A New Overpotential — Capacitance Mechanism for H2 Electrode

The H2 electrode is commonly assumed to be a half-cell, 2 H + 2e == H2, and explained by the Nernst equation. We cannot assume that the H is easily reduced to H2 in an H2 saturated solution, and H2 becoming oxidized to H in a strongly acid solution against the equilibrium principle. How can the H2 gas is involved from a basic solution where there is practically no H ions? Another equilibrium has been postulated, H2 (soln) = 2H (adsorbed on metal) = 2 H + 2e. This paper reports the results of studying the H2 electrode using various techniques, such as adsorption, bubbling with H2, and N2, charging, discharging, and recharging, replacing the salt bridge with a conducting wire, etc. An interesting overpotential was observed that bubbling H2 into the solution caused a sudden change of potential to more negative without changing the solution pH. The H2 may be replaced by N2 to give a similar calibration curve without the overpotential. The results contradict the redox mechanism. When the Pt is separated by H2 coating, it cannot act as a catalyst in the solution. Our results seem to explain the H2 electrode mechanism as the combination of its overpotential and capacitance potential. Bubbling of H2 or N2 only removes interfering gases such as O2 and CO2. Since neither H2 nor N2 is involved in the potential development, it is improper to call the H2 or N2 electrode. A term of pH / OH Pt electrode, like the pH / OH glass electrode, is suggested.