# Surface area contact with catalyst effect on hydrogen redox

• CraigH
In summary, the conversation discusses the relationship between surface area of the electrode and the reaction rate of hydrogen in fuel cells. Increasing the surface area of contact with the anode will increase the number of hydrogen atoms in contact with the catalyst, potentially leading to an increase in the number of oxidization half cell reactions. The question asks about the mathematical relationship governing the number of reactions, and if it is not possible to determine an exact relationship, what is a good approximation. The use of "current density" as a parameter in cell design is also mentioned.
CraigH
I have also posted this question here: Relationship between surface area of electrode and reaction rate of hydrogen in fuel cells, but I really need an answer before tomorrow morning so I hope you don't mind me posting it here as well!

I am looking at the effects of increasing the surface area of which the flowing hydrogen fuel is in contact with the anode in a fuel cell.

At the anode the hydrogen is catalytically split into protons and electrons. The catalyst used is most commonly platinum. So, for a fixed flow rate of hydrogen, increasing the contact surface area with the anode will increase the number of hydrogen atoms in contact with the catalyst, and the duration that they are in contact with it. Therefore the number of oxidization half cell reactions will increase. But what is the mathematical relationship that governs the number of reactions that will occur? Is it just a linear relationship, i.e doubling the surface area doubles the number of reactions, or is it more complex?

If it is impossible to get an exact mathematical relationship, what is a good approximation on how these variables will scale with each other? Also, how do chemist usually predict the number of reactions/reaction rate, and could this be applied to my example?

Thanks!

Have you heard about a "current density"? Measured in A/m2? It is an important parameter in a cell design.

## 1. How does surface area contact affect the efficiency of a catalyst in hydrogen redox reactions?

The surface area contact between a catalyst and reactant is a key factor in determining the efficiency of a catalyst in hydrogen redox reactions. This is because a larger surface area allows for more active sites for the reactant to come into contact with, thus increasing the chances of a successful reaction. Additionally, a larger surface area allows for a higher concentration of reactant molecules in close proximity to the catalyst, which also enhances the efficiency of the reaction.

## 2. What is the relationship between surface area contact and the rate of hydrogen redox reactions?

The rate of hydrogen redox reactions is directly proportional to the surface area contact between the catalyst and reactant. This means that as the surface area contact increases, the rate of reaction also increases. This is because a larger surface area allows for more reactant molecules to come into contact with the catalyst, leading to a higher frequency of successful reactions.

## 3. How does the size of the catalyst particles affect surface area contact in hydrogen redox reactions?

The size of the catalyst particles can greatly impact the surface area contact in hydrogen redox reactions. Smaller particles have a larger surface area compared to larger particles, which allows for more efficient contact with the reactant molecules. This is why catalysts are often finely divided into smaller particles to increase their surface area and improve their effectiveness in reactions.

## 4. Is there an optimum surface area for catalytic activity in hydrogen redox reactions?

Yes, there is an optimum surface area for catalytic activity in hydrogen redox reactions. This is because while a larger surface area allows for more efficient contact with the reactant, too much surface area can also lead to a decrease in catalytic activity. This is due to factors such as increased chances of catalyst deactivation and diffusion limitations. Therefore, finding the right balance of surface area is crucial for optimal catalytic activity.

## 5. How can surface area contact be increased in hydrogen redox reactions?

There are several ways to increase surface area contact in hydrogen redox reactions. One way is to use a finely divided catalyst with smaller particles, as mentioned earlier. Another method is to use a support material that has a high surface area, such as activated carbon or zeolites. Additionally, optimizing the reactor design and operating conditions, such as temperature and pressure, can also help increase surface area contact and improve the efficiency of the reaction.

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