# Electric field required to split water into oxygen and hydrogen

Others sources typically say that the minimum voltage required to split water into hydrogen and oxygen is 1.229 V. Overvoltage is typically required in a practical device due to inefficiency leading to heat production.

However, suppose that two electrodes are separated by a large distance. This will result in a very low electric field strength (generally, electric field equals $$V/d$$ where $$d$$ is the distance of separation). Is there a threshold electric field level required for electrolysis to take place?

• Pardon? A. I'm not doing homework. B. I am asking a serious question. Yes, maybe I am stupid but that has never stopped me from asking and this seemed like the appropriate place to do it. My apologies for asking a question that any high school student should be able to answer. – Marco Aug 30 '15 at 3:36
• When it comes to separating charge and many other things, the electric field strength is the important characteristic. Yet, with splitting water, the only thing that is ever mentioned is the voltage required. It seems to me that there would be an electric field threshold for splitting the water, but nothing seems to ever be said about this. – Marco Aug 30 '15 at 3:43
• This is nothing to do with the "electric field strength" between the electrodes (in vacuum or with solution, whatever), because this is not a process when you literally tear apart the molecule by this field. It is a chemical reaction, and equilibrium with some reaction barrier and the potential required to overcome the free energy difference between reactant(s) and product(s). – Greg May 11 '19 at 18:05

## 1 Answer

In part, there is no abrupt cutoff because the gradient of the field is not spread evenly across the electrolyte: the gradient is steep at the interface between electrodes and the electrolyte, where gas evolution actually takes place, not in the body of the electrolyte. Note where bubbles arise in this video.

However, if the conductivity of the electrolyte is low, whether due to electrode separation or low ionization, then electrolysis proceeds more slowly, perhaps imperceptibly, though there is no complete cutoff point.

• Thank you for the answer. The thin film in which the gasses are produced is exactly what I am working on. Gas production is a nuisance that I want to avoid or minimize, so understanding the dynamics of gas production is important in my work. I can describe the electric field strength as a function of position and was hoping that keeping the value under a threshold would solve the problem. The film effect that you cite seems to be the basis for people ignoring the role that electric field strength plays in the process. – Marco Aug 30 '15 at 7:36