Electrodes show superior water-splitting efficiency to produce oxygen
Using paper coated with nickel nanoparticles and model catalysts as electrodes, researchers at Indian Institute of Science Education and Research (IISER) Kolkata have been able to split water and generate oxygen and hydrogen gas with very low overpotentials (voltage applied over and above the theoretical voltage to split water).
The flexible electrodes recorded 98% water-splitting efficiency and maintained robustness and durability even after more than 10 continuous days of operation.
The current produced by the nickel-coated paper electrodes remained constant even when the material was subjected to extreme deformation — bending up to 180 degree. Similarly, the electrodes remained stable even when the electrolyte (potassium hydroxide) was made highly corrosive — more than 10 days of continuous operation at 1M (pH 14) and at least 12 hours at 10 M concentration.
“The paper-electrode has highly porous catalytic surface and this increases the kinetics of the reaction — ability of water molecules to reach the active sites in the electrode.
How does it work?
The porous nature of the paper and abundance of functional groups on cellulose microfibres help in strongly binding different metal ions and finally nickel nanoparticles in a three-step immersion process. Coating the paper with nickel makes it electrically conductive. The nickel-coated paper is then coated with two different catalysts (nickel-iron oxyhydroxide and nickel-molybdenum alloy) to serve as an anode and a cathode.
Splitting water to generate oxygen and hydrogen gas requires cost-effective and stable catalysts that have high activity — generate higher current at lower applied voltage. The more current produced the more will be amount of water split and hydrogen gas produced.
The researchers were able to split water and generate oxygen when the voltage applied (on top of the theoretical voltage to split water) was as low as 240 millivolt to get a current density of 50 milliamperes per sq.cm. In the case of hydrogen, the applied voltage was just 32 millivolt to generate 10 milliamperes per sq.cm current density.