An EQCM-D study of the influence of chloride on the lead anodic oxidation

An electrochemical quartz crystal microbalance (EQCM) based on microelectrode arrays allows to distinguish between adsorption and electrodeposition

Using a precise electrochemical quartz crystal microbalance (EQCM), it was shown that electrogravimetry can be carried out with microelectrode arrays (MEAs). MEAs were prepared on the resonator surface by coating it with a thin polymer layer containing holes, where the holes constitute the microelectrodes. The preparation procedures, their benefits, and their limitations are discussed. Microelectrode-based electrogravimetry is challenging because the reduced active area reduces the QCM signal. It is still feasible. This work is limited to linear voltage ramps (as opposed to steps). The processes chosen for demonstration were the electrodeposition/stripping of copper and the redox cycling of methyl viologen dichloride (MVC). The current trace often showed microelectrodic behavior, depending on the sweep rate. For the case of copper deposition, the mass transfer rate was proportional to the electric current. For the case of MVC, the electric current showed a plateau at the ends of the current-voltage diagram, but the mass transfer rate did not change. The difference can be explained by adsorption and desorption going into saturation at the two ends of the voltage range. Based on whether or not a microelectrodic gravimetric signal is seen, it can be stated whether the mass transfer is closely linked to the current. Further advantages of the microelectrode-based EQCM are an improved access to fast processes, reduced effects of double layer recharging, and the possibility to work at a low electrolyte support.

A possible channel effect of the organics adsorbed to the electrode surface on interfacial electron transfer in the alkaline Pb electrodeposition process

A possible electron transfer channel in solid–liquid interface.

Downplaying the role of water in the rheological changes of conducting polymers by using water-in-salt electrolytes

Volumetric changes associated with solvent/electrolyte exchange in electronic conducting polymers (ECPs) play an important role in the mechanical stability of the polymers, as these changes are a critical factor in ECP-based energy storage devices. Thus, the present work explores the hindering of such volumetric deformations for polypyrrole films doped with dodecylbenzenesulphonate (PPy(DBS)) by employing highly concentrated aqueous electrolytes (or water-in-salt electrolytes, WiSEs), and their effects over the corresponding electrochemical capacitor cell energy retention. Electrochemical quartz crystal microbalance with dissipation monitoring measurements for thin PPy(DBS) films in the WiSEs revealed negligible dissipation changes (ΔDn ≈ 0), in contrast with those in dilute aqueous electrolyte (ΔDn ≠ 0), indicating inexpressive structural deformation of PPy(DBS) in the WiSE. This phenomenon is observed for thick freestanding PPy(DBS) films, which presented a maximum bending angle decay from ∼56° (diluted aqueous electrolyte) to 3.5° when working in the WiSE, thus proving the hindering of film bending. The observed trends are reflected in the PPy(DBS) cell energy retention, where the use of a WiSE decreased cell energy fading by 30% after 600 cycles, in comparison with cells based on diluted electrolytes.

Roll-to-roll printed high voltage supercapattery in lead-contaminated aqueous electrolyte

This work investigated the potential application of roll-to-roll printed PEDOT:PSS on an ITO/PET substrate using Pb2+ containing 0.1 M NaCl aqueous solution for a supercapattery. The PEDOT:PSS/ITO/PET electrode achieved 2.2 μAh cm-2 (46.5 mAh g-1) in 0.1 M NaCl and 10 μAh cm-2 (216.8 mAh g-1) in 2 mM Pb2+/0.1 M NaCl at a current density of 0.2 mA cm-2 (4.34 A g-1). The electrode also shows good cyclic performance that retains 63% of its initial capacitance after 1000 charge-discharge cycles. A device operating at a high voltage of 1.8 V was built using PEDOT:PSS/ITO/PET in aqueous electrolyte. The energy density of the symmetric PEDOT:PSS/ITO/PET device is 6.2 Wh kg-1 in 0.1 M NaCl and is improved to 11 Wh kg-1 in 3 mM Pb2+/0.1 M NaCl.

Magnesium Oxide Embedded Nitrogen Self-Doped Biochar Composites: Fast and High-Efficiency Adsorption of Heavy Metals in an Aqueous Solution

Lead (Pb) pollution in natural water bodies is an environmental concern due to toxic effects on aquatic ecosystems and human health, while adsorption is an effective approach to remove Pb from the water. Surface interactions between adsorbents and adsorbates play a dominant role in the adsorption process, and properly engineering a material's surface property is critical to the improvement of adsorption performance. In this study, the magnesium oxide (MgO) nanoparticles stabilized on the N-doped biochar (MgO@N-biochar) were synthesized by one-pot fast pyrolysis of an MgCl₂-loaded N-enriched hydrophyte biomass as a way to increase the exchangeable ions and N-containing functional groups and facilitate the adsorption of Pb²⁺. The as-synthesized MgO@N-biochar has a high performance with Pb in an aqueous solution with a large adsorption capacity (893 mg/g), a very short equilibrium time (<10 min), and a large throughput (∼4450 BV). Results show that this excellent adsorption performance can be maintained with various environmentally relevant interferences including pH, natural organic matter, and other metal ions, suggesting that the material may be suitable for the treatment of wastewater, natural bodies of water, and even drinking water. In addition, MgO@N-biochar quickly and efficiently removed Cd²⁺ and tetracycline. Multiple characterizations and comparative tests have been performed to demonstrate the surface adsorption and ion exchange contributed to partial Pb adsorption, and it can be inferred from these results that the high performance of MgO@N-biochar is mainly due to the surface coordination of Pb²⁺ and C═O or O═C-O, pyridinic, pyridonic, and pyrrolic N. This work suggests that engineering surface functional groups of biochar may be crucial for the development of high performance heavy metal adsorbents.