Visualization of aquaionic splitting via iron corrosion

Abstract

We report a water decomposition mode called 'Aquaionic Splitting (AiS)' by means of iron corrosion in aqueous solution. in this paper, we investigated the phenomenon by controlling the reaction between iron and water. A pseudo-sacrificial protection method with oil paint was employed to select the anode and cathode formation locations that govern iron corrosion. then, the AiS reaction was visualized by using BtB solution, whose colour corresponds to pH, to produce colour patterning that corresponds to the aquaion distribution. it has become clear that water can be selectively separated into protons and hydroxide ions by corrosion control treatment. In this vein, the diffusion coefficient of protons was estimated by using the colour patterning of BtB solution that accompanies iron corrosion, and aquaion distribution was then computer simulated by solving the diffusion equation. In metal corrosion in an aqueous solution, for example, iron corrosion in water, the formation of oxides and hydroxides is accompanied by the generation of local anodes and cathodes on the surface of a base material 1-4. Simultaneously, a substantial decomposition reaction of water occurs in conjunction with the corrosion reaction. It is well known that water electrolysis generates hydrogen gas and oxygen gas by the complete decomposition of water 5 (H 2 O → H 2 + 1/2 O 2) and that the generation of and hydroxide ions from water, that is, the aquaionic splitting (AiS) (H 2 O → H + + OH −) reaction of water, takes place as a cooperative reaction. In addition, it is noteworthy that the AiS reaction occurs at an energy of 0.83 eV as calculated by HSC Chemistry software (Outokumpu Research Oy, Pori, Finland), which is lower than the energy (1.23 eV) required for the complete electrolysis of water. Accordingly, we found similarities between the water decomposition reaction of electrolysis and the AiS reaction associated with iron corrosion. Generally, it is difficult to corrode a whole piece of iron in aqua because the oxidation/reduction reaction proceeds with random formation of the anode and the cathode. However, to observe a substantial water decomposition reaction, it is necessary to clearly distinguish and control the places where the oxidation and reduction reactions occur. Anticorrosion is then expected to control the corrosion location, and the plating method, which is a sacrificial anticorrosion method, is a well-known example 6,7. We focused on sacrificial protection in the present study. However, in addition to the need for preparation of the electrolyte in the plating method 8 , there are concerns about the introduction of impurities because other metals are used 9. Therefore, we adopted a facile corrosion protection method using a conductive oil-based paint, which is expected to have a pseudo-sacrificial effect, in addition to other similar proposed methods 10,11. By controlling the corrosion areas locally, we tried to observe the AiS reaction of water accompanying iron corrosion, which is visualized by using a bromothymol blue (BT...

Halochromic Polymer Nanosensors for Simple Visual Detection of Local pH in Coatings

“…Metal corrosion, which leads to dysfunctions and huge economic losses in industrial sectors, , involves redox and acid–base reactions. During the corrosion process, the anodic area becomes acidic while the cathodic area is alkaline. , A significant acidification was detected on coated galvanized steel after 1 day of immersion in a saline solution . Furthermore, the corrosion of metallic implantable medical devices can affect the safety of humans due to the production of metallic ions and change of local pH value near the implant .…”

Quantitative Evaluation of the Diffusion Coefficients of Aqua Ions in Hydrogels via Iron Corrosion

“…It appeared yellow under acidic conditions (pH < ∼6), blue under alkaline conditions (pH > ∼7.6), and green under neutral conditions. 13 Protons were generated from the corroded area, and hydroxide ions were generated from the anticorrosion area, as shown by the arrows in Figure 1b, which indicates aqua ion diffusion. The actual pH was also measured by a pH meter (Horiba LAQUA, F-74).…”

“…Hydrogen generation via iron corrosion (reaction 2) was confirmed using a chromic iron-doped tungstic acid (Fe-WO 3 •nH 2 O) gel without BTB, which was previously developed with iron ionized water, tungsten dissolved hydrogen peroxide water, and agar. 17 The iron ionized water was prepared by the aqua ionic splitting method, 13 where a partially anticorrosive Fe plate was placed in a partitioned water−ion separation cell filled with 200 mL of distilled water for 48 h. Water on the corrosion side was used as the iron ionized water. Then, 0.5 g of tungsten (99.95%, Nilaco, Japan) was dissolved in 20 mL of 15 wt % hydrogen peroxide (FUJIFILM Wako Pure Chemical Corporation, Osaka, Japan).…”

“…It is well-known that water electrolysis generates hydrogen gas and oxygen gas by completely decomposing water molecules (H 2 O → H 2 + 1/2O 2 ), 12 and the generation of protons and hydroxide ions from water, i.e., the aqua ion splitting (AiS) (H 2 O → H + + OH − ) reaction 13 of water, occurs as a cooperative reaction. The AiS reaction occurs with an energy of 0.83 eV, which is lower than the energy required to completely electrolyze water (1.23 eV).…”