ABSTRACT
It is essential to develop novel catalysts with high catalytic activity, strong durability, and good stability for further application in methanol fuel cells. In this work, we present for the first time the effect of the chemical functional groups (thiol and amine) with different electron affinity in reduced graphene oxide supports on the morphology and catalytic activity of platinum nanoparticles for the methanol oxidation reaction. Hydroxyl groups on graphene oxide were initially brominated and then transformed to the desired functional groups. The good dispersion of metal nanoparticles over functionalized carbon substrates (particle size less than 5 nm) with good durability, even at a limited functionalization degree (less than 7%) has been demonstrated by morphological and structural studies. The durability of the catalysts was much improved via strong coordination between the metal and nitrogen or sulfur atoms. Impressively, the catalytic activity of platinum nanoparticles on aminated reduced graphene oxide was found to be much better than that on thiolated graphene oxide despite the weaker affinity between amine and noble metals. These findings support further developing new graphene derivatives with the desired functionalization for electronics and energy applications..
ABSTRACT
In the present work, the localized electrochemical behavior of redox molecule in ionic liquid has been investigated using scanning electrochemical microscopy. The electrochemical response of ferrocenyl-imidazolium redox mediator was studied by recording approach curves over a conducting and insulating substrate in an undiluted ionic liquid. The SECM approach curve over the conducting substrate displays a positive feedback, as observed in classical solvent. However, in the case of the insulating substrate, the approach curve reveals different shapes, depending on the used approach speed. In this configuration, low approach speed is necessary to reach the expected negative feedback. Interestingly, at a very close distance between the UME and the insulating substrate, a thin film behavior is revealed. In addition, the approach curves on both insulator and conducting substrates can be reconstructed from punctual responses at different distance tip-substrate. The latter match perfectly with the expected theoretical curves over conducting and insulating under diffusion control.
ABSTRACT
In recent years, redox flow batteries (RFBs) and derivatives have attracted wide attention from academia to the industrial world because of their ability to accelerate large-grid energy storage. Although vanadium-based RFBs are commercially available, they possess a low energy and power density, which might limit their use on an industrial scale. Therefore, there is scope to improve the performance of RFBs, and this is still an open field for research and development. Herein, a combination between a conventional Li-ion battery and a redox flow battery results in a significant improvement in terms of energy and power density alongside better safety and lower cost. Currently, Li-ion redox flow batteries are becoming a well-established subdomain in the field of flow batteries. Accordingly, the design of novel redox mediators with controllable physical chemical characteristics is crucial for the application of this technology to industrial applications. This Review summarizes the recent works devoted to the development of novel redox mediators in Li-ion redox flow batteries.
ABSTRACT
In the present work, we reported the fabrication of a novel electrochemical sensing platform to detect 2,4-dichlorophenol (2,4-DCP) by using a copper benzene-1,3,5-tricarboxylate-graphene oxide (Cu-BTC/GO) composite. The sensor was prepared by drop-casting Cu-BTC/GO suspension onto the electrode surface followed by electrochemical reduction, leading to the generation of an electrochemically reduced graphene oxide network (ErGO). By combining the large specific area of the Cu-BTC matrix with the electrical percolation from the graphene network, the number of accessible reaction sites was strongly increased, which consequently improved the detection performance. The electrochemical characteristics of the composite were revealed by cyclic voltammetry and electrochemical impedance spectroscopy. For the detection of 2,4-DCP, differential pulse voltammetry was used to emphasize the faradaic reaction related to the oxidation of the analyte. The results displayed a low detection limit (83 × 10-9 M) and a linear range from 1.5 × 10-6 M to 24 × 10-6 M alongside high reproducibility (RSD = 2.5% for eight independent sensors) and good stability. Importantly, the prepared sensors were sufficiently selective against interference from other pollutants in the same electrochemical window. Notably, the presented sensors have already proven their ability in detecting 2,4-DCP in real field samples with high accuracy (recovery range = 97.17-104.15%).
ABSTRACT
Platinum and palladium are the first choice electrocatalysts to drive the hydrogen evolution reaction. In this report, surface modification was introduced as a potential approach to generate hybrid electrocatalyst. The immobilized polymer brush, poly(1-allyl-3-methylimidazolium) (PAMI), was used as a nanostructured template for guiding the electrochemical deposition of metallic nanoparticles (Pd, Pt). The intrinsic properties of the polymer brush in term of nanostructured architecture and the anions mobility within the polymer was exploited to generate a hybrid electrocatalyst. The latter was generated using two different approaches including the direct electrochemical deposition of Pd or Pt metal and the indirect approach through the anion exchange reaction followed by the electrochemical deposition under self-electrolytic conditions. The hybrid structure based on the polymer/metallic NP exhibits an enhancement of the catalytic performance toward hydrogen evolution reaction with a low Tafel slope and overpotential. Interestingly, the indirect approach leads to decrease the metal loading by two orders of magnitude, when compared to those generated in the absence of the polymeric layer, while retaining the electrocatalytic performance.
ABSTRACT
The redox targeting reaction of Li+-storage materials with redox mediators is the key process in redox flow lithium batteries, a promising technology for next-generation large-scale energy storage. The kinetics of the Li+-coupled heterogeneous charge transfer between the energy storage material and redox mediator dictates the performance of the device, while as a new type of charge transfer process it has been rarely studied. Here, scanning electrochemical microscopy (SECM) was employed for the first time to determine the interfacial charge transfer kinetics of LiFePO4/FePO4 upon delithiation and lithiation by a pair of redox shuttle molecules FcBr2+ and Fc. The effective rate constant keff was determined to be around 3.70-6.57 × 10-3 cm/s for the two-way pseudo-first-order reactions, which feature a linear dependence on the composition of LiFePO4, validating the kinetic process of interfacial charge transfer rather than bulk solid diffusion. In addition, in conjunction with chronoamperometry measurement, the SECM study disproves the conventional "shrinking-core" model for the delithiation of LiFePO4 and presents an intriguing way of probing the phase boundary propagations induced by interfacial redox reactions. This study demonstrates a reliable method for the kinetics of redox targeting reactions, and the results provide useful guidance for the optimization of redox targeting systems for large-scale energy storage.
