Water to Fuel project question

[jrparticlehunters]

Hi, Norman40 and other experts. We are using Cobalt-nitrate in a .1M phosphate solution for our water splitting project to compare catalysts' effect on voltage. For the sake of controlling our variables, if we use Nickel-nitrate as another catalyst (and try other metal catalysts as well), can we still use the .1M phosphate buffer solution? In other words, will the phosphate buffer solution work for lots of different kinds of catalysts?

Thank you so much for any help.

[norman40]

Hi jrparticlehunters,

I'm assuming that you're working on the project described here:

https://www.sciencebuddies.org/science- ... ll#summary

You should use the 0.1 M phosphate buffer for your tests with cobalt, nickel and other metals you might try (like iron or manganese). And you should stay with the nitrate salts of the various metals. That way the metal is the only variable and you have a fair test of the metal effect on voltage.

I hope this helps. Please post again if you have more questions.

A. Norman

[jrparticlehunters]

Thank you so much for your help!!!

[jrparticlehunters]

Dear Norman,

We have a very important question for you about something said during the Science Buddies video for this project.

During the video while Yogi and his partners conduct the water splitting experiment, Yogi says, "The current is directly proportional to the rate at which we're making oxygen and hydrogen." Does this mean that the best performing catalyst will always use the least amount of voltage AND produce the most amount of oxygen and hydrogen? And that the next best performing catalyst will use the second least amount of voltage AND produce the second most amount of oxygen and hydrogen? And so on?

We are wondering this because we had an idea to modify the experiment to measure the gas collected in test tubes, but if the oxygen and hydrogen produced are always going to be proportional to the drop in voltage used, then maybe that very complex modification isn't necessary.

Thank you for so much help.

[norman40]

Hi jrparticlehunters,

Yes, an improved water splitting catalyst would increase the rate of oxygen/hydrogen production with less energy input. And you can use energy input and reaction rate to rank the performance of different catalysts without collecting the gases.

Actually the voltage you mention is an indication of the efficiency of the reaction. Higher voltage measurements translate to better efficiency. You'd expect higher efficiency with a catalyst than without. And you'd expect higher efficiency with a better catalyst than with a less effective one. Take a look at Technical Note #2 in the project procedure for more on this.

The cell current determines the reaction rate. You can change the current by altering the value of the 10k ohm resistor in the cell circuit. Better catalysts will have low cell voltages at high currents. In other words, high reaction efficiency at a high reaction rate. Technical Note #3 has more information about this and a method for comparing different catalysts.

I hope this helps. Please post again if you have more questions.

A. Norman

[jrparticlehunters]

Hi again. Thanks for responding so quick!

We read the Technical Notes you mentioned and #3 says "Higher voltages lead to lower efficiency". Did you make a type when you wrote "Higher voltage measurements translate to better efficiency"? Did you mean "Lower"?

[norman40]

Hi jrparticlehunters,

My apologies! You are correct. I should have written “Lower voltage measurements translate to better efficiency”. Thanks for following up.

I hope this helps. Please post again if you have more questions.

A. Norman

[jrparticlehunters]

Hi again, Norman. We have one last important question. When we ran our experiment using different catalysts, both the copper-phosphate catalyst and calcium-phosphate catalysts started out with the best energy efficiencies, but dropped to the worst efficiency the longer the test went on, which coincided with small bumpy spots of white crust material forming on the surface of the anode. Do you know what might have caused that crusty scale with the copper-phosphate catalyst and calcium-phosphate catalyst plus electricity? (We have an idea that the calcium-phosphate scale relates to the same kind of white calcium scale in swimming pools, but we're really not sure about the copper-scale.)
Thanks!

[norman40]

Hi jrparticlehunters,

Sorry, but I'm not sure what the “white crust” that you observed might be. It's interesting that a white material formed in your experiment with copper. Because copper phosphate and nitrate are blue (or green) the white material you saw may not include copper.

The white material formed on the anode, which should attract negative ions (anions). This implies that the white material might be an ionic complex of either copper or calcium with phosphate that plated on the anode. I think it's likely that the same thing happened with both calcium and copper.

You might try running the experiment without any catalyst in the solution. Not observing the white material on the anode would suggest that materials you saw included copper or calcium.

I hope this helps. Please post again if you have more questions.

A. Norman