density increases noticeably with increasing boron content, indicating a strong dependence of the ORR performance on boron content. Moreover, the origin of the electrocatalytic activity of BCNTs including the role of the boron dopant has been revealed by density functional theory (DFT) calculations. The experimental and theoretical results provide a new strategy to explore carbon-based metal-free electrocatalysts that are significant to the development of fuel cells.Using chemical vapor deposition (CVD) with benzene, triphenylborane (TPB), and ferrocene as precursors and catalyst, BCNTs were synthesized with tunable boron content of 0-2.24 at % by using different TPB concentrations. BCNTs with boron content of 0.86, 1.33, and 2.24 at %, as determined by X-ray photoelectron spectroscopy (XPS), were denoted as B 1 CNTs, B 2 CNTs, and B 3 CNTs, respectively (Supporting Information, S1

While the carbon-based metal-free electrocatalysts for oxygen reduction reaction (ORR) have experienced great progress in recent years, the fundamental issue on the origin of ORR activity is yet far from being clarified. To date, the ORR activities of these electrocatalysts are usually attributed to different dopants, while the contribution of intrinsic carbon defects has been little touched. Herein, we report the high ORR activity of the defective carbon nanocages, which is better than that of the B-doped carbon nanotubes and comparable to that of the N-doped carbon nanostructures. Density functional theory (DFT) calculations indicate that pentagon and zigzag edge defects are responsible for the high ORR activity. The mutually corroborated experimental and theoretical results reveal the significant contribution of the intrinsic carbon defects to ORR activity, which is crucial for understanding the ORR origin and exploring the advanced carbon-based metal-free electrocatalysts.

A hierarchical nanostructure composed of NiMn‐layered double hydroxide (NiMn‐LDH) microcrystals grafted on carbon nanotube (CNT) backbone is constructed by an in situ growth route, which exhibits superior supercapacitive performance. The resulting composite material (NiMn‐LDH/CNT) displays a three‐dimensional architecture with tunable Ni/Mn ratio, well‐defined core‐shell configuration, and enlarged surface area. An electrochemical investigation shows that the Ni3Mn1‐LDH/CNT electrode is rather active, which delivers a maximum specific capacitance of 2960 F g–1 (at 1.5 A g–1), excellent rate capability (79.5% retention at 30 A g–1), and cyclic stability. Moreover, an all‐solid‐state asymmetric supercapacitor (SC) with good flexibility is fabricated by using the NiMn‐LDH/CNT film and reduced graphene oxide (RGO)/CNT film as the positive and negative electrode, respectively, exhibiting a wide cell voltage of 1.7 V and largely enhanced energy density up to 88.3 Wh kg–1 (based on the total weight of the device). By virtue of the high‐capacity of pseudocapacitive hydroxides and desirable conductivity of carbon‐based materials, the monolithic design demonstrated in this work provides a promising approach for the development of flexible energy storage systems.

Fuel cells are clean, sustainable energy conversion devices for power generation, and they most commonly use platinum as the electrocatalyst. [1] However, Pt-based catalysts suffer from very limited reserves, high cost, and inactivation by CO poisoning; these are major obstacles that fuel cells have to overcome for commercialization. [1][2][3][4][5][6] Thus, exploring nonprecious metal or even metal-free catalysts to rival platinum in activity and durability is absolutely crucial, with a potentially revolutionary impact on fuel-cell technologies. Very recently, metal-free PEDOT [6] and nitrogen-doped carbon nanotubes (NCNTs) [7,8] have shown a striking electrocatalytic performance for the oxygen reduction reaction (ORR). These breakthroughs have activated an exciting field for exploring the advanced metal-free electrocatalysts and understanding the related mechanism.As one of the most important carbon nanostructures, carbon-based nanotubes have been widely studied as the support of electrocatalysts for fuel cells in recent years. [9][10][11][12] Recent progress involving doping carbon nanotubes (CNTs) with electron-rich nitrogen to transform CNTs into superb metal-free electrocatalysts for the ORR [7,8] has motivated our curiosity to examine the corresponding performance of its counterpart by doping CNTs with electron-deficient boron. Intuitively, the adsorption of O 2 on boron dopant should be quite easy owing to the large difference of electronegativity between boron and oxygen, which is the precondition for the subsequent O 2 dissociation. In this study, BCNTs with tunable boron content of 0-2.24 atom % were synthesized. The ORR onset and peak potentials shift positively and the current density increases noticeably with increasing boron content, indicating a strong dependence of the ORR performance on boron content. Moreover, the origin of the electrocatalytic activity of BCNTs including the role of the boron dopant has been revealed by density functional theory (DFT) calculations. The experimental and theoretical results provide a new strategy to explore carbon-based metal-free electrocatalysts that are significant to the development of fuel cells.Using chemical vapor deposition (CVD) with benzene, triphenylborane (TPB), and ferrocene as precursors and catalyst, BCNTs were synthesized with tunable boron content of 0-2.24 at % by using different TPB concentrations. BCNTs with boron content of 0.86, 1.33, and 2.24 at %, as determined by X-ray photoelectron spectroscopy (XPS), were denoted as B 1 CNTs, B 2 CNTs, and B 3 CNTs, respectively (Supporting Information, S1.

Conspectus The generalized energy-based fragmentation (GEBF) approach provides a very simple way of approximately evaluating the ground-state energy or properties of a large system in terms of ground-state energies of various small "electrostatically embedded" subsystems, which can be calculated with any traditional ab initio quantum chemistry (X) method (X = Hartree-Fock, density functional theory, and so on). Due to its excellent parallel efficiency, the GEBF approach at the X theory level (GEBF-X) allows full quantum mechanical (QM) calculations to be accessible for systems with hundreds and even thousands of atoms on ordinary workstations. The implementation of the GEBF approach at various theoretical levels can be easily done with existing quantum chemistry programs. This Account reviews the methodology, implementation, and applications of the GEBF-X approach. This method has been successfully applied to optimize the structures of various large systems including molecular clusters, polypeptides, proteins, and foldamers. Such investigations could allow us to elucidate the origin and nature of the cooperative interaction in secondary structures of long peptides or the driving force of the self-assembly processes of aromatic oligoamides. These GEBF-based QM calculations reveal that the structures and stability of various complex systems result from a subtle balance of many types of noncovalent interactions such as hydrogen bonding and van der Waals interactions. The GEBF-based ab initio molecular dynamics (AIMD) method also allows the investigation of dynamic behaviors of large systems on the order of tens of picoseconds. It was demonstrated that the conformational dynamics of two model peptides predicted by GEBF-based AIMD are noticeably different from those predicted by the classical force field MD method. With the target of extending QM calculations to molecular aggregates in the condensed phase, we have implemented the GEBF-based multilayer hybrid models, which could provide satisfactory descriptions of the binding energies between a solute molecule and its surrounding waters and the chain-length dependence of the conformational changes of oligomers in aqueous solutions. A coarse-grained polarizable molecular mechanics model, furnished with GEBF-X dipole moments of subsystems, exhibits some advantages of treating the electrostatic polarization with reduced computational costs. We anticipate that the GEBF approach will continue to develop with the ultimate goal of studying complicated phenomena at mesoscopic scales and serve as a practical tool to elucidate the structure and dynamics of chemical and biological systems.

storage. [2][3][4][5][6][7] Among them, aqueous zinc batteries have aroused extensive interest and attention, which benefits from many advantages of zinc anode, including high theoretical capacity (820 mAh g −1 ), appropriate redox potential (−0.762 V vs the standard hydrogen electrode (SHE)), and intrinsic safety in aqueous system. [8][9][10][11][12][13][14][15][16][17][18][19][20] Inspired by conventional Li + storage reaction, intercalation reaction of transition metal oxides are employed to storage Zn 2+ in the mild aqueous solution. For example, Zn 0.25 V 2 O 5 ·nH 2 O, [9] Prussian blue analogue, [15] VO 2 , [17] MnO 2 , [18] Zn 3 V 2 O 7 (OH) 2 ·2H 2 O, [19] CuV 2 O 6 [20] have been used as cathodes for zinc batteries. However, the hydrated Zn 2+ and H + usually result in large volumetric change and serious structural collapse of these inorganic compounds with the insertion of a large amount of hydrated Zn 2+ , [21][22][23][24][25] showing significant capacity fading and limited cycle life. In recent years, the organic compounds containing carbonyl groups have been employed to store Li + and Na + through reversible coordination reaction (i.e., the CO/C-O-Li + /Na + conversion), and thus many batteries based on organic electrodes were proposed by using monovalent ion (Li + /Na + ) as charge carrier. [26][27][28][29][30][31] Then, it was demonstrated that such coordination reaction can also be used to store divalent ions (e.g., Mg 2+ and Zn 2+ ), which evoked the enthusiasm for developing divalent ion batteries using organic electrode. [32][33][34][35][36][37] Very recently, Chen's group reported the first Zn-organic (C 4 Q//Zn) battery with high energy and long life. [38] Chen and co-workers work indicates that it should be a good choice for building zinc batteries to use organics as the alternative to inorganic host materials to store Zn 2+ . However, many organics with carbonyl groups (CO) and/or their reduced products (C-O-) suffer from the inherent instability and solubility in electrolyte. [39][40][41][42][43] It is well known that the solubility can lead to the crossover of electrode active materials between cathode and anode. As a result, expensive ion exchange membranes generally are required to prevent the crossover. [38] Furthermore, owing to the inevitable presence of H + in mild aqueous electrolyte (e.g., aqueous ZnSO 4 electrolyte generally shows a pH value of 4-5), H + can also react with carbonyl groups of organic compounds before or in parallel with the storage of Zn 2+ , which might aggravate the poor cycle life arising from the inherent The newly emerged aqueous Zn-organic batteries are attracting extensive attention as a promising candidate for energy storage. However, most of them suffer from the unstable and/or soluble nature of organic molecules, showing limited cycle life (≤3000 cycles) that is far away from the requirement (10 000 cycles) for grid-scale energy storage. Here, a new aqueous zinc battery is proposed by using sulfur heterocyclic quinone dibenzo[b,i]thianthrene-5,7,12,1...

Organic sodium-ion batteries (OSIBs) have numerous promising advantages for foreseeable large-scale applications, particularly including the convenience of performance optimization through molecular design. However, the reported organic cathodes still suffer from limited capacity, low cyclability, and poor rate performance. The tailoring of the p-conjugated system reported here can enhance the p-p intermolecular interactions, leading to insolubility, long-range layer-by-layer p-p stacking, fast-charge transport, and extraordinary stability and ionic conductivity (10 À9 cm 2 s À1 ). Consequently, the obtained cathodes delivered high electrochemical performance with high capacity ($290 mAh g À1 ), superior fast-chargedischarge ability ($160 and 100 mAh g À1 at 10 and 50 A g À1 , respectively), and ultra-long cycle life (capacity as high as 97 mAh g À1 after 10,000 cycles at 50 A g À1 ).

The catalytic conversion of nitrogen to ammonia is one of the most important processes in nature and chemical industry. However, the traditional Haber-Bosch process of ammonia synthesis consumes substantial energy and emits a large amount of carbon dioxide. Solar-driven nitrogen fixation holds great promise for the reduction of energy consumption and environmental pollution. On the basis of both experimental results and density functional theory calculations, here we report that the oxygen vacancy engineering on ultrathin BiOBr nanosheets can greatly enhance the performance for photocatalytic nitrogen fixation. Through the addition of polymetric surfactant (polyvinylpyrrolidone, PVP) in the synthesis process, V O-BiOBr nanosheets with desirable oxygen vacancies and dominant exposed {001} facets were successfully prepared, which effectively promote the adsorption of inert nitrogen molecules at ambient condition and facilitate the separation of photoexcited electrons and holes. The oxygen defects narrow the bandgap of V O-BiOBr photocatalyst and lower the energy requirement of exciton generation. In the case of the specific surface areas are almost equal, the V O-BiOBr nanosheets display a highly improved photocatalytic ammonia production rate (54.70 μmol·g–1·h–1), which is nearly 10 times higher than that of the BiOBr nanoplates without oxygen vacancies (5.75 μmol·g–1·h–1). The oxygen vacancy engineering on semiconductive nanomaterials provides a promising way for rational design of catalysts to boost the rate of ammonia synthesis under mild conditions.