Search

Engineering high-performance robust electrocatalysts expediting oxygen evolution reaction (OER) for generating sustainable hydrogen presents major scientific challenges. Utilizing density functional theory (DFT), we show fluorine (F) substitution in Ni2P (Ni2P: x wt. % F) causes unique electronic structure modification leading to enhanced alkaline mediated OER performance. Consequently, Ni2P:5 F exhibits improved charge transfer resistance (10.65 O cm2), lower over-potential (230 mV @ 10 mA cm-2), and Tafel slope (28.06 mV dec-1) while also offering excellent durability for OER. Calculations using DFT attribute this superior performance of Ni2P:5 F to optimized electronic structure leading to OER barrier reduction, thus improving the OER reaction kinetics. [ABSTRACT FROM AUTHOR]

The spinel oxide, Cu1.5Mn1.5O4 (CMO) is a promising precious group metal-free electrocatalyst (EC) known for acid-mediated oxygen evolution reaction (OER). By employing density functional theory (DFT) based Bader analysis for active sites identification, the effective electronic charges of constituent ions in the ordered-disordered crystal structures were calculated. Accordingly, for DFT result validation, structurally disordered Cu1.5Mn1.5O4 ECs were experimentally synthesized by heat treatment to 200 °C (CMO-200). The disorder—order transitions of CMO related change in surface atomic arrangement and alteration in the Mn3+/Mn4+ and Cu2+/Cu1+ states are modulated via corresponding heat treatment (200 °C–800 °C) of CMO, revealing significant influence on OER electrocatalytic activity and durability. The measured higher electrocatalytic activity of disordered CMO-200 contrasted with ordered CMO is attributed to higher Mn3+/Mn4+ and Cu2+Cu1+ states, signifying the beneficial role of Mn3+ and Cu2+ for facilitating OER. The ordered CMO structures containing lower Mn3+/Mn4+ and Cu2+/Cu1+ ratios albeit reveal higher electrochemical stability than the disordered CMO. The present study, thus, provides fundamental insights into the influence of ordered-disordered structures and rearrangement of the oxidation state of active species and their combined synergistic effects on the electrochemical performance for engineering high-performance ECs for acidic OER. [ABSTRACT FROM AUTHOR]

The prowess of Li4SiO4, a known Li-ion conductor for effectively trapping solvents while enabling Li-ion migration contributing to Li-S battery stability was previously demonstrated. Herein Li-ion conductivity enhancement of Li4SiO4 was investigated using first principles calculations and correspondingly, Ca, Mg and F ion substituted Li4SiO4 were shown to yield ~3–4 order improvement in room temperature Li+ ion conductivities with reduced activation barriers via vacancy mechanism favoring easy diffusion. To demonstrate effects on Li-S battery performance, high sulfur loading cathodes (~3.8 mg S cm−2) were generated by coating substituted silicates onto sulfur infiltrated copper bipyridine complex framework material (S-Cu-bpy-CFM) electrodes. These ions substituted Li4SiO4 coated sulfur electrodes demonstrated high areal capacities (~2.21–2.67 mAh cm−2), good capacity retention (~0.19%–0.33%/cycle) and rate capabilities (~800 mAh g−1−700 mAh g−1 @100 mA g−1, 600 mAh g−1− 500 mAh g−1 @300 mA g−1, 400 mAh g−1−300 mAh g−1 @ 500 mA g−1 and ~250 mAh g−1–190 mAh g−1 @1000 mA g−1) contrasted with unsubstituted Li4SiO4. Post cycle electrochemical impedance spectroscopy analysis of the batteries also shows that the difference in charge-transfer resistance (Rct) between the 1st and the 100th cycle is 49.7Ω for the pristine Li4SiO4 coated electrodes while only 2.14Ω is observed for the calcium substituted Li4SiO4 coated cathodes justifying the cycling performance improvements using the ion-substituted Li4SiO4 coating. [ABSTRACT FROM AUTHOR]

Lithium-sulfur (Li-S) secondary batteries with sulfur cathodes and theoretical energy density of ~2600 Wh/kg, are promising high energy-density system for next-generation electric-vehicles (EVs) potentially mitigating the gravimetric and volumetric energy density limitations of existing lithium-ion (Li-ion) batteries. Herein, a chemically synthesized sulfonic acid-based complex framework material (CFM) termed as (SCFM), was used as sulfur host (S-SCFM) to prevent polysulfide dissolution in Li-S batteries. The SSCFM based CFM cathodes show an initial capacity of 1190 mAh/g and a capacity of 1044 mAh/g after 100 cycles. In addition, the S-SCFM based CFM cathodes exhibited good cycling stability with a minimal fade rate of ~0.0012% per cycle. XPS analysis of the cycled separators with the S-SCFM electrodes shows complete absence of polysulfide species after 100 charge-discharge cycles. It was also identified that the SCFM based CFM chemically binds sulfur via -C-S- linkages thereby exhibiting an affinity for the polysulfide species formed during the charge-discharge cycles. As a result, the SCFM based CFM prevent polysulfide species from dissolving and diffusing into the electrolyte. A thorough understanding of these engineered SCFM based CFM sulfur host in Li-S battery outlined herein will be vital in designing promising sulfur hosts for next generation sulfur cathodes in Li-S batteries. [ABSTRACT FROM AUTHOR]