Title: Novel functional semiconductor-Ionic materials

Abstract

Recent research and development on semiconductor-ionic materials (SIMs) with superionic conduction as alternative electrolytes lead to a new trend in low temperature solid oxide fuel cell (SOFC) and proton ceramic fuel cell (PCFC). This can be traced from a radical new invention of single-layer fuel cell (SLFC) or electrolyte-free fuel cell (EFFC), i.e. one semiconductor-ionic component instead of anode/electrolyte/cathode three components can realize fuel cell technology. Such SIMs can integrate the functionalities of fuel cell’s anode, electrolyte, and cathode into one component. This could represent a major progress and breakthrough in fuel cell science and technology and lay grounds for a new era of fuel cell R&D and commercialization. The SOFC technology depends on the electrolyte, yttrium stabilized zirconium (YSZ), but it requires a temperature over 700°C to operate properly due to requirement of sufficient ionic conductivity. The situation could now be improved if replacing YSZ with a SIM with high ionic conductivity to develop semiconductor-ionic fuel cells (SIFCs). The SIFC may demonstrate high performance at temperatures well below 550°C. Current SIMs may be classified into three types I) Single phase semiconductors, e.g. perovskite and layered structured oxides, SmNiO3, LiCoAlO2, LiNiFeO2, etc. These semiconductors have shown metal or high electronic (hole) conductivity with narrow or zero bandgap to experience a transition to ionic conduction by proton insertion from fuel cell operation; II) Wide bandgap materials, typically, oxygen deficit oxides, e.g. fluorite structure CeO2-d. The CeO2-d can change from insulating or electronic conduction to a proton conductor in the fuel cell operation; III) Both semiconductor and ionic conduction form a two-phase heterostructural nanocomposite, where percolation of both electron and ion conducting paths result in comparable or balanced electronic and ionic conduction.