Double layer structure in a supercritical fluid

This work reports the first double layer capacitance measurements in a pola r supercritical fluid. The capacitance of a tetrabutylammonium tetrafluorob orate (TBA BF4) electrolyte in supercritical difluoromethane (HFC 32) at a platinum electrode is shown to be strongly dependent on fluid density. At h igh pressures the capacitance-potential plots exhibit a double layer respon se similar to that in the liquid state, but as the pressure is lowered towa rd the critical value the diffuse layer collapses and a pure Helmholtz resp onse is observed.