Legendre transforms in nonequilibrium thermodynamics: an illustration in electrical systems

A Legendre transform is proposed between a nonequilibrium thermodynamic potential for electrical systems using the electric flux as a nonequilibrium variable and another one using the electric field. Such a transform clarifies the definition of the chemical potential in nonequilibrium steady states and may be also useful in other contexts where the relaxation times of the fluxes play a relevant role. The relation between this proposal and some Legendre transforms used in the context of dissipative potentials is examined.