Showing papers by "K. M. Abraham published in 2019"
TL;DR: It is shown that the alkaline HER/HOR kinetics can be unified by the catalytic roles of the adsorbed hydroxyl (OHad)-water-alkali metal cation (AM+) adducts, on the basis of the observations that enriching the OHad abundance via surface Ni benefits the HER/hOR; increasing the AM+ concentration only promotes the HER, while varying the identity of AM+ affects both HER and HOR.
Abstract: Despite the fundamental and practical significance of the hydrogen evolution and oxidation reactions (HER/HOR), their kinetics in base remain unclear. Herein, we show that the alkaline HER/HOR kinetics can be unified by the catalytic roles of the adsorbed hydroxyl (OHad)-water-alkali metal cation (AM+) adducts, on the basis of the observations that enriching the OHad abundance via surface Ni benefits the HER/HOR; increasing the AM+ concentration only promotes the HER, while varying the identity of AM+ affects both HER/HOR. The presence of OHad-(H2O)x-AM+ in the double-layer region facilitates the OHad removal into the bulk, forming OH–-(H2O)x-AM+ as per the hard–soft acid–base theory, thereby selectively promoting the HER. It can be detrimental to the HOR as per the bifunctional mechanism, as the AM+ destabilizes the OHad, which is further supported by the CO oxidation results. This new notion may be important for alkaline electrochemistry.
181 citations
TL;DR: In this article, a Li-rich layered 0.5LiMn1/3Ni 1/3Co1/ 3O2 (LMNCO) pristine cathode material was further coated with silver and the effects of silver coating on the material structure and performance of the as-prepared cathode are systemically studied with X-ray diffraction (XRD), scanning electron microscope (SEM), galvanostatic charge/discharge, cyclic voltammetry (CV), and electrochemical impedance spectra (EIS).
Abstract: In this work, a Li-rich layered 0.5Li2MnO3.0.5LiMn1/3Ni1/3Co1/3O2 (LMNCO) pristine cathode material synthesized with a glycine-nitrate combustion method is further coated with silver. The effects of silver coating on the material structure and performance of the as-prepared cathode are systemically studied with X-ray diffraction (XRD), scanning electron microscope (SEM), galvanostatic charge/discharge, cyclic voltammetry (CV), and electrochemical impedance spectra (EIS). Material characterizations and electrochemical measurements show that the surface modification does not lead to the change of crystal lattice parameter and particle morphology. It is found that the rate capability and cyclability can be significantly improved, which could be attributed to the enhancement of electronic conductivity of the particle surface of the cathode. It has been found that the obtained silver-coated LMNCO cathode exhibits excellent electrochemical characteristics. For example, it can deliver a high initial discharge capacity of 290 mAh g−1 between 2.0 and 4.9 V at a rate of 0.05C at room temperature and a discharge capacity of 159 mAh g−1 at 1 C, 128 mAh g−1at 2 C, and 101 mAh g−1 even at 5 C. EIS result shows that Rsf and Rct values of LMNCO are bigger than those of silver-coated LMNCO cathode.
7 citations
TL;DR: In this article, chemical structures of lithium and tetrabutylammonium (TBA) salt solutions in DMAc and N,N-dimethylacetamide (DMAc) and two high donor number organic solvents, have been studied.
Abstract: Chemical structures of lithium and tetrabutylammonium (TBA) salt solutions in N,N-dimethylacetamide (DMAc) and N,N-diethylacetamide (DEAc), two high Donor Number organic solvents, have been studied. In LiX salt solutions (where X = PF6−, CF3SO3−, ClO4− and NO3−), solvation occurs when the Li+ bonds with the solvent’s carbonyl group forming Li+[O=C(CH3)N(CH3)2]nX− ion pairs. Infrared and 13C-NMR spectra are consistent with the ion pair being solvent-separated when the anion is PF6−, ClO4− or NO3−, and a contact ion pair in the case of CF3SO3−. Chemical interactions between TBA+ and the solvents to form conducting solutions appeared to be dipolar in nature. Ionic conductivities of TBA+ and Li+ electrolytes were measured and correlated with their viscosities. In 0.1M TBAPF6/DMAc, the O2 solubility and diffusion coefficient (3.09 × 10−6 mol/cm−3 and 5.09 × 10−5 cm2s−1, respectively) measured using microelectrode technique are typical of values measured in several TBA+ solutions. Microelectrode voltammetry revealed steady-state limiting current behavior for oxygen reduction reactions (ORR) in TBAX/DMAc electrolytes indicating a reversible ORR process. Conversely, microelectrode current-voltage data for ORR in LiX/DMAc electrolytes revealed irreversible behavior mainly ascribed to the blockage of the electrode surface by insoluble ORR products. The ORR in DMAc correlated with its high Donor Number and the overall process conformed to the Hard-Soft Acid-Base theory. © The Author(s) 2019. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0941902jes]
5 citations