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The oxidizing gas (e.g., pure O 2, O 2 in air, CO 2, etc.) percolates through a hydrophobic layer on the gas diffusion electrode, acting as a cathode. After the gas diffuses to the electrically conducting layer acting as an electrocatalyst (e.g., hydrophilic activated carbon), the gas is electrochemically reduced.
Townsend's early experimental apparatus consisted of planar parallel plates forming two sides of a chamber filled with a gas.A direct-current high-voltage source was connected between the plates, the lower-voltage plate being the cathode and the upper-voltage the anode.
Steam is fed into the porous cathode. When a voltage is applied, the steam moves to the cathode-electrolyte interface and is reduced to form pure H 2 and oxygen ions. The hydrogen gas then diffuses back up through the cathode and is collected at its surface as hydrogen fuel, while the oxygen ions are conducted through the dense electrolyte.
Principle of the gas diffusion electrode. The principle of gas diffusion is illustrated in this diagram. The so-called gas distribution layer is located in the middle of the electrode. With only a small gas pressure, the electrolyte is displaced from this pore system. A small flow resistance ensures that the gas can freely flow inside the ...
During the aqueous deposition process, gas is being formed at both electrodes. Hydrogen gas is being formed at the cathode, and oxygen gas at the anode. For a given amount of charge transfer, exactly twice as much hydrogen is generated compared to oxygen on a molecular basis. This has some significant effects on the coating process.
The vertical scale is the electrode potential of hydrogen or non-interacting electrode relative to an SHE electrode, the horizontal scale is the pH of the electrolyte (otherwise non-interacting). Neglecting overpotential , above the top line the equilibrium condition is oxygen gas, and oxygen will bubble off of the electrode until equilibrium ...
The diaphragm further avoids the mixing of the produced hydrogen and oxygen at the cathode and anode, [13] [14] respectively. The thickness of asbestos diaphragms ranges from 2 to 5 mm, while Zirfon diaphragms range from 0.2 to 0.5 mm. [11] Typically, Nickel based metals are used as the electrodes for alkaline water electrolysis. [15]
In cold cathode tubes, the electric discharge in gas has three regions, with distinct current–voltage characteristics: [1] I: Townsend discharge, below the breakdown voltage. At low voltages, the only current is that due to the generation of charge carriers in the gas by cosmic rays or other sources of ionizing radiation.