Family Tree for Aqueous Organic Redox Couples for Redox Flow Battery Electrolytes: A Conceptual Review

Redox flow batteries (RFBs) are an increasingly attractive option for renewable energy storage, thus providing flexibility for the supply of electrical energy. In recent years, research in this type of battery storage has been shifted from metal-ion based electrolytes to soluble organic redox-active compounds. Aqueous-based organic electrolytes are considered as more promising electrolytes to achieve “green”, safe, and low-cost energy storage. Many organic compounds and their derivatives have recently been intensively examined for application to redox flow batteries. This work presents an up-to-date overview of the redox organic compound groups tested for application in aqueous RFB. In the initial part, the most relevant requirements for technical electrolytes are described and discussed. The importance of supporting electrolytes selection, the limits for the aqueous system, and potential synthetic strategies for redox molecules are highlighted. The different organic redox couples described in the literature are grouped in a “family tree” for organic redox couples. This article is designed to be an introduction to the field of organic redox flow batteries and aims to provide an overview of current achievements as well as helping synthetic chemists to understand the basic concepts of the technical requirements for next-generation energy storage materials.

Synthesis of Ag–decorated vertical graphene nanosheets and their electrocatalytic efficiencies

Herein, we report the successful preparation of Ag–decorated vertical–oriented graphene sheets (Ag/VGs) via helicon wave plasma chemical vapor deposition (HWP–CVD) and radio frequency plasma magnetron sputtering (RF–PMS). VGs were synthesized in a mixture of argon and methane (Ar/CH4) by HWP–CVD, and then the silver nanoparticles on the prepared VGs were modified using the RF-PMS system under different sputtering times and RF power levels. The morphology and structure of the Ag nanoparticles were characterized by scanning electron microscopy (SEM), and the results revealed that Ag nanoparticles were evenly dispersed on the mesoporous wall of the VGs. X-ray diffraction (XRD) results showed that the diameter of the Ag particles increased with the increase of silver loading, and the average size was between 10.49 nm and 25.9 nm, which were consistent with transmission electron microscopy (TEM) results. Ag/VGs were investigated as effective electrocatalysts for use in an alkaline aqueous system. Due to the uniquely ordered and interconnected wall structure of VGs, the area of active sites increased with the Ag loading, which made the Ag/VGs have high oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) performance. The double–layer capacitance (Cdl) of the Ag/VGs under different silver loadings were studied, and the results showed that highest silver content is the best (1.04 mF/cm2). The results showed that, Ag/VGs expected to be a credible electrocatalytic material.

Trivalent ion overcharging on electrified graphene

The structure of the electrical double layer (EDL) formed near graphene in aqueous environments strongly impacts its performance for a plethora of applications, including capacitive deionization. In particular, adsorption and organization of multivalent counterions near the graphene interface can promote nonclassical behaviors of EDL including overcharging followed by co-ion adsorption. In this paper, we characterize the EDL formed near an electrified graphene interface in dilute aqueous YCl3 solution using in situ high resolution x-ray reflectivity (also known as crystal truncation rod (CTR)) and resonant anomalous x-ray reflectivity (RAXR). These interface-specific techniques reveal the electron density profiles with molecular-scale resolution. We find that yttrium ions (Y3+) readily adsorb to the negatively charged graphene surface to form an extended ion profile. This ion distribution resembles a classical diffuse layer but with a significantly high ion coverage, i.e., 1 Y3+ per 11.4 ± 1.6 Å2, compared to the value calculated from the capacitance measured by cyclic voltammetry (1 Y3+ per ~240 Å2). Such overcharging can be explained by co-adsorption of chloride that effectively screens the excess positive charge. The adsorbed Y3+ profile also shows a molecular-scale gap (≥5 Å) from the top graphene surfaces, which is attributed to the presence of intervening water molecules between the adsorbents and adsorbates as well as the lack of inner-sphere surface complexation on chemically inert graphene. We also demonstrate controlled adsorption by varying the applied potential and reveal consistent Y3+ ion position with respect to the surface and increasing cation coverage with increasing the magnitude of the negative potential. This is the first experimental description of a model graphene-aqueous system with controlled potential and provides important insights into the application of graphene-based systems for enhanced and selective ion separations.

Biogeochemical Niche of Magnetotactic Cocci Capable of Sequestering Large Polyphosphate Inclusions in the Anoxic Layer of the Lake Pavin Water Column

Magnetotactic bacteria (MTB) are microorganisms thriving mostly at oxic–anoxic boundaries of aquatic habitats. MTB are efficient in biomineralising or sequestering diverse elements intracellularly, which makes them potentially important actors in biogeochemical cycles. Lake Pavin is a unique aqueous system populated by a wide diversity of MTB with two communities harbouring the capability to sequester not only iron under the form of magnetosomes but also phosphorus and magnesium under the form of polyphosphates, or calcium carbonates, respectively. MTB thrive in the water column of Lake Pavin over a few metres along strong redox and chemical gradients representing a series of different microenvironments. In this study, we investigate the relative abundance and the vertical stratification of the diverse populations of MTB in relation to environmental parameters, by using a new method coupling a precise sampling for geochemical analyses, MTB morphotype description, and in situ measurement of the physicochemical parameters. We assess the ultrastructure of MTB as a function of depth using light and electron microscopy. We evidence the biogeochemical niche of magnetotactic cocci, capable of sequestering large PolyP inclusions below the oxic–anoxic transition zone. Our results suggest a tight link between the S and P metabolisms of these bacteria and pave the way to better understand the implication of MTB for the P cycle in stratified environmental conditions.

Immobilization of Air-Stable Copper Nanoparticles on Graphene Oxide Flexible Hybrid Films for Smart Clothes

Through the use of organic/inorganic hybrid dispersants—which are composed of polymeric dispersant and two-dimension nanomaterial graphene oxide (GO)—copper nanoparticles (CuNPs) were found to exhibit nano stability, air-stable characteristics, as well as long-term conductive stability. The polymeric dispersant consists of branched poly(oxyethylene)-segmented esters of trimellitic anhydride adduct (polyethylene glycol−trimethylolpropane−trimellitic anhydride, designated as PTT). PTT acts as a stabilizer for CuNPs, which are synthesized via in situ polymerization and redox reaction of the precursor Cu(CH3COO)2 within an aqueous system, and use graphene oxide to avoid the reduction reaction of CuNPs. The results show that after 30 days of storage the CuNPs/PTT/GO composite film maintains a highly conductive network (9.06 × 10−1 Ω/sq). These results indicate that organic/inorganic PTT/GO hybrid dispersants can effectively maintain the conductivity stability of CuNPs and address the problem of CuNP oxidation. Finally, the new CuNPs/PTT/GO composite film was applied to the electrocardiogram (ECG) smart clothes. This way, a stable and antioxidant-sensing electrode can be produced, which is expected to serve as a long-term ECG monitoring device.

From Waste to Waste: Iron Blast Furnace Slag for Heavy Metal Ions Removal from Aqueous System

Blast furnace slag (BFS) is considered a cheap sorbent for the get rid of Co2+ and Pb2+ ions from an aqueous medium. The slag is characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), N2 adsorption-desorption isotherms, energy dispersive X-ray analysis (EDX), scanning electron microscopy (SEM), and zeta potential. The removal of Co2+ and Pb2+ ions was carried out using batch adsorption experiments from an aqueous medium. The influence of several variables as pH, duration, sorbent quantity, temperature, and preliminary ions concentration was considered. The isotherm, kinetic, thermodynamic, and recyclability were also conducted. The maximum uptake capacity for Co2+ and Pb2+ was 43.8 and 30.2 mg g-1 achieved at pH 6 after 60 min. contact duration. The adsorption kinetics and isotherms of BFS for Co2+ and Pb2+ fitted well to Avrami and Freundlich models, respectively. The main sorption mechanism between BFS and the metal ions was ion exchange. The regeneration of the used slag was studied for reuse many cycles. In terms of economics and scalability, the treatment with the unmodified BFS has great potentials.

Fabrication and Characterization of Xanthan Gum-cl-Poly(Acrylamide-co-Alginic Acid) Hydrogel for Adsorption of Cadmium Ions from Aqueous Medium

The present research demonstrates the facile fabrication of xanthan gum-cl-poly(acrylamide-co-alginic acid) (XG-cl-poly(AAm-co-AA)) hydrogel by employing microwave-assisted copolymerization. Simultaneous copolymerization of acrylamide (AAm) and alginic acid (AA) onto xanthan gum (XG) was carried out. Different samples were fabricated by changing the concentrations of AAm and AA. A sample with maximum swelling percentage was chosen for adsorption experiments. The structural and functional characteristics of synthesized hydrogel were elucidated using diverse characterization tools. Adsorption performance of XG-cl-poly(AAm-co-AA) hydrogel was investigated for the removal of noxious cadmium (Cd(II)) ions using batch adsorption from the aqueous system, various reaction parameters optimized include pH, contact time, temperature, and concentration of Cd(II) ions and temperature. The maximum adsorption was achieved at optimal pH 7, contact time 180 min, temperature 35 °C and cadmium ion centration of 10 mg·L−1. The XG-cl-poly(AAm-co-AA) hydrogel unveiled a very high adsorption potential, and its adsorption capacities considered based on the Langmuir isotherm for Cd(II) ions was 125 mg·g−1 at 35 °C. The Cd(II) ions adsorption data fitted nicely to the Freundlich isotherm and pseudo-first-order model. The reusability investigation demonstrated that hydrogel retained its adsorption capacity even after several uses without significant loss.

Ionic Liquids Based on Chromotropic Acid: Excellent Lubricating Additives for Aqueous System

In this paper, four ionic liquids based on chromotropate (CAILs) were prepared and applied to heighten the tribological performance of aqueous system on different metal friction contacts. Taking for the potential choice for water-based lubricating additive, CAILs exhibited excellent water solubility and corrosion resistance. Tribological results showed that the CAILs, especially the phenolic hydroxyl group decorated samples (TsnN4444 and TsnP4444), demonstrated extremely effective lubricating properties with the efficient friction and wear descent (69% and 83% for Fe, 47% and 94% for Cu, 74% and 69% for Al, respectively). Especially, the excellent load-carrying capacity was also presented with the highest PB (833N) and PD (1568N) values for TsnP4444. It is speculated that the CAIL molecular adsorption on the interface and further generation of tribochemical films are beneficial for their lubricating effects. resulting from the systematic discussion and analysis of CA, QCM, SEM, XPS, and FIB-TEM tests. However, TsN4444 and TsP4444 showed less effective lubricating performances and poor load-carrying capacities due to tribocorrosion of hydroxyl groups at the interface.