Potential of a Platinum Electrode at Low Partial Pressure of Hydrogen and Oxygen

Abstract

A tight electrochemical system was constructed in which the PO2 above the cell solution was <10−9 atm. Comparing potentials with data from a previous paper (1) showed that very small amounts of O2 leaking into a closed system can have marked effects on potential behavior at low PH2 . Reduction of the oxygen leak to negligible proportions showed that: (a) the Nernst equilibrium relation for the H+/H2 couple holds only for PH2 in excess of 10−6 atm; (b) at low PH2 , trace amounts of O2, even in the presence of several orders of magnitude more hydrogen, acted as an electrode poison causing a positive deviation from the theoretical Nernst behavior; (c) in O2‐free solution, at PH2 normalbelow 10−6 normalatm , the potential remained at 0.18v positive to NHE and was independent of PH2 . The potential‐determining reaction in this region may be an exchange of H− in solution with H atoms dermasorbed in the Pt. The potential vs. oxygen partial pressure relation was essentially the same as found in previous work from this laboratory. Residual hydrogen associated with Pt at potentials from 0.18 to 0.2v did not react with oxygen.

The redox potential: Its use and control in biotechnology

“…From (5) it can be seen that for an equilibrium the Ela will decrease by 14.8 mV for a decrease in ao~ by a factor of 10. This is in opposition to what has been reported by several authors (Schuldiner et al, 1966;Jacob, 1971 ;Kjaergaard, 1976). However, the latter two refer to Schuldiner et al and obviously they have not calculated the value themselves.…”

“…However, they do not compare the measured Eh values with the concentration of dissolved oxygen to elucidate whether oxygen is the acting redox oxidant and water the reductant. Kantere (1972) and Balakireva et al (1974) did not compare the obtained results for Eh and dissolved oxygen (DO), neither did Jacob (1971), who refers to Schuldiner et al (1966). Wimpenny (1969) and Wimpenny and Necklen (1971) Although these calculations might be very defective, it is significant that the redox potential at lower DO-values decreases much more than that which can be calculated (1971) and Necklen (1971) and Necklen (1971) and Necklen (1971) and Necklen (1971) Jacob ( …”

“…However, the latter two refer to Schuldiner et al and obviously they have not calculated the value themselves. Neither have Schuldiner et al (1966) calculated the value 59.1 mV; however, by measuring the open-circuit rest potential on bright platinum as a function of the partial pressure of oxygen in an electrolyte consisting of 1 M H2SO4 maintained at 25 ° + 2 °C when the partial pressure of 02, po 2 , was in the range 10-6-10 -2 atm, they found that a 10-fold increase in Po~ yielded an increase in the measured potential of 0.06 V. In the same paper, they showed that the Eh value decreases by 0.030 V when the partial pressure of H2, pit 2, increases by a factor of 10 for pit 2 in the range 10-6-10 -2 atm. Since the Eh for the hydrogen-hydrogen ion redox system…”

Microbially — related redox changes in a subtropical lake I.In situ monitoring of the annual redox cycle

“…The reason for this electrode performance is the low electron exchange density of oxygen at the platinum surface (Bockris & Huq 1970;Stumm & Morgan 1984). Only in pure water and with an extremely long response time, a linear relationship between the platinum electrode potential and the concentration of dissolved oxygen is measurable (Schuldiner et al 1966). Because of the slow kinetic of dissolved oxygen, mixed potentials from aerobic systems are dominated by traces of reductants rather than by the actual oxygen concentration.…”

Influence of Pretreatment of the Redoxpotential Electrode on the Determination of Oxygen Pressure in Bacterial Cultures

“…The dependence of ROP on pO" has been described by Squires and H osler [1958] and later by others [M atkovics et al, 1959;T engerdy, 1962;Lengyel and N y ir i, 1965;Marek et al, 1966], More recently, G rosz and F armer [1967] reported on the ROP of blood as a function of p 0 2. The electrochemical experiments by Schuldiner et al [1966] have shown that a positive correlation exists between pO., and ROP in the p 0 2 range of 1 to 10~9 atmospheres. A change in pO., of one order of magnitude causes a ROP change of about 60 mV.…”