Ambient-air-stable Li3InCl6 halide solid electrolyte, with high ionic conductivity of 1.49 × 10−3 S cm−1 at 25 °C, delivers essential advantages over commercial sulfide-based solid electrolyte.

This review focuses on fundamental understanding, various synthesis routes, chemical/electrochemical stability of halide-based lithium superionic conductors, and their potential applications in energy storage as well as related challenges.

Electrocatalytic nitrate reduction into recyclable ammonium under benign conditions is significant. However, the development of such a process has been retarded by the lack of efficient electrocatalysts for highly selective synthesis of ammonia from nitrate electroreduction. In this work, TiO 2 nanotubes with rich oxygen vacancies (TiO 2-x ) are reported to exhibit high Faradaic efficiency (85.0%) and selectivity (87.1%) toward the ammonium synthesis from nitrate electroreduction. 15 N isotope labeling experiments prove that ammonium originates from nitrate reduction. Both the 1 H nuclear magnetic resonance (NMR) spectra and colorimetric methods are performed to quantify ammonia. Online differential electrochemical mass spectrometry (DEMS) and density functional theory calculations reveal the function of oxygen vacancy in nitrate electroreduction, that is, the oxygen atom in nitrate fills in oxygen vacancies of TiO 2-x to weaken the N−O bonding and restrain the formation of byproducts, resulting in high Faradaic efficiency and ammonium selectivity. This strategy may open a paradigm for the development of rationally designed nanostructures as the electrocatalysts for selective nitrate electroreduction to ammonium.

In this review, we summarize the reaction mechanism, in situ characterization, theoretical simulation, and kinetics analysis. The performance evaluation parameters, standard test methods, and an outlook for nitrate electroreduction are discussed.

The enabling of high energy density of all-solid-state lithium batteries (ASSLBs) requires the development of highly Li+-conductive solid-state electrolytes (SSEs) with good chemical and electrochemical stability. Recently, halide SSEs based on different material design principles have opened new opportunities for ASSLBs. Here, we discovered a series of Li x ScCl3+x SSEs (x = 2.5, 3, 3.5, and 4) based on the cubic close-packed anion sublattice with room-temperature ionic conductivities up to 3 × 10–3 S cm–1. Owing to the low eutectic temperature between LiCl and ScCl3, Li x ScCl3+x SSEs can be synthesized by a simple co-melting strategy. Preferred orientation is observed for all the samples. The influence of the value of x in Li x ScCl3+x on the structure and Li+ diffusivity were systematically explored. With increasing x value, higher Li+, lower vacancy concentration, and less blocking effects from Sc ions are achieved, enabling the ability to tune the Li+ migration. The electrochemical performance shows that Li3ScCl6 possesses a wide electrochemical window of 0.9–4.3 V vs Li+/Li, stable electrochemical plating/stripping of Li for over 2500 h, as well as good compatibility with LiCoO2. LiCoO2/Li3ScCl6/In ASSLB exhibits a reversible capacity of 104.5 mAh g–1 with good cycle life retention for 160 cycles. The observed changes in the ionic conductivity and tuning of the site occupations provide an additional approach toward the design of better SSEs.

To promote the development of solid‐state batteries, polymer‐, oxide‐, and sulfide‐based solid‐state electrolytes (SSEs) have been extensively investigated. However, the disadvantages of these SSEs, such as high‐temperature sintering of oxides, air instability of sulfides, and narrow electrochemical windows of polymers electrolytes, significantly hinder their practical application. Therefore, developing SSEs that have a high ionic conductivity (>10−3 S cm−1), good air stability, wide electrochemical window, excellent electrode interface stability, low‐cost mass production is required. Herein we report a halide Li+ superionic conductor, Li3InCl6, that can be synthesized in water. Most importantly, the as‐synthesized Li3InCl6 shows a high ionic conductivity of 2.04×10−3 S cm−1 at 25 °C. Furthermore, the ionic conductivity can be recovered after dissolution in water. Combined with a LiNi0.8Co0.1Mn0.1O2 cathode, the solid‐state Li battery shows good cycling stability.

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Transition metal chalcogenides (TMCs) are efficient oxygen evolution reaction (OER) pre‐electrocatalysts, and will in situ transform into metal (oxy)hydroxides under OER condition. However, the role of chalcogen is not fully elucidated after oxidation and severe leaching. Here we present the vital promotion of surface‐adsorbed chalcogenates on the OER activity. Taking NiSe2 as an example, in situ Raman spectroscopy revealed the oxidation of Se‐Se to selenites (SeO32−) then to selenates (SeO42−). Combining the severe Se leaching and the strong signal of selenates, it is assumed that the selenates are rich on the surface and play significant roles. As expected, adding selenites to the electrolyte of Ni(OH)2 dramatically enhance its OER activity. And sulfates also exhibit the similar effect, suggesting the promotion of surface‐adsorbed chalcogenates on OER is universal. Our findings offer unique insight into the transformation mechanism of materials during electrolysis.