Nickel foam conducts electricity through its interconnected metal framework. Its electrical behaviour depends on both the nickel and the geometry of that framework. A handbook resistivity value for solid nickel cannot be used directly as the effective resistivity of a porous sheet.
For electrode supports and current collectors, it is useful to separate three terms: resistance of the measured piece, effective resistivity of the foam, and resistance at its contacts with other components.
Resistance and effective resistivity
Resistance describes opposition to current through a particular measured path. It is calculated from the measured voltage drop divided by the current and is expressed in ohms.
Resistivity relates resistance to specimen geometry. For a uniform specimen in a suitable measurement arrangement, the familiar relationship is resistivity = resistance × cross-sectional area ÷ path length. With foam, the stated area may be the overall specimen cross-section, including void space. A value calculated on that basis is an effective property of the porous structure, rather than the intrinsic resistivity of solid nickel.
This distinction matters when comparing a foam measurement with a handbook value or with another supplier’s report. Using different definitions of cross-sectional area or different measurement directions can produce values that are not directly comparable.
Why the porous structure matters
Current travels through the connected metal ligaments. Porosity, ligament geometry and continuity of the network therefore form part of the electrical path. Experimental work on nickel foam and porous-metal resistivity has shown that porosity can be related to effective resistivity through a model of the structure.
A pore-size label alone leaves much of that structure undescribed. Two sheets may have similar cell counts while differing in thickness, metal content or the way they are measured. PPI is useful for describing foam structure; it is not a standalone electrical specification.
Contact resistance belongs in the comparison
The foam also has to make electrical contact with a tab, plate, clamp or neighbouring layer. In a two-terminal measurement, the reported resistance can include contributions from leads and contacts as well as the specimen. Changing how a sample is held can therefore change the measured result without changing its composition.
A four-wire, or Kelvin, measurement uses separate connections for the applied current and sensed voltage. This reduces the influence of lead resistance on low-resistance measurements. Probe positions still define the measured path, and the arrangement must suit the specimen geometry. Four wires alone do not make every reported value a directly comparable material resistivity.
Read electrical data in context
A useful test report identifies the sample dimensions, measurement direction, temperature and contact arrangement. For a clamped foam sheet, the compressed thickness or applied load also helps describe the state that was measured. These details allow repeated samples or alternative grades to be compared on a consistent basis.
In-plane measurements follow a path along the sheet. Through-plane measurements follow a path between its faces. Choosing the direction that represents the intended current path makes the result more useful for the component being developed.
HuiRui’s nickel foam product page provides material information. For application context, see the guides to nickel foam current collectors and nickel foam in alkaline water electrolysis. You can contact HuiRui for product information or a quotation.