3 ms·

> it roughly doubled the current density at the anode without requiring any additional voltage Do I understand correctly that the magnet just makes the anode b

by p1mrx 7y ago

> it roughly doubled the current density at the anode without requiring any additional voltage Do I understand correctly that the magnet just makes the anode behave like a bigger anode, and does not make the process more energy-efficient?

TaylorAlexander 7y ago
Good question. Energy efficiency is what’s really important.
- nomel 7y ago
  For generating hydrogen for use, total cost is most important. Cost reductions are just as important as energy reductions since they both bring total cost down. This is a potential cost reduction.
- Qwertious 7y ago
  The cheaper renewables get, the less important energy efficiency becomes. Meanwhile, if the build-cost gets low enough then it suddenly becomes worth installing electrolysers for those occasional times when the cost of electricity goes negative and all that matters is throughput.
philipkglass 7y ago
Sort of. It keeps the overpotential of the oxygen evolution reaction down at increased current densities. This means that a compact electrode arrangement can split water faster without losing efficiency. Normally more current would increase both current density and overpotential, so that efficiency would go down. This discovery maintains efficiency that would normally require a larger electrode surface. It doesn't double the chemical energy output from the electrical energy input. That would be impossible as conventional electrolyzers are already more than 50% efficient. It (potentially) improves the economic efficiency more than the thermodynamic efficiency. https://en.m.wikipedia.org/wiki/Overpotential https://en.m.wikipedia.org/wiki/Overpotential
- strainer 7y ago
  I think an efficiency improvement is also perhaps implied. They say a strong magnetic field doubles the current flow with no change in input voltage. Basically with V=IR and Power = I* I* R ,if the current has increased without change in voltage then the resistance has gone down. In a perfectly efficient process all of the resistance would owe to H2O splitting, but we know that's not the case - about half the resistance energy was creating waste heat. If its like an LEDs resistance which has a voltage drop component which produces light and a linear ohmic resistance which produces waste heat. This would be like getting twice the current (and light) across an LED from the same voltage. Either the voltage drop has been reduced, or the ohmic resistance is reduced. Either way, we can lower the voltage and produce the same amount of light that was possible without the magnetic hack. Same current with less voltage is less power, for same amount of light or H2O split.
  - philipkglass 7y ago
    Yes, it improves efficiency under certain circumstances. This approach doesn't appear help if you wanted to set a record for world's most efficient water electrolyzer. But it does offer an efficiency improvement at industrially relevant (high) current densities. A lot of reported efficiency advances are relevant to setting records in the laboratory, but would be irrelevant to industry for various reasons. This appears to be the rarer case of the opposite limitation: not useful for setting new efficiency records in the laboratory, but potentially useful for improving industrial devices. If you look at the full paper through sci-hub [1], it's an efficiency improvement specifically at higher current densities. In the left hand side of Figure 1, the magnetic/non-magnetic curves are indistinguishable at very low current densities. Those low current densities also have the lowest overvoltage and highest efficiency per gram of H2 produced. But for an industrially optimized device you want to push production rates higher for a given electrode area, which requires more current density, which also requires more voltage. Higher current density implies higher energy wastage since the voltage has to go up too. The voltage increase with higher current density rises more slowly in the presence of a magnetic field. By the time current density reaches 50 mA/cm^-2, the setup with the magnetic field needs several millivolts less than the control setup without a magnetic field. [1] https://sci-hub.tw/10.1038/s41560-019-0404-4 https://sci-hub.tw/10.1038/s41560-019-0404-4

by p1mrx 7y ago

TaylorAlexander 7y ago

Good question. Energy efficiency is what’s really important.

nomel 7y ago
For generating hydrogen for use, total cost is most important. Cost reductions are just as important as energy reductions since they both bring total cost down. This is a potential cost reduction.
Qwertious 7y ago
The cheaper renewables get, the less important energy efficiency becomes. Meanwhile, if the build-cost gets low enough then it suddenly becomes worth installing electrolysers for those occasional times when the cost of electricity goes negative and all that matters is throughput.

philipkglass 7y ago

Sort of. It keeps the overpotential of the oxygen evolution reaction down at increased current densities. This means that a compact electrode arrangement can split water faster without losing efficiency. Normally more current would increase both current density and overpotential, so that efficiency would go down. This discovery maintains efficiency that would normally require a larger electrode surface. It doesn't double the chemical energy output from the electrical energy input. That would be impossible as conventional electrolyzers are already more than 50% efficient. It (potentially) improves the economic efficiency more than the thermodynamic efficiency. https://en.m.wikipedia.org/wiki/Overpotential https://en.m.wikipedia.org/wiki/Overpotential

strainer 7y ago
I think an efficiency improvement is also perhaps implied. They say a strong magnetic field doubles the current flow with no change in input voltage. Basically with V=IR and Power = I* I* R ,if the current has increased without change in voltage then the resistance has gone down. In a perfectly efficient process all of the resistance would owe to H2O splitting, but we know that's not the case - about half the resistance energy was creating waste heat. If its like an LEDs resistance which has a voltage drop component which produces light and a linear ohmic resistance which produces waste heat. This would be like getting twice the current (and light) across an LED from the same voltage. Either the voltage drop has been reduced, or the ohmic resistance is reduced. Either way, we can lower the voltage and produce the same amount of light that was possible without the magnetic hack. Same current with less voltage is less power, for same amount of light or H2O split.
- philipkglass 7y ago
  Yes, it improves efficiency under certain circumstances. This approach doesn't appear help if you wanted to set a record for world's most efficient water electrolyzer. But it does offer an efficiency improvement at industrially relevant (high) current densities. A lot of reported efficiency advances are relevant to setting records in the laboratory, but would be irrelevant to industry for various reasons. This appears to be the rarer case of the opposite limitation: not useful for setting new efficiency records in the laboratory, but potentially useful for improving industrial devices. If you look at the full paper through sci-hub [1], it's an efficiency improvement specifically at higher current densities. In the left hand side of Figure 1, the magnetic/non-magnetic curves are indistinguishable at very low current densities. Those low current densities also have the lowest overvoltage and highest efficiency per gram of H2 produced. But for an industrially optimized device you want to push production rates higher for a given electrode area, which requires more current density, which also requires more voltage. Higher current density implies higher energy wastage since the voltage has to go up too. The voltage increase with higher current density rises more slowly in the presence of a magnetic field. By the time current density reaches 50 mA/cm^-2, the setup with the magnetic field needs several millivolts less than the control setup without a magnetic field. [1] https://sci-hub.tw/10.1038/s41560-019-0404-4 https://sci-hub.tw/10.1038/s41560-019-0404-4