Chemical Engineering: Research @ Brunel

Research published by Brunel staff

Below are recent articles (co-)authored by Brunel academic staff. Please click the title of the article to access the full-text.

• Progress and challenges in engineering the atomic structure of oxygen electrocatalysts for zinc-air batteries
  Choi, J.
  Chemical Engineering Journal, Vol 497, Art No. 154561 (Oct 2024)
  Rechargeable zinc-air batteries are presently regarded as promising candidates for next-generation energy storage systems, owing to their high specific energy density, environmental-friendliness, and safety. Despite these advantages, zinc-air batteries still suffer from low energy efficiency and poor cycle life due to sluggish electrochemical kinetics of oxygen species. Therefore, modification strategies for catalysts to improve the performance of rechargeable zinc-air batteries are necessary. This review focuses on strategies used for modifying catalysts from nanoarchitecture and electronic structural perspectives. In the review, we first describe the overall mechanism and component of the zinc-air battery. Then, we analyze the effects of charge redistribution and enhanced electron transport within the molecular structures of the air cathode by forming heterogeneous nanostructures. We also analyze the relationship between modulation of d-band center of the catalyst and the coordination environment of atom within the air cathode. We also describe the strategies for incorporating vacancies in the molecular structure to improve the performance of air cathodes. Finally, we provide a general perspective on the overall limitations of current zinc-air batteries.

• Evaluating the performance of citric acid and maleic acid for mixed-acid leaching of critical metals from spent lithium-ion batteries
  Burgess, C. et al.
  Journal of Material Cycles and Waste Management, [Early access article] (Aug 2024)
  Leaching, especially using mixtures of organic acids, can reduce the chemical requirement of organic acid leaching of metals. This work investigates the performance of maleic acid and citric acid and their potential synergy in a mixed-acid leaching system for the recovery of valuable metals from the cathode material of spent lithium-ion batteries (LIBs). The influence of key leaching parameters such as acid concentration, temperature and reducing agent (fructose) were examined. As single acids, citric acid proved to be a stronger lixiviant than maleic acid. 83% Li, 84%Mn, 80% Co and 80%Ni was leached using 0.5 M citric acid at a temperature of 90 degrees C after 60 min. As mixtures, the leaching of the metals showed significant dependence on the ratio of the acids and increased with the proportion of citric acid, indicating that citric acid is the dominant lixiviant. However, the performance of the mixtures of citric acid and maleic acid was lower than that of the individual acids, thus demonstrating lack of synergy. Spectra analysis of the leachates confirmed the formation of metal complexes and interactions between citric and maleic acid, and explains the observed performance of the acid mixtures. Overall, this work reveals that not all organic acid mixtures are synergic.

• A cavitation enabled green leaching of metals from spent lithium-ion batteries
  Okonkwo, E. G. et al
  Chemical Engineering and Processing-Process Intensification, Vol 202, Art No. 109850 (Aug 2024)
  As the world dabbles with increasing quantities of spent lithium-ion batteries (LIBs) and the need to recover valuable metals therein, sustainable approaches to achieving this need have become a necessity. In this work, we present the findings of an ultrasound-assisted intensification of a leaching process for the recovery of cobalt, nickel, manganese and lithium from spent LIBs. Molasses, methanesulfonic acid and ultrasonication were used together to enhance the leaching of the metals. The influence of ultrasonic modes, namely, sonication under isothermal and non-isothermal conditions, and leaching parameters, such as temperature, sonication amplitude, time, solid-liquid ratio, and reductant dosage, were evaluated. The leaching of metals was found to be strongly dependent on amplitude, temperature, and time. Compared to conventional mechanical stirring, the application of ultrasonic waves improves the leaching of metals by similar to 22-74 %, with the degree of enhancement dependent on the temperature and the metal. The non-isothermal sonication mode (sonication without temperature control) has a lower energy input yet can yield a similar leaching performance as sonication under controlled temperature (isothermal mode). The results suggest that the introduction of ultrasonic waves created cavitation bubbles, which caused solid fragmentation, enhanced the mass transfer and diffusion of the reactants, and formed products that led to significant improvements in the leaching efficiency.