The Study Of PEM-based Electrochemical Hydrogen Pump

Hydrogen is a pollution-free secondary energy source and has attracted more and moreattention around the world. In addition to the technology of hydrogen production, thedevelopment of efficient, low cost, reliable and scale hydrogen separation, purification andcompression technologies is very important for hydrogen economy. Electrochemical hydrogenpump （EHP） or known as electrochemical hydrogen compressor/concentrator is a new kind ofdevice for hydrogen separation or purification. Its structure is similar to a PEM fuel cell, canoxidize and reduce hydrogen at the anode and cathode respectively, in an electrolytic mode. Themain advantages of EHP are that hydrogen separation （purification） and compression areachieved in a single one-step process, and there is only a cost for those hydrogen molecules thatare transported across the membrane, thus minimizing power requirements.This study was based on the mature proton exchange membrane fuel cell technology in ourlaboratory, and the MEA （membrane electrode assembly） used in electrochemical hydrogenpump was prepared by a novel heat setting CCM-MEA method. We have studied the basicperformance of electrochemical hydrogen pump, and successfully extracted hydrogen fromH₂/CO₂and H₂/N2gas mixtures.The results show that increase the operating temperature will enhance the power efficiencyand the purity of hydrogen. Increase the pressure of anode compartment will enhance the powerefficiency, but decrease the purity of the hydrogen because of the increasing permeation flow ofimpurities. During the separation process, with the percentage of hydrogen in gas mixturedecline, the concentration of hydrogen molecule in anode chamber will drop, leaded toseparation voltage increasing, but had little effect on the purity of hydrogen. At the currentdensity of300mA·cm^-2, the maximum power consumption of H₂/N2gas mixture （H₂content50%） separation was only0.15kWh·Nm^-3, the recovery rate could reach95%, and the purity ofrecovered hydrogen was more than98%.In the separation of H₂/CO₂gas mixtures, carbon dioxide can react with H₂to generatecarbon monoxide under the catalysis of Pt particles. This is a reverse water gas shift reactionand carbon monoxide produced has poison effect on Pt catalyst, which leads to gradual increaseof the separation voltage. With a small amount of oxygen or air blending in the anode gas, thecarbon monoxide poisoning effect could be alleviated and result in significant separationvoltage decrease. Appropriate amount of oxygen or air blending could make separation voltage reduce by40%to50%. Similarly, the same method can also be applied to the separation ofmixtures containing carbon monoxide. High purity hydrogen, more than98%（Volume ratio）,can be achieved from a low purity （50%, Volume ratio） H₂/CO₂mixture by this device.