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

Abstract

Recently, IrV‐based perovskite‐like materials were proposed as oxygen evolution reaction (OER) catalysts in acidic media with promising performance. However, iridium dissolution and surface reconstruction were observed, questioning the real active sites on the surface of these catalysts. In this work, Sr2MIr(V)O6 (M=Fe, Co) and Sr2Fe0.5Ir0.5(V)O4 were explored as OER catalysts in acidic media. Their activities were observed to be roughly equal to those previously reported for La2LiIrO6 or Ba2PrIrO6. Coupling electrochemical measurements with iridium dissolution studies under chemical or electrochemical conditions, we show that the deposition of an IrOx layer on the surface of these perovskites is responsible for their OER activity. Furthermore, we experimentally reconstruct the iridium Pourbaix diagram, which will help guide future research in controlling the dissolution/precipitation equilibrium of iridium species for the design of better Ir‐based OER catalysts.

Identifying the Activation Mechanism and Boosting Electrocatalytic Activity of Layered Perovskite Ruthenate

“…Additionally, the Ru K‐edge X‐ray absorption fine structure (XAFS) spectra show the same pattern for SrRuO 3 before and after testing in both k and E spaces, implying the local structure keep almost unchanged (Figure 1C; and Figure S7A, Supporting Information). The structural stability confirmed the activation mechanism for SrRuO 3 in this system is unlike most of perovskites in oxygen evolution reaction (OER) process, where the continuously increased OER current is connected with the newly formed higher activity amorphous‐based heterostructure by the cation leaching from surface layer of perovskites during electrochemical testing . R‐space patterns display the characteristic peak for metallic Ru (around ≈2.3A, marked as pink vertical line) has been absent in SrRuO 3 before and after HER testing (Figure S7B, Supporting Information), indicating no Ru reduction occurs in the SrRuO 3 during HER testing.…”

Anodic Oxidation Enabled Cation Leaching for Promoting Surface Reconstruction in Water Oxidation

“…[1,2] To improve the sluggish reaction kinetics of OER, hence the overall efficiency for hydrogen production, recent research focuses on the development of earth-abundant transition metal oxides/ (oxy)hydroxides as electrocatalysts showing promising performances in alkaline conditions. [2][3][4][5][6][7][8][9] Ar ational design of catalysts can be guided by understanding their structural/elemental properties which determine the reaction mechanism and activity.Following pioneering work performed on the dimensionally stable anode (DSA) in the 70s [10] and 80s, [11,12] from 2011 onwards,s everal novel activity descriptors have been developed, [2,[13][14][15][16][17][18][19][20] such as electron occupancy, covalency, structure and exchange interaction for transition metal oxides which can be related to M-O binding energy.W hile several research works have reported the surface reconstruction for some very active materials, [21][22][23][24][25][26][27][28] it remains yet almost impossible to predict the activity of these materials based on their M-O binding energy as ac onsequence of the constantly evolving surface during OER. [29][30][31] Forinstance,the surface of Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3Àd (BSCF) [22,32,33] rapidly evolves into an amorphous oxyhydroxide after few cycles under OER conditions,t his process is accompanied by the leaching of soluble Ba 2+ and Sr 2+ ions, and the dissolution and redeposition of Co 3+ and Fe 3+ transition metal cations.…”

Ultrafine Defective RuO2 Electrocatayst Integrated on Carbon Cloth for Robust Water Oxidation in Acidic Media

“…However, the efficiency of such device is limited by high Ohmic resistance of alkaline electrolyte and low operating pressure. [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] Compared with iridium oxides, ruthenium oxides possess higher OER activity and lower cost, but lower stability. Unfortunately, the widespread application of PEM electrocatalysis is restricted by the lack of efficient and durable electrocatalysts for oxygen evolution reaction (OER) in acidic media.…”

“…Unfortunately, the widespread application of PEM electrocatalysis is restricted by the lack of efficient and durable electrocatalysts for oxygen evolution reaction (OER) in acidic media . Significant progresses made during the past decades have pointed out that ruthenium and iridium oxides are benchmarking catalyst at low pH . Compared with iridium oxides, ruthenium oxides possess higher OER activity and lower cost, but lower stability .…”