Study of the Fe(CN)3−6/Fe(CN)4−6 redox system on Pt by EMIRS

Shedding light on the calculation of electrode electroactive area and heterogeneous electron transfer rate constants at graphite screen-printed electrodes

We present in detail the most known and commonly used methods for the calculation of electrode electroactive area ([Formula: see text]) and heterogeneous electron transfer rate constants ([Formula: see text]). The correct procedure for the calculation of these parameters is often disregarded due to either lack of a minimum theoretical background or oversimplification of each method's limitations and prerequisites. The aim of this work is to provide the theoretical background as well as a detailed guide for the implementation of these measurements by impressing upon the electrochemists the parameters that need to be considered so that the obtained results are safe and useful. Using graphite screen-printed electrodes, [Formula: see text], and [Formula: see text] were calculated with different methods and techniques. Data are compared and discussed.

Rechargeable Mg-M (M = Li, Na and K) dual-metal-ion batteries based on a Berlin green cathode and a metallic Mg anode

Mg-M (M = Li, Na and K) dual-metal-ion batteries featuring a dendrite-free Mg anode and an alkali-metal-ion storage cathode are promising safe energy storage systems. However, the compatibility between cathode materials and insertion cations might largely limit the electrochemical performance of the cathodes. In this work, three types of Mg-M (M = Li, Na and K) dual-metal-ion batteries are constructed with a Berlin green (FeFe(CN)6) cathode. The FeFe(CN)6 cathode is compatible with the dual-salt Mg2+/M+ (M = Li, Na and K) electrolytes, and delivers a high reversible capacity of 120 mA h g-1 at 50 mA g-1, with no capacity fading over 50 cycles in Mg-Na batteries. The Mg-Na battery also shows an outstanding rate capability, providing 85 mA h g-1 at 1000 mA g-1 and superior long-term cyclability over 800 cycles. The electrochemical performance comparison between Mg-Li, Mg-Na and Mg-K dual-metal-ion batteries demonstrates the significance of the appropriate hydrated ionic radius and dehydrated ionic radius for the insertion of cations with the FeFe(CN)6 cathode. This work provides new design strategies for stable and high energy density cathodes, and opens a new avenue for building safe and high-performance Mg-M (M = Li, Na and K) dual-metal-ion batteries for practical applications.

Prussian Blue Mg-Li Hybrid Batteries

The major advantage of Mg batteries relies on their promise of employing an Mg metal negative electrode, which offers much higher energy density compared to graphitic carbon. However, the strong coulombic interaction of Mg2+ ions with anions leads to their sluggish diffusion in the solid state, which along with a high desolvation energy, hinders the development of positive electrode materials. To circumvent this limitation, Mg metal negative electrodes can be used in hybrid systems by coupling an Li+ insertion cathode through a dual salt electrolyte. Two "high voltage" Prussian blue analogues (average 2.3 V vs Mg/Mg2+; 3.0 V vs Li/Li+) are investigated as cathode materials and the influence of structural water is shown. Their electrochemical profiles, presenting two voltage plateaus, are explained based on the two unique Fe bonding environments. Structural water has a beneficial impact on the cell voltage. Capacities of 125 mAh g-1 are obtained at a current density of 10 mA g-1 (≈C/10), while stable performance up to 300 cycles is demonstrated at 200 mA g-1 (≈2C). The hybrid cell design is a step toward building a safe and high density energy storage system.

Raman Studies on the Interaction of the Reactants with the Platinum Nanoparticle Surface during the Nanocatalyzed Electron Transfer Reaction

Raman studies are conducted to understand the specific interactions between the individual reactants and the platinum nanoparticle surface during the nanocatalyzed electron transfer reaction between hexacyanoferrate (III) ions and thiosulfate ions. When Pt nanoparticles are added to the thiosulfate ion solution, a shift in the symmetric SS stretching mode is observed compared to the frequency observed for the free thiosulfate ions in solution, suggesting that binding to the Pt nanoparticle surface occurs via the S- ion. It is also observed that there are no shifts in the symmetric and asymmetric OSO bending or SO stretching frequencies. This suggests that the thiosulfate ions do not bind to the nanoparticle surface via the O- ion. When platinum nanoparticles are added to the hexacyanoferrate(III) ion solution, evidence is found for both adsorbed hexacyanoferrate(III) ions and a platinum cyanide complex. For adsorbed hexacyanoferrate(III) ions, the CN stretching frequency is observed at 2101 cm(-1) and the Fe-C stretching frequency is found at 368 cm(-1). The observed CN stretching frequencies located at 2147 and 2167 cm(-1) provide strong evidence that there is a Pt(CN)4(2-) platinum cyanide complex formed. In addition, the Pt-CN band is also observed at 2054 cm(-1). These observed bands provide spectroscopic evidence that the hexacyanoferrate(III) ions dissolve by forming a complex with the surface platinum atoms of the nanoparticles. Raman spectra of the product mixtures are obtained after the completion of the reaction when carried out with higher reactant concentrations to observe the Raman spectra, but with a similar 10:1 ratio of thiosulfate to hexacyanoferrate(III) ions as used previously, with and without PVP-Pt nanoparticles at a correspondingly higher concentration. It is observed that there are no shifts in the characteristic Raman bands associated with hexacyanoferrate(II) ions and no evidence for the formation of adsorbed hexacyanoferrate(II) species or platinum cyanide complexes in the presence of the platinum nanoparticles. In addition, there is evidence for the shifted symmetric SS stretching mode, suggesting that some of the unreacted thiosulfate (present in large excess) is bound to the Pt nanoparticle surface. Thus, under the actual reaction conditions, the hexacyanoferrate(III) ions preferentially react with adsorbed thiosulfate ions to form the reaction products, and this supports the surface catalytic mechanism we proposed previously.

Electrochemical study on screen-printed carbon electrodes with modification by iron nanoparticles in Fe(CN)6 4−/3− redox system

The remarkable enhancement of electron transfer on screen-printed carbon electrodes (SPCEs) with modification by iron nanoparticles (Fe(nano)), coupled with Fe(CN)(6) (4-/3-) redox species, was characterized with an increase of electroactive area (A (ea)) at electrode surface together with a decrease of heterogeneous electron transfer rate constant (k degrees ) in the system. Hence, Fe(nano)-Fe(CN)(6) (3-) SPCEs with deposition of glucose oxidase (GOD) demonstrated a higher sensitivity to various glucose concentrations than Fe(CN)(6) (3-)/GOD-deposited SPCEs. In addition, an inhibited diffusion current from cyclic voltammograms was also observed with an increase in redox concentration and complicated the estimation of A (ea). Further analysis by the electrochemical impedance method, it was shown that this effect might be resulted from the electrode surface blocking by the products of activated complex decomposition.