A system for producing an ion concentration gradient and a temperature-responsive electrolyte material which are utilizable, for example, for efficiently converting heat energy that has been discarded into reusable energy or for efficiently recovering an acid gas, such as carbon dioxide is provided. A temperature-responsive electrolyte is used to produce an ion concentration gradient by means of a temperature gradient. The temperature-responsive electrolyte is used in the state of an aqueous solution and also in the state of a solid phase.