Chapter 2: Water Electrolysis Technology and Challenges

In this chapter, four main water electrolysis technologies, namely alkaline, PEM, AEM and SOEC electrolysis, are compared with respect to a number of key techno-economic aspects. These include the polarization curve, the economic polarization curve (which is a new concept that includes stack costs), gas crossover, balance of plant design, and durability. Together, these aspects determine the capital and operating costs and hence the competitiveness of a water electrolysis technology. Currently, alkaline technology outperforms the other technologies mainly due to its relatively low stack costs. Yet there is some uncertainty concerning its durability in flexible operation with frequent shutdowns. PEM technology can be operated efficiently at high current densities, but suffers from relatively high stack costs. AEM and SOEC technologies both hold promise to outperform the other technologies, but they first need to become sufficiently durable. Which technology will be most competitive in the future will depend on technical improvements in the field of membranes, electrodes, cell design and operating conditions. It should be taken into account that improvements in one techno-economic aspect can lead to deterioration in another.