# Figuring out electrolysis at higher temps and pressures

• Ronin2004
In summary, the conversation revolves around calculating the energy requirements for breaking water into hydrogen and oxygen through electrolysis. The discussants mention using thermo tables and formulas for enthalpy and entropy, as well as the potential of using Gibbs free energy to determine the amount of work needed to split water. The question of whether treating hydrogen and oxygen as ideal gases is also brought up. Additionally, there is a discussion on the possibility of using fuel cells to bond hydrogen and oxygen, and the issue of recycling water produced by the cell. The conversation ends with a mention of using the formula dS=S(T2)-S(T1)-R LN(P2/P1) to calculate entropy at different temperatures and pressures.
Ronin2004
Ok so I am working my way around fuel cell technology and i was trying to see the energy requirements for the breaking of the water into hyrdogen and oxygen. I was looking at http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/electrol.html
and it outlines the thermodynamic process for the amount of energy that is required to convert water to hydrogen and Oxygen but that's only at stp The question I have is how do you caclulate the energy requirements if you have different temps and pressures.

I am looking up thermo tables and I get a enthapy for water at various pressures and temps but the problem I am having is finding the entropy of H2 and O2 at the same temps and pressures all i can find is STP entropy. Is there an way to find the values instead of doing the intergration of Dq/T.

And is caclulating the the gibs free energy the best way to see how much work is required to split water
G=H-TS

with regards to the entropy of hydrogen and oxygen gas at different temperatures and pressures... can you not treat them as ideal gasses to calculate the entropy value at your temperature and pressure?

Yeah i think that might work if i hold Volume to be a constant but pouring through my thermo textbook i found this formula

S2 - S1 = Cp * ln ( T2 / T1) - R * ln ( p2 / p1)

so this will give me a change in entropy related to a temp and pressure. I can now get enthalpy at various temps and pressures using this formula.

dH=Cp*dT

Now given that i can look up Cp of ideal gases in thermo tables and i can get both H values and S values. What does i use for the second temperature and pressure. When we try eletrolysis at higher temps and pressures does They hydrogen and Oxygen released at same temp and pressure or does it go stp

Is using gibs free energy a good way of calculating the energy needed to split water
dG=dH-Tds

don't fuel cells bond hydrogen and oxygen rather than disassociate them?
are you thinking of a way to recycle the water produced by the cell?

hmm, the temperature change upon electrolysis is a good question...

is it not true that the gibbs free energy is what splits the water molecule, while the rest of the energy you put in is turned into heat in the system?

its been awhile since i last did thermodynamics, so I am more than a little unpracticed in these things by now

Yeah I am pretty sure that is it. Gibbs free Energy is the total energy used. Usually You just Use Enthalpy to determine the change but the TdS is the thermal energy from the reaction. So the higher the temp the higher the TdS which means the less energy needed from the enthalpy which is usually your voltage source. So if it was hot enough it would require no energy and water would just naturally split. But if H and S are both functions of Temperature then how do I calculate them. I think I can Use the formula

dS=S(T2)-S(T1)-R LN(P2/P1)
where S(t) is from the tables and is the change of entropy at different temps but one atm

## 1. How does temperature affect electrolysis?

As temperature increases, the rate of electrolysis also increases. This is because higher temperatures provide more energy for the electrolysis reaction to occur, leading to faster reaction rates. However, extremely high temperatures can also cause the electrolyte solution to evaporate, so it is important to find the optimal temperature for electrolysis.

## 2. What are the challenges of conducting electrolysis at higher temperatures and pressures?

One of the main challenges is finding materials that can withstand the high temperatures and pressures without corroding or breaking down. Additionally, maintaining a stable and controlled environment at higher temperatures and pressures can be difficult and requires specialized equipment.

## 3. Can any electrolyte solution be used at higher temperatures and pressures?

No, not all electrolyte solutions are suitable for use at higher temperatures and pressures. Some solutions may break down or produce unwanted byproducts under these conditions. It is important to carefully select an appropriate electrolyte solution for the desired temperature and pressure range.

## 4. What are the potential applications of electrolysis at higher temperatures and pressures?

Electrolysis at higher temperatures and pressures has the potential to be used for various industrial processes, such as in the production of metals and chemicals. It can also be used for energy storage and conversion, such as in high-temperature fuel cells.

## 5. How can the efficiency of electrolysis at higher temperatures and pressures be improved?

Efficiency can be improved by using more efficient and durable materials, optimizing the electrolyte solution composition, and controlling the temperature and pressure conditions for maximum reaction rates. Further research and development in this area can also lead to advancements in the technology and processes used for electrolysis at higher temperatures and pressures.

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