Electrolytic MnO2 via non-isothermal electrode heating:: a promising approach for optimizing performances of electroactive materials

A thermal-modulated electrodeposition technique is proposed for enhancing the physico-chemical characteristics of electrolytic manganese dioxide (EMD). Synthesis is conducted on the basis of non-isothermal electrode heating at ambient pressure. Electrode substrates are heated continuously during the anodic deposition processes in boiling sulfuric acid solutions. Bath temperatures and deposition parameters are held constant. Anode temperatures are varied in the range 98-150degreesC. Two series of products, one deposited on a lead and the other on a Ti cylinder, are investigated. These are compared with EMD prepared by the conventional isothermal method which is similarly produced in a boiling solution. At optimized anode temperatures (120-135 degreesC), both series of products display enhanced charge-discharge performance. This is consistent with the compact surface morphologies which are obtained for thin layers of EMD deposited on graphite substrates. The positive effects of localized heating are detected by electrochemical impedance spectroscopy. Several physico-chemical parameters of the solvent, as well as of the electrodes, are varied as a function of electrode temperatures. Conservation of energy can be obtained through a relatively safe, simple and low-cost process. This method has potential for application to other electroactive materials with industrial prospects. (C) 2003 Elsevier B.V. All rights reserved.