Tafel Overpotential
Calculate the activation overpotential by the Tafel equation, η = a + b × log₁₀(i), from the Tafel constant a (V), the Tafel slope b (V/decade) and the current density i. The result, in volts, is the overpotential — how far an electrode's potential departs from equilibrium — needed to sustain a given current density in an activation-controlled electrochemical reaction. The Tafel relation is central to electrode kinetics, corrosion (extrapolation to obtain the corrosion current) and electrolysis. Enter the Tafel constant, slope and current density.
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Sobretensão de Tafel
Para que uma reação eletroquímica ocorra a uma velocidade apreciável, o eletrodo precisa ser polarizado além do seu potencial de equilíbrio — esse excesso é a sobretensão (ou sobrepotencial) η. Quando a reação é controlada pela cinética de ativação (a barreira de energia da transferência de carga), a relação entre a sobretensão e a densidade de corrente segue a equação de Tafel: η = a + b × log₁₀(i). Aqui b é a inclinação de Tafel (em volts por década de corrente — quanto a sobretensão sobe quando a corrente aumenta 10×), e a é a constante que embute a densidade de corrente de troca. A forma logarítmica reflete o fato de que a corrente cresce exponencialmente com a sobretensão (relação de Butler-Volmer na região de Tafel). Esse comportamento é a chave da cinética de eletrodos e tem aplicações práticas importantes: em corrosão, extrapolar as retas de Tafel das reações anódica e catódica até o cruzamento fornece a corrente de corrosão e, portanto, a taxa de corrosão; em eletrólise, as inclinações de Tafel indicam a eficiência de um eletrocatalisador (quanto menor b, melhor). Informe a constante de Tafel, a inclinação e a densidade de corrente.
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