## 3 Results and Discussion
### Discharge Performance
of the original carbon cloth was neglected, and the discharge specific capacity in this experiment was calculated only based on the weight of the commercial carbons coated on the electrodes, excluding the weight of the original carbon cloth substrate and binders. Each carbon electrode was tested three times, and the average of the three test results was taken as the experimental result. The single deep discharge capacity comparison is shown in Figure 6. When the binder ratio is within the range of 10-50%, the single deep discharge specific capacity of the three different carbon electrodes initially decreases and then increases. The minimum value is observed at a binder ratio of 20%, while the maximum is reached at a binder ratio of 50%. Among them, the Ketjen Black carbon electrode with a 50% PTFE coating achieved the highest discharge specific capacity of 11.86 Ah/g. The average discharge voltage for one hour and the single deep discharge specific capacity are adopted as indicators of the seawater battery performance. Combined with the results of the one-hour constant current discharge experiment, it is evident that when the binder ratio is within the range of 10-50%, the performance of the carbon electrode initially decreases and then promotes with the increase in the binder ratio. The performance is the worst at a binder ratio of 20% and the best at a binder ratio of 50%. The detailed analyses are shown as follows. Before the detailed discussion on those results, it should be clarified that the battery usually works in seawater. Thus, the oxygen supply for the electrochemical reaction is mainly affected by the oxygen dissolved in the seawater and oxygen transfer in the porous electrode. Based on the experimental results shown in Figures 5 and 6, when the binder ratio is less than 20%, the performance of the three carbon electrodes worsens with the  
Figure 6: Depth discharge of the different carbon electrodes. increase in the binder ratio. Seawater batteries use seawater as the electrolyte, and the dissolved oxygen in seawater is low. When the binder ratio is less than 20%, most of the electrode surface is wetted and the dissolved oxygen meets the demand of the reaction. The wetted surface (active reaction sties) dominates the battery performance. Therefore, when the proportion of binder increases from 10% to 20%, the electrode wettability decreases, leading to a decrease in battery performance. When the binder ratio is greater than 20%, the performance of the three carbon electrodes becomes better with the increase in the binder ratio. Although the number of reaction sites decreases within these bind ratios, the higher binder ratio has a greater impact on the wettability and porous structure of the carbon electrode. The decrease in electrode wettability enhances oxygen diffusion in non-wetted pores, and the increase in the binder ratio increases the proportion of mesopores and macropores in the carbon electrode, improving the utilization of mesopores and macropores. Both promote oxygen transfer, improving oxygen supply and enhancing cell performance. At this point, oxygen transfer has the primary influence on the cell performance. This is the reason for the initial decrease and subsequent increase in the performance of the seawater cell with increasing binder ratio. In summary, under the same test conditions and the same PTFE ratio, the average discharge voltage follows the order of Ketjen Black > Acetylene Black > VulcanXC-72R. The single deep discharge specific capacity follows the order of Ketjen Black > Acetylene Black > VulcanXC-72R. Therefore, it can be concluded that the Ketjen Black carbon electrode exhibits the best performance in this study. Moreover, after adding the binder, the utilization of mesopores and macropores in the Ketjen Black carbon electrode is higher than that in Acetylene Black and VulcanXC-72R carbon electrodes. Further, when the binder ratio is higher than 50%, the performance of the battery may be reduced.