Influence of a Magnetic Field on the Electrochemical Double Layer

The electrode/electrolyte interface is the seat of electrochemical redox reactions, which are controlled by the structure of ions and solvent molecules at an interfacial double layer, 0.5–10 nm thick. Here, we show that a magnetic field can exert a large and unexpected influence on the double layer—a 0.5 T in-plane field modifies its capacitance and charge-transfer resistance by up to 50%. The effects are observed in nitrobenzene, a model electrochemical system, and they indicate a shift of the outer Helmholtz plane of up to 0.25 nm caused by Maxwell stress acting on the paramagnetic NB•– radicals in solution close to the electrode. There are prospects of using magnetic fields to explore the internal terra incognita lying a nanometer or so from the electrode surface and control critical interface phenomena involving nucleation or surface wetting.