In situ detection of reactive oxygen species spontaneously generated on lead acid battery anodes: a pathway for degradation and self-discharge at open circuit.

Prospects for refurbishing and recycling energy storage technologies such as lead acid batteries (LABs) prompt a better understanding of their failure mechanisms. LABs suffer from a high self-discharge rate accompanied by deleterious hard sulfation processes which dramatically decrease cyclability. Furthermore, the evolution of H2, CO, and CO2 also poses safety risks. Despite the maturity of LAB technologies, the mechanisms behind these degradation phenomena have not been well established, thus hindering attempts to extend the cycle life of LABs in a sustainable manner. Here, we investigate the effect of the oxygen reduction reaction (ORR) on the sulfation of LAB anodes under open circuit (OC). For the first time, we found that the sulfation reaction is significantly enhanced in the presence of oxygen. Interestingly, we also report the formation of reactive oxygen species (ROS) during this process, known to hamper cycle life of batteries via corrosion. Electron spin resonance (ESR) and in situ scanning electrochemical microscopy (SECM) unambiguously demonstrated the presence of OH˙ and of H2O2 as the products of spontaneous ORR on LAB anodes. High temporal resolution SECM measurements of the hydrogen evolution reaction (HER) during LAB anode corrosion displayed a stochastic nature, highlighting the value of the in situ experiment. Balancing the ORR and HER prompts self-discharge while reaction of the carbon additives with highly oxidizing ROS may explain previously reported parasitic reactions generating CO and CO2. This degradation mode implicating ROS and battery corrosion impacts the design, operation, and recycling of LABs as well as upcoming chemistries involving the ORR.

In Situ Surface Fluorination of TiO2 Nanocrystals Reinforces Interface Binding of Perovskite Layer for Highly Efficient Solar Cells with Dramatically Enhanced Ultraviolet-Light Stability.

Low-temperature solution-processed TiO2 nanocrystals (LT-TiO2) have been extensively applied as electron transport layer (ETL) of perovskite solar cells (PSCs). However, the low electron mobility, high density of electronic trap states, and considerable photocatalytic activity of TiO2 result in undesirable charge recombination at the ETL/perovskite interface and notorious instability of PSCs under ultraviolet (UV) light. Herein, LT-TiO2 nanocrystals are in situ fluorinated via a simple nonhydrolytic method, affording formation of Ti─F bonds, and consequently increase electron mobility, decrease density of electronic trap states, and inhibit photocatalytic activity. Upon applying fluorinated TiO2 nanocrystals (F-TiO2) as ETL, regular-structure planar heterojunction PSC (PHJ-PSC) achieves a champion power conversion efficiency (PCE) of 22.68%, which is among the highest PCEs for PHJ-PSCs based on LT-TiO2 ETLs. Flexible PHJ-PSC devices based on F-TiO2 ETL exhibit the best PCE of 18.26%, which is the highest value for TiO2-based flexible devices. The bonded F atoms on the surface of TiO2 promote the formation of Pb─F bonds and hydrogen bonds between F- and FA/MA organic cations, reinforcing interface binding of perovskite layer with TiO2 ETL. This contributes to effective passivation of the surface trap states of perovskite film, resulting in enhancements of device efficiency and stability especially under UV light.