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DOE OSTI2020

Materials Data on MgIr by Materials Project

MgIr is beta Uranium-derived structured and crystallizes in the orthorhombic Cmce space group. The structure is three-dimensional. there are twelve inequivalent Mg sites. In the first Mg site, Mg is bonded in a 4-coordinate geometry to seven Mg and seven Ir atoms. There are a spread of Mg–Mg bond distances ranging from 2.93–3.32 Å. There are a spread of Mg–Ir bond distances ranging from 2.80–3.36 Å. In the second Mg site, Mg is bonded in a 8-coordinate geometry to one Mg and eight Ir atoms. There are a spread of Mg–Ir bond distances ranging from 2.77–3.10 Å. In the third Mg site, Mg is bonded in a 1-coordinate geometry to one Mg and six Ir atoms. There are a spread of Mg–Ir bond distances ranging from 2.70–2.98 Å. In the fourth Mg site, Mg is bonded in a 1-coordinate geometry to two Mg and seven Ir atoms. The Mg–Mg bond length is 2.93 Å. There are a spread of Mg–Ir bond distances ranging from 2.69–3.07 Å. In the fifth Mg site, Mg is bonded in a 3-coordinate geometry to two equivalent Mg and seven Ir atoms. There are a spread of Mg–Ir bond distances ranging from 2.59–3.02 Å. In the sixth Mg site, Mg is bonded in a 10-coordinate geometry to four Mg and eleven Ir atoms. There are a spread of Mg–Mg bond distances ranging from 2.93–3.06 Å. There are a spread of Mg–Ir bond distances ranging from 2.89–3.24 Å. In the seventh Mg site, Mg is bonded in a 3-coordinate geometry to four Mg and twelve Ir atoms. The Mg–Mg bond length is 2.91 Å. There are a spread of Mg–Ir bond distances ranging from 2.91–3.17 Å. In the eighth Mg site, Mg is bonded in a 7-coordinate geometry to two Mg and seven Ir atoms. There are a spread of Mg–Ir bond distances ranging from 2.81–2.94 Å. In the ninth Mg site, Mg is bonded in a 7-coordinate geometry to seven Ir atoms. There are a spread of Mg–Ir bond distances ranging from 2.83–2.98 Å. In the tenth Mg site, Mg is bonded in a 2-coordinate geometry to one Mg and eight Ir atoms. There are a spread of Mg–Ir bond distances ranging from 2.70–3.17 Å. In the eleventh Mg site, Mg is bonded in a 10-coordinate geometry to one Mg and eleven Ir atoms. There are a spread of Mg–Ir bond distances ranging from 2.97–3.31 Å. In the twelfth Mg site, Mg is bonded in a 1-coordinate geometry to three Mg and seven Ir atoms. There are a spread of Mg–Ir bond distances ranging from 2.62–2.87 Å. There are thirteen inequivalent Ir sites. In the first Ir site, Ir is bonded to seven Mg and five Ir atoms to form distorted IrMg7Ir5 cuboctahedra that share corners with five IrMg7Ir5 cuboctahedra, edges with five IrMg8Ir4 cuboctahedra, and faces with thirteen IrMg8Ir4 cuboctahedra. There are a spread of Ir–Ir bond distances ranging from 2.53–2.67 Å. In the second Ir site, Ir is bonded to eight Mg and four Ir atoms to form distorted IrMg8Ir4 cuboctahedra that share corners with eight IrMg8Ir4 cuboctahedra, edges with five IrMg7Ir5 cuboctahedra, and faces with eleven IrMg8Ir4 cuboctahedra. There are a spread of Ir–Ir bond distances ranging from 2.47–2.67 Å. In the third Ir site, Ir is bonded to seven Mg and five Ir atoms to form distorted IrMg7Ir5 cuboctahedra that share corners with eight IrMg8Ir4 cuboctahedra, an edgeedge with one IrMg7Ir5 cuboctahedra, and faces with eleven IrMg8Ir4 cuboctahedra. There are a spread of Ir–Ir bond distances ranging from 2.55–2.67 Å. In the fourth Ir site, Ir is bonded to eight Mg and four Ir atoms to form distorted IrMg8Ir4 cuboctahedra that share corners with nine IrMg7Ir5 cuboctahedra, edges with two IrMg7Ir5 cuboctahedra, and faces with nine IrMg8Ir4 cuboctahedra. There are one shorter (2.51 Å) and one longer (2.65 Å) Ir–Ir bond lengths. In the fifth Ir site, Ir is bonded in a 11-coordinate geometry to eight Mg and three Ir atoms. The Ir–Ir bond length is 2.49 Å. In the sixth Ir site, Ir is bonded in a 1-coordinate geometry to nine Mg and three Ir atoms. The Ir–Ir bond length is 2.47 Å. In the seventh Ir site, Ir is bonded to eight Mg and four Ir atoms to form distorted IrMg8Ir4 cuboctahedra that share corners with twelve IrMg7Ir5 cuboctahedra, an edgeedge with one IrMg8Ir4 cuboctahedra, and faces with twelve IrMg8Ir4 cuboctahedra. Both Ir–Ir bond lengths are 2.64 Å. In the eighth Ir site, Ir is bonded in a 9-coordinate geometry to eight Mg and one Ir atom. In the ninth Ir site, Ir is bonded in a 10-coordinate geometry to eight Mg and two equivalent Ir atoms. Both Ir–Ir bond lengths are 2.59 Å. In the tenth Ir site, Ir is bonded to seven Mg and five Ir atoms to form distorted IrMg7Ir5 cuboctahedra that share corners with eight IrMg8Ir4 cuboctahedra, edges with two IrMg7Ir5 cuboctahedra, and faces with eleven IrMg8Ir4 cuboctahedra. The Ir–Ir bond length is 2.67 Å. In the eleventh Ir site, Ir is bonded to eight Mg and four Ir atoms to form a mixture of distorted edge, corner, and face-sharing IrMg8Ir4 cuboctahedra. The Ir–Ir bond length is 2.48 Å. In the twelfth Ir site, Ir is bonded in a 12-coordinate geometry to nine Mg and three Ir atoms. In the thirteenth Ir site, Ir is bonded to eight Mg and four Ir atoms to form a mixture of distorted corner and face-sharing IrMg8Ir4 cuboctahedra.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Interfacial engineering via laser ablation for high-performing PEM water electrolysis

A rationalized interfacial design strategy was applied to tailor the porous transport layer (PTL)-catalyst layer (CL) contact and the PTL bulk-phase architecture. Particularly, at the PTL-CL interface, our results reveal that laser ablated sintered titanium power-based PTLs improve electrolyzer performance at both the H2NEW Consortium baseline catalyst loading of 0.4 mgIr cm -2 as well as at the ultra-low catalyst loading of 0.055 mgIr cm -2 . Under ultra-low catalyst loadings, the laser ablated PTL demonstrates maximum reduction of 230 mV compared to the commercial PTL at 4 A cm -2 , and reduces by 68 mV at 3.2 A cm -2 under H2NEW baseline loading. Laser ablation alters the titanium phase at the interface, so it forms more uniform structure like a microporous layer or a backing layer, leading to an increase in the surface area in contact with the catalyst layer while preventing the membrane from deforming into the PTL. Moreover, we reveal that bulk-phase architecture modification of the PTL by ablating patterned pores at the flow field-PTL interface improves mass transport without sacrificing contact at the CL-PTL interface. Overall, laser ablation of the PTL is an effective method to customize interfacial design to enhance proton exchange membrane electrolyzer performance.

08 HYDROGEN↗

DOE OSTI2026

Electrospun Ti–Zr Oxide Heterostructures Enable Strongly Anchored Ultralow-Ir Anodes for Durable Acidic Oxygen Evolution

Proton-exchange-membrane water electrolysis (PEMWE) requires acidic oxygen-evolution-reaction (OER) anodes that combine high activity, high durability, and low Ir loading. Here, we report a Ti-Zr composite electrospun oxide (ESO) nanorod support that enables ultralow-Ir anodes for high-performance PEMWE. Zr-containing Ti oxide heterostructures stabilize anatase-rich TiO2, tune the local oxygen-coordination environment, and strengthen interfacial anchoring of IrOx under acidic anodic conditions. The electrospun nanorod network further creates an open, mechanically coherent catalyst layer that improves Ir utilization, ionomer penetration, and mass transport. At an anode loading of 0.2 mgIr cm-2, the optimized Ir/TiZr20-ESO anode delivers a PEMWE mass activity of 0.99 A mgIr-1 at 1.45 V, 28.3 and 43.0 times higher than commercial Ir black and commercial IrO2/TiO2, respectively. The same anode reaches 3.0 and 4.0 A cm-2 at 1.75 and 1.83 V, respectively, and sustains 2000 h operation at 2.0 A cm-2. Also, accelerated stress tests up to 525 hours over 31,500 cycles confirm promising long-term durability, with an insignificant performance decay of 0.4 μV per cycle. Density functional theory indicates that the Ti-Zr oxide heterostructure suppresses Ti demetallation and strengthens IrO2 interfacial binding, rationalizing the improved high-current-density stability.

25 ENERGY STORAGE↗

DOE OSTI2024

Ultrathin Microporous Transport Layers: Implications for Low Catalyst Loadings, Thin Membranes, and High Current Density Operation for Proton Exchange Membrane Electrolysis

Porous transport layers (PTL) and their surface properties have the potential to improve the performance of proton exchange membrane water electrolyzers (PEMWE), which is imperative to reduce feedstock costs and lead to their widespread implementation. This work introduces a novel generation of titanium microporous layers (MPLs) with ultra-low thicknesses of approx. 20 um which reduces raw material costs. They also feature advanced interfacial properties tailored to maximize catalyst utilization at low Ir-loadings. The bulk morphology and surface properties of the hierarchically structured PTLs are assessed by X-ray tomographic microscopy. The low surface roughness of the MPL allows the use of thinner membranes since it minimizes possible deformations in the membrane. Cells containing the MPLs outperformed those containing state-of-the-art commercially available PTL materials by up to 100 mV at 7 A cm-2 in combination with low-loaded catalyst-coated membranes of 0.4 mgIr cm-2. Hydrogen crossover is also reduced, especially at low current densities, leading to a larger turndown ratio which can enable more cost-effective operating strategies. Finally, these rationally designed MPLs also lead to high catalyst utilization by overcoming the naturally occurring high in-plane resistance of low-loaded catalyst layers.

hydrogen crossover↗

DOE OSTI2021

Morphology engineering of iridium electrodes via modifying titanium substrates with controllable pillar structures for highly efficient oxygen evolution reaction

Nowadays, Ti is the well-chosen anode substrate material for proton exchange membrane electrolyzer cells (PEMECs) and modifications of the substrate surfaces are essential for the fabrication of highly efficient electrodes. Herein, we introduce the morphology engineering of Ir/Ti electrodes with different acid treatments of hydrochloric acid (HCl) and oxalic acid (OA), and the comparative benefits of these two acid treatment methods are studied from the aspects of their impacts on the morphology, interfacial contact resistance (ICR), and oxygen evolution reaction (OER) performances of resultant electrodes. Notably, compared to the flat surface from OA treatment, Ti substrates with the pillar structure could be successfully achieved via HCl etching. Further, the HCl and the oxalic acid (OA) treatments would reduce the interfacial contact resistance (ICR) to 15.2% and 5.5% of the pristine Ti substrate at 1.38 MPa, respectively. By iridium electrodeposition on Ti substrates, Ir/Ti electrodes with different catalyst loadings are fabricated. With similar low-loadings of about 0.05 mgIr cm –2 , an Ir/Ti electrode with HCl treated substrate exhibits a lower overpotential of ~283 mV at 10 mA cm –2 current density than 305 mV from OA treatment, due to the boosted reaction areas from HCl treatment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2026

Optimizing Porous Transport Layer Porosity for Proton Exchange Membrane Water Electrolysis

An empirical model is presented that describes anode-side losses related to porous transport layer (PTL) morphology in proton exchange membrane water electrolysis (PEMWE). The model is based on an advanced voltage breakdown analysis that links various overpotentials to PTL morphology. Custom Ti PTLs, spanning uncommonly low porosities (22 - 31%), were fabricated and analyzed with X-ray CT to obtain pore and particle size distributions. Particle size distributions were consistent across samples with an average particle diameter of 12.0?..mu..m, whereas average pore diameters ranged from 6.0 to 7.0?..mu..m. The PTLs were tested in standard PEMWE cell assemblies with anode catalyst loadings of 0.1 mgIr cm-2 to obtain polarization curves, electrochemical impedance spectra, and augmented Tafel analysis. The PTL-dependent anode side losses were deconvoluted and assigned to excess utilization, concentration, ion transport resistance, and electrical contact resistance overpotentials. The data and model reveal an optimal 20 - 28% PTL porosity region where utilization and contact resistance overpotentials are minimized without triggering concentration and ion transport losses related to water deprivation. The optimal PTL porosity depends on the operating current density and is demonstrated at realistic PEMWE water flow rates to establish PTL design guidance for operation at scale.

08 HYDROGEN↗