Oxygen evolution reaction (OER) electrocatalysts with high activity, high stability, and low costs are needed for proton-exchange membrane (PEM) electrolyzers. Based on the high cost and limited supply of iridium, approaches that result in iridium-based OER catalysts with increased catalytic activity are of significant interest. We report a carbon-free, self-supported hydrous iridium−nickel oxide two-dimensional nanoframe structure synthesized by thermal treatment of iridium-decorated nickel oxide nanosheets under reducing conditions and subsequent chemical leaching in acid. The catalyst nanoarchitecture contains an interconnected network of metallic iridium−nickel alloy domains with hydrous iridium oxide and nickel oxide located in the surface region. The electrochemical oxidation step maintains the three-dimensional nanoarchitecture and results in a thin (∼5 Å) oxide/hydroxide surface layer. The temperature used for thermal reduction was found to strongly affect the catalyst surface structure and OER activity. Using a lower thermal reduction temperature of 200 °C was determined to provide a higher relative surface concentration of hydroxides and nickel oxide and result in higher OER activities compared with materials treated at 300 °C. The 200 °C-treated hydrous iridium−nickel oxide electrocatalyst showed 15 times higher initial OER mass activity than commercial IrO 2 , and the activity remained 10 times higher than IrO 2 after accelerated durability testing. Density functional theory (DFT) calculations and analysis of the experimental Tafel slopes support that the second electron transfer step is the rate-limiting step for the reaction. The DFT calculations demonstrate that Ni substitution on the IrO 2 surface lowers the activation energy for adsorbed intermediates of the second electron transfer step of the OER reaction. This work establishes that noble metal-decorated metal oxide nanosheets can be transformed into high surface area, carbon-free electrocatalyst nanostructures with high catalytic activities and molecular accessibility and reveals the importance of using controlled thermal reduction temperatures to alter the surface structure and OER activity.

The use of high-concentration salts in electrolyte solutions of lithium–sulfur (Li–S) batteries has been shown to be beneficial for mitigating some effects such as polysulfide shuttle and dendrite growth at the Li metal anode. Such complex solutions have structural-, dynamical-, and reactivity-associated issues that need to be analyzed for a better understanding of the reasons behind such beneficial effects. A passivation interfacial layer known as solid–electrolyte interphase (SEI) is generated during battery cycling as a result of electron transfer from the metal anode causing electrolyte decomposition. Here, using density functional theory and ab initio molecular dynamics simulations, we investigate the salt decomposition, solvation effects, interactions among intermediate products and other species, and potential components of the SEI layer as a function of chemical nature and concentration of the salt for lithium bis­(trifluoromethanesulfonyl)­imide (LiTFSI) and lithium bis­(fluorosulfonyl)­imide (LiFSI) at 1 and 4 M concentrations in dimethoxyethane. It is found that LiTFSI undergoes a less complete reduction and facilitates charge transfer from the anode, whereas LiFSI shows a more complete decomposition forming LiF as one of the main SEI products. In addition, the specific decomposition mechanisms of each salt clearly point to the initial SEI components and the potential main products derived from them. Very complex networks are found among the salt and solvent molecules in their attempt to maximize Li ion solvation that is quantified through the determination of coordination numbers.

Due to their high energy density and reduced cost, lithium–sulfur batteries are promising alternatives for applications such as electrical vehicles. However, a number of technical challenges need to be overcome in order to make them feasible for commercial uses. These challenges arise from the battery highly interconnected chemistry, which besides the electrochemical reactions includes side reactions at both electrodes and migration of soluble polysulfide (PS) species produced at the cathode to the anode side. The presence of such PS species alters the already complex reactivity of the Li anode. In this work, interfacial reactions occurring at the surface of Li metal anodes due to electrochemical instability of the electrolyte components and PS species are investigated with density functional theory and ab initio molecular dynamics methods. It is found that the bis­(trifluoromethane)­sulfonimide lithium salt reacts very fast when in contact with the Li surface, and anion decomposition precedes salt dissociation. The anion decomposition mechanisms are fully elucidated. Two of the typical solvents used in Li–S technology, 1,3-dioxolane and 1,2-dimethoxyethane, are found stable during the entire simulation length, in contrast with the case of ethylene carbonate that is rapidly decomposed by sequential 2- or 4-electron mechanisms. On the other hand, the fast reactivity of the soluble PS species alters the side reactions because the PS totally decomposes before any of the electrolyte components forming Li2S on the anode surface.

Parasitic reactions of electrolyte and polysulfide with the Li-anode in lithium sulfur (Li–S) batteries lead to the formation of solid-electrolyte interphase (SEI) layers, which are the major reason behind severe capacity fading in these systems. Despite numerous studies, the evolution mechanism of the SEI layer and specific roles of polysulfides and other electrolyte components are still unclear. We report an in situ X-ray photoelectron spectroscopy (XPS) and chemical imaging analysis combined with ab initio molecular dynamics (AIMD) computational modeling to gain fundamental understanding regarding the evolution of SEI layers on Li-anodes within Li–S batteries. A multimodal approach involving AIMD modeling and in situ XPS characterization uniquely reveals the chemical identity and distribution of active participants in parasitic reactions as well as the SEI layer evolution mechanism. The SEI layer evolution has three major stages: the formation of a primary composite mixture phase involving stable lithium compounds (Li2S, LiF, Li2O, etc.) and formation of a secondary matrix type phase due to cross interaction between reaction products and electrolyte components, which is followed by a highly dynamic monoanionic polysulfide (i.e., LiS5) fouling process. These new molecular-level insights into the SEI layer evolution on Li-anodes are crucial for delineating effective strategies for the development of Li–S batteries.

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