Determination of cathode current efficiency for electrodeposition of ferromagnetic cobalt nanowire arrays in nanochannels with extremely large aspect ratio

Cathode current efficiency for the electrodeposition of cobalt from an acidic aqueous solution, which took place in anodized aluminum oxide (AAO) nanochannels with an average diameter of ca. 25 nm, was determined by Faraday's first law of electrolysis. The electrodeposited metallic cobalt crystals were grown as an array of nanowires embedded in the nanochannels. The amount of charge consumed for the electrochemical reduction in the nanochannels was estimated considering the time dependence of the cathode current during the electrodeposition of the cobalt nanowires. Meanwhile, the volume of electrodeposition on the cobalt nanowires was determined from the saturated magnetic moment of the nanowires, which was obtained from the magnetization curves. The cathode current efficiency for the electrodeposition of the cobalt nanowire arrays remained at a high level (over 75%) in the cathode potential ranging from -0.70 V to -0.85 V vs. Ag/AgCl. At the cathode potential of - 0.80 V, the cathode current efficiency reached 97%. The texture coefficient TG((0 0 2)) of the cobalt nanowire arrays increased as the cathodic overpotential for the electrodeposition of cobalt decreased. Due to the extremely large aspect ratio (more than 1000), the cobalt nanowire arrays were spontaneously magnetized in the direction parallel to the long axis of the nanowires. With increasing TG((0 0 2)), the coercivity and squareness of the cobalt nanowire arrays also increased up to ca. 1.6 kOe and 0.8, respectively, at room temperature.