Monitoring SEIRAS on a Graphitic Electrode for Surface-Sensitive Electrochemistry: Real-Time Electrografting.

The ubiquity of graphitic materials in electrochemistry makes it highly desirable to probe their interfacial behavior under electrochemical control. Probing the dynamics of molecules at the electrode/electrolyte interface is possible through spectroelectrochemical approaches involving surface-enhanced infrared absorption spectroscopy (SEIRAS). Usually, this technique can only be done on plasmonic metals such as gold or carbon nanoribbons, but a more convenient substrate for carbon electrochemical studies is needed. Here, we expanded the scope of SEIRAS by introducing a robust hybrid graphene-on-gold substrate, where we monitored electrografting processes occurring at the graphene/electrolyte interface. These electrodes consist of graphene deposited onto a roughened gold-sputtered internal reflection element (IRE) for attenuated total reflectance (ATR) SEIRAS. The capabilities of the graphene-gold IRE were demonstrated by successfully monitoring the electrografting of 4-amino-2,2,6,6-tetramethyl-1-piperidine N-oxyl (4-amino-TEMPO) and 4-nitrobenzene diazonium (4-NBD) in real time. These grafts were characterized using cyclic voltammetry and ATR-SEIRAS, clearly showing the 1520 and 1350 cm-1 NO2 stretches for 4-NBD and the 1240 cm-1 C-C, C-C-H, and N-È® stretch for 4-amino-TEMPO. Successful grafts on graphene did not show the SEIRAS effect, while grafting on gold was not stable for TEMPO and had poorer resolution than on graphene-gold for 4-NBD, highlighting the uniqueness of our approach. The graphene-gold IRE is proficient at resolving the spectral responses of redox transformations, unambiguously demonstrating the real-time detection of surface processes on a graphitic electrode. This work provides ample future directions for real-time spectroelectrochemical investigations of carbon electrodes used for sensing, energy storage, electrocatalysis, and environmental applications.

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.

The design of zinc-substituted cobalt (pyro)phosphates as efficient bifunctional electrocatalysts for zinc-air batteries.

In an effort to rationally design economic electrocatalysts, zinc-substituted cobalt phosphate and pyrophosphate were prepared using facile template-free combustion synthesis. They act as efficient stable bifunctional electrocatalysts due to the tuning of oxygen affinity by zinc substitution and catalytically active cobalt sites. Exploiting their bifunctional activity, these cobalt (pyro)phosphates were incorporated into a zinc-air battery in an alkaline electrolyte.