Negative electrodes sulfation

Lead oxide (PbO) (also called litharge) is formed when the lead surface is exposed to oxygen. Furthermore, it is important as a primary product in the manufacturing process of the active material for the positive and negative electrodes. It is not stable in acidic solution but it is formed as an intermediate layer between lead and lead dioxide at the surface of the corroding grid in the positive electrode. It is also observed underneath lead sulfate layers at the surface of the positive active material. 

In the lead-acid battery, sulfuric acid has to be considered as an additional component of the charge-discharge reactions. Its equilibrium constant influences the solubility of Pb2+ and so the potential of the positive and negative electrodes. Furthermore, basic sulfates exist as intermediate products in the pH range where Fig. 1 shows only PbO (cf. corresponding Pour-baix diagrams in Ref. [5], p. 37, or in Ref. [11] the latter is cited in Ref. [8]). Table 2 shows the various compounds. 

The charge-discharge reaction of the negative electrode corresponds to curve A in Fig. 1, but the Pb2+ ion activity is now determined by the solubility of lead sulfate (PbS04). Thus Eq. (12) has to be modified into... 

During the first trials with synthetic separators around 1940 it had already been observed that some of the desired battery characteristics were affected detrimentally. The cold crank performance decreased and there was a tendency towards increased sulfation and thus shorter battery life. In extended test series, these effects could be traced back to the complete lack of wooden lignin, which had leached from the wooden veneer and interacted with the crystallization process at the negative electrode. By a dedicated addition of lignin sulfonates — so called organic expanders -— to the negative mass, not only were these disadvantages removed, but an improvement in performance was even achieved. 

This mechanism is followed in particular in the reactions of lead sulfate in the electrodes of lead-acid storage batteries. At the negative electrode. 

The lead and lead dioxide electrodes sit in the sulfuric acid solution. The solution connects the electrodes chemically. At the negative electrode, lead reacts with sulfate ions to produce lead sulfate and an electron ... 

The electrochemistry of the pyrosulfate was clearly more complex than that of sulfate. For example, at a negative electrode Durand [46] had shown it is reduced, actually evolving S02 ... 

It consists of two beakers in which the two half-reactions can occur, one containing copper(II) sulfate solution and a copper rod as the positive electrode, the other containing zinc sulfate solution with a zinc rod as the negative electrode. The two solutions are brought into electrical contact with a salt bridge - a tube containing an agar gel and potassium chloride. 

During battery discharge, as shown in Figure 1 with the Daniell cell as an example, the electrode (a zinc rod immersed in a zinc sulfate solution) at which the oxidation reaction takes place is called the anode, and is the negative electrode. The other electrode (a copper rod immersed in a copper sulfate solution) at which the reduction reaction takes place is called the cathode and is the positive electrode. The electron flow in the external circuit is from anode to cathode (the current, /, conventionally flows in the opposite direction to that of the electrons), and in the electrolyte phase the ionic flow closes the circuit. The net result of the charge flow round the circuit is the cell reaetion, which is made up of the two half-reactions of charge transfer that describe the chemical changes at the two electrodes. 

The characteristic of the lead-acid battery is that both electrodes are based on the chemistry of lead. The discharge-charge process is known as the double sulfate reaction, with the positive and negative electrodes being the seats of a dissolving-precipitating (and not some kind of solid-state ion transport or film formation) mechanism of the lead sulfate. The cell, the electrode reactions and the cell reaction are ... 

Mesoporous tin was deposited from LLC surfactant phases in order to provide a nanostructured negative electrode material for applications in lithium ion batteries. Whitehead et al. [67,68] electrodeposited tin films from lyotropi-cally liquid crystalline solutions of tin sulfate in the hexagonal phase of Brij 76 onto copper foil. The authors further employed n-heptane as an inert swelling agent in order to tailor the dimensions of the resulting electrode materials. 

The positive electrode is made of lead dioxide (Pb02) and is reduced to lead sulfate (PbS04), while sponge metallic lead (Pb) is oxidized to lead sulfate at the negative electrode. The electrolyte is sulfuric acid (H2SO4), which provides the sulfate ion (S04 ) for the discharge reactions. 

By way of example consider the electrolytic cell of Fig. 6.1.1 with two copper electrodes in a solution of cupric sulfate. The cupric sulfate will dissociate into charged cupric ions Cu " and sulfate ions SO . When a potential difference is applied between the electrodes, there will be a current flow and reactions at the electrode. The electric field drives the cupric ions (cations) toward the negative electrode (cathode) and the sulfate ions (anions) toward the positive electrode (anode). At the anode there will be a dissolution of copper. 

Daniell cell /dan-yel/ A type of primary cell consisting of two electrodes in different electrolytes separated by a porous partition. The positive eletrode is copper immersed in copper(II) sulfate solution. The negative electrode is zinc-mercury amalgam in either dilute sulfuric acid or zinc sulfate solution. The porous pot prevents mixing of the electrolytes, but allows ions to pass. With sulfuric acid the e.m.f. is... 

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