Advanced redox flow fuel cell using ferric chloride as main catalyst for complete conversion from carbohydrates to...

Liquid catalyzed fuel cell (LCFC) is a kind of redox flow fuel cell directly converting carbohydrates to electricity. To improve its efficiency, ferric chloride (FeCl₃) was introduced as main catalyst. As mono catalyst, phosphomolybdic acid (PMo₁₂) was much better than phosphotungstic acid (PW₁₂) and FeCl₃ was intermediate between them. Compared with PMo₁₂ at the optimal dose of 0.30 mol/L, the combination of FeCl₃ (1.00 mol/L) and PW₁₂ (0.06 mol/L) achieved similar power output from glucose (2.59 mW/cm²) or starch (1.57 mW/cm²), and even improved the maximum power density by 57% from 0.46 to 0.72 mW/cm² when using cellulose as the fuel. Long-term continuous operation of the LCFC indicated that carbohydrates can be hydrolyzed to glucose and then oxidized stepwise to carbon dioxide. At the latter stage, there was a linear relationship between the electron transfer number from glucose to catalyst and the subsequent cell performance. Based on these findings, the contribution of FeCl₃ to LCFC should be derived from the accelerated hydrolysis and oxidation of carbohydrates and the enhanced electron transfer from glucose to anode. The addition of FeCl₃ reduced the usage of polyoxometalates by 80%, and the replacement implied that LCFC can be operated less toxically and more economically.