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Phytoremediation of sites contaminated with iron cyanides can be performed using poplar and willow trees. Poplar and willow trees were grown in potting substrate spiked with ferrocyanide concentrations of up to 2,000 mg kg⁻¹for 4 and 8 weeks respectively. Soil solution and leaf tissue of different age were sampled for total cyanide analysis every week. Chlorophyll content in the leaves was determined to quantify cyanide toxicity. Results showed that cyanide in the soil solution of spiked soils differed between treatments and on weekly basis and ranged from 0.5 to 1,200 mg l⁻¹. The maximum cyanide content in willow and poplar leaves was 518 mg kg⁻¹fresh weight (FW) and 148 mg kg⁻¹FW respectively. Cyanide accumulated in the leaves increased linearly with increasing cyanide concentration in the soil solution. On the long term, significantly more cyanide was accumulated in old leaf tissue than in young tissue. Chlorophyll content in poplar decreased linearly with increasing cyanide in the soil solution and in leaf tissue, and over time. The inhibitory concentration (IC₅₀) value for poplars after 4 weeks of exposure was 173 mg l⁻¹and for willow after 8 weeks of exposure—768 mg l⁻¹. Results show that willows tolerate much more cyanide and over a longer period than poplars, making them very appropriate for remediating sites highly contaminated with iron cyanides.

Thermogalvanic cells offer a cheap, flexible and scalable route for directly converting heat into electricity. However, achieving a high output voltage and power performance simultaneously from low-grade thermal energy remains challenging. Here, we introduce strong chaotropic cations (guanidinium) and highly soluble amide derivatives (urea) into aqueous ferri/ferrocyanide ([Fe(CN) 6 ] 4− /[Fe(CN) 6 ] 3− ) electrolytes to significantly boost their thermopowers. The corresponding Seebeck coefficient and temperature-insensitive power density simultaneously increase from 1.4 to 4.2 mV K −1 and from 0.4 to 1.1 mW K −2 m −2 , respectively. The results reveal that guanidinium and urea synergistically enlarge the entropy difference of the redox couple and significantly increase the Seebeck effect. As a demonstration, we design a prototype module that generates a high open-circuit voltage of 3.4 V at a small temperature difference of 18 K. This thermogalvanic cell system, which features high Seebeck coefficient and low cost, holds promise for the efficient harvest of low-grade thermal energy. Achieving high thermopower in liquid-state thermogalvanic cells is vital to realize a low-cost technology solution for thermal-to-electrical energy conversion. Here, the authors present aqueous thermogalvanic cells based on modified electrolyte with enhanced Seebeck coefficient and thermopower.

Urea is often present in waste water but can be used in powering fuel cells and as an alternative oxidation substrate to water in an electrolyser. However, an insufficient mechanistic understanding and the lack of efficient catalysts for the urea oxidation reaction have hampered the development of such applications. Here we demonstrate that a nickel ferrocyanide (Ni 2 Fe(CN) 6 ) catalyst supported on Ni foam can drive the urea oxidation reaction with a higher activity and better stability than those of conventional Ni-based catalysts. Our experimental and computational data suggest a urea oxidation reaction pathway different from most other Ni-based catalysts that comprise NiOOH derivatives as the catalytically active compound. Ni 2 Fe(CN) 6 appears to be able to directly facilitate a two-stage reaction pathway that involves an intermediate ammonia production (on the Ni site) and its decomposition to N 2 (on the Fe site). Owing to the different rate-determining steps with more favourable thermal/kinetic energetics, Ni 2 Fe(CN) 6 achieves a 100 mA cm −2 anodic current density at a potential of 1.35 V (equal to an overpotential of 0.98 V). Urea oxidation could be a lower-energy alternative to water oxidation in hydrogen-producing electrolysers, but improved catalysts are required to facilitate the reaction. Geng et al. report nickel ferrocyanide as a promising catalyst and suggest that it operates via a different pathway to that of previous materials.

Proton exchange membranes with short-pathway through-plane orientated proton conductivity are highly desirable for use in proton exchange membrane fuel cells. Magnetic field is utilized to create oriented structure in proton exchange membranes. Previously, this has only been carried out by proton nonconductive metal oxide-based fillers. Here, under a strong magnetic field, a proton-conducting paramagnetic complex based on ferrocyanide-coordinated polymer and phosphotungstic acid is used to prepare composite membranes with highly conductive through-plane-aligned proton channels. Gratifyingly, this strategy simultaneously overcomes the high water-solubility of phosphotungstic acid in composite membranes, thereby preventing its leaching and the subsequent loss of membrane conductivity. The ferrocyanide groups in the coordinated polymer, via redox cycle, can continuously consume free radicals, thus helping to improve the long-term in situ membrane durability. The composite membranes exhibit outstanding proton conductivity, fuel cell performance and durability, compared with other types of hydrocarbon membranes and industry standard Nafion ® 212. Proton exchange membranes with short-pathway through-plane proton conductivity are attractive for proton exchange membrane fuel cells. Here the authors align proton conducting channels orthogonal to the plane of composite proton exchange membranes using a magnetic field for improved fuel cell performance.

Aqueous sodium-ion batteries (AIBs) are promising candidates for large-scale energy storage due to their safe operational properties and low cost. However, AIBs have low specific energy (i.e., <80 Wh kg −1 ) and limited lifespans (e.g., hundreds of cycles). Mn-Fe Prussian blue analogues are considered ideal positive electrode materials for AIBs, but they show rapid capacity decay due to Jahn-Teller distortions. To circumvent these issues, here, we propose a cation-trapping method that involves the introduction of sodium ferrocyanide (Na 4 Fe(CN) 6 ) as a supporting salt in a highly concentrated NaClO 4 -based aqueous electrolyte solution to fill the surface Mn vacancies formed in Fe-substituted Prussian blue Na 1.58 Fe 0.07 Mn 0.97 Fe(CN) 6  · 2.65H 2 O (NaFeMnF) positive electrode materials during cycling. When the engineered aqueous electrolyte solution and the NaFeMnF-based positive electrode are tested in combination with a 3, 4, 9, 10-perylenetetracarboxylic diimide-based negative electrode in a coin cell configuration, a specific energy of 94 Wh kg –1 at 0.5 A g −1 (specific energy based on the active material mass of both electrodes) and a specific discharge capacity retention of 73.4% after 15000 cycles at 2 A g −1 are achieved. Mn-based Prussian blue is an ideal positive electrode material for aqueous sodium-ion batteries but still suffers from Mn dissolution. Here, the authors introduce an Mn-ion trapping agent as an electrolyte additive to produce a 94 Wh kg−1 Na-ion aqueous battery with a long lifespan.

The Middle East respiratory syndrome corona virus (MERS-CoV) is highly pathogenic. An immunosensor for the determination of MERS-CoV is described here. It is based on a competitive assay carried out on an array of carbon electrodes (DEP) modified with gold nanoparticles. Recombinant spike protein S1 was used as a biomarker for MERS CoV. The electrode array enables multiplexed detection of different CoVs. The biosensor is based on indirect competition between free virus in the sample and immobilized MERS-CoV protein for a fixed concentration of antibody added to the sample. Voltammetric response is detected by monitoring the change in the peak current (typically acquired at a working potential of −0.05 V vs. Ag/AgCl) after addition of different concentrations of antigen against MERS-CoV. Electrochemical measurements using ferrocyanide/ferricyanide as a probe were recorded using square wave voltammetry (SWV). Good linear response between the sensor response and the concentrations from 0.001 to 100 ng.mL −1 and 0.01 to 10,000 ng.mL −1 were observed for MERS-CoV and HCoV, respectively. The assay was performed in 20 min with detection limit as low as 0.4 and 1.0 pg.mL −1 for HCoV and MERS-CoV, respectively. The method is highly selective over non-specific proteins such as Influenza A and B. The method is single-step, sensitive and accurate. It was successfully applied to spiked nasal samples. Graphical abstract An electrochemical immunoassay is described for the Middle East Respiratory Syndrome Corona Virus (MERS-CoV). The method is based on a competitive assay carried out on a carbon array electrodes (DEP) nanostructured with gold nanoparticles. The array electrodes enable the multiplexed detection of different types of Corona Virus.

Seawater direct electrolysis (SDE) using renewable energy provides a sustainable pathway to harness abundant oceanic hydrogen resources. However, the side-reaction of the chlorine electro-oxidation reaction (ClOR) severely decreased direct electrolysis efficiency of seawater and gradually corrodes the anode. In this study, a redox-mediated strategy is introduced to suppress the ClOR, and a decoupled seawater direct electrolysis (DSDE) system incorporating a separate O 2 evolution reactor is established. Ferricyanide/ferrocyanide ([Fe(CN) 6 ] 3−/4− ) serves as an electron-mediator between the cell and the reactor, thereby enabling a more dynamically favorable half-reaction to supplant the traditional oxygen evolution reaction (OER). This alteration involves a straightforward, single-electron-transfer anodic reaction without gas precipitation and effectively eliminates the generation of chlorine-containing byproducts. By operating at low voltages (~1.37 V at 10 mA cm −2 and ~1.57 V at 100 mA cm −2 ) and maintaining stability even in a Cl − -saturated seawater electrolyte, this system has the potential of undergoing decoupled seawater electrolysis with zero chlorine emissions. Further improvements in the high-performance redox-mediators and catalysts can provide enhanced cost-effectiveness and sustainability of the DSDE system. Seawater direct electrolysis using renewable energy provides an appealing pathway to harness abundant oceanic hydrogen resources. Here, authors report a redox-mediated decoupled seawater direct electrolysis strategy to suppress the chlorine electro-oxidation side reaction.

The main purpose of this study is to synthesize reduced graphene oxide (rGO) using graphite (GR) as a starting material. This paper explains didactic step-by-step of the synthesis, the role of each reagent, showing pictures of the entire process and including a well-explained characterization study. The rGO was prepared using modified Hummer’s method, followed by thermal reduction. The materials were characterized from the starting material (GR), through the intermediate material (GO) and finally the material of interest (rGO). Various techniques and procedures were used to characterize the materials such as X-ray diffraction, infrared and Raman spectroscopy, scanning electron microscopy, electrochemical characterization and dispersion analysis. Morphological and structural characterization of the obtained materials suggests that the synthesis and reduction to obtain rGO were effective. The obtained materials were electrochemically evaluated using ferri/ferrocyanide redox probe. The association of chemical oxidation of GR with KMnO 4 in the presence of H 2 SO 4 with further thermal reduction makes possible to produce rGO in large scale and with quality as noticed by outstanding electrochemical behavior toward the redox couple [Fe(CN) 6 ] 3− /[Fe(CN) 6 ] 4− probe.

The limited availability of a high-performance catholyte has hindered the development of aqueous organic redox flow batteries (AORFB) for large-scale energy storage. Here we report a symmetry-breaking design of iron complexes with 2,2′-bipyridine-4,4′-dicarboxylic (Dcbpy) acid and cyanide ligands. By introducing two ligands to the metal centre, the complex compounds (M 4 [Fe II (Dcbpy) 2 (CN) 2 ], M = Na, K) exhibited up to a 4.2 times higher solubility (1.22 M) than that of M 4 [Fe II (Dcbpy) 3 ] and a 50% increase in potential compared with that of ferrocyanide. The AORFBs with 0.1 M Na 4 [Fe II (Dcbpy) 2 (CN) 2 ] as the catholyte were demonstrated for 6,000 cycles with a capacity fading rate of 0.00158% per cycle (0.217% per day). Even at a concentration near the solubility limit (1 M Na 4 [Fe II (Dcbpy) 2 (CN) 2 ]), the flow battery exhibited a capacity fading rate of 0.008% per cycle (0.25% per day) in the first 400 cycles. The AORFB cell with a nearly 1:1 catholyte:anolyte electron ratio achieved a cell voltage of 1.2 V and an energy density of 12.5 Wh l –1 . The development of aqueous organic redox flow batteries suffers from the limited availability of high-performance catholytes. Here the authors design a metal organic complex catholyte material with a tunable redox potential, which offers promise for high-energy long-lasting flow batteries.

The electropolymerization of anthranilic acid (2-aminobenzoic acid) has been shown to lead to the production of a redox polymer functionalized with carboxylate groups capable of complexing metal ions. The polymer was exploited as a means of capturing ferric ion from solution with the iron decorated polymer chains used as seeding points for the formation of Prussian blue (PB). Nanoclusters of PB were dispersed throughout the three-dimensional polymer matrix with deposition achieved through direct electrochemical means or via a dip process. The latter exploited the chemical combination of Fe(III) + Ferrocyanide to yield PB allowing its dispersal of the PB throughout the polymer film. The polymer film and its subsequent modification have been characterized by electron microscopy, X-ray analysis, Raman spectroscopy and electrochemical analysis. The stability toward peroxide has also been explored. Graphical Abstract