There is great economic and environmental value in recovering valuable metal ions from spent lithium-ion batteries (LIBs). A novel method that employs organic acid recovery using citric acid and salicylic acid was used to enhance the leaching of metal ions from the cathode materials of spent LIBs. The effects of the acid concentration, reducing agent content, solid to liquid (S : L) ratio, temperature, and leaching time were systematically analyzed and the optimal acid leaching process condition was determined through the results. The kinetics of the leaching process with different temperatures was analyzed to explore and verify the relationship between the leaching mechanism and temperature. The results of TG/DSC analysis showed that the optimum calcination temperature was 500 °C for 1 h and 600 °C for 3 h. The XRD and micromorphology analysis results showed that cathode material powders without impurities were obtained after pretreatment. The experimental results demonstrated that the optimal leaching efficiencies of the metals ions were 99.5% Co and 97% Li and the optimal corresponding condition was 1.5 M citric acid, 0.2 M salicylic acid, a 15 g L⁻¹ S : L ratio, 6 vol% H₂O₂, 90 °C, and 90 min. Afterward, the infrared tests and SEM morphologies results indicated that only salicylic acid was present in the residue after filtration because of the microsolubility of the salicylic acid. Finally, it was obvious that the temperature had a great influence on the leaching process as observed through the kinetics and thermodynamics analyses, while the E_a values for Co and Li were obtained as 37.96 kJ mol⁻¹ and 25.82 kJ mol⁻¹ through the kinetics model. The whole process was found to be efficient and reasonable for recovering valuable metals from the industrial electrodes of spent LIBs.

PEMFC are considered to be the most promising for automotive energy because of their good working effect, low temperature, high efficiency, and zero pollution. Stainless steel as a PEMFC bipolar plate has unparalleled advantages in strength, cost, and processability, but it is easy to corrode in a PEMFC working environment. In order to improve the corrosion resistance, the surface modification of 316L stainless steel is a feasible solution for PEMFC bipolar plates. In the present study, the plasma-nitrided coating and CrN_x coating were prepared by the plasma-enhanced balanced magnetron sputtering technology on the 316L stainless steel surface. The microstructures, phase compositions, and corrosion resistance behavior of the coatings were investigated. The corrosion behavior of the prepared plasma-nitrided coating and CrN_x coating was investigated by potentiodynamic polarization, potentiostatic polarization, and electrochemical impedance spectroscopy (EIS) in both cathodic and anodic environments. The experimental results show that corrosion resistance of the CrN_x coating was better than the plasma-nitrided coating. It was indicated that the technology process of nitriding first and then depositing Cr was better than nitriding only.

The corrosion behavior of a medium-Mn steel in a simulated marine splash zone was studied by a dry–wet cyclic corrosion experiment and electrochemical experiment. The corrosion products were characterized by corrosion rate calculation, composition detection, morphology observation, element distribution detection, valence analysis, polarization curve, and electrochemical impedance test. The results show that the corrosion products of the sample mainly include γ-FeOOH, Fe_xO_y, Mn_xO_y, and a small amount of (Fe,Mn)_xO_y, and the valence state of iron compounds and manganese compounds in different corrosion stages changed obviously. In the initial corrosion products, Mn is enriched significantly and facilitates the electrochemical reaction of corrosion process. The content of Ni in the inner rust layer is high. The semi-quantitative analysis of the corrosion product elements shows that the atomic concentrations of Cr and Mo increase significantly in later corrosion products, indicating that the dense isolation layer formed by alloy element compounds in the corroded layer is the main factor to improve the protection ability of the rust layer at the end corrosion stage of the sample. With the corrosion durations, the corrosion current density of the sample with the corrosion product film first increases and then decreases, and the corrosion potential first moves negative and then shifts in a positive direction subsequently, indicating that the protective effect of the corrosion product film is gradually significant.