Dear Kiran Donthula ,

'there_will_not_be_water_molecule_splitting_in_Lead_acid_battery (LAB) as_electrolyte', because each one (half cell's) electrode should respect[1] this (1.23 V vs SHE[2], near 25oC) blocking-drawback[3,4] of the potential (vs SHE) .

However, an ideal aqueous electrolyte based supercapacitor (or an ideal LAB) might stretch/go up to: 2.46 V [= 1.23 V - (-1.23 V)], as a maximum cell voltage.

1. A reference electrode is an electrode that has a stable and well-known electrode potential. The overall chemical reaction taking place in a cell is made up of two independent half-reactions, which describe chemical changes at the two electrodes. https://en.wikipedia.org/wiki/Reference_electrode

2. In electrochemistry, the standard hydrogen electrode (abbreviated SHE), is a redox electrode which forms the basis of the thermodynamic scale of oxidation-reduction potentials. https://en.wikipedia.org/wiki/Standard_hydrogen_electrode

3. Chapter 1 - Introduction to battery technology https://www.sciencedirect.com/science/article/abs/pii/B9780443188626000021

4. https://www.researchgate.net/post/How-the-potential-window-of-aqueous-electrolytes-can-be-extended-beyond-123V-in-asymmetric-supercapacitor-cells-without-electrolysis-of-electrolyte

Dear Kiran Donthula ,

A small amount of water decomposition occurs regularly in lead-acid batteries. However, this is not a practical problem because both the positive and negative electrodes have large hydrogen overpotential and oxygen overpotential, so water decomposition is suppressed.

There are two types of lead-acid batteries: the type that requires refilling water and the maintenance-free type. Maintenance-free type batteries use a lead-tin-calcium alloy with a higher overpotential for the current collector (grid).

The idea of large overpotential as mentioned by Hidetoshi Abe follows my logic.

It is most probable that your potential (or range) of operation is not capable (or in the region) of sufficient water splitting reaction.

A favorable thermodynamics does not guarantee that the reaction will proceed spontaneously. A human body is thermodynamicaly unstable and is not burned in air. There is such thing as chemical kinetics. Water splitting is kinetically very demanding. For this reason we need two catalysts, for HER and for OER.