Innovative design of coal utilization – A green pathway for direct conversion of coal to electricity through flow fuel cell technology

Highlights: •Direct conversion of coal to electricity at low-temperature was first achieved. •Mechanisms are completely different from any reported coal fuel cells. •Polyoxometalates were used as both catalysts and charge carriers. •This process is low cost and environmentally friendly with high power density. •Completely noble metal-free without complicated coal pretreatment. -- Abstract: 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 (H₃[PMo₁₂O₄₀], denoted as POM-A) in solution on anode tank at 100–200 °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 (H₁₂[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 mW cm⁻².