Chromium-VI from Stainless Steel (SS) Electrodes in Alkaline Water Electrolysis
Hi all,
I want to build a high-power (1kW+) alkaline water electrolyser. The primary aim of the project will be to demonstrate the power-to-hydrogen concept
for storing surplus renewable electricity as chemical energy. I also want to make the electrolyser design as simple, accessible, and cost-effective
as I can. It will be roughly based on a smaller model that I built previously(1).
SS is an attractive choice of electrode material because it’s inexpensive and widely available. This has led to the widespread use of SS in
“HHO” generators – that is water electrolyers which produce a gaseous mixture of hydrogen and oxygen. Better still, research has demonstrated
that SS anodes make for efficient electrolysis cells, with a realively low overvoltage(2). However, I am a little concerned about using stainless
steel for fear of chromium-VI formation.
On one hand, researchers found no corrosion on their SS anode 30 days of operation(2). However, the same research report states that they did find
corrosion in preliminary experiments with SS anodes that were aged for a shorter period of time. The noted “a very faint yellow tint during the
experiment and then green at the end” and some magnetic black powder accumulating on the cathode. The authors do say though that the corrosion
appeared to stop after a while.
Further research was done by The DIY Science Guy who built an alkaline water electrolyser with SS electrodes(3). He tested his solution for chromate
after the device had been operating for some time. The test appeared to show a negative/very low result. I’m just a little bit concerened that he
didn’t acidify the solution quite enough before testing. Any thoughts on this?
On this forum, plante1999 has reported getting sodium chromate upon electrolysing SS in a Na2CO3 electrolyte at 20V. http://www.sciencemadness.org/talk/viewthread.php?tid=21562&...
Not all chromium compounds are particularly toxic. For instance, chromium-III is a popular dietary suppliment that has been used in doses up to 1
gram per day in clinical trials for diabetes(4). On the other hand, chromium-VI is a well-established human carcinogen and is considered to be
approximately 100 times more toxic than chromium-III(5). For a time, California set a limit of 10 μg/L of chromium-VI in drinking water(6).
One more consideration is that I plan to plama-cut my electrodes to size. This is an issue because intense heat can disrupt the chormium oxide layer
that typically protects stainless steel from corrosion(7). On the other hand, I hope that I can remove the affected area to leave a clean bare
surface for better corrosion resistance.
I would love to hear your thoughts on this. In particular, what does electrochemistry theory have to say? Is chromium-VI formation likely to be a
problem in theory? Is it dependent on voltage? Or do the conditions favour chromium-III? etc... Unfortunately electrochemistry is not my strong
point.
References:
1. Dominic Ó Gallachóir. Build an Alkaline Water Electrolyser to Produce H2 | High Output [Internet]. Donegal, Ireland; 2019. Available from: https://www.youtube.com/watch?v=CpF2j6SwHSg
2. Colli AN, Girault HH, Battistel A. Non-precious electrodes for practical alkaline water electrolysis. Materials. 2019 Apr 24;12(8):1336.
3. The DIY Science Guy. Opening up the hydrogen generator, am I producing hexavalent chromium? [Internet]. 2019. Available from: https://www.youtube.com/watch?v=xc45jylwiiU
4. Landman GW, Bilo HJ, Houweling ST, Kleefstra N. Chromium does not belong in the diabetes treatment arsenal: Current evidence and future
perspectives. WJD. 2014;5(2):160.
5. Wang Y, Su H, Gu Y, Song X, Zhao J. Carcinogenicity of chromium and chemoprevention: a brief update. OTT. 2017 Aug;Volume 10:4065–79.
6. California Water Boards. Chromium-6 Drinking Water MCL [Internet]. 2018 [cited 2020 Jun 4]. Available from: https://www.waterboards.ca.gov/drinking_water/certlic/drinki...
7. redazione. Avoiding loss of corrosion resistance when welding stainless steels [Internet]. Metalworking World Magazine. 2014. Available from: https://www.metalworkingworldmagazine.com/avoiding-loss-of-c...
TLDR: Will an alkaline water electrolyser with stainless steel electrodes produce chromium-VI?
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