Durability Testing of Low-Iridium PEM Water Electrolysis Membrane Electrode Assemblies

Abstract

Lowering the iridium loading at the anode of proton exchange membrane (PEM) water electrolyzers is crucial for the envisaged GW-scale deployment of PEM water electrolysis. Here, the durability of a novel iridium catalyst with a low iridium packing density, allowing for low iridium loadings without decreasing the electrode thickness, is being investigated in a 10-cell PEM water electrolyzer short stack. The anodes of the membrane electrode assemblies (MEAs) of the first five cells utilize a conventional iridium catalyst, at loadings that serve as benchmark for today’s industry standard (2 mgIr/cm2). The last five cells utilize the novel catalyst at 8-fold lower loadings (0.25 mgIr/cm2). The MEAs are based on Nafion® 117 and are tested for 3700 h by load cycling between 0.2 and 2.0 A/cm2, with weekly polarization curves and impedance diagnostics. For both catalysts, the performance degradation at low current densities is dominated by an increase of the overpotential for the oxygen evolution reaction (OER), whereby the OER mass activity of the novel catalyst remains ≈4-fold higher after 3700 h. The temporal evolution of the OER mass activities of the two catalysts will be analyzed in order to assess the suitability of the novel catalyst for industrial application.

Progress of Heterogeneous Iridium-Based Water Oxidation Catalysts

“…64,65 To differentiate OER from catalyst dissolution, a stability number as a metric to benchmark electrocatalyst stability is suggested, 66 and durability testing using membrane electrode assemblies is recommended. 67…”

“…The metal cations released from the lattice oxygen evolution process can recombine with aqueous oxygen anions to dissolve in the electrolyte or reach a precipitation/dissolution equilibrium, and Figure B shows a possible Ir dissolution pathway. , To differentiate OER from catalyst dissolution, a stability number as a metric to benchmark electrocatalyst stability is suggested, and durability testing using membrane electrode assemblies is recommended …”

Nanostructured IrOx supported on N-doped TiO2 as an efficient electrocatalyst towards acidic oxygen evolution reaction

“…However, compared with these reported PEMWE cells employing Ir-based anode catalysts, [59][60][61][62][63][64][65] this IrO x /N-TiO 2 jjPt/ C(CM)-based cell displays relatively mediocre level for the stability performance. Therefore, systematic optimization of the cell fabrication should be the further research emphasis for enhancing the practical cell performance, especially the operating stability.…”

Iridium Stabilizes Ceramic Titanium Oxynitride Support for Oxygen Evolution Reaction

“…Presently, the crucial bottleneck is the anode side of the electrolyzers, where the sluggish oxygen evolution reaction (OER) dictates the employment of expensive and scarce iridium to an unsustainable extent . Therefore, there is a strong incentive to minimize the amount of currently still irreplaceable iridium in the catalyst layer and enhance its activity and durability. , Following the main concepts of fuel cells and platinum-based catalysts, most approaches for decreasing the loading of iridium are based on synthesizing catalyst core–shell morphologies with minimal Ir content − by alloying iridium with other metals ,− or by mixing iridium nanoparticles with less expensive oxides of earth-abundant elements . Especially effective is dispersing iridium nanoparticles on a high-surface-area support. ,− However, supported OER catalysts represent a multidimensional platform encompassing many unresolved phenomena such as support electroconductivity, metal–support interactions, support morphology, and stability, , to name a few.…”

“… 2 Therefore, there is a strong incentive to minimize the amount of currently still irreplaceable iridium in the catalyst layer and enhance its activity and durability. 3 , 4 Following the main concepts of fuel cells and platinum-based catalysts, most approaches for decreasing the loading of iridium are based on synthesizing catalyst core–shell morphologies with minimal Ir content 5 − 8 by alloying iridium with other metals 7 , 9 − 13 or by mixing iridium nanoparticles with less expensive oxides of earth-abundant elements. 14 Especially effective is dispersing iridium nanoparticles on a high-surface-area support.…”