NOVELTY - A system using and/or processing a fuel comprises at least one element having a catalytic activity, where the element comprises at least one stabilizing additive capable of protecting the catalytic activity of the element in presence of an impurity. The impurity is present in the fuel, and the fuel is susceptible of being at least partially used in an energy conversion system. The impurities comprise sulfur in elemental and/or compound form. The stabilizing additive comprises a non-metal element (preferably nonmetal of group VIIa and/or its compounds, especially fluorine and/or chlorine).    USE - As system using and/or processing a fuel such as a fuel cell system, a solid oxide fuel cell (SOFC), and molten carbonate fuel cell (MCFC) (claimed) for converting chemical energy to electrical energy.    ADVANTAGE - The system is a fuel cell having an optimal operation temperature which is greater than or equal to 140 (preferably greater than or equal to 400) degrees C. The additive (preferably halides or halide compounds) desensitizes elements of solid oxide fuel cell systems against impurities; and protects the system from impurities such as elemental sulfur and compounds containing sulfur. The additive reduces the sensitivity of the fuel processing systems to impurities or additives present in the fuels such as commercial natural gas; and reduce the sensitivity of the catalytic elements in fuel processing system. The fuel cell does not suffer loss of performance due to impurities containing sulfur in the fuel. The system is reliable and cost-effective.    DETAILED DESCRIPTION - A system using and/or processing a fuel comprises at least one element having a catalytic activity, where the element comprises at least one stabilizing additive capable of protecting the catalytic activity of the element in presence of an impurity. The impurity is present in the fuel, and the fuel is susceptible of being at least partially used in an energy conversion system. The impurities comprise sulfur in elemental and/or compound form. The stabilizing additive comprises a non-metal element (preferably a nonmetal of group VIIa and/or its compounds, especially fluorine (F) and/or chlorine (Cl)). The element is an anode comprising Ni; or is cermet further comprising conducting oxide. The oxide comprises at least one of Zr, Ce, Ga and Bi. The element comprising at least one stabilizing additive is an element of a solid oxide fuel cell (preferably anode of a solid oxide fuel cell). The system comprises a further stabilizing additive, where the further stabilizing additive is a metal (preferably a transition metal). The system comprises an electrolyte selected from an oxygen ionic conductor, a hydrogen ionic conductor, and/or carbonate ionic conductor. The element is at least one of a fuel processing subsystem, interconnect or a gas supply channel. INDEPENDENT CLAIMS are included for the following:    (1) desensitizing an element of a system using and/or processing a fuel against impurities potentially present in the fuel, where the fuel is suitable to be consumed by the system, involving incorporating at least one stabilizing additive in and/or on the element. The step of incorporating at least one stabilizing additive in and/or on the catalytically active element involves at least one step selected from impregnating the element with at least one stabilizing additive dissolved or suspended in a liquid; reacting the element with at least one stabilizing additive provided in a gaseous and/or plasma phase; and incorporating at least one stabilizing additive in the element prior to a high temperature sintering and/or reduction step;    (2) protecting a catalytic activity of an element in a system using and/or processing a fuel against impurities potentially present in the fuel, involving incorporating at least one protective additive in and/or on the element; and    (3) making a catalytically active element for a system using and/or processing a fuel involving incorporating at least one protective additive in and/or on the element.