Nickel Structures as a Template Strategy to Create Shaped Iridium Electrocatalysts for Electrochemical Water Splitting

Abstract

Low-cost, highly active, and highly stable catalysts are desired for the generation of hydrogen and oxygen using water electrolyzers. To enhance the kinetics of the oxygen evolution reaction in an acidic medium, it is of paramount importance to redesign iridium electrocatalysts into novel structures with organized morphology and high surface area. Here, we report on the designing of a well-defined and highly active hollow nanoframe based on iridium. The synthesis strategy was to control the shape of nickel nanostructures on which iridium nanoparticles will grow. After the growth of iridium on the surface, the next step was to etch the nickel core to form the NiIr hollow nanoframe. The etching procedure was found to be significant in controlling the hydroxide species on the iridium surface and by that affecting the performance. The catalytic performance of the NiIr hollow nanoframe was studied for oxygen evolution reaction and shows 29 times increased iridium mass activity compared to commercially available iridium-based catalysts. Our study provides novel insights to control the fabrication of iridium-shaped catalysts using 3d transition metal as a template and via a facile etching step to steer the formation of hydroxide species on the surface. These findings shall aid the community to finally create stable iridium alloys for polymer electrolyte membrane water electrolyzers, and the strategy is also useful for many other electrochemical devices such as batteries, fuel cells, sensors, and solar organic cells.

Multistep Sulfur Leaching for the Development of a Highly Efficient and Stable NiSx/Ni(OH)2/NiOOH Electrocatalyst for Anion Exchange Membrane Water Electrolysis

“…The crystal information of Ni–S catalysts was studied by X-ray powder diffraction (D8 DISCOVER, Bruker) with a Cu K α target. The morphology, elemental distribution, and detailed structural information were studied by scanning transmission electron microscopy (STEM), and energy-dispersive X-ray (EDX) spectroscopy on a Titan 80-200 electron microscope (Thermo Fisher Scientific) with a probe corrector (CEOS) and a high-angle annular dark-field (HAADF) detector, and high-resolution transmission electron microscopy (HRTEM) on a Titan 80-300 electron microscope (Thermo Fisher Scientific). , The chemical valence states of Ni–S samples were studied by X-ray photoelectron spectroscopy (XPS, Phi5000 VersaProbeII, ULVAC-Phi Inc) with Al Kα as the monochromatic (1.486 keV) source . The catalysts for XRD and XPS were coated on the carbon paper (ca.…”

“…73,74 The chemical valence states of Ni−S samples were studied by X-ray photoelectron spectroscopy (XPS, Phi5000 VersaProbeII, ULVAC-Phi Inc) with Al Kα as the monochromatic (1.486 keV) source. 10 The catalysts for XRD and XPS were coated on the carbon paper (ca. 2.0 mg cm −2 ) by the drop-by-drop method with the same ink for RDE.…”

“…Water electrolysis is of great importance for mitigating the greenhouse gas effect and producing high-purity hydrogen. − However, proton exchange membrane water electrolysis (PEMWE) has been impeded by high stack cost and scarcity of platinum-group metal (PGM)-based catalysts, ,− while classic alkaline water electrolysis shows poor polarization performance due to low conductivity of porous diaphragms . Therefore, an anion exchange membrane (AEM), − combined with non-PGM catalysts, has been proposed as a scalable and cost-effective route for large-scale applications, yet still hindered by poor stability and low operating current density. − In particular, the kinetically sluggish oxygen evolution reaction (OER) slows down the overall anion exchange membrane water electrolysis (AEMWE), as it involves four electrons and must first break O–H and then overcome the formation energy of the O–O bond. − Therefore, it is needed to develop highly active, stable, and low-cost PGM-free OER catalysts for AEMWE.…”

Supported Iridium‐based Oxygen Evolution Reaction Electrocatalysts ‐ Recent Developments

“…[70,71] Therefore, different treatments (thermal vs electrochemical oxidation [31,72] ) or synthesis were studied to obtain the best activity/stability ratio for the material. [73,74] The second approach is to increase the number of active sites by optimizing the morphology of the catalyst (control of the shape [75] or morphology, [76] porous structure, [77] self-supported catalyst [78] ) or by the deposition of nanoparticles of the active material on a high-surface-area support. [79] Preferably, both strategies should be applied simultaneously, therefore increasing the number of active sites as well as their intrinsic activity.…”

Cation-Exchange Method Enables Uniform Iridium Oxide Nanospheres for Oxygen Evolution Reaction

“…In other words, controlling the shape of nanostructures can change the physical, chemical, and surface properties, which can improve intrinsic catalytic activity. Many types of nanostructures have been reported by various synthetic approaches, such as homogeneous nucleation, − seed-mediated growth, − galvanic replacement, − and others. − Using already prepared templates, − the design of nanostructures can be made more accurate. Moreover, the fabrication process can be better controlled by the separate synthesis procedure.…”