A Dissolution/Precipitation Equilibrium on the Surface of Iridium‐Based Perovskites Controls Their Activity as Oxygen Evolution Reaction Catalysts in Acidic Media

Abstract

Recently,I r V -based perovskite-like materials were proposed as oxygen evolution reaction (OER) catalysts in acidic media with promising performance.H owever,i ridium dissolution and surface reconstruction were observed, questioning the real active sites on the surface of these catalysts.In this work, Sr 2 MIr (V) O 6 (M = Fe,Co) and Sr 2 Fe 0.5 Ir 0.5 (V) O 4 were explored as OER catalysts in acidic media. Their activities were observed to be roughly equal to those previously reported for La 2 LiIrO 6 or Ba 2 PrIrO 6 .C oupling electrochemical measurements with iridium dissolution studies under chemical or electrochemical conditions,w es howt hat the deposition of an IrO x layer on the surface of these perovskites is responsible for their OER activity.F urthermore,w ee xperimentally reconstruct the iridium Pourbaix diagram, whichw ill help guide future researchi nc ontrolling the dissolution/precipitation equilibrium of iridium species for the design of better Irbased OER catalysts.The electrochemical production of hydrogen fuel by water splitting has long been explored as ap otential way to store clean and renewable energy.T he key challenge for water splitting lies in improving the efficiency of the kinetically slow, rate-limiting oxygen evolution reaction (OER) (2 H 2 O! 4H + + O 2 + 4e À ). [1,2] While alarge variety of transition metal oxides have been studied as promising OER catalysts in alkaline media, [3][4][5][6] thedesign of active and stable catalysts in acidic media has proven challenging. [7][8][9][10][11] Thef ew materials established as suitable OER catalysts in acidic media are mostly Ir-based metal oxides,such as rutile IrO 2 , [12,13] 14] or more recently Ni-substituted IrO x . [15][16][17] Recently,Ir-based perovskites have been reported as promising candidates in acidic media. [18][19][20] Thehigh OER activity of these Ir-based perovskites was ascribed to the formation of electrophilic O (IÀ) surface species favoring the nucleophilic attack of water. [11,20,21] However,dissolution of iridium, alkali and/or rare earth elements in acidic electrolytes has been observed after close examinations of some Ir V -based perovskites,such as La 2 LiIr (V) O 6[20] and Ba 2 PrIr (V) O 6 , [7,19] indicating their drastic structural instabilities in harsh acidic conditions. [12] Furthermore,the presence of IrO 2 nanoparticles was revealed on the surface of La 2 LiIr (V) O 6 after cycling. [8] Given this array of observations,alegitimate question arises over the origin of the OER activity on the surface of these perovskites.Therefore,itisimportant to understand the OER mechanism of these Ir V -based perovskites,aswell as the effect of iridium dissolution on their catalytic behaviors,inorder to improve their performances and/or guide future research in designing new active and stable OER catalysts in acidic media.We herein investigate the catalytic behaviors of three Ir Vbased OER catalysts in acidic media, Sr 2 MIr (V) O 6 (M = Fe, Co) with ad ouble perovskite structure and Sr 2 Fe 0.5 Ir 0.5 (V) O 4 with a...

Utilizing ion leaching effects for achieving high oxygen-evolving performance on hybrid nanocomposite with self-optimized behaviors

“…Based on prior studies 5,8,18,[21][22][23][24]34,35 , we propose the possible basic models for the variations of electrocatalyst surface triggered by ion leaching effects during OER in alkaline solutions here.…”

Strategies to Break the Scaling Relation toward Enhanced Oxygen Electrocatalysis

“…157 For OER, these catalysts can be oxidized and self-reconstructed into amorphous hydrous oxide phases of unknown stoichiometries at the operating potentials. 143,[158][159][160][161][162] Understanding of the reasons for their insufficient stability and mitigation of such activity loss deserves more research attention. In addition, stability tests are often performed on electrodes with a high catalyst loading and tested at constant current over a period of time; if the measured potential change is minimal, it is considered stable.…”

Amorphization mechanism of SrIrO 3 electrocatalyst: How oxygen redox initiates ionic diffusion and structural reorganization

“…The current picture is that the transformation process involves the collapse of the pristine structure and the reformation of Ir compounds, for example, segregated Ir oxides/hydroxides (16,21) associated with higher degrees of disorder (6). This amorphization could originate from a direct metal dissolution or electrochemically from the close proximity of the O p-band to the Fermi level (16,22). In the latter mechanism, the lattice oxygen redox can be activated, leading to the lattice oxygen activation, a process that allows the lattice oxygen to directly participate in the electrochemical reaction.…”