(Invited) Membrane Coated Electrocatalysts for Seawater Electrolysis

One obstacle to the widespread adoption of water electrolysis powered by renewable sources is the availability of highly pure water required by conventional electrolyzers. This is particularly true for hot, dry coastal regions which have access to seawater and great potential for harvesting solar and wind energy, but where fresh water is often scarce. Additionally, seawater makes up 97% of the water on Earth, and although desalination is possible, it adds cost to the electrolysis system. Thus, direct seawater electrolysis could be a more cost effective approach to hydrogen production that doesn’t strain fresh water resources. However, direct seawater electrolysis is challenging due to the large concentration of Cl - ions, which can be detrimental to electrocatalyst stability and is a reactant for the undesirable chlorine evolution reaction (CER) that competes with the oxygen evolution reaction (OER) at the anode. Mitigating the CER is important because Cl 2 is toxic and harmful to the environment. Our group has shown that ultrathin semi permeable oxide overlayers can be designed to modulate transport of reactants to the active catalyst at the buried interface. Thus, the oxide overlayer acts as a membrane, rendering the material a membrane coated electrocatalyst (MCEC). An additional advantage of the MCEC architecture compared to conventional electrocatalysts is enhanced stability. The overlayer can act as a glue holding catalyst particles in place, which we have shown comparing SEM images before and after chronoamperometry in 0.6 M NaCl. This work describes how MCECs can be applied to seawater electrolysis to i) improve catalyst stability and ii) enable selectivity for OER over CER by impeding transport of Cl - ions to the buried interface.