Increase In Open Circuit Potential Research Articles

Developments in photoelectrochemistry: light-addressable photoelectrochemical cyanide sensors

The photopotential of several semiconductors when immersed in solution and illuminated respond to the concentration of specific ions in solution. Trends observed for alkaline ferrocyanide electrolytes in contact with illuminated CdSe and CdTe comprise a substantial negative shift of flat-band cyanide potential V fb and an increase in open circuit potential V oc with increasing concentration. Based on this increase in V oc, a one-dimensional light-addressable photoelectrochemical (LAP) sensing configuration capable of probing five distinct 2 mm 2 regions along a 1 mm × 10 mm surface area of a single n-CdSe detector is demonstrated for cyanide analysis. This permits a single sensing LAP element which can be externally illuminated in different regions to provide both spatial and temporal information on the analyte concentration. Spatial sensing is achieved without sensor movement and with fewer electrical contacts as compared with a conventional array scheme. In solution, the photopotential has a linear response to cyanide of 120 mV × log[KCN].

Biofilm development during ennoblement of stainless steel in Baltic Sea water: A microscopic study

This paper describes the development of biofilm on stainless steel during the increase of open circuit potential (ennoblement, E corr) that follows the exposure of AISI 316 stainless steel to natural seawater. The ennoblement occurred in the laboratory model ecosystem (mesocosm) reproducibly and similarly to that observed under field conditions in the Baltic Sea, provided that natural seawater was used as the feed, and the hydraulic flow was sufficiently high (10–30 mm s −1). Features distinguishing the ennobling biofilm from the non-ennobling, were studied using scanning (SEM) and transmission electron microscopy (TEM) as well as confocal laser scanning microscopy (CLSM). The increase of open circuit potential started in the laboratory (23°C±1) after 8 days and was complete ( ΔE of 300–500 mV) after 21 days. In the field (10–14°C), ennoblement progressed from 21 days to 42 days ( δE of 400–500 mV). When more than ten initially adhered cells per mm 2 had grown into mushroom-like structures of > 50 μm in diameter and > 10 μm in height, covering 1–5% of the steel surface, the ennoblement started. The potential continued to increase while the biofilm mushrooms grew in height to 100 μm, and reached a plateau at 300–400 mV vs. SCE (standard calomel electrode) when the coverage of the steel surface reached 10–20%. Compared to the non-ennobling biofilms, those on the ennobled stainless steels attached more firmly to steel, were impermeable to lipophilic (acridine orange) and hydrophilic (lectin conjugates) dyes and grew as individual biofilm mushrooms of an average size of 0.5…2×10 6 μm 3 containing 0.3–1×10 6 of tiny (< 1 μm) bacterial cells dispersed in interstitial matter. Biofilms on nonennobled stainless steels in the same seawater were easily removable, fluffy and permeable. The option of explaining the ennoblement (increase of cathodic reaction) of the stainless steel by microbial oxidation of organic residues inside the impermeable biofilm mushroom at the expense of Fe 3+ reduction is discussed.

Effect of photosynthetic biofilms on the open‐circuit potential of stainless steel

Periodic illumination of photosynthetic biofilms on AISI* 316L stainless steel resulted in evolution of oxygen (1–7 mg.1‐1) and a corresponding increase in open circuit potential (Ecorr) from 2 to 15 mV. The change in E^ depended on the interval of illumination. When the dark cycle began, elevation in potential was followed by an immediate drop. Illumination did not affect Ecorr in sterile systems or in systems that contained only nonphotosynthetic eubacteria. Radiated heat from illumination accounted for changes of 4 to 5°C in temperature which, in the absence of oxygen production, should decrease dissolved oxygen by 0.75 mgl‐1 and decrease Ecorr by 1 mV. Positive shifts of Ecorr induced by periodic illumination of photosynthetic biofilms are primarily the result of oxygen production.

Effects of biguanides on short-circuit current in frog skin.

The addition of phenformin to the solution bathing the mucosal side of frog skin resulted in a sustained stimulation of short-circuit current accompanied by an increase in open-circuit potential and total conductance of the membrane. The flux of 22Na from the mucosal to the serosal side of the skin was increased by phenformin, whereas no significant effect on the flux from the serosal to the mucosal side was observed. The increases in the short-circuit current and total conductance with phenformin were completely abolished by the addition of 5 X 10(-5) M amiloride, which blocks sodium permeability at the apical surface of the membrane. Thus, the stimulation of active sodium transport in frog skin by phenformin would be due to the increase in the amiloride-sensitive sodium permeability of the membrane. Phenformin may prove to be a useful tool for the study of sodium transport in amphibian epithelia.

Impedance and Potential Behavior of Surface Oxide Films on Hafnium Electrodes

Abstract The open circuit behavior of hafnium at different surface film thicknesses, immersed in 0.5N H2SO4 has been investigated using potential and impedance measurements. When the anodic current is interrupted, a decrease in oxide film thickness (thinning) was attributed mainly to chemical dissolution of the barrier film. A full inertness of the surface is attained when the polarization potential reaches around 25 V (NHE) where the surface film becomes insoluble in the surrounding electrolyte. It was found also that with gradual accumulation of the oxide layer, a pronounced increase of the open circuit potential was observed. At the thickness corresponding to the polarization potential 25 V (NHE), the rate of increase of open circuit potential after cessation of the current becomes very much reduced and thus a perfect, compact, and continuous oxide film was assumed to be formed on the metal surface.