(Invited) High-Performance and Long-Lifetime Oxygen Evolution Catalysts for Proton Exchange Membrane Water Electrolysis

Hydrogen production from proton exchange Hydrogen production from proton exchange membrane (PEM) water electrolysis is attractive due to its simple and clean nature.  However, the technology is still expensive due to high materials cost for the catalysts, membrane, and bipolar plate. In most commercial processes, iridium (Ir) black is used as an oxygen evolution reaction (OER) catalyst at the anode. A high precious group metal (PGM) loading (> 4mg/cm²) has been used due to significant anode activation loss caused by sluggish kinetics of the OER.

Instead of using commercial Ir black, we have developed two types of high-performance OER catalysts for PEM water electrolysis. One is Ir dispersed on some supports with high oxidation resistance; the other is extended continuous nanostructures including Ir nanowires and Ir nanotubes (see Figure 1).   

First, Ir nanoparticles have been dispersed on tungsten-doped titanium oxide (Ir/W-TiO₂). Doping of TiO₂ with an element W can substantially enhance the electronic conductivity of TiO₂ while maintaining its high corrosion resistance at high electrolyzer operating voltages. A series of Ir/ W-TiO₂ catalysts with decreasing Ir loading from 70 wt. % to 25 wt. % has been synthesized. TEM images illustrates that Ir nanoparticles vary from 1 nm to 5 nm. The electrochemical surface area (ECSA) has been measured via mercury underpotential deposition (UPD).

In addition to Ir/W-TiO_2, Ir nanotubes have been synthesized via a porous alumina template.  The template was coated with an iridium precursor by subliming iridium precursor at an appropriate temperature. The template support was removed via chemical   etchings. The average length of the Ir nanotubes is 5mm and the diameter ranges from 250 – 400 nm with a wall thickness of ≤50 nm. The template pore size and process conditions are being varied to change the dimension of the Ir nanotubes.  

The activity and durability of these catalysts have been evaluated in rotating disk electrodes (RDEs) and electrolyzers. Selected catalysts have reduced PGM loading of electrodes by a factor of 10 while maintaining equivalent electrolyzer performance. These catalysts will help to lower the PEM electrolyzer capital cost making PEM water electrolysis more viable for a variety of applications.