High Performance AEM Water Electrolysis with PGM-Free Electrocatalysts

Abstract

Water electrolysis technologies for hydrogen production are getting much attention due to drastic cost reduction in renewable energy sources, like solar, wind, tidal etc. Traditional alkaline water electrolysis has limitations of low current density operation, slow system response and low hydrogen discharge pressure. Proton exchange membrane (PEM) water electrolysis offers compact design, high current density operation, fast system response and pressurized discharge hydrogen. However, PEM electrolyzers require the use of Platinum Group Metal (PGM) based electrocatalysts, expensive perfluorinated membranes and specialized component materials due to its acidic environment. These are all hurdles to its widespread commercial adoption. A relatively new technology, the anion exchange membrane (AEM) electrolyzer can potentially combine benefits from PEM and traditional alkaline electrolyzers, offering high current density operation, pressurized discharge gas and low cost – by utilizing PGM-free electrocatalysts and inexpensive component materials due to the less corrosive alkaline operating environment.However, modern AEM electrolyzers have continued to use high loadings of PGM catalysts in both the cathode and anode. Given the magnitude and recent volatility in the market price of many PGM-group metal catalysts (e.g. Ru, Ir, etc.), it is now even more important for AEM electrolyzers to be realized with significantly lower PGM content – and eventually approaching the complete elimination of PGMs.In this study, we evaluate the performance of several low-PGM and PGM-free electrocatalysts for the oxygen evolution (OER) and hydrogen evolution (HER) reactions for high performance and durability. Here, PGM-free Lanthanum Strontium Cobalt (LSC), Nickel Ferrite (NiFeOx) and low PGM Lead Ruthenate (PbRuOx) were used at the anode for the OER. For the HER cathode, PGM-free Nickel Molybdenum (NiMo) and low-PGM PtNi electrocatalysts were evaluated for their in-situ activity and durability. It will be shown that LSC and NiFeOx show comparable performance to IrOx, with a typical steady-state operating voltage at 60oC and 1.0 A/cm2 (with 0.3 M KOH fed to the anode only) below 1.80 V. Cells with PGM-free anode catalysts were operated stably for over 100 hours. At the cathode, NiMo showed relatively higher overpotentials compared to Pt black, PtNi or Pt/C for the HER. Because of this, various strategies were adopted to reduce the PGM loading while achieving high performance and durable AEM electrolyzer operation. The achieved experimental results provide important insights for the development of AEM based water electrolyzer systems and represent an active step towards its commercial viability.