| Faced with the growing scarce of fossil energy and increasingly environmental pollution caused by burning fossil fuels, many countries accelerate the rate of development and utilization for marine resources, and large amounts of electrical power is required to operate the instruments for long-term deep-sea research and underwater operations. However, conventional battery is difficult to meet the requirements of long-life and safety. As a distributed power source, dissolved-oxygen seawater battery (DO-SWB) demonstrates broad application prospect. The properties of DO-SWB are not only affected by electrode materials, but also related to seawater environmental factors (such as oxygen concentration, flow rate) and battery parameters (such as working current, distance between positive and negative) because of its open structure. Therefore, it is of vital significance for the practical application of DO-SWB to study the effects of above factors on the properties of DO-SWB.In this paper, the electrochemical properties of Mg-Ga-Hg alloy in seawater were thoroughly studied by measuring the open circuit potential, potentiodynamic polarization curves, galvanostatic discharge curves and mass loss data, in terms of the working conditions of DO-SWB. As the positive materies for DO-SWB, the electrocatalytic performance of modified and unmodified PAN-based carbon fiber for oxygen reduction were tested by measuring the polarization curves (E-i) under steady state conditions. Furthermore, the effects of oxygen concentration, seawater flow rate, working current, by-product on the electrochemical properties of modified PAN-based carbon fiber (MPAN-CF) electrode were tested by measuring E-i curves under steady state conditions and galvanostatic discharge curves. Finally, the effects of interelectrode distance on the output voltage of seawater battery were also evaluated. In this paper, the results were obtained as following:1. The self-discharge rate of Mg-Ga-Hg alloy at open circuit potential is 0.381mA/cm2, and Mg-Ga-Hg alloy had good electrochemical activities in static or dynamic seawater with> 1.5%salinity:the open circuit potential was-1.91～1.95V; the activation time was less than 10s and the discharge voltages were negative than-1.9V at 1～9mA/cm2 current density. Moreover, it had good intermittent discharge behavior and its current efficiency reached 70%. Therefore, the Mg-Ga-Hg alloy can be used as anode material of DO-SWB.2. The electrocatalytic activity for oxygen reduction of MPAN-CF is improved significantly, and MPAN-CFB (a brush electrode of MPAN-CF) benefits to mass transfer. The electrochemical properties of MPAN-CFB are enhanced with increasing the oxygen concentration and flow rate of seawater. The current density of MPAN-CFB electrode at -400mV reached -32.3mA/g with 2cm/s flow rate and 3mg/L oxygen concentration in seawater. Even though in the harsh deep-sea environment (seawater flow rate:2cm/s; oxygen concentration:3mg/L; temperature:4℃), the current density of MPAN-CF electrode at-400mV could reach-10.9mA/g, indicating that it is suitable for cathode material of DO-SWB.3. It was suitable for MPAN-CFB electrode to work at less than 200mA. The effect of by-product on the electrochemical properties of MPAN-CFB was more serious in the initial stage, and the steady discharge voltages were-247 and-343mV at 50 and 100mA, respectively. Moreover, the distance between positive and negative should be reasonably designed according to the working current of DO-SWB, and it increased from 12cm to 25cm when the working current of MPAN-CFB reduced from 100mA to 50mA. |
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