Episode #74: This is why concentration gradients don't cause diffusion

[@timlinn3149]

You mentioned nickel/nickel oxide electrochemistry. I have tried to turn Ni foam (of course with a NiO surface) into nickel oxyhydroxide via cathodic and anodic cycling in alkaline solution. With sufficient cycles NiOOH is produced and redox pairs of NiOOH/NiOH2 are found, with increasing currents. If the foam is removed while at the NiOOH state, with the foam a black color and high OCP, over the course of days the NiOOH disappears, with it the dark color and OCP. Why would that be? Is it possible to affix it to be stable electrochemically or is this not possible?

[@Pineresearch]

To be honest, I am not sure I can perfectly answer this question without seeing the electrochemical data myself. However, to the best of my knowledge, NiOOH only forms at higher potentials and if you are not persistently holding the electrode at a positive enough potential, NiOOH may not exist permanently. I believe this Ni3+ species is not necessarily stable by itself the way the Ni2+ species (NiO or Ni(OH)2) are, so my only guess is that any NiOOH you are forming might not be very stable by itself over long periods of time while not under a polarization of positive potential.