Studies On The Sodium Polysulfide/Bromine Redox Flow Battery For Energy Storage

The work described in this thesis is supported by National 863 Program of China (No.2005AA516020). At present, there are still several technical obstacles for the commercialization of sodium polysulfide/bromine flow battery (PSB) intended for utility scale energy storage. Firstly, the preparation cost of carbon felt based electrodes is considerably high, while the activated carbon based electrode demonstrates energy efficiency less than 60%. In addition, the synthesis methods of sodium polysulfide from melt sodium and sulfur or H₂S are very complex and expensive, so they are not suitable for large-scale production. Furthermore, the present commercialized cation exchange membrane does not show 100% cation selectivity, so anions can permeate through it and cause crossover contamination during long term operation.Impregnation followed hydrogen reduction (IR) and electroless plating were carried out to prepare catalyst directly on carbon felts. The latter method shows more uniform catalyst dispersion than the former that only 10 mg cm^-2 is needed to form a continuously deposit film. At current density of 40 mA cm^-2, the PSB single cell using Co coated carbon felt as negative electrode illustrated cyclic energy efficiency greater than 80% within 500 h but only decreased 2%. Owe to the newly added electrically conductive agent and pore precursor, the initial energy efficiency of activated carbon based electrode has been enhanced to be 67⁷0%. However, its mass transport property still cannot satisfy a practical current density. During cycling operation, the element sulfur is accumulating...