4 ms·

Probably overhyped, but Hydrogen Oxygen gas liberation from H20 followed by recombination and electricity production in an H2 fuel cell (exhausting water again)

Probably overhyped, but Hydrogen Oxygen gas liberation from H20 followed by recombination and electricity production in an H2 fuel cell (exhausting water again) is very well known and used frequently. The difference is that normally the Hydrogen is produced off-vehicle. That's because normally carrying around the mass of the feed water and reaction chamber is inefficient (i.e. you avoid lugging around that mass and avoid the cost of a reaction chamber if you produce the H2 off-vehicle). However, there are absolutely ways to fill a vehicle's water tank with water, use some catalyst to liberate H2, and then combining with pure O2 or O2 scavenged from ambient air in a fuel cell to generate electricity. In underwater vehicles, because they're surrounded by water, you avoid the need to carry a water tank around and instead, you can just carry an Aluminum (typically an Aluminum compound designed to prevent formation of a reaction inhibiting oxydized aluminum layer). The Al reacts with water to produce H2 on the vehicle which is then used with a fuel cell to produce elctrucity. This is not "free energy" - the energy potential is resident within the catalyst, and the catalyst itself must be 're-energized' or replaced. In the case of oxidized Aluminum, you must inject large amounts of energy to regenerate the pure aluminum catalyst.

lowbloodsugar 2y ago
If a "catalyst" needs to be "re-energized" then its the fuel, not a catalyst.
- causal 2y ago
  "Break the first law of thermodynamics with this one simple trick!"
  - mojomark 2y ago
    I'm not sure why I'm bothering, but here is the definition of a "catalyst" [1], which states that a catalyst promotes a reaction that would otherwise require higher temperature. Here is a description of how hydrogen can be liberated by increasing thermal energy of a sample [2]. What exactly is the issue, and where are your citations supporting your argument? 1. "Thermodynamics of High Temperature Gases" by Joseph Hilsenrath and Bertrand Hirschfelder, which discusses the breakdown of water at extreme temperatures. 2. "Thermodynamics of High Temperature Gases" by Joseph Hilsenrath and Bertrand Hirschfelder, which discusses the breakdown of water at extreme temperatures.
    - lowbloodsugar 2y ago
      I notice that you haven’t refuted my claim.
    - eesmith 2y ago
      I cannot verify that citation exists. I looked in archive.org and Google Scholar. No such title found. Joseph Hilsenrath was an employee at the National Bureau of Standards in the 1960s. It seems he was involved in making tables concerning gases, but not in catalysis. There appears to be no publications by Bertrand Hirschfelder. How did you come across this apparently obscure publication, and why are your [1] and [2] the same? It seems gauche to suggest it, but my experience with LLMs is they often give bad citations like this. If you are using a second-hand source for your information, you may want to verify they are not giving you LLM swill. I ask because your summary of what a catalyst means is pretty poor, and I wanted to see what your source material says. For example, as https://en.wikipedia.org/wiki/Catalysis https://en.wikipedia.org/wiki/Catalysis points out, a catalyst does not alter the equilibrium constant. It adds that if a catalyst were to change the equilibrium constant, the result "would be a perpetual motion machine, a contradiction to the laws of thermodynamics." Then if we go to https://en.wikipedia.org/wiki/Electrolysis_of_water https://en.wikipedia.org/wiki/Electrolysis_of_water we see "The decomposition of pure water into hydrogen and oxygen at standard temperature and pressure is not favorable in thermodynamic terms". Higher temperatures work "because the electrolysis reaction is more efficient at higher temperatures. In fact, at 2500 °C, electrical input is unnecessary because water breaks down to hydrogen and oxygen through thermolysis. Such temperatures are impractical; proposed HTE systems operate between 100 °C and 850 °C.", says https://en.wikipedia.org/wiki/High-temperature_electrolysis https://en.wikipedia.org/wiki/High-temperature_electrolysis . Thus, raising the temperature in order to shift the hydrolysis equilibrium constant, as you described it, cannot be characterized as catalysis.
roelschroeven 2y ago
> the catalyst itself must be 're-energized' or replaced That does not exactly fit the definition of a catalyst, to put it politely. Honest question: are you trolling, or do you simply need a refresher on the basic principles of thermodynamics?
- kibibu 2y ago
  Honest question: have you never heard of catalyst decay or deactivation? These are known issues in production systems.
- tomohelix 2y ago
  That is overly hostile and ironically wrong. Some catalysts do get "degraded" over time and need to be regenerated. Look up palladium sintering or zeolite coking. The catalyst itself is not "damaged" but by catalyzing a reaction, its physical shape is altered (get clogged or fused together) which reduce its effectiveness. These can be regenerated by burning off the clogging or heating them up. And if you get into the enzymes, which are biological catalysts, they are even more likely to degrade and need to be replaced. Don't try to be smart by insulting others when you yourself are not an expert.
  - eesmith 2y ago
    The term used was "re-energized" because "the energy potential is resident within the catalyst." That is NOT a catalyst, as roelschroeven correctly commented. Otherwise a rechargeable battery would be a "catalyst" because it too needs to be re-energized or replaced. What a catalyst does is lower the activation barrier between two states, without providing net energy. Getting H2 from H2O, i.e. electrolysis, requires adding energy. We know this because fuel cells work in the other direction to produce power, and entropy always increases.
    - mojomark 2y ago
      I was not referring to electrolysis, I was referring to the chemical reaction between water and certain Aluminum compounds to liberate H2 (which creates Aluminum oxide and other byproducts, and if you want to recover the Aluminum catalyst, you must add energy to remove the Oxygen from the Aluminum oxide (i.e. "re-energizing" the catalyst so that it can be used again in a reaction with water). Pretty straight forward.

lowbloodsugar 2y ago

If a "catalyst" needs to be "re-energized" then its the fuel, not a catalyst.

causal 2y ago
"Break the first law of thermodynamics with this one simple trick!"
- mojomark 2y ago
  I'm not sure why I'm bothering, but here is the definition of a "catalyst" [1], which states that a catalyst promotes a reaction that would otherwise require higher temperature. Here is a description of how hydrogen can be liberated by increasing thermal energy of a sample [2]. What exactly is the issue, and where are your citations supporting your argument? 1. "Thermodynamics of High Temperature Gases" by Joseph Hilsenrath and Bertrand Hirschfelder, which discusses the breakdown of water at extreme temperatures. 2. "Thermodynamics of High Temperature Gases" by Joseph Hilsenrath and Bertrand Hirschfelder, which discusses the breakdown of water at extreme temperatures.
  - lowbloodsugar 2y ago
    I notice that you haven’t refuted my claim.
  - eesmith 2y ago
    I cannot verify that citation exists. I looked in archive.org and Google Scholar. No such title found. Joseph Hilsenrath was an employee at the National Bureau of Standards in the 1960s. It seems he was involved in making tables concerning gases, but not in catalysis. There appears to be no publications by Bertrand Hirschfelder. How did you come across this apparently obscure publication, and why are your [1] and [2] the same? It seems gauche to suggest it, but my experience with LLMs is they often give bad citations like this. If you are using a second-hand source for your information, you may want to verify they are not giving you LLM swill. I ask because your summary of what a catalyst means is pretty poor, and I wanted to see what your source material says. For example, as https://en.wikipedia.org/wiki/Catalysis https://en.wikipedia.org/wiki/Catalysis points out, a catalyst does not alter the equilibrium constant. It adds that if a catalyst were to change the equilibrium constant, the result "would be a perpetual motion machine, a contradiction to the laws of thermodynamics." Then if we go to https://en.wikipedia.org/wiki/Electrolysis_of_water https://en.wikipedia.org/wiki/Electrolysis_of_water we see "The decomposition of pure water into hydrogen and oxygen at standard temperature and pressure is not favorable in thermodynamic terms". Higher temperatures work "because the electrolysis reaction is more efficient at higher temperatures. In fact, at 2500 °C, electrical input is unnecessary because water breaks down to hydrogen and oxygen through thermolysis. Such temperatures are impractical; proposed HTE systems operate between 100 °C and 850 °C.", says https://en.wikipedia.org/wiki/High-temperature_electrolysis https://en.wikipedia.org/wiki/High-temperature_electrolysis . Thus, raising the temperature in order to shift the hydrolysis equilibrium constant, as you described it, cannot be characterized as catalysis.

roelschroeven 2y ago

> the catalyst itself must be 're-energized' or replaced That does not exactly fit the definition of a catalyst, to put it politely. Honest question: are you trolling, or do you simply need a refresher on the basic principles of thermodynamics?

kibibu 2y ago
Honest question: have you never heard of catalyst decay or deactivation? These are known issues in production systems.
tomohelix 2y ago
That is overly hostile and ironically wrong. Some catalysts do get "degraded" over time and need to be regenerated. Look up palladium sintering or zeolite coking. The catalyst itself is not "damaged" but by catalyzing a reaction, its physical shape is altered (get clogged or fused together) which reduce its effectiveness. These can be regenerated by burning off the clogging or heating them up. And if you get into the enzymes, which are biological catalysts, they are even more likely to degrade and need to be replaced. Don't try to be smart by insulting others when you yourself are not an expert.
- eesmith 2y ago
  The term used was "re-energized" because "the energy potential is resident within the catalyst." That is NOT a catalyst, as roelschroeven correctly commented. Otherwise a rechargeable battery would be a "catalyst" because it too needs to be re-energized or replaced. What a catalyst does is lower the activation barrier between two states, without providing net energy. Getting H2 from H2O, i.e. electrolysis, requires adding energy. We know this because fuel cells work in the other direction to produce power, and entropy always increases.
  - mojomark 2y ago
    I was not referring to electrolysis, I was referring to the chemical reaction between water and certain Aluminum compounds to liberate H2 (which creates Aluminum oxide and other byproducts, and if you want to recover the Aluminum catalyst, you must add energy to remove the Oxygen from the Aluminum oxide (i.e. "re-energizing" the catalyst so that it can be used again in a reaction with water). Pretty straight forward.