Electron Correlations Engineer Catalytic Activity of Pyrochlore Iridates for Acidic Water Oxidation

Abstract

The development of highly efficient oxygen‐evolving catalysts compatible with powerful proton‐exchange‐membrane‐based electrolyzers in acid environments is of prime importance for sustainable hydrogen production. In this field, understanding the role of electronic structure of catalysts on catalytic activity is essential but still lacking. Herein, a family of pyrochlore oxides R2Ir2O7 (R = rare earth ions) is reported as acidic oxygen‐evolving catalysts with superior‐specific activities. More importantly, it is found that the intrinsic activity of this material significantly increases with the R ionic radius. Electronic structure studies reveal that the increased R ionic radius weakens electron correlations in these iridate oxides. This weakening induces an insulator–metal transition and an enhancement of IrO bond covalency, both of which promote oxygen evolution kinetics. This work demonstrates the importance of engineering the electron correlations to rationalize the catalytic activity toward water oxidation in strongly correlated transition‐metal oxides.

Perovskite‐Type Solid Solution Nano‐Electrocatalysts Enable Simultaneously Enhanced Activity and Stability for Oxygen Evolution

“…, which is about thirty-nine times higher than that (39 A g Ir , [32][33][34][35][36][37][38][39][40] only three ones (including Irbased single-atom catalyst and nanostructured metallic Ir-based alloys) [29][30][31] exhibit higher iridium mass activity than SZIO. The results overall demonstrate that SZIO is among the most active Ir-based electrocatalysts for OER under acidic conditions.…”

“…As shown in Figure 2b, SZIO requires a lower overpotential (240 mV) to achieve 10 mA cm geo −2 current density than most of other previouslyreported Ir-containing oxygen evolution materials, including nanostructured metallic iridium-based catalysts [24][25][26][27][28][29][30][31] and oxidetype catalysts with various crystal structures. [18,[32][33][34][35][36][37][38][39] Besides the apparent catalytic activity, the iridium mass activity (evaluated at a potential of 1.53 V) of SZIO is also compared with the previously-reported, representative catalysts. As shown in Figure 2c, SZIO gives an iridium mass activity of 1540 A g Ir −1…”

Activating Inert, Nonprecious Perovskites with Iridium Dopants for Efficient Oxygen Evolution Reaction under Acidic Conditions

“…[3,4] As shown in Figure 3c,Ir-STO contains the least amount of iridium among these materials.T he iridium mass fraction of Ir-STOisonly 28 wt %, which is 57 wt %less than that of IrO 2 .F igure 3d shows the j Ir comparison of the iridium-based oxide catalysts,w hich reveals Ir-STO having the highest catalytic activity.F or instance,I r-STO gives an ultrahigh j Ir of 820 Ag Ir À1 ,which is 34 times as high as that of IrO 2 .T he j Ir of Ir-STO is 11 times higher than that of 6H-SrIrO 3 (a highly active perovskite catalyst reported previously) and is about 2.3 times as high as that of Pr 2 Ir 2 O 7 ,t he best pyrochlore catalyst. Thec omparison reveals that Ir-STO( 247 mV overpotential at 10 mA cm geo À2 ) is among the most active iridium-based oxide catalysts toward OER in acid, although there might be some differences in methods adopted by different researchers in their catalytic tests,s uch as catalyst loading, electrode fabrication, and electrolyte.W ef urther compare the iridium content and iridium mass activity of Ir-STO (normalized by mass of iridium, j Ir )with some recently published iridium-based oxide catalysts.…”

“…The Ir-STOc ontains 57 wt %l ess iridium relative to the benchmark catalyst IrO 2 ,b ut it exhibits more than 10 times higher catalytic activity for OER. [3,4] Despite recent efforts to explore low-iridium OER electrocatalysts working in acid, the progress is quite slow. Theoretical results reveal that the incorporation of iridium dopants in the STOm atrix activates the intrinsically inert titanium sites,s trengthening the surface oxygen adsorption on titanium sites and therebyg iving nonprecious titanium catalytic sites that have activities close to or even better than iridium sites.…”

“…[1] Thes tate-of-the-art electrocatalysts mainly include iron, cobalt, nickel-based bi-/multi-metallic (hydro)oxides with various types of crystalline/amorphous structures. [3,4] Despite recent efforts to explore low-iridium OER electrocatalysts working in acid, the progress is quite slow. At present, iridium-based metal oxides,such as IrO 2 ,a re still the only OER electrocatalysts with reasonable activity and stability in acid.…”