Enhanced Oxygen Reduction at Composite Electrodes Producing a Large Magnetic Gradient

A platinum-coated electrode is designed to produce a magnetic field with ∇ B 2 in excess of 10 5 T 2 m − 1 at its surface in an applied field of 1 T . It is based on an array of cobalt nanowires embedded in an anodized alumina membrane. Performance for a series of electrochemical measurements on a model oxygen reduction reaction in an alkaline medium is compared with those of control electrodes with no cobalt, or with a continuous cobalt film behind the platinum surface. The measurements include rotating disk electrode cyclic voltammetry, steady-state polarization, and chronoamperometry. The limiting current for the field gradient electrode is enhanced by more than an order of magnitude compared to the controls, and the enhancement is retained when the electrode rotates. The effect is attributed to a concentration of paramagnetic species, H O 2 − and O 2 , at the surface of the field gradient electrode. The results demonstrate the potential of using magnetic field gradient electrodes for electrochemical reactions involving paramagnetic species.