Capacitive deionization apparatus and methods of treating a fluid using the same

The present disclosure relates to a spacer structure that is configured to be disposed between a pair of electrodes in a capacitive deionization apparatus so as to provide a space for flowing a fluid therethrough. The spacer structure includes a copolymer prepared by copolymerizing a mixture of a polyurethane backbone including a carboxyl group or a sulfonic acid group, an ion conductive monomer including a carboxyl group and a cation exchange group, and a second polymer including a functional group that reacts with the carboxyl group or sulfonic acid group and forms a cross-linking bond with the polyurethane backbone.