Hiroki Muroyama

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Heteropolyanions (HPAs) are known as the candidate for an anode redox mediator for redox flow polymer electrolyte fuel cells (PEFCs). The electrochemical properties of HPAs differ depending on the transition elements and heteroatoms in HPAs. For example, heteropolytungstate anions (W−HPAs), in which the transition element is tungsten, have a lower one‐electron reduction potential than other HPAs. Therefore, it has been reported that redox flow PEFCs adapted with W−HPAs exhibit high power generation performance. On the other hand, studies on the heteroatoms of HPAs are limited only to electrochemical properties, and statistical and comprehensive studies on the power generation performance of redox flow PEFCs are lacking. Thus, it is beneficial to clarify the optimal heteroatom in order to design anolytes suitable for redox flow PEFCs. In this study, heteropolytungstate anions with different heteroatoms were adapted as anodic redox mediators in a redox flow PEFC. In power generation tests, the redox flow PEFC with an anolyte of zinctungstate anion showed the highest performance. Zinctungstate anion exhibited the fastest reduction and oxidation rates among the W−HPAs investigated in this study.

For decades, many efforts have been devoted to develop proton conductors applicable to electrochemical devices at intermediate temperatures. However, promising materials which possess sufficient conductivity have not been realized yet. This study demonstrates the development of novel proton conductors operative at intermediate temperatures, especially 300-400 ºC, through the simple ion-exchange method. The Li⁺/H⁺ ion-exchange was conducted for Li₁₄Zn(GeO₄)₄, one of the members of lithium super ionic conductors (LISICONs), in non-aqueous solutions. The chemical formula of the resultant sample was determined as Li_3.13H_0.37Zn_0.25GeO₄ from instrumental analyses. The electrical conductivity of this material was evaluated to be 87.0 mS cm^‒1, 39.0 mS cm^‒1, and 5.5 mS cm^‒1 at 400 ºC, 300 ºC, and 200 ºC, respectively, in 10% H₂O‒90% N₂. Furthermore, the main charge carrier in this electrolyte was identified as proton from the H/D isotopic exchange study. These findings open up the possibility of realizing new electrochemical devices operative at 200-400 °C.

The oxygen reduction reaction mechanism on the Ba ₅ SrGd ₂ Co ₄ O ₁₅ –BaCe _0.5 Pr _0.3 Y _0.2 O _3−δ (BSGC–BCPY) composite cathode for proton-conducting fuel cells.

CO₂methanation proceeded over Ni/Al₂O₃viathe formation of CO species. Formate adsorbate served as the main intermediate for Ni/Y₂O₃.

Ammonia has been considered a promising alternative energy carrier due to its high hydrogen content and lack of carbon. Since ammonia readily decomposes into hydrogen and nitrogen at high temperatures, it can be used as a fuel for solid oxide fuel cells (SOFCs). In this work, the effect of the ammonia decomposition reaction over an anode on the performance of direct ammonia-fueled SOFCs was evaluated by electrochemical measurements and catalytic activity tests. A Ni–BaCe_0.4Zr_0.4Y_0.2O_3−δ cermet with excellent catalytic activity for ammonia decomposition was employed as the anode material. Impedance analyses revealed that the total cell resistance strongly depended on the ammonia fuel supply conditions. Particularly, the polarization resistance, which was attributed to a mass transfer process in the anode, increased at high ammonia concentrations and flow rates. On the other hand, in the catalytic activity tests, the conversion of ammonia over the cermet decreased under such fuel supply conditions. Hence, it was concluded that the performance of direct ammonia-fueled SOFCs significantly depended on the ammonia conversion over the anode. Additionally, a considerable reduction in the anode temperature as a result of the endothermic ammonia decomposition reaction was confirmed.