electrochemical compression, membrane, metal hydride
This paper describes working mechanism of electrochemical compressor (ECC), which compresses hydrogen using electrochemical process through membranes. The electrochemical process is governed by Nernst equation. The paper documents experimental study to characterize performance of a prototype electrochemical compressor. The experimental setup is introduced and the measured results of hydrogen mass flow rate, electrochemical efficiency and isentropic compression efficiency are given. The experimental results demonstrate that the prototype compressor is able to pump hydrogen flow from 25 psia to 140 psia, and deliver the flow rate as predicted by Nernst equation. On the other hand, its efficiency level is low, having the electrochemical efficiency less than 40%, and isentropic efficiency below 47%. Using two identical ECC compressors in parallel will reduce the current density and ohm loss, which can increase the isentropic efficiency up to 67% with increased cost. Further improvements on the compressor are suggested, e.g. using more conductive membrane, etc. Furthermore, we estimate energy saving potential of a refrigerator using an electrochemical compressor and metal hydride heat exchangers, versus a baseline refrigerator using a single-speed reciprocating compressor. The ECC technology has is more efficient at high pressure ratio and has better part-load performance. In addition, metal hydrides are solid absorbents suitable for extensive applications, having larger formation heat. It has the potential to achieve energy saving over 20% than the baseline refrigerator, after the technical barriers can be broken on the path.