It is well known that the electrical current of an electrochemical process is proportional to the real surface area of the electrode. The presence of surface rugosities due to steps, holes, kinks, and terraces can result in an electrode real surface area that is larger than the geometric one. The electrode real surface area can be evaluated by determining the amount of gas that adsorbs onto the electrode surface. This calculation is possible because every adsorbed gas molecule is attached to one metal atom on the electrode surface, forming a gas monolayer. From crystallographic data the surface atom density can be obtained in consideration of a theoretically flat metal surface. These data allow us to determine the real electrode surface area.In this paper we propose a simple experiment to determine the real surface area of a Pt electrode by voltammetry. The hydrogen adsorption on this metal is achieved by applying sufficiently negative potentials to a Pt electrode in contact with an aqueous solution. Each adsorbed hydrogen atom requires the transfer of one electron. Hydrogen gas evolution starts only when the monolayer is completed. Then the cathodic current rapidly rises. The hydrogen monolayer formation charge transference can be calculated by integrating the voltammetric curves. The integration limits are the potentials at which the hydrogen adsorption and evolution start.

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