fourelectrode

Four-electrode, sometimes written fourelectrode, refers to a measurement configuration that uses four electrodes to separate current injection from potential measurement. This arrangement is common in electrochemistry and geophysics because it can yield more accurate readings by reducing the influence of electrode polarization and contact resistances.

In a typical four-electrode setup, two outer electrodes inject a known current into the medium, while two inner electrodes measure the resulting potential difference. The measured potential drop between the inner electrodes reflects the impedance or resistance of the material between them, with the outer electrodes largely decoupled from the sensing circuitry. This separation improves accuracy for low-conductivity or high-impedance samples and for measurements where precise potential control is important.

Advantages over two-electrode systems include reduced errors from electrode polarization, minimized effect of lead resistance, and the ability to measure a wider range of impedances, especially at higher current excitation or at various frequencies in impedance spectroscopy. The method is foundational in electrochemical impedance spectroscopy, battery and corrosion testing, and other applications that require precise impedance data.

Common implementations appear in electrochemical cells with four electrodes and in geophysical surveys employing arrays such as Wenner or Schlumberger, which use four or more electrodes to estimate soil resistivity and subsurface properties. Electrode materials vary by application and include inert conductors like platinum, gold, graphite, or stainless steel, with practical considerations focusing on stable contact, spacing, and compatibility with the medium.