###### Abstract  
Protonic ceramic fuel cells (PCFCs) offer direct and efficient conversion of hydrocarbon fuels into electricity. In this study, three internal-reforming (IR)-PCFC/gas turbine (GT) hybrid systems are proposed and analyzed to achieve higher system efficiency. High-quality heat from GT in system 1 and system 2 is supplied to anode and cathode preheaters, respectively, whereas in system 3, the heat is simultaneously split into both preheaters. Effects of air flow rate, fuel utilization factor (U\({}_{I}\)), and steam to carbon ratio (S/C) are also investigated. It is found that the best system design can be achieved by effectively utilizing GT exhaust heat for both electrode preheaters, as indicated in system 3. The maximum energy system efficiency obtained among the hybrid systems analyzed in this study is 71% with total exergy destruction of 686.7 kW. When fueled by methane, the hybrid system can achieve energy and exergy efficiencies of 71% and 77%, respectively, with 0.85 U\({}_{I}\). On the other hand, propane-fueled systems can achieve energy and exergy efficiencies of 68% and 75%, respectively. As S/C increases from 2 to 7, system efficiency decreases from 71% to 50%. When system 3 is fueled with butane or propane, system efficiency is only 3% lower than that fueled by methane. p _applied_  
_sciences_  
Footnote †: Copyright** © 2022 by the authors. Liconssee MDPI, Basel, Switzerland. thermal energy from the combustion chamber (CC) flows sequentially into the anode preheater, cathode preheater, and turbine to sustain their operating temperature. They reported that the highest efficiency of 58% was obtained with a single-stack SOFC/GT hybrid system. [PERSON] et al. [28] aimed to reduce the complexity and implementation of the hybrid power generation system. The ambient pressure of their syngas-fed IR-SOFC/GT hybrid system was varied to achieve maximum system efficiency of 57%. The higher fuel cell temperature led the turbine to generate more power, and such non-complex configurations proved to be easy to operate. [PERSON] et al. [29] thermodynamically analyzed and compared the maximum efficiency of the methane-fueled external reforming (ER) SOFC/GT, and SOFC/ST. Their results indicated that an SOFC/ST hybrid system with a fuel utilization (U\({}_{\text{f}}\)) of 0.9 has the same efficiency as a pressurized SOFC/GT hybrid system with a U\({}_{\text{f}}\) of 0.72, which is about 62%. However, a pressurized SOFC/GT hybrid system is a better choice for a power plant because steam turbines require higher installation and operation costs. SOFCs are classified into oxygen ion-conducting SOFCs (O-SOFCs) and proton-conducting SOFCs (P-SOFCs) based on the electrolyte used in the cell. P-SOFCs are also known as protonic ceramic fuel cells (PCFCs). The above-mentioned papers are all based on O-SOFCs. According to the mathematical modeling study of [PERSON] et al. [30], the maximum efficiency of PCFCs can be higher than that of O-SOFCs, as higher concentration of hydrogen can be utilized in the former. For example, the efficiency of PCFCs operating at U\({}_{\text{f}}\) = 0.8 and oxygen utilization of 0.2 is 11% higher than O-SOFCs. In addition, PCFCs can be operated at lower temperatures than SOFCs, which makes the choice of materials wider. [PERSON] et al. [31] studied a direct H\({}_{2}\)-fed PCFC/GT hybrid system. The influence of anode stoichiometry and cathode stoichiometry were analyzed, and they found an overall efficiency of 51% could be obtained with a U\({}_{\text{f}}\) of 0.9 at 1023 K. In our previous study [32], a methanol-fed ER-PCFC/GT was analyzed. The results showed that the hybrid system had a promising prospect as the efficiency could reach 66%. However, that system had a complex configuration, and could only be fed with low-reforming temperature fuels. To the extent of our knowledge, very few works investigated PCFC/GT hybrid systems. In this work, three different IR-PCFC/GT hybrid systems are analyzed to obtain the optimum system efficiency.