Prussian Blue Analogues as Promising Thermal Power Generation Materials

The thermal coefficient (α=dV/dT) of redox potential (V) enables an efficient thermal power generation using waste heat. Actually, a battery-type thermocell, which consists of two kinds of redoxable solids with different α as anode and cathode, is demonstrated to produce electric energy in thermal cycles. To fabricate high performance device, α is systematically investigated in three kinds of Prussian blue analogues (PBAs), Na_xCo[Fe(CN)₆]_0.71 (abbreviated as NCF71), Na_xCo[Fe(CN)₆]_0.90 (NCF90) and Na_xMn[Fe(CN)₆]_0.83 (NMF83), against the Na⁺ concentration (x). NCF90 shows the highest positive α (=1.4 mV K⁻¹) in the lower-lying plateau while NMF83 shows the highest negative α (=−0.4 mV K⁻¹) in the lower-lying plateau. In addition, the NCF90/NMF83 thermocell produces 5.5 meV/NCF90 in the initial cycle between T_L (=286 K) and T_H (=313 K). The thermal efficiency (η=2.3 %) reaches 27 % of the Carnot efficiency (η_carnot=8.7 %). Thus, PBAs are promising materials for thermal power generation.