Abstract
Liquid catalyzed fuel cell (LCFC) is a kind of redox flow fuel cell directly converting carbohydrates to electricity. To improve its efficiency, ferric chloride (FeCl(3)) was introduced as main catalyst. As mono catalyst, phosphomolybdic acid (PMo(12)) was much better than phosphotungstic acid (PW(12)) and FeCl(3) was intermediate between them. Compared with PMo(12) at the optimal dose of 0.30 mol/L, the combination of FeCl(3) (1.00 mol/L) and PW(12) (0.06 mol/L) achieved similar power output from glucose (2.59 mW/cm(2)) or starch (1.57 mW/cm(2)), and even improved the maximum power density by 57% from 0.46 to 0.72 mW/cm(2) 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 FeCl(3) 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 FeCl(3) reduced the usage of polyoxometalates by 80%, and the replacement implied that LCFC can be operated less toxically and more economically.