Highly Active and Durable Ir Catalyst for Oxygen Evolution Reaction for Proton Exchange Membrane Electrolysis

Abstract

In the proton exchange membrane (PEM) water electrolysis, iridium (Ir) or iridium oxide (IrOx) black is the primary catalyst for the oxygen reduction reaction (OER) at the anode. Changing Ir black to Ir nanoparticles (3-4 nm) could significantly increase the catalyst activity of the OER and thus lowering the Ir loading. Under harsh PEM water electrolysis operating conditions, it is challenging to find electrically conductive and electrochemically stable supports to deposit Ir or IrOx nanoparticles The high operating potential, oxidation atmosphere and strong acid conditions has limited the application of carbon black, a most common support used in PEM fuel cells. In this work, iridium nanoparticles with a conductive chain was formed and deposited on high surface area tungsten doped TiO2 support (Ti1-xWxO2), named as Ir/Ti1-xWxO2. The continuous conductive chain could be formed by manipulating the catalyst synthesis conditions. To demonstrate the significance of the conductive chain in the electrochemical test, the Ir/Ti1-xWxO2 catalyst modified with an additional layer of IrO2, named as Ir/IrO2/Ti1-xWxO2, was prepared. Partial amount of iridium nanoparticles without conductive chain was oxidized to iridium oxide, and subsequently, another layer of iridium nanoparticles was deposited on the IrO2/Ti1-xWxO2 support to form an iridium/iridium oxide conductive chain. The electrochemical tests demonstrated that these two categories of catalysts with conductive chain exhibited high initial performance and durability for OER in PEM electrolyzers. The synthesized catalyst Ir/ WxTi1-xO2 demonstrated 5-time higher mass activity than industrial standard Ir black baseline, from rotating-disk electrodes (RDE) studies. While being tested in real water electrolyzers, the synthesized catalyst enabled to lower the Ir loading by an order of magnitude while retaining a similar electrolzyer performance of the baseline Ir black catalyst. The Ir/WxTi1-xO2 catalyst also demonstrated remarkable stability as only small voltage (<20 mV) increase was observed in a 3000-hour durability at a constant current density of 2000 mA/cm2.