A Highly Active, Long‐Lived Oxygen Evolution Electrocatalyst Derived from Open‐Framework Iridates

Abstract

active phase thanks to potential-driven redox reactions and/or corrosive electrolyte-induced component change. This reconstruction phenomenon is widely observed in electrocatalysts, ranging from metals and alloys [11][12][13] to (hydr)oxides [14][15][16][17][18] and non-oxides (e.g., chalcogenides and borides). [19][20][21] It has become a common understanding that the primitive structure of pre-electrocatalyst is not the same as that in the final active phase, [14][15][16] but it is necessarily to determine reconstruction process and the outcome during electrocatalysis. Therefore, understanding structural transformation of electrocatalysts and revealing initial structure-active phase relationship have been attractive issues. And moreover, designing suitable preelectrocatalysts to produce high-performance catalytic active phases is far from straightforward due to the complexity and unpredictability of electrochemical reconstruction process.One of the most prominent examples is the perovskite-type strontium iridate (i.e., SrIrO 3 ), a pre-electrocatalyst that in situ forms amorphous IrO x H y active phase with excellent electrocatalytic activity in acid for the oxygen evolution reaction (OER). [14] Inspired by this pioneering work, a number of perovskite-type iridates with a variety of crystal structures and compositions have been explored as oxygen evolution (pre)electrocatalysts. [14][15][16] In addition, some non-perovskite iridates, including pyrochlore, fluorite, and P2-layered structures, have also been studied recently. [22][23][24][25] These iridates, like perovskite SrIrO 3 , also generate amorphous IrO x H y active phases during OER in acid, although local microstructures of these amorphous active phases may be quite different and strongly dependent on the crystal structures and defects of initial iridates as well as their preparation history. The recently developed iridates-derived electrocatalysts with amorphous active phases generally exhibit more than ten times higher activity, yet worse structural stability (or more serious iridium leaching) than crystalline IrO 2 nanocatalyst. And the majority of them only retain the high catalytic activity for less than 50 h under electrocatalysis conditions. Hence, it would be desirable to explore new iridate (pre-)electrocatalysts that can evade the crystalline-to-amorphous phase transformation in traditional ones, and thereby realize the simultaneous improvement of catalytic activity and lifetime.Herein, we report, for the first time, the phase-selective synthesis of a metastable, open-framework strontium iridate The acidic oxygen evolution reaction underpins several important electricalto-chemical energy conversions, and this energy-intensive process relies industrially on iridium-based electrocatalysts. Here, phase-selective synthesis of metastable strontium iridates with open-framework structure and their unexpected transformation into a highly active, ultrastable oxygen evolution nano-electrocatalyst are presented. This transformation involves two major ste...

Structurally Robust Honeycomb Layered Strontium Iridate as an Oxygen Evolution Electrocatalyst in Acid

“…The slope is ≈ −60 mV pH –1 , which approximates to the value of IrO 2 . This implies that the oxygen generation follows an adsorbate evolution mechanism (AEM) at Ir sites of SrIr 2 O 6 , which undergoes a proton-coupled electron transfer (PCET) process involving the conversion of HO*, O*, and HOO* reaction intermediates. − We further carried out in situ differential electrochemical mass spectrometry (DEMS), coupling with the 18 O isotope-labeling experiment (see details in the Supporting Information). The ratio of 34 O 2 / 32 O 2 in the gaseous product is 0.45% (Figure g), when using the 18 O-labeled SrIr 2 O 6 to electrocatalyze OER in the H 2 16 O electrolyte.…”

Engineering Iridium-Based Oxygen Evolution Reaction Electrocatalysts for Proton Exchange Membrane Water Electrolyzers

“…In 2016, the Jaramillo group reported a novel IrO x /SrIrO 3 catalyst with high catalytic ability for OER, which was activated by leaching of Sr from the surface of SrIrO 3 thin films during an electrochemical process . Since then, numerous Ir-based perovskite oxides have been explored with the aim of reducing Ir loading, as well as improving mass activity and stability. − Zou’s group first reported the phase-selective synthesis of strontium iridate (γ-SIO) with a metastable open framework and deployed it as an OER precatalyst (Figure a,b) . Compared with the aforementioned pre-electrocatalyst (SrIrO 3 ) with a dense structure, γ-SIO achieved complete protonation in an acid medium and maintained the integrity of its unique open framework structure, exhibiting excellent catalytic ability (η 10 , 200 mV) and impressive stability with stable output of 10 mA cm –2 over 1000 h in 0.1 M HClO 4 (Figure c).…”

“…(c) Polarization curves of H-γ-SIO-1, β-SIO and α-SIO. Reproduced with permission ref . Copyright 2023 Wiley.…”

“…130−134 Zou's group first reported the phase-selective synthesis of strontium iridate (γ-SIO) with a metastable open framework and deployed it as an OER precatalyst (Figure 9a,b). 130 Compared with the aforementioned pre-electrocatalyst (SrIrO 3 ) with a dense structure, γ-SIO achieved complete protonation in an acid medium and maintained the integrity of its unique open framework structure, exhibiting excellent catalytic ability (η 10 , 200 mV) and impressive stability with stable output of 10 mA cm −2 over 1000 h in 0.1 M HClO 4 (Figure 9c). To further explore the immersion and evolution mechanism, a series of Sr 2 MIrO 6 (Ca, Mg, Zn) perovskites were prepared by Rojas et al, among which Sr 2 CaIrO 6 exhibited the best catalytic performance.…”

Pyridine functionalized silver nanosheets for nitrate electroreduction

“…Currently, various noble-metal-based electrocatalysts such as Rh, Ir, Pd, Ru, and Pt have been developed for different energyrelated reactions. [22][23][24][25][26][27][28][29][30] Among them, Ag based nanostructures have emerged as a potential catalyst for NO 3 RR due to the good chemical stability, the low HER activity, unique electronic structure and relatively low price. 31,32 However, pure Ag electrocatalysts still face limitations in terms of unsatisfactory electroactivity due to the weak adsorption ability of nitrogencontaining intermediates on their surface.…”