Advancements in single-atom-based catalysts are crucial for enhancing oxygen evolution reaction (OER) performance while reducing precious metal usage. A comprehensive understanding of underlying mechanisms will expedite this progress further. Here we report Ir single atoms coordinated out-of-plane with dimethylimidazole (MI) on CoFe hydroxide (Ir₁/(Co,Fe)-OH/MI). This Ir₁/(Co,Fe)-OH/MI catalyst, which was prepared using a simple immersion method, delivers ultralow overpotentials of 179 mV at a current density of 10 mA cm⁻² and 257 mV at 600 mA cm⁻² as well as an ultra-small Tafel slope of 24 mV dec⁻¹. Furthermore, Ir₁/(Co,Fe)-OH/MI has a total mass activity exceeding that of commercial IrO₂ by a factor of 58.4. Ab initio simulations indicate that the coordination of MI leads to electron redistribution around the Ir sites. This causes a positive shift in the d-band centre at adjacent Ir and Co sites, facilitating an optimal energy pathway for OER.

Hypercrosslinked pyrrole was synthesized via the Friedel-Crafts reaction and then carbonized to obtain urchin-like nitrogen-doped carbon (UNC). Ultrasmall iron oxide nanoparticles were then supported on UNC, and the composite was used to prepare an electrochemical sensor for detecting uric acid (UA) in human urine. Fe_xO_y/UNC was characterized and analyzed via scanning electron microscopy, transmission electron microscopy, energy dispersive spectrometry, X-ray diffraction, and X-ray photoelectron spectroscopy. A glassy carbon electrode (GCE) modified with Fe_xO_y/UNC was used as an electrochemical sensor to effectively identify UA. The electrochemical behavior of the Fe_xO_y/UNC-based UA sensor was studied using differential pulse stripping voltammetry, and the optimal conditions were determined by changing the amount of Fe_xO_y/UNC, pH of the buffer solution, deposition potential, and deposition time. Under optimal conditions, the Fe_xO_y/UNC-based electrochemical sensor detected UA in the range of 2-200 μM, where the limit of detection (LOD) for UA was 0.29 μM. Anti-interference experiments were performed, and the sensor was applied to the actual analysis of human urine samples. Urea, glucose, ascorbic acid, and many cations and anions present at 100-fold concentrations relative to UA did not strongly interfere with the response of the sensor to UA. The Fe_xO_y/UNC electrochemical sensor has high sensitivity and selectivity for uric acid in human urine samples and can be used for actual clinical testing of UA in urine.

γ-Valerolactone (GVL) and 1,4-pentanediol (1,4-PDO) are value-added chemicals that can be produced from levulinic acid/ester via hydrogenation coupled with acid/base-catalyzed reactions. In this study, we demonstrate that the Cu-based catalysts produced via the hydrotalcite precursors with tunable distribution of acidic and basic sites could, according to the requirement of the target products, effectively tune the production of GVL or to 1,4-PDO from levulinic acid/ester. The abundant Brønsted acid sites over the CuAl catalyst suppressed the opening of the ring of GVL, achieving a higher GVL selectivity while inhibiting 1,4-PDO formation. The introduction of Mg species to the catalyst significantly increased the abundance of the basic sites on the surface of the catalyst, which was essential for the selective conversion of GVL to 1,4-PDO via the opening of the ring structure of GVL, the rate-determining step in the conversion from levulinic acid/ester to 1,4-PDO. In addition, the CuMgAl catalyst showed a much superior catalytic stability to the CuMg or CuAl catalyst due to the more stable crystal structure, the more developed porous structure, the higher dispersion of the Cu species and the higher capability to suppress the growth of metallic Cu species under hydrothermal conditions.