Design And Performance Of Direct Liquid Redox Fuel Cell

The direct liquid redox fuel cell (DLRFC) substitutes the oxygen reductioncathode of low temperature fuel cells with an redox couple of a redox flow battery.This approach helps address many issues with low temperature fuel cells. Such as, theissues of fuel crossover are no longer a concern as methanol is not electrochemicallyactive at the carbon cathode used for the redox couple reduction reaction. On the otherhand, the overall cost of the battery is greatly reduced because of the redox couplewithout using a noble metal catalyst.In order to conduct a preliminary evaluation of the DLRFC performance, ADLRFC single cell test system consisting of fuel-supply part, temperature-control part,the electrochemical reaction unit and performance testing part was designed and built.Taking into account the properties of materials and battery testing requirements, PTFEtube and graphite plate were selected as the pipe and flow field plate material,respectively. The structure of anode flow field and the cathode slots were focused on.Finally, a variety of connectors and fasteners were used to assemble all components,so as to provide a stable and reliable platform for DLRFC single cell performancetesting.Graphite felt (GF) was used as a cathode material for DLRFC. Heat treatment inan air atmosphere, the sulfuric acid treatment and the mixing treatment were appliedto GF in order to improve its activity. The results showed heat treatment waspreferable to sulfuric oxidation treatment in enhancing hydrophilic andelectrochemical activity of GF. DLRFC assembly with GF treated in450℃for2hexhibited the best performance, of which the maximum current density was up to128.9mA·cm-2better than DLRFC assembly with untreated graphite felt. Surfaceanalysis of treated and untreated felts showed that the–COOH functional groupsincreased after heat treatment, resulting in the decrease of resistance in the electrontransfer reaction and improving the electrochemical activity of graphite felt.Finally, the performance of DLRFC was evaluated from the structure,preparation process and operating conditions aspects. The experimental resultsdemonstrated that the optimum catalyst loading of metal in anode was2mg·cm-2andthe best content of Nafion ionomer in anode layer was30wt%. The influence ofhot-pressing procedure on the performance of anodic half membrane electrode(AHME) used in direct liquid redox fuel cell was investigated. The results revealedthat the optimal conditions in hot-pressing procedure were with the pressure of200kgf·cm-2at120℃for120s. In order to achieve DLRFC maximum performance,three activation procedures were compared including hot water circulation, constant current discharge and variable current discharge. The effect of activation conditionson the electrochemical properties of DLRFC was also studied during the constantcurrent discharge procedure. The results showed that the discharge method waspreferable for the activation of DLRFC single cell to water circulation method. Thebest activation time, temperature and current density were3h,60℃and20mA·cm-2, respectively.