Glucose was selectively oxidized to gluconic acid in a membraneless, flow-through electroenzymatic reactor operated in the mode of co-generating chemicals and electrical energy. At the anode the enzyme glucose oxidase (GOx) in combination with the redox mediator tetrathiafulvalene (TTF) was used as catalyst, while the cathode was equipped with an enzyme cascade consisting of GOx and horseradish peroxidase (HRP). The influence of the electrode preparation procedure, the structural and the operating parameters on the reactor performance was investigated in detail. Under optimized conditions, an open circuit potential of 0.75 V, a current density of 0.6 mA cm(-2) and a power density of 100 mu A cm(-2) were measured. The space time yield of gluconic acid achieved at a glucose conversion of 47% was 18.2 g h(-1) cm(-2). (C) 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).