Purifying hydrogen from dilute hydrogen-natural gas mixtures using HT-PEM electrochemical hydrogen pumps

Abstract

Reducing the cost of hydrogen transport is an important priority for proliferation of clean hydrogen to decarbonize various sectors of industry and heavy-duty vehicle transportation. Pipeline transport of gases is the lowest cost delivery method for gases over long distances, but there are only a few pipeline networks dedicated to hydrogen. It is possible to alleviate clean hydrogen transportation costs by delivering it via existing natural gas pipeline infrastructures. This strategy, however, necessitates dilution of hydrogen by blending it with natural gas as the hydrogen can embrittle existing pipeline materials. An electrochemical hydrogen pump (EHP) is a separation platform capable of de-blending hydrogen from natural gas mixtures at end use locations because many applications require purified hydrogen. In this work, we deploy high-temperature polymer electrolyte membrane (HT-PEM) EHPs to purify hydrogen from dilute hydrogen-natural gas mixtures (i.e., 5 to 20 vol% hydrogen). The HT-PEM EHP uses an ion-pair HT-PEM with perfluorosulfonic acid-phosphonic acid ionomer blends as electrode binders. Interestingly, we observe that activation overpotentials govern HT-PEM EHP polarization when feeding dilute hydrogen mixtures. We ascribe this observation to interfacial mass transfer resistance of hydrogen through the ionomer binder to the electrocatalyst surface resulting in a lower surface concentration of hydrogen and a lower exchange current density. Pressurizing the anode to 1.76 barabs ameliorates the interfacial mass transfer resistance and enabled us to achieve an EHP limiting current of 1.4 A cm-2 with a 10 vol% of hydrogen in natural gas feed. This configuration also pressurized the hydrogen at the cathode to 2.51 barabs. The HT-PEM EHP showed a small degradation rate, 44 µV h-1, during a 100-hour durability test purifying 10 vol% hydrogen-natural gas feed mixtures to 99.3 vol% hydrogen.