Electrode pair DC voltage

If different metals are used in a PU electrode pair, the different half-cell potentials may easily create a DC voltage output of 1 V or more. This may represent a source of noise and may saturate the input stage of the biopotential amplifier used. Inhomogeneous surfaces may create local potential differences, local DC current flow, and local corrosion, even with zero current flow in the electrode wires. If an AgCl surface is partly stripped its coating so that some pure silver surface appears, the DC voltage will change and the noise level will increase (see Table 7.2 for half-cell potentials). 

Two equal AgCl plates immersed in a homogeneous chloride electroljrte, wiU in practice generate 1 mV DC, under well-controlled conditions just a few microvolts. 

The noble metals in saline solution are highly polarizable, and the DC voltage wiU be unstable and poorly defined unless under strict zero current conditions. Metal aUoy inhomogeneity will create noise as a function of local current flow between different parts of the metal surface. The noise generation of stainless steel electrodes is very dependent on the alloy composition (see Section 7.3). 

Under zero current condition, many metal electrodes are of interest in biological work. 

The platinum electrode for instance becomes an interesting redox potential recording 

---