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Acidic oxygen evolution reaction (OER) electrocatalysts that provide high activity, lower costs, and long-term stability are needed for the wide-scale adoption of proton-exchange membrane (PEM) water electrolyzers for generating hydrogen through electrochemical water splitting. We report the effects of chromium substitution and temperature treatments on the structure, OER activity, and electrochemical stability of ruthenium oxide (RuO2) aerogel OER electrocatalysts. RuO2 and Cr-substituted RuO2 aerogels (Ru0.6Cr0.4O2) were synthesized using sol–gel chemistry and then thermally treated at different temperatures. Introducing chromium into the synthesis increased the surface area (7–11 times higher) and pore volume (5–6 times higher) relative to RuO2 aerogels. X-ray diffraction analysis is consistent with s that Cr was substituted into the rutile RuO2 structure. X-ray photoelectron spectroscopy showed that trivalent Cr substitution altered the surface electronic structure and ratio of surface hydroxides. The specific capacitance values of Cr-substituted RuO2 aerogels were consistent with charge storage within a hydrous surface. Cr-substituted RuO2 aerogels exhibited 26 times the OER mass activity and 3.5 times the OER specific activity of RuO2 aerogels. Electrochemical stability tests show that Cr-substituted RuO2 aerogels exhibit similar stability to commercial RuO2. Understanding how metal substituents can be used to alter OER activity and stability furthers our ability to obtain highly active, durable, and lower-cost OER electrocatalysts for PEM electrolyzers. 

Global climate is regulated by the ocean, which stores, releases, and transports large amounts of mass, heat, carbon, and oxygen. Understanding, monitoring, and predicting the exchanges of these quantities across the ocean’s surface, their interactions with the atmosphere, and their horizontal and vertical pathways through the global oceans, are key for advancing fundamental knowledge and improving forecasts and longer-term projections of climate, weather, and ocean ecosystems. The existing global observing system provides immense value for science and society in this regard by supplying the data essential for these advancements. The tropical ocean observing system in particular has been developed over decades, motivated in large part by the far-reaching and complex global impacts of tropical climate variability and change. However, changes in observing needs and priorities, new challenges associated with climate change, and advances in observing technologies demand periodic evaluations to ensure that stakeholders’ needs are met. Previous reviews and assessments of the tropical observing system have focused separately on individual basins and their associated observing needs. Here we provide a broader perspective covering the tropical observing system as a whole. Common gaps, needs, and recommendations are identified, and interbasin differences driven by socioeconomic disparities are discussed, building on the concept of an integrated pantropical observing system. Finally, recommendations for improved observations of tropical basin interactions, through oceanic and atmospheric pathways, are presented, emphasizing the benefits that can be achieved through closer interbasin coordination and international partnerships.