Abstract: Disclosed microreactors operate in an electrical discharge mode, such as a pulse mode, an arc mode or a corona discharge mode, and most preferably in a corona discharge mode. A microreactor may comprise multiple, simultaneously operating corona discharges. The microreactor typically has at least one feature measured on a millimeter scale. Certain disclosed microreactors comprised multiple reactor plates in a stack. Each plate comprised plural corona discharge electrodes positioned in series along each of plural corresponding microchannels. A method for using disclosed microreactors and systems comprising disclosed microreactors, such as for chemical transformations, fluid purifications, or both, also is disclosed.