PEM Electrolysis: Ready for Impact

The need for energy storage has never been so pressing; due to their increasing proliferation and the intermittent nature of wind and solar power sources, many regional grids can no longer accept more of these sources.  Electrolysis of water using polymer electrolyte membranes (PEMs) has long held the promise of large-scale energy storage, needing only the simplest of reactants, water.  More importantly it is perfectly suited for storing excess energy from these sources as they can handle tremendously high ramp rates as well as many start-stop cycles.  The adoption of PEM electrolyzers has been impeded due to the headwinds of high capital cost, (including expensive high precious metal content), poor efficiency, and the empty promises made by the hydrogen economy from many years.  Numerous incremental improvements, and increasing economies of scale over the past 10 years have led to very large decreases in the cost of PEM electrolysis.  The complexity of the electrolyzer stack and precious metal content have been decreased, while simultaneously increasing lifetime.  Increasing operating temperature has had the largest impact on efficiency and output, while improved membrane supports have allowed for higher differential pressures; reducing the need and cost of ancillary systems (see Figure 1).  These advances have had the combined effect of reducing the cost of hydrogen from PEM electrolysis by nearly an order of magnitude, allowing it to approach the cost of pumped hydro, the standard in large-scale energy storage.  Subsequently, whereas only a few years ago there were no commercial PEM electrolyzer stacks in the 1 MW range, today no fewer than five companies are at or near launch of MW electrolyzer systems.

Figure 1.  Total cost of hydrogen as a function of plant size and operating current