Achieving energy densities exceeding 350 Wh kg(-1 )while operating at elevated voltages (>4.5 V vs Li/Li+) is attainable through judicious selection of electrochemical pairs at the cathode and anode. However, current state-of-the-art electrolytes exhibit limited stability when exposed to systems operating at or above 4.3 V. This limitation contributes to the degradation of electrode materials and raises critical safety concerns, impeding the commercialization of such systems. Consequently, there has been a notable surge in research efforts aimed at developing innovative electrolyte compositions capable of supporting high-voltage lithium-ion batteries (LIBs). A substantial portion of this research has focused on the family of organosulfur molecules, which possess high oxidative stability. Organosulfur salts also facilitate the formation of dense, ionically conductive solid electrolyte interfaces (SEI) and demonstrate excellent solubility. This article provides a comprehensive overview of the field of organosulfur electrolyte components for their applications in energy storage, encompassing solvents, alternative conducting salts, and additives. It emphasizes the idea that the deliberate design of electrolyte compositions is instrumental in controlling electrode passivation, with organosulfur-based structures historically proving advantageous in every aspect of the electrolyte. Crucially, it should be noted that many of these components are commercially available, holding significant implications for industrial applications.

The interaction between catalyst surfaces and adsorbed oxygen intermediates is critical to catalytic performance for electrochemical water oxidation to oxygen. However, the relationship between adsorption energetics and electrocatalytic activity is primarily assessed for pristine catalyst materials, which leaves much unknown about the dynamics of these properties in relationship to catalyst performance during long-term operation. In this work, we experimentally assess OH and O adsorption on Ca2IrO4 nanoparticles and monitor their evolution during extensive chronoamperometry tests at highly oxidizing potentials in a range of low pH electrolytes. In situ x-ray absorption spectroscopy reveals changes for surface adsorbate energetics and local iridium structures with applied potentials. Increasingly unfavorable adsorption of OH and formation of O intermediates after long-term operation is correlated with severe metal dissolution, distorted [IrO6] octahedral linkages, and a decreased average Ir valence. This work establishes connections between surface adsorption energetics, Ir structure, OER kinetics, and material stability outcomes.

Water electrolysis using proton exchange membrane technology offers an ideal process for green hydrogen production, but widespread deployment is inhibited by insufficient catalyst activity, stability and affordability. Iridium-based oxides provide the best overall performance for acidic water oxidation, the limiting reaction for this process, but further improvements are impeded by poor understanding of the restructured active catalyst surface that forms under reaction conditions. Here we present a combination of X-ray and electron scattering data that reveals direct evidence for three paracrystalline structural motifs at the restructured surfaces of highly active catalysts (including rutile IrO2 and perovskite SrIrO3) that have previously been described as amorphous. These insights enable the design of a paracrystalline IrOx catalyst that is independent of the bulk crystalline support and maintains higher activity, longer stability and more effective use of iridium to promote the production of green hydrogen. Iridium-based oxides are the most active catalysts for acidic water oxidation, but a complete understanding of their surface reconstruction under operation remains elusive. Now three key paracrystalline structural motifs are identified on the seemingly amorphous reconstructed IrOx surface.

An improved understanding of catalyst dynamics for the oxygen evolution reaction (OER) in acid is critical for informing the development of highly efficient, stable, and cost-effective OER catalysts for proton exchange membrane water electrolysis applications. Herein highly tunable, active, and dynamic Ir 5+ materials are studied, Ln(3)IrO(7) (Ln = Pr, Nd, Sm, and Eu). Leveraging a combination of in situ and ex situ characterization, as well as an advanced mercury underpotential deposition technique for Ir surface site quantification, the dynamic nature of Ln(3)IrO(7) materials throughout electrochemical activation under OER conditions is characterized. The trends are elucidated between intrinsic OER activity, surface Ir site quantity, and metal site dissolution behavior as tuned by the Ln site's atomic number. A critical relationship is uncovered to show that maintenance of excellent OER activity throughout performance testing is correlated with a catalysts' ability to preserve a high degree of Ir enrichment, where heightened stability of Ir sites interestingly parallels reduced stability of Ln sites throughout testing. It is found that as the Ln site's atomic number is decreased, the materials' intrinsic OER performance improves, due to an increased thermodynamic driving force for Ln dissolution, which is hypothesized to enable the maintenance of highly active Ir-based surface motifs.

Research drives development of sustainable electrocatalytic technologies, but efforts are hindered by inconsistent reporting of advances in catalytic performance. Iridium-based oxide catalysts are widely studied for electrocatalytic technologies, particularly for the oxygen evolution reaction (OER) for proton exchange membrane water electrolysis, but insufficient techniques for quantifying electrochemically accessible iridium active sites impede accurate assessment of intrinsic activity improvements. We develop mercury underpotential deposition and stripping as a reversible electrochemical adsorption process to robustly quantify iridium sites and consistently normalize OER performance of benchmark IrO x electrodes to a single intrinsic activity curve, where other commonly used normalization methods cannot. Through rigorous deconvolution of mercury redox and reproportionation reactions, we extract net monolayer deposition and stripping of mercury on iridium sites throughout testing using a rotating ring disk electrode. This technique is a transformative method to standardize OER performance across a wide range of iridium-based materials and quantify electrochemical iridium active sites.

The development of active and acid-stable iridium-basedcatalystsis crucial to meet the requirements of proton exchange membrane technologiesfor the sustainable production of hydrogen via water electrolysis.However, long-term stability remains a critical challenge. In thiswork, we focus on a Ca2IrO4 catalyst to developa holistic picture of catalyst electronic and geometric structureevolution under various applied potentials by probing electrochemicallyactive surface area, metal dissolution, Ir valence, and surface morphology.We observe an initial activity increase in parallel with increasingcapacitance and minor iridium dissolution. Extensive chronoamperometrytests at oxidizing potentials lead to significant activity loss thatoccurs simultaneously with a dramatic drop in capacitance and a changein impedance. Using a combination of electrochemical and spectroscopictools, we provide fundamental insights to these material degradationprocesses to enable future catalyst design with balanced activityand long-term stability.

The stability of electrocatalysts is a concern for nearly all materials; degradation can occur via dissolution, leaching, sintering, amorphization, or reduction/oxidation processes. Extreme pH or large applied potentials often exacerbate these effects, but scant fundamental understanding of these processes exists due to complex structural and nanoscale effects in electrocatalysis. Instead, "catalyst stability" is often reported using broad electrode performance metrics, such as measured activity over time. To advance the fundamental understanding and comparison of catalyst materials, we propose that it is necessary to establish improved benchmarking metrics that reflect intrinsic material dynamics and stabilities of catalysts, supports, and substrates as a function of testing parameters, to complement existing metrics that primarily capture the performance of the complete electrode. We consider many degradation processes of lab-scale aqueous media systems, as well as membrane electrode assemblies and proton exchange membrane water electrolyzers, and consider the relatability between the two systems. Herein, we summarize various approaches to standardizing or benchmarking electrocatalyst performance, consider their strengths and weaknesses, and provide an outlook for advancing the rigor, specificity, and reproducibility of these techniques.

Employing benchmarking metrics to capture the activity and stability of electrocatalysts for the oxygen evolution reaction (OER) in acid is a critical practice that enables meaningful comparison of catalyst material candidates reported throughout the literature. In this work, we find that ubiquitously used glassy carbon electrode substrates oxidize under typical OER operating conditions, forming a pacified, electrically insulating, and oxygen-rich surface layer that causes drastic loss of current density over the course of extended chronoamperometric stability tests at an anodic potential of 1.7 VRHE. We show that the experimentally observed stability of glassy carbon-based electrodes is approximately two orders of magnitude lower than that expected solely from dissolution-based catalyst intrinsic stability of Ir-based catalysts. We additionally find that glassy carbon-based electrode stability measured by chronoamperometric holds is greatly impacted by catalyst loading, with high catalyst loadings improving the stability of the overall electrode via a protective effect on the glassy carbon substrate. Overall, our investigation highlights that glassy carbon is not electrochemically inert under OER conditions on the timescale of common stability tests, which can cause electrodes to exhibit performance losses that do not reflect the intrinsic stability of the actual catalyst material being investigated. In light of our findings, we underscore the usefulness of metrics, such as the S-number, to reflect intrinsic catalyst material stability.

An illustration of solar-driven synthesis of ammonia using nitrates with >10% solar-to-fuel efficiencies that can potentially decarbonize and decentralize ammonia production.

While iridium-based perovskites have been identified as promising candidates for the oxygen evolution reaction (OER) in proton exchange membrane (PEM) electrolyzer applications, an improved fundamental understanding of these highly dynamic materials under reaction conditions is needed to inform more robust future catalyst design. Herein, we study the highly active SrIr0.8Zn0.2O3 perovskite for the OER in acid by employing electrochemical experiments with in situ and ex situ characterization techniques to understand the dynamic nature of this material at both short and long time scales. We observe initial intrinsic OER activity improvement with electrochemical cycling as well as an initial increase of Ir oxidation state under OER conditions via in situ X-ray absorption spectroscopy. We discover that the SrIr0.8Zn0.2O3 perovskite experiences an OER-induced metal to insulator transition (MIT) with extensive electrochemical cycling, caused by surface reorganization and changes to the material crystallinity that occur with exposure to an acidic and oxidizing environment. Our novel identification of an OER-induced MIT for iridate perovskites reveals an additional stability concern for iridate catalysts which are known to experience material dissolution challenges; this work ultimately aims to inform future catalyst material design for PEM water electrolysis applications.

Stability of metal-organic frameworks (MOFs) under hydrogen is of particular importance for a diverse range of applications, including catalysis, gas separations, and hydrogen storage. Hydrogen in gaseous form is known to be a strong reducing agent and can potentially react with the secondary building units of a MOF and decompose the porous framework structure. Moreover, rapid pressure swings expected in vehicular hydrogen storage could create significant mechanical stresses within MOF crystals that cause partial or complete pore collapse. In this work, we examined the stability of a structurally representative suite of MOFs by testing them under both static (70MPa) and dynamic hydrogen exposure (0.5 to 10MPa, 1000 pressure cycles) at room temperature. We aim to provide stability information for development of near room-temperature hydrogen storage media based on MOFs and suggest framework design rules to avoid materials unstable for hydrogen storage under relevant technical conditions.

Non-monotonic catalytic behavior in an isoreticular MOF series results from subtle structural differences that alter the substrate binding energy.

Metal-Organic Frameworks (MOFs) that catalyze hydrogenolysis reactions are rare and there is little understanding of how the MOF, hydrogen, and substrate molecules interact. In this regard, the isoreticular IRMOF-74 series, two of which are known catalysts for hydrogenolysis of aromatic C-O bonds, provides an unusual opportunity for systematic probing of these reactions. The diameter of the 1D open channels can be varied within a common topology owing to the common secondary building unit (SBU) and controllable length of the hydroxy-carboxylate struts. We show that the first four members of the IRMOF-74(Mg) series are inherently catalytic for aromatic C-O bond hydrogenolysis and that the conversion varies non-monotonically with pore size. These catalysts are recyclable and reusable, retaining their crystallinity and framework structure after the hydrogenolysis reaction. The hydrogenolysis conversion of phenylethylphenyl ether (PPE), benzylphenyl ether (BPE), and diphenyl ether (DPE) varies as PPE > BPE > DPE, consistent with the strength of the C-O bond. Counterintuitively, however, the conversion also follows the trend IRMOF-74(III) > IRMOF-74(IV) > IRMOF-74(II) > IRMOF-74(I), with little variation in the corresponding selectivity. DFT calculations suggest the unexpected behavior is due to much stronger ether and phenol binding to the Mg(ii) open metal sites (OMS) of IRMOF-74(III), resulting from a structural distortion that moves the Mg2+ ions toward the interior of the pore. Solid-state 25Mg NMR data indicate that both H2 and ether molecules interact with the Mg(ii) OMS and hydrogen-deuterium exchange reactions show that these MOFs activate dihydrogen bonds. The results suggest that both confinement and the presence of reactive metals are essential for achieving the high catalytic activity, but that subtle variations in pore structure can significantly affect the catalysis. Moreover, they challenge the notion that simply increasing MOF pore size within a constant topology will lead to higher conversions.

Chemistry is the scientific study of the composition and properties of matter and the investigation of the laws that govern them. Classically, chemistry is divided into several subdisciplines. Organic chemistry deals primarily with carbon compounds; inorganic chemistry, with compounds of the other elements. Physical chemistry seeks to describe relationships between the chemical and physical properties of all substances. Analytical chemistry studies the analysis of the chemical composition of all substances. Biological chemistry pursues the chemistry of living organisms. At the borders of these subdisciplines are many hybrid areas of study: physical organic, organometallic, bioinorganic, and others. At the interface of chemistry with other sciences, several active fields are fueled by insights gained from two ways of thinking about things: for example, chemical physics, chemical biology, organic geochemistry, and the extensive chemical problems in biotechnology, nanotechnology, material sciences, and molecular medicine. In all of these areas the chemist’s approach may be theoretical, experimental, or both.

Sub-50 mV operation of nano-electro-mechanical relays is demonstrated for the first time, enabled by an anti-stiction molecular coating. Specifically, a self-assembled monolayer of perfluorodecyltriethoxysilane (PFDTES) is shown to be effective for reducing the switching hysteresis voltage, without dramatically increasing its ON-state resistance, enabling stable device operation at very low voltages.