Low-rank coal, such as lignite, normally has low combustion heat and little commercial value. Combustion of low-rank coals will generate large amount of fly ashes and cause serious environmental problems. New technology for more effective use of low-rank coals with significantly less pollution is highly desired. In this study, we report an alternative method to convert coal chemical energy directly to electricity using flow fuel cell without complicated pretreatment. Practically, low-rank coal particles were first oxidized by polyoxometalate (H-3[PMo12O40], denoted as POM-A) in solution on anode tank at 100-200 degrees C. The reduced POM transferred the accepted electrons to the anode of the flow fuel cell. These electrons passed through the external circuit and were captured by another polyoxometalate (H-12[P3Mo18V7O85], denoted as POM- B) at cathode tank. The novel conversion method does not generate any fly ashes. The power density of the direct lignite flow fuel cell could reach as high as 120 mWcm(-2). (C) 2017 Elsevier Ltd. All rights reserved.