Comment by strainer | Hacker News Reader

Comment by strainer | Hacker News Reader

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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.

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

Thanks. Tantalizingly, some plain efficiency measurements seem to be contained in articles supplementary material.

> "Online O2 detection also confirmed quantitative OER Faradaic efficiency with and without the presence of a magnetic field (Supplementary Fig. 17)."

But it looks to me like this effect is demonstrated as really significant already, for all the catalysts bar one. Application of it cant be far away. A bit like sticking a magnet on an engine block and getting loads more horsepower !

> A bit like sticking a magnet on an engine block and getting loads more horsepower !

Typical motors used in electric cars are a lot more powerful and efficient than their internal combustion engine counterparts ;)

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