Electrochemical reactor

An electrochemical reactor (10) for carrying out an electrochemical main reaction, said electrochemical reactor (10) comprising

• at least one electrolyte compartment (4) comprising an aqueous electrolyte, wherein at least one of the side walls of said electrolyte compartment is an electrode or a feeder electrode (1) and an opposite side wall comprises or consist of a separator element (2),
• a plurality of electrically conductive granules forming a working electrode (6) for the electrochemical main reaction in the electrolyte compartment (4) and enclosed in the electrolyte compartment (4), said granules comprising or consisting of a first material exhibiting at least a first activation overpotential for an electrochemical side reaction within a distance d from the separator element (2), characterized in that the electrochemical reactor (10) further comprises
• a spacer element (5) for maintaining the conductive granules at least at the distance d from the separator element (2) on at least the electrolyte-facing side of the separator element (2), wherein the spacer element (5) is electrically conductive and wherein the spacer element (5) comprises or consists of a second material exhibiting a second activation overpotential for the electrochemical side reaction within the distance d from the separator element (2) and wherein the second activation overpotential is larger than the first activation overpotential, and
• the electrochemical side reaction is either one of the half reactions of electrolysis of water.