Effect of the IrO_x Conductivity on the Anode Electrode/Porous Transport Layer Interfacial Resistance in PEM Water Electrolyzers

Abstract

In this study, a commercial IrO2/TiO2 catalyst (75 wt% Ir, named “Benchmark”) for the oxygen evolution reaction (OER) is compared to a newly developed IrO(OH)x/TiO2 catalyst (45 wt% Ir, named “P2X”). Due to its lower Ir packing density and higher OER activity vs the Benchmark catalyst (440 vs 12 A gIr −1 at 1.43 ViR-free), the P2X catalyst shows an improved PEM (proton exchange membrane) water electrolyzer performance at ≈9 times reduced Ir loading, however, only if a platinum-coated porous transport layer (PTL) at the anode is used. While the performance of membrane electrode assemblies (MEAs) with the Benchmark catalyst is unaffected when using an untreated titanium PTL, MEAs with the P2X catalyst perform poorly, which can be attributed to a contact resistance at the anode/PTL interface due to the low electrical conductivity of the P2X catalyst (0.7 S cm−1) vs the Benchmark catalyst (416 S cm−1) and the passivation of the Ti-PTL. A heat treatment procedure is used to transform the amorphous IrO(OH)x of the P2X catalyst into crystalline IrOx and, hence, increases its electrical conductivity. The optimum temperature for heat treatment to maximize electrical conductivity, OER activity and MEA performance will be evaluated.

Recent developments of iridium-based catalysts for the oxygen evolution reaction in acidic water electrolysis

“…160 Besides, recent studies show that too much binder content will fill electrode voids resulting in an increased contact resistance, while performance losses occur at lower ionomer contents owing to the higher proton conduction resistance. 162 Nobel metal (Au, Pt, Ir) coated titanium-based PTLs can decrease the contact resistance significantly by 60 mΩ cm −2 as revealed by Gasteiger, 166 Carmo, 148 Ahn 165 and Zhang teams 150,167 (Fig. 14b).…”

Potential Pitfalls in the Operando XAS Study of Oxygen Evolution Electrocatalysts

“…One of the main challenges in the scale-up of polymer electrolyte membrane water electrolysis (PEMWE) is the required decrease in the loading of the costly and scarce Ir-based materials used as the oxygen evolution catalysts. − These Ir-loading reductions require the design of improved OER catalysts, which will in turn occur by deepening our understanding of the OER mechanism on the IrO 2 -based materials implemented in state-of-the-art PEMWEs.…”

Kinetic Insights of Proton Exchange Membrane Water Electrolyzer Obtained by Operando Characterization Methods

“…The H + then transfers to the cathode and combines with an e – to evolve molecular H 2 at the surface of the hydrogen evolution reaction (HER) catalyst. The activity of catalysts, , transport resistance of electrons and protons, , and complex two-phase flow , greatly influence the performance of PEMWEs. For example, Ir-based catalysts are used in PEMWEs due to their high activities and durability in harsh conditions. , Ti-based PTLs , and FFs , are usually coated with noble metals (e.g., Pt, Ir, or Au) to reduce contact resistance.…”

“…This unexpected interface is associated with high electron transfer resistance at the interface between the PTL and CL. For example, a bare Ti-based PTL connected with a poorly conductive catalyst, like IrO­(OH) x , will make this interface effect more pronounced …”

“…For example, a bare Ti-based PTL connected with a poorly conductive catalyst, like IrO(OH) x , will make this interface effect more pronounced. 10 By adoption of the transmission-line model, shown in Figure 3d, the proton transport resistance in the CL can be estimated by EIS. 31,40 Herein, the cathode is flowed with hydrogen to simulate the reversible hydrogen electrode (RHE), and the anode is purged with fully humidified N 2 or deionized water.…”