Development of a High Surface Area Cathode for an Environmentally Friendly Magnesium Reserve Battery

Open Access
Author:
Vadella, Robert Joseph
Graduate Program:
Engineering Science and Mechanics
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
November 12, 2013
Committee Members:
  • Barbara Shaw, Thesis Advisor
  • Elzbieta Sikora, Thesis Advisor
Keywords:
  • Magnesium
  • Graphite
  • PEDOT
  • Conducting Polymers
  • Thin Films
  • Reserve Battery
  • Corrosion
  • Electrochemistry
  • Discharge
Abstract:
In this thesis, various materials and fabrication techniques were examined in an attempt to develop a cathode material for a “green” magnesium reserve battery. The candidate cathode materials could be classified as one of two types – conducting polymers and graphite materials – both of which are carbon-based. Three important factors that influence the effectiveness of cathode materials are surface area, electrical conductivity, and a large potential difference with the anode which in this study is a magnesium alloy. The surface of each candidate material (or substrate on which a material was deposited) was examined using scanning electron microscopy. The candidate cathode materials were then subjected to electrochemical experiments which enabled for the candidate electrodes to be compared against one another. The anode material that was used in every experiment was a chunk of bulk magnesium AZ91 alloy. Two different electrolytes – saturated sodium chloride and artificial seawater – were tested as well. Using the Gamry Reference 3000 potentiostat, the electrochemical cells were tested together in a full cell configuration. The two main tests that were run were the read voltage experiment which measures the cell voltage over time and the constant current discharge experiment which measures the voltage response of the cell as a constant current is forced through the cell. Read voltage experiments indicated that the conducting polymer cathodes, polypyrrole and poly(3,4-ethylenedioxythiophene) (PEDOT), provided a stable cell voltage of over 1.8 V when coupled with AZ91 in either electrolyte solution. However, the conducting polymer cathodes failed in the constant current discharge tests likely due to the relatively low conductivity of the samples. While the materials are “conducting” polymers, their conductivity is still orders of magnitude lower than graphite and metallic materials. The graphite cathodes displayed lower cell voltages of between 1.6 to 1.8 V, but were much better in the constant current discharge experiments. Two materials that stood out among the graphite materials were the Zorflex double weave graphite fabric and the pressed powder graphite made using powder metallurgy techniques. The high surface area and electrical conductivity of these materials allowed for large currents to run through the cell while the cell voltage still remained high.