Core-shell NiS2@C encased by thin carbon layer as high-rate and durable electrode for aqueous rechargeable battery

Nickel sulfides, as promising candidate for aqueous rechargeable battery, have aroused broad attention on account of abundant natural resources, rich phases, moderate price and high theoretical capacity. Nevertheless, tremendous volume expansion during repeated charging-discharging procedure leads to the poor rate capability and cycling stability of nickel sulfide electrodes. Therefore, in this work, core-shell NiS₂@C encapsulated by thin hydrothermal carbon (HC) layer (NiS₂@C/HC) has been designed and prepared without any surfactants or templates assistance, which avoid tedious process and shorten preparation cycle greatly. When matched with the treated iron powder (TIP) electrode to form NiS₂@C/HC//TIP aqueous rechargeable battery, the NiS₂@C/HC//TIP battery exhibits a high discharge capacity of 205.1 mAh g^-1 at 1 A g^-1, remarkable rate ability (176.4 mAh g^-1 at 5 A g^-1, about 86% capacity conversation) and superiorly durable stability (80.8 % capacity retention after 10,000 cycles at ultra-high current density of 15 A g^-1). The outstanding high-rate capability and cycling stability for aqueous rechargeable battery can be ascribed to the distinct cowpea-like architecture and intrinsic properties of NiS₂@C/HC. Specifically, the interior porous carbon provides a space to tolerate the volume expansion of the NiS₂ nanoparticles and prevent NiS₂ nanoparticles from aggregation, guaranteeing its high-rate capability. Meanwhile, the exterior HC layer is conducive to improve the electric conductivity to facilitate the electrons transfer and promote the mechanical strength of the whole active materials, ensuring its robust cycling stability.

Sensitivity Detection of Uric Acid and Creatinine in Human Urine Based on Nanoporous Gold

Given the significance of uric acid and creatinine in clinical diagnostic, disease prevention and treatment, a multifunctional electrochemical sensor was proposed for sensitive detection of uric acid and creatinine. The sensitive detection of uric acid was realized based on the unique electrochemical oxidation of nanoporous gold (NPG) towards uric acid, showing good linearity from 10 μM to 750 μM with a satisfactory sensitivity of 222.91 μA mM−1 cm−2 and a limit of detection (LOD) of 0.06 μM. Based on the Jaffé reaction between creatinine and picric acid, the sensitive detection of creatinine was indirectly achieved in a range from 10 to 2000 μM by determining the consumption of picric acid in the Jaffé reaction with a detection sensitivity of 195.05 μA mM−1 cm−2 and a LOD of 10 μM. For human urine detection using the proposed electrochemical sensor, the uric acid detection results were comparable to that of high-performance liquid chromatography (HPLC), with a deviation rate of less than 10.28% and the recoveries of uric acid spiked in urine samples were 89~118%. Compared with HPLC results, the deviation rate of creatinine detection in urine samples was less than 4.17% and the recoveries of creatinine spiked in urine samples ranged from 92.50% to 117.40%. The multifunctional electrochemical sensor exhibited many advantages in practical applications, including short detection time, high stability, simple operation, strong anti-interference ability, cost-effectiveness, and easy fabrication, which provided a promising alternative for urine analysis in clinical diagnosis.