Reduction of Iridium Loading to the Minimum Level Required for Water Oxidation Electrocatalysis without Sacrificing the Electrochemical Stability

Abstract

Iridium­(Ir)-based electrocatalyst exhibits an optimal trade-off between catalytic activity and stability and thus is considered one of the most promising candidates in acidic water oxidation electrocatalysis. Due to its cost and scarcity, however, the sparing use of it has become the top priority in this field. In this contribution, we demonstrate the immense potential of coaxial arc plasma deposition (APD) as catalyst coating technology for water oxidation. Taking advantage of controllable pulsed plasma generation with high kinetic energy, APD enables the rigid coating of uniform and ultrathin Ir films on the substrate surface. The strong anchoring propensity of the films is observed, and thereby, unless the Ir loading is too little to overcome the catalyst loss and dissolution caused during repetitive electrochemical redox cycling for full electrocatalyst activation, the electrocatalytic performance of the films remains unaffected even after thousands of cyclic water oxidation testing. In this regard, we scrutinize the threshold Ir loading required to elude the entire loss of catalyst and report the threshold value as a result of an analytic investigation into the correlation between the number of APD shots and the resulting mass of the iridium loading.

Iridium oxide fabrication and application: A review

“…Not only electrodes made of iridium but also electrodes coated with iridium can act as precursors and can be activated [114] . In the latter case, the following preparative route can be adopted to prepare the iridium coating: atomic layer deposition, arc plasma deposition, e-beam processing, electrodeposition, sol-gel, sputtering (RF sputtering, DC magnetron sputtering), the reduction of iridium oxide by heat and hydrogen, etc.…”

Substituent Effects on the Activity of Cp*Ir(pyridine-carboxylate) Water Oxidation Catalysts: Which Ligand Fragments Remain Coordinated to the Active Ir Centers?

“…In the vast realm of known WO catalysts (WOCs), significant progress has been recently made in the exploitation of base metals (e.g., Fe, Co, and Ni); − yet, the performance of noble metal systems (e.g., Ru and Ir) − still appears more promising, especially in terms of durability. This is why many research groups have engaged in the development of molecular, − heterogenized, ,− and heterogeneous − WOCs following a “noble-metal atom economy” approach . Despite the noticeable progress over the last decade, however, catalytic performance is still far from that desirable for commercial application.…”

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

“…7−10 For this reason, IrO 2 is still regarded as the benchmark catalyst for oxygen evolution under acidic conditions. [11][12][13][14][15][16][17][18][19]53 Besides, not many publications were found to report a significant reduction of the noble metal amount, simultaneously boosting the electrocatalytic performance of iridium catalysts. 20−24 One route is the fabrication of hollow nanostructures 25−30 that allows a much larger surface area available for the reaction compared to conventional nanoparticles.…”

“…There have been extensive research initiatives attempting to develop cost-efficient electrocatalysts that can be used in various electrochemical energy storage and conversion devices such as fuel cells, batteries, and photocatalytic conversion reactors. , For PEM water electrolyzers, much fewer catalysts alternatives that can replace or at least effectively reduce the amount of iridium exist. To date, RuO 2 and IrO 2 have still shown the highest activity for the oxygen evolution reaction in acidic media, but RuO 2 is far less stable than IrO 2 as it undergoes strong dissolution over time. − For this reason, IrO 2 is still regarded as the benchmark catalyst for oxygen evolution under acidic conditions. − , Besides, not many publications were found to report a significant reduction of the noble metal amount, simultaneously boosting the electrocatalytic performance of iridium catalysts. − One route is the fabrication of hollow nanostructures − that allows a much larger surface area available for the reaction compared to conventional nanoparticles. − These hollow structures are thought to facilitate ion movement toward the electrolyte, promoting reaction kinetics. Many hollow nanostructures ranging from 1D to 3D have been introduced, but not much effort has been made to design hollow structures based on iridium that is expected to exhibit high catalytic activity.…”