Proton-exchange membrane or polymer electrolyte membrane (PEM) electrolysis technology produces hydrogen from water using electricity. The electrolysis reaction takes place in cells, that are connected in series to make units (called a ‘stack’). An installation generally consist of multiple stacks. Sectors that have shown interest in (sustainable) hydrogen production are the (petro) chemical sector and the fertilizer sector (Berenschot 2017).
PEM operates at a temperature of around 60-70 degrees Celsius (Weeda, 2018). Electricity is used to split water (H2O) into oxygen (O2) and hydrogen (H2). The technology consists on one side of a positive terminal (anode), where water (H2O) reacts with a catalyst to form oxygen, electrons (e-) and hydrogen protons (H+). The hydrogen protons are then conducted across the polymer electrolyte membrane. At the negative terminal (cathode) of the installation, the electrons then combine with the hydrogen protons to produce H2 (SA 2014). PEM uses a polymeric membrane that has a high proton conductivity when the membrane is hydrated (Feroldi & Basualdo, 2012).
A PEM installation can produce hydrogen at a pressure of 5-50 bar (ECN 2018) which can subsequently be further compressed to 80-950 bar to reduce the need for storage capacity. An 80 bar pressure is necessary for injection in the natural gas network, whereas a pressure of 350-950 bar is necessary for using hydrogen in transport, for example in trucks and passenger vehicles (De Vita et al. 2018). Note that for almost all applications H2 needs to be compressed. According to NOW (2018) the pressure output of a PEM installation could potentially reach 110 bar by 2050.
The potential for PEM is high but is considered currently not economically feasible due to, among others, the high CAPEX (currently estimated around 4 times higher than economically viable). The levelised costs of hydrogen by electrolysis is about 5 €/kg (baseload production), which compares unfavourably with the cost of hydrogen from natural gas at 1-1.5 €/kg using SMR (Berenschot 2017).