An electrochemical capacitor (300) for use with a biofilm is presented. The electrochemical capacitor includes a first electrode (324) coupled to a first porous layer (326), a second electrode (334) coupled to a second porous layer (336); and an electrolyte (310) provided between the first porous layer (326) and the second porous layer (336). At least one of the first porous layer (326) and the second porous layer (336) has a plurality of cavities adapted to receive redox-active metabolites produced by the biofilm. Also presented is an electrochemical capacitor device, such as a skin patch that includes a support layer attached to the electrochemical capacitor (300). Also presented is a power source that includes the electrochemical capacitor (300) and a biofilm provided between the first electrode (324) and the second electrode (334) of the electrochemical capacitor (300).