Taking advantage of the self-assembling function of amino acids, cobaltalanine complexes are synthesized by straightforward process of chemical precipitation. Through a controllable calcination of the cobalt-alanine complexes, N-doped Co 3 O 4 nanostructures (N-Co 3 O 4 ) and N-doped CoO composites with amorphous carbon (N-CoO/C) are obtained. These N-doped cobalt oxide materials with novel porous nanostructures and minimal oxygen vacancies show a high and stable activity for the oxygen evolution reaction. Moreover, the influence of calcination temperature, electrolyte concentration, and electrode substrate to the reaction are compared and analyzed. The results of experiments and density functional theory calculations demonstrate that N-doping promotes the catalytic activity through improving electronic conductivity, increasing OH − adsorption strength, and accelerating reaction kinetics. Using a simple synthetic strategy, N-Co 3 O 4 reserves the structural advantages of micro/nanostructured complexes, showing exciting potential as a catalyst for the oxygen evolution reaction with good stability.

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Sodium-ion batteries (NIBs), due to the advantages of low cost and relatively high safety, have attracted widespread attention all over the world, making them a promising candidate for large-scale energy storage systems. However, the inherent lower energy density to lithium-ion batteries is the issue that should be further investigated and optimized. Toward the grid-level energy storage applications, designing and discovering appropriate anode materials for NIBs are of great concern. Although many efforts on the improvements and innovations are achieved, several challenges still limit the current requirements of the large-scale application, including low energy/power densities, moderate cycle performance, and the low initial Coulombic efficiency. Advanced nanostructured strategies for anode materials can significantly improve ion or electron transport kinetic performance enhancing the electrochemical properties of battery systems. Herein, this Review intends to provide a comprehensive summary on the progress of nanostructured anode materials for NIBs, where representative examples and corresponding storage mechanisms are discussed. Meanwhile, the potential directions to obtain high-performance anode materials of NIBs are also proposed, which provide references for the further development of advanced anode materials for NIBs.

We report a density functional theory (DFT) study of microscopic detailed effects of the bonding configuration of nitrogen-doped graphene (N-graphene) within the carbon lattice (including pyridinic, pyrrolic, and graphitic N) on the reactivity and mechanistic processes of H2O2 reduction reaction. We simulated the adsorption process of H2O2, analyzed the mechanistic processes, and calculated the reversible potential of each reaction step of the H2O2 reduction reaction on N-graphene. The results indicate that the adsorption of H2O2 on the pristine and N-doped graphene surfaces occurs via physisorption without the formation of a chemical bond. When H(+) is introduced into the system, a series of reactions can occur, including the breakage of the O-O bond, the formation of an O-C chemical bond between oxygen and graphene, and the creation of water molecules. The results also indicate a decrease in the energy of the system and a positive reversible potential for each reaction step. The calculations of the relative energy of each reaction step and the value of the onset potential for H2O2 reduction reaction suggest that the reactivity of pristine and N-doped graphene has the following order: pyridinic N-graphene > pyrrolic N-graphene > graphitic N-graphene > pristine graphene. We also proposed an explanation based on electrostatic potential calculations for this dependence of the reactivity order on the bond configuration of the doping in N-graphene. The results of this study should help in the atomic-scale understanding of the dependence of the reactivity of N-graphene on its microstructure, inspire the study of various types of heteroatom-doped graphenes to improve their catalytic efficiency, and provide a theoretical framework to analyze their reactivities.

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Graphyne, a new two-dimensional periodic carbon allotrope with a one-atom-thick sheet of carbon built from triple-and double-bonded units of two sp-and sp 2hybridized carbon atoms, has been shown in recent studies to have the potential for high-density hydrogen and lithium storage. We report here a density functional theory (DFT) study of an oxygen reduction reaction (ORR) involving graphyne and demonstrate that graphyne is a good, metal-free electrocatalyst for ORRs in acidic fuel cells. We optimized the geometrical structure, calculated the charge densities on each carbon atom in the graphyne, and simulated each step of the ORR reaction involving graphyne. The simulation results indicate that the distribution of the charge density at each carbon atom on the graphyne plane is not uniform and that a large number of positively charged carbon atoms, which are beneficial to the adsorption of O 2 and OOH + molecules, can behave as catalytic sites to facilitate ORRs. When H + is introduced into the system, a series of reactions can occur including the formation of an O−C chemical bond between oxygen and graphyne, breakage of the O−O bond, and the creation of water molecules. The results also indicate a decrease in the energy of the system and a positive value of the reversible potential for each reaction step on the graphyne surface. In addition, a spontaneous electron transformation process occurs during the ORR along a four-electron pathway. The results presented here should lead to an improvement in the catalytic efficiency of carbon nanomaterials and provide a theoretical framework for the analysis of their catalytic activity. This paper highlights the urgent need for new experimental syntheses for graphyne.

HEVs (PHEVs), besides the traditional applications in portable devices. To build the next generation LIBs with higher performances, high energy density materials are urgently pursued worldwide. [1][2][3] Lithium-rich (Li-rich) materials, with the specific capacity over 260 mAh g −1 and energy density up to ≈1000 Wh kg −1 , [4] have attracted great interest in the past decades. It is reported that Li-rich materials are composed of two phases of Li 2 MnO 3 (C 2/m ) and LiMO 2 (R m 3 ) (M = Ni, Co, Mn, etc.). [5][6][7][8][9] Despite the above advantages, several concerns including structural instability and the resulted voltage degradation, as well as the poor diffusion kinetics at the interface have become the bottlenecks of Li-rich materials. [9][10][11][12][13] In this regard, multifarious modification approaches, such as doping and surface coating, have been intensively investigated. [14][15][16] Particularly, Li + diffusion at the cathode-electrolyte interphase (CEI) is widely regarded as the rate determining step in LIBs. [17][18][19] From this viewpoint, metal fluorides (FeF 3 , [20] MOF, [21,22] AlF 3 , [23,24] etc.), metal oxides (MgO, [25] Al 2 O 3 , [26,27] etc.), metal phosphates (AlPO 4 , [28] LaPO 4 , [29] Li 3 PO 4 , [30] FePO 4 /Li 3 PO 4 , [31] Li-Mn-PO 4 , [32] etc.), and those with similar structure of Li-rich Li 2 MnO 3 (Li 2 SiO 3 [33,34] and Li 2 SnO 3 , [35] ) have been widely applied to modify the surface of bulk Li-rich materials. Recently, fast lithium-ion conductors (LiVO 3 , [36] Li 2 ZrO 3 , [37] Li-La-Ti-O, [38,39] LiPON, [40] etc.) have also been proposed to decorate the surface of Li-rich cathodes to enhance the apparent diffusion coefficients. All the aforesaid surface modification materials, unexceptionally, have been proved to be effective in both stabilizing the structure and facilitating the Li + kinetics. Nevertheless, in general, the decoration layers themselves seem rather "passive" in promoting Li + diffusion. Assuming they are Li + conductive (e.g., solid electrolyte materials), fast Li + diffusion channels will be provided besides the general separation effect (in suppressing side reactions and inevitable TM dissolution). As for Li + insulators (e.g., metal fluorides), only the benefit of physical barriers could be exploited. Therefore, a more "initiative" function interface is imperative to be built to more effectively promote the Li + transport at the electrode-electrolyte interphase.It is noteworthy that piezoelectric material, as an important category in the energy-conversion community, works on the As one of the most promising cathodes for next-generation lithium ion batteries (LIBs), Li-rich materials have been extensively investigated for their high energy densities. However, the practical application of Li-rich cathodes is extremely retarded by the sluggish electrode-electrolyte interface kinetics and structure instability. In this context, piezoelectric LiTaO 3 is employed to functionalize the surface of Li 1.2 Ni 0.17 Mn 0.56 Co 0.07 O 2 (LNMCO), aiming to boost t...

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