A device for producing a product via a reaction requiring reducing equivalents, comprising: a. an anode contained in an anode chamber and a cathode contained in a cathode chamber; b. deionized water in the anode chamber in contact with the anode; c. a proton permeable membrane that separates the anode and cathode chambers; d. a liquid phase in the cathode chamber continuously in contact with the cathode, said liquid phase comprising an electron transfer mediator (ETM) capable of transferring reducing equivalents to a redox enzyme system, said redox enzyme system comprising a redox enzyme and a cofactor; e. a process stream containing a substrate to be transformed via catalysis by the redox enzyme system into a desired product; f. an asymmetric membrane located between the cathode and the process stream, said asymmetric membrane capable of preventing the ETM and the redox enzyme system from significantly entering into the process stream; wherein the asymmetric membrane has one or more pores extending therethrough, wherein the pores have a first opening on a first surface of the asymmetric membrane facing the cathode and have a second opening on a second surface of the asymmetric membrane facing the process stream, wherein the second opening is larger in size than the first opening; wherein the first opening is sufficiently small to prevent molecules having a molecular weight greater than 1 KDa from substantially passing through, and wherein the second opening is sufficiently large to permit at least a portion of the redox enzyme contained within the pores to contact the substrate in the process stream; and g. an external power source providing a voltage between the anode and the cathode. a. an anode contained in an anode chamber and a cathode contained in a cathode chamber; b. deionized water in the anode chamber in contact with the anode; c. a proton permeable membrane that separates the anode and cathode chambers; d. a liquid phase in the cathode chamber continuously in contact with the cathode, said liquid phase comprising an electron transfer mediator (ETM) capable of transferring reducing equivalents to a redox enzyme system, said redox enzyme system comprising a redox enzyme and a cofactor; e. a process stream containing a substrate to be transformed via catalysis by the redox enzyme system into a desired product; f. an asymmetric membrane located between the cathode and the process stream, said asymmetric membrane capable of preventing the ETM and the redox enzyme system from significantly entering into the process stream; wherein the asymmetric membrane has one or more pores extending therethrough, wherein the pores have a first opening on a first surface of the asymmetric membrane facing the cathode and have a second opening on a second surface of the asymmetric membrane facing the process stream, wherein the second opening is larger in size than the first opening; wherein the first opening is sufficiently small to prevent molecules having a molecular weight greater than 1 KDa from substantially passing through, and wherein the second opening is sufficiently large to permit at least a portion of the redox enzyme contained within the pores to contact the substrate in the process stream; and g. an external power source providing a voltage between the anode and the cathode. <EOS>