Iridium Oxide Coatings with Templated Porosity as Highly Active Oxygen Evolution Catalysts: Structure‐Activity Relationships

Abstract

Iridium oxide is the catalytic material with the highest stability in the oxygen evolution reaction (OER) performed under acidic conditions. However, its high cost and limited availability demand that IrO2 is utilized as efficiently as possible. We report the synthesis and OER performance of highly active mesoporous IrO2 catalysts with optimized surface area, intrinsic activity, and pore accessibility. Catalytic layers with controlled pore size were obtained by soft-templating with micelles formed from amphiphilic block copolymers poly(ethylene oxide)-b-poly(butadiene)-b-poly(ethylene oxide). A systematic study on the influence of the calcination temperature and film thickness on the morphology, phase composition, accessible surface area, and OER activity reveals that the catalytic performance is controlled by at least two independent factors, that is, accessible surface area and intrinsic activity per accessible site. Catalysts with lower crystallinity show higher intrinsic activity. The catalyst surface area increases linearly with film thickness. As a result of the templated mesopores, the pore surface remains fully active and accessible even for thick IrO2 films. Even the most active multilayer catalyst does not show signs of transport limitations at current densities as high as 75 mA cm(-2) .

Combining theory and experiment in electrocatalysis: Insights into materials design

“…All surfaces studied among these broad classes of metal oxide materials were found to obey a scaling relation between OOH* and OH* that is not ideal (ΔG OOH = ΔG OH + 3.2 ± 0.2 eV), similar to the case of metals investigated for the ORR, again hindering the development of a catalyst with zero theoretical overpotential (109). For OER catalysis in acid, IrO 2 is a reasonably active metal oxide catalyst, and theory has helped to explain why based on reasonable binding energies to reaction intermediates (113)(114)(115)(116)(117). Although this catalyst has indeed been shown experimentally to be among the better OER catalysts today based on activity and stability under reaction conditions, it is far from an ideal OER catalyst activity and is not completely stable under high oxidative potentials (65,105,118).…”

Future Challenges in Heterogeneous Catalysis: Understanding Catalysts under Dynamic Reaction Conditions

“…A deeper understanding must therefore be an integral part of new approaches to design improved catalysts. This includes in particular transient concentration profiles under fluctuating operation conditions,130 as well as synthesis methods with improved structural control over pore systems131, 132 and particle properties 132, 133…”

Electro‐Oxidation of Ni42 Steel: A Highly Active Bifunctional Electrocatalyst

“…Generally very few metal oxides can survive under oxidative potentials in acidic regimes [92] and metal oxide based catalysts have very rarely been checked for catalytic activity under both, alkaline and acidic conditions. Again Rutile type IrO 2 and RuO 2 seem to be the material of choice when good water splitting properties are desired at low (<< 7) and high (>>7) pH values [93,94,92,95,96] . In terms of the overall OER activity and stability under acidic catalysis conditions IrO 2 is considered as the best compromise [96] .…”