Fuel cells are well-known electrochemical devices for the production of electricity and heat. However also other functionalities are induced into the fuel cell by the membrane electrolyte that can be used advantageously. In contrast to combustion in which only one exhaust gas exits the combustion chamber a fuel cell is a device with two inlets and two separate outlet gas streams. This allows for the use of a fuel cell as a separator device. An example is the separation of CO2 gas from the off gas of a coal-fired power plant, using a molten carbonate fuel-cell. It also allows for the development of fuel cell reactors being a generalized concept of the fuel cell in which chemicals can be produced via electrochemical reactions using electric control for optimizing the process. In this paper an overview is given of these innovative possibilities and functionalities. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.