04,03,2026 2 views
Recently, Professor Tan Peng's team from the Department of Thermal Science and Energy Engineering at the School of Engineering Sciences, University of Science and Technology of China, made new progress in the field of aqueous zinc batteries. The research team successfully developed in-situ 3D pH visualization technology, which achieved three-dimensional, in-situ, and quantitative imaging of the pH field at the zinc electrode reaction interface. The research findings, titled "Three Dimensional Visualization of Chemical Stratification and Pathological Reduction in Aquatic Zinc Batteries," were published in the internationally renowned journal ACS Energy Letters and selected as the cover paper.
Water based zinc batteries have shown great potential in the next generation of large-scale energy storage due to their inherent advantages of safety, low cost, and environmental friendliness. However, the interface instability of metal zinc negative electrodes in aqueous electrolytes seriously hinders the commercialization process. The coupling of dendrite growth, hydrogen evolution side reactions, surface passivation, and self corrosion results in battery cycle life far below theoretical expectations. In fact, these failure behaviors are all controlled by the local chemical microenvironment at the electrode/electrolyte interface, especially the dynamic evolution of proton activity (i.e. local pH). Localized acidic environments can easily induce chemical corrosion of active zinc and exacerbate hydrogen evolution reactions, while localized alkalization promotes the generation of insulating by-products such as basic zinc sulfate or zinc oxide, leading to interface passivation and uneven deposition. The interface pH is not a passive response variable, but a core parameter that directly determines the selectivity and evolution direction of zinc negative electrode reactions. Therefore, the development of characterization methods that can capture the three-dimensional evolution process of interface chemical environment in situ and deeply understand its impact on electrode stability is of great significance for revealing the failure mechanism of aqueous zinc batteries and improving battery performance.
In response to the above issues, the research team designed an electrochemical testing device that can be optically observed, and introduced a fluorescent pH indicator into the electrolyte. Through laser confocal imaging technology, the electrolyte area near the interface was scanned layer by layer, achieving real-time monitoring and high-precision quantitative reconstruction of the pH field of the reaction interface in three-dimensional space.
With the help of this tool, the research team conducted real-time monitoring of the chemical environment at the zinc electrode interface. Firstly, under static conditions, three-dimensional imaging reveals a significant pH stratification along the direction of gravity, where the pH in the area below the electrode is significantly higher than in the area above, with a pH difference of approximately 0.3 at 600 seconds. Furthermore, in-situ monitoring was conducted under the constant current operating conditions of the symmetrical zinc battery, and it was found that a high pH region rapidly formed below the interface during the electro dissolution stage. The vertical pH gradient increased rapidly, and the pH difference between the upper and lower regions reached about 0.6 at 180 seconds; Although there was some relaxation during the sedimentation stage, it remained above 0.4 at the end of the cycle. These results indicate that stable vertical chemical stratification will form at the zinc electrode interface during both static and electrochemical operation.
The research team combined multiple physical field simulations to systematically elucidate that this chemical stratification is a direct result of gravity coupled material transport regulation, and revealed a novel electrode failure mechanism: the redistribution of active substances driven by chemical gradients. Specifically, the low pH and low Zn2+concentration in the upper part accelerate hydrogen evolution corrosion and dissolution reactions, while the high pH and high Zn2+concentration in the lower part inhibit hydrogen evolution corrosion and promote zinc deposition. As the cycle progresses, this difference drives the migration of active zinc in the vertical direction, ultimately forming a structural differentiation of "upper depletion lower enrichment" and causing electrode failure.
This work successfully achieved three-dimensional visualization of chemical stratification at the interface of aqueous zinc batteries, revealing the redistribution mechanism of active materials in zinc electrodes driven by chemical gradients. It not only provides new insights into the failure mechanism of metal negative electrodes in aqueous zinc batteries, but also provides universal guidance for the rational design of other aqueous metal batteries.
The first authors of the paper are Zhao Zhongxi and Chen Yongtang, and the corresponding author is Professor Tan Peng. This work was supported by the National Natural Science Foundation of China's Young Student Basic Research Project (523B2061) and the National Innovation Talent Program's Youth Project (GG2090007001).
