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 Investigation of the Cytotoxic and Interfacial Characteristics of Titanium When Galvanically Coupled with Magnesium Using Scanning Electrochemical Microscopy.

Recently, the cytotoxic properties of galvanically coupled Ti-Mg particles have been shown in different cells. This cytotoxic effect has been attributed mainly to Mg due to its tendency to undergo activation when coupled with Ti, forming a galvanic cell consisting of an anode (Mg) and a cathode (Ti). However, the role of the Ti cathode has been ignored in explaining the cytotoxic effect of Ti-Mg particles due to its high resistance to corrosion. In this work, the role of titanium (Ti) in the cytotoxic mechanism of galvanically coupled Ti-Mg particles was examined. A model galvanic cell (MGC) was prepared to simulate the Mg-Ti particles. The electrochemical reactivity of the Ti sample and the pH change in it due to galvanic coupling with Mg were investigated using scanning electrochemical microscopy (SECM). It was observed that the Ti surface changed from passive to electrochemically active when coupled with Mg. Furthermore, after only 15 min of galvanic coupling with Mg, the pH in the electrolyte volume adjacent to the Ti surface increased to an alkaline pH value. The effects of the galvanic coupling of Ti and Mg, as well as those of the alkaline pH environment, on the viability of Hs27 fibroblast cells were investigated. It was shown that the viability of Hs27 cells significantly diminished when Mg and Ti were galvanically coupled compared to when the two metals were electrically disconnected. Thus, although Ti usually exhibited high corrosion resistance when exposed to physiological environments, an electrochemically active surface was observed when galvanically coupled with Mg, and this surface may participate in electron transfer reactions with chemical species in the neighboring environment; this participation resulted in the increased pH values above its surface and enhanced generation of reactive oxygen species. These features contributed to the development of cytotoxic effects by galvanically coupled Ti-Mg particles.