Enhanced high temperature fuel cell systems, such as solid oxide fuel cell systems and molten carbonate fuel cell systems are disclosed. Embodiments of the disclosure include solid oxide and molten carbonate fuel cell systems incorporating gas separation apparati facilitating the recycle of hydrogen fuel from fuel cell anode exhaust for supply to the fuel cell anode inlet, such systems capable of improved power densities and efficiencies of operation. Further embodiments of the disclosure include solid oxide and molten carbonate fuel cell systems incorporating inventive combinations of anode materials conducive to combination with enriched hydrogen fuel. Other embodiments of the disclosure include gas separation apparati for providing enriched oxygen feed to the cathode inlet of solid oxide and molten carbonate fuel cells.