Currently known organic electrode materials for lithium-ion batteries have severe cost and resource constraints and are difficult to implement in applications for large-scale electrical energy storage. Compared to lithium-ion battery electrode materials, sodium-ion battery electrode materials are more abundant and more cost effective. However, methods for the prediction of organic electrode materials for sodium-ion batteries are not perfect at present. A fast and accurate theoretical method for finding possible candidates for organic electrode materials for Na-ion batteries is urgently needed. In the present work, dispersion-corrected hybrid density functional theory is applied to study five organic electrode materials for Na-ion batteries. The results of this study show that the D2 dispersion-corrected hybrid functional method (HSE06-D2) can precisely calculate the potential of organic materials with a small average error of approximately 3.68%. The band gap values are approximately lower than 2.5 eV, which proves that the materials have good conductivity and are expected to be candidates for organic electrode materials for sodium-ion batteries.Download high-res image (154KB)Download full-size image

The high-throughput screening scheme is constructed to pick out the potential candidates of organic electrode materials. The organic electrode materials’ potentials could be accurately predicted with the HSE06-D2 method. The band gap, calculated through HSE06-D2, is consistent with the experimental results from UV absorption spectra.Organic electrode materials have gained significant attention due to their flexibility, lightweight characteristics, abundant resources in nature, and low CO2 emission. It's urgently needed for setting up an accurate high-throughput screening theoretical scheme that could find out possible candidates of electrode materials. Currently, the error between the theoretical potentials calculated by the PBE-D2 (DFT-D2, dispersion-corrected density functional theory) method and the experimental values is larger than 12%. Thus, it's essential to finding a more accurate method. In the present work, hybrid functionals and vdW correction methods are applied to investigate six reported organic electrode materials for Li-ion batteries. The results show that the hybrid functional combined with the D2 dispersion corrected method, i.e., HSE06-D2 (Heyd, Scuseria, and Ernzerhof, dispersion-corrected), is able to predict the potential of the organic material precisely with an average error of approximately 5%. This method occupies much hardware resources and being very time consuming, but it could be applied as the final ultrafine step in the high-throughput screening program.Flow chart of high throughput screening scheme.Download high-res image (377KB)Download full-size image

In the present work, we synthesized and characterized an electrocatalyst consisting of sub-nanometric Pt clusters uniformly dispersed on a TiO2 support. X-ray photoelectron spectra (XPS) and X-ray adsorption fine structure (XAFS) data demonstrate that these sub-nanometric Pt clusters are in a highly oxidized state and possess two localized Pt–O coordination structures. The Pt–O bonds between the oxidized Pt clusters and the TiO2 give rise to a strong metal–support interaction (SMSI). When applied to the hydrogen evolution reaction (HER), this catalyst exhibits significantly enhanced catalytic activity (increased by a factor of up to 8.4) and enhanced stability compared with the state-of-the-art commercial Pt/C catalysts. Particularly, the additional XPS and XAFS characterizations of the catalyst after long-term electrolysis demonstrate the absence of metallic Pt species, confirming that the catalytic active site comes from the oxidized Pt clusters rather than from the the metallic Pt species. This improved performance is considered to be induced by the unique electronic structure of the oxidized Pt clusters and by the SMSI. Based on the results of density functional theory calculations, the 5d orbital of the oxidized Pt cluster atoms appears to hybridize with the H 1s orbital to form weak Pt–H valence bonds, leading to a ΔG (relative free energy) value of approximately zero eV for H* absorption. This effect explains the mechanism responsible for the excellent catalytic activity of these oxidized Pt clusters for the HER. This work therefore provides important insights into the role of oxidized Pt clusters as an HER electrocatalyst. The evident stabilization of the oxidized Pt clusters on TiO2 supports via the charge-transfer mechanism provides a useful approach for improving the durability of electrocatalysts that may be applicable to other noble metal/support systems.

The mechanism of Pt-M (3d-metal)-enhanced performance compared to that of pure platinum as the cathode catalyst in fuel cells is not entirely clear. In this paper, a DFT calculation is applied to study the electronic structures of Pt-Fe alloys and ORR (Oxygen Reduced Reaction) on Pt(1 1 1), Pt-skinned Pt3Fe(1 1 1) and Pt-skinned PtFe3(1 1 1) surfaces. With the charge transfer between Pt and Fe, the electronic structure thoroughly differs from that of pure Pt. Consequently, a further change in interaction between the surface and adsorbates, which are produced during the ORR process, primarily causes the improvement in ORR performance. When used as a catalyst, the Pt-skinned Pt-Fe alloy surface is superior to the Pt surface and has three main advantages: (i) a more appropriate potential for each electron step (closer to the stand reversible potential), (ii) a smaller O2 adsorption energy, and (iii) a smaller H2O desorption energy. The theoretical results also show that the Pt-skinned PtFe3(1 1 1) surface has obviously higher activity than the Pt-skinned Pt3Fe(1 1 1), which implies that activity is improved with the increase in Fe content. This work provides a new approach to understand the excellent ORR performance of Pt-M alloys and design other non-noble metal catalysts.

Organic materials have been considered a promising alternative as electrodes for rechargeable lithium-ion batteries. However, there are some obvious shortcomings, especially poor dynamics performance. Approaches to understand the reason for the poor dynamic performance are the main point of the present work. In this paper, an organic electrode material,C12H4N4, is selected as a sample, and studied by dispersion-corrected density functional theory (DFT-D2). The calculation results show that the band gaps of delithiated and lithiated states are about 0.9 and 1.0 eV, respectively, which is consistent with the conventional conjugated organic materials implying the good electronic conductivity. The Li-ion migration pathway forms a complicated three-dimensional (3D) network. The migration energy barrier is higher than 0.53 eV, which is obviously higher than that of the inorganic electrode material, demonstrating the poor ionic conductivity. In organic materials, although the steric hindrance is lowered due to the large intermolecular space, the coulomb potential is significantly improved at the same time, which is the main reason for the high energy barrier of Li-ion migration. Effective ways to lower the lithium migration energy barrier and improve the ionic conductivity should be considered when synthesizing new organic electrode materials.

Screening the appropriate organic electrode material of a lithium battery from the organic structure database by the theoretical method efficiently is crucial for the further experimental study. Unfortunately, the density functional theory is not appropriate due to that it fails to calculate the van der Waals interaction between the organic molecules. In this work, dispersion-corrected density functional theory (DFT-D2) was applied to study nine experimentally reported organic electrode materials, and the theoretical method successfully predicted their potentials, which suggests that it is a feasible method to search and investigate the organic electrode material. The method is further applied to investigate 31 organic crystallines selected from the CCDC (Cambridge Crystallographic Data Centre) database. The theoretical results show that the potentials range from 0.01 eV to 2.76 V, while the capacities distribute from 150 to 623 mAh·g–1, and most of the band gaps are smaller than 2.5 eV, which indicates that they are typical organic semiconductors with high electronic conductivity. The materials with a relatively high potential, high capacity, and small band gap are highligthed, including BAKGOJ, MEHROH, SUQDEN, and NUXGIW, which may be further investigated by experimenters.

Organic molecules are potential candidates for electrode materials of rechargeable lithium batteries because of their beneficial properties such as cost-effective, environmentally friendly, and sustainable. Until now, the efficient theoretical method to study the organic electrode materials remains elusive. In this paper, an organic electrode material of a lithium battery, Li2C18O8H12·4H2O, is investigated by the dispersion-corrected density functional theory method. Two outlined points are presented: (1) the method is a powerful tool to predict the geometry structure and the discharge potential of the organic electrode material; and (2) the periodic crystal structure does more to determine the property of the organic electrode material than the single molecular structure. The intermediate structure corresponding to the first discharge plateau is explored, in which the reversible inserted Li ion occupying layers and the unoccupying layers are arranged alternatively. The special structure makes the intermediate state have a closed-shell electron configuration and lowers the electron kinetic energy on the Fermi level of the system. The band gap is about 1.0 eV, which means that the organic electrode material has a good electron conductivity.

A theoretical study of the oxygen reduction mechanism catalyzed by cobalt–polypyrrole is investigated in detail by means of density functional theory method using the BLYP/DZP basis set. The calculations suggest that the cobalt–polypyrrole has a platinum-like catalytic behavior based on the adsorption energetics of the reaction intermediates. The di-cobalt–polypyrrole catalyst exhibits a higher catalytic activity than that of mono-cobalt–polypyrrole, due to the fact that the PPy chains in di-cobalt–polypyrrole have a regular structure.

A theoretical study on the oxygen reduction mechanism catalyzed by metal–polyaniline is investigated in detail by means of density functional theory. In the oxygen reduction process, we find that −OH, not H2O2, is the reaction intermediate. The catalytic activities for the studied models decrease in the sequence CoFe–PANI > Fe–PANI (FeFe–PANI) > Co–PANI. This is due to a synergistic effect between heterogeneous metal atoms in CoFe–PANI, which facilitates additional electron donation from the active sites to the adsorbed oxygen reduction intermediates. The doping with cobalt may also decrease the HOMO–LUMO gap in CoFe–PANI, making it more active.