TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The reaction resistance decreases along the flow direction. The electrochemical cell is graded for varying the reaction resistance along the flow direction, preferably with respect to a material strength, a material density, a material porosity, a material selection, a surface resistivity, an electrical resistance, a diffusion resistor, an activation polarization and/or polarization resistance. The anode layer comprises an anode, an anode functional layer and/or an anode contact element, where the anode, the anode functional layer and/or the anode contact element are formed graded for varying the reaction resistance. The cathode layer comprises a cathode, a cathode functional layer and/or a cathode contact element, where the cathode, the cathode functional layer and/or the cathode contact element are formed graded for varying the reaction resistance. The electrolyte layer is formed graded for varying the reaction resistance. The reaction resistance varied along the flow direction is adjusted such that a constant reaction rate is obtained along the flow direction despite a decrease in concentration and/or decrease in density of the reaction media resulting from the reaction of the reaction media to each other, along the flow direction, and the electrochemically active layer has an uniform current density distribution during operation of the electrochemical cell during operation of the electrochemical cell. The electrochemical cell comprises gas channels for supplying the reaction medium to the electrochemically active layer, where the gas channels have continuous and/or constant widening or narrowing flow cross-section along the flow direction. The gas channels are formed at least partially by at least one interconnector element of the electrochemical cell. The electrochemically active layer has a contact surface, at which the electrochemically active layer is contacted electrically during operation of the electrochemical cell and/or is contacted with the reaction medium, where the contact surface varies, preferably increases along the flow direction and/or is at least partially formed triangular. The gas channels extend along the flow direction, and are fluidically connected to one another by means of transverse channels. At least one flow path-junction is provided for merging several gas channels. Contacting regions and non-contacting regions are formed by the anode layer and/or the cathode layer, preferably by anode contact element and/or a cathode contact element of the electrochemical cell, where a portion of the contacting regions on a total surface area of the anode layer and/or the cathode layer varies, preferably continuously increases or decreases compared to a portion of the non-contacting regions on the total area of the anode layer and/or the cathode layer along the flow direction. An anode of the anode layer, and/or an anode functional layer of the anode layer have a material properties varying along the flow direction, preferably electric conductivity varying along the flow direction. The contacting regions and non-contacting regions are formed by anode of the anode layer and/or an anode layer of the anode functional layer, where a portion of the contacting regions on a total surface area of the anode layer increases or decreases compared to a portion of the non-contacting regions on the total area of the anode layer along the flow direction. A cathode of the cathode layer, and/or a cathode functional layer of the cathode layer have material properties varying along the flow direction, preferably electric conductivity varying along the flow direction. The contacting regions and non-contacting regions are formed by the cathode of the cathode layer and/or the cathode functional layer of the cathode layer, where a portion of the contacting regions on a total surface of the cathode layer increases or decreases compared to a portion of the non-contacting regions on the total area of the cathode layer along the flow direction.