Prussian Blue Analogues as Promising Thermal Power Generation Materials

The thermal coefficient (alpha=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 alpha as anode and cathode, is demonstrated to produce electric energy in thermal cycles. To fabricate high performance device, alpha is systematically investigated in three kinds of Prussian blue analogues (PBAs), NaxCo[Fe(CN)(6)](0.71) (abbreviated as NCF71), NaxCo[Fe(CN)(6)](0.90) (NCF90) and NaxMn[Fe(CN)(6)](0.83) (NMF83), against the Na+ concentration (x). NCF90 shows the highest positive alpha (=1.4 mV K-1) in the lower-lying plateau while NMF83 shows the highest negative alpha (=-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 (eta=2.3 %) reaches 27 % of the Carnot efficiency (eta(carnot)=8.7 %). Thus, PBAs are promising materials for thermal power generation.