Improved Durability of Highly Active IrO x Electrodes for Electrocatalytic Oxygen Evolution Reaction

Hydrated iridium oxide (IrO x · n H 2 O)–based materials exhibit high catalytic activity for electrochemical oxygen evolution reaction (OER) over a wide pH range of the electrolytes, but suffer from a drawback of low durability. Previous heat treatments traded off the activity against the durability. In the present study, we broke this trade-off relation by vacuum heat treatments at low temperatures (40–80 °C). The non-treated IrO x electrode using a glass substrate covered with F-doped SnO 2 initially yielded a high OER current density at a given applied potential in an electrolyte of near-neutral pH, however, followed by a rapid decrease in the current density because of detachment of the IrO x particles. The vacuum heat treatments up to 80 °C significantly suppressed the degradation with maintaining high current densities. SEM observations and XRF analyses confirmed a reduction in the detachment of the IrO x particles. Infrared absorption spectroscopy measurements revealed a decrease in the amount of hydrated water and hydroxyl groups surrounding the IrO x particles with increasing treatment temperature, suggesting the important roles of these species on the inter-particle binding force and OER activity. The IrO x /FTO electrodes vacuum-heat-treated under the optimal condition of 60 °C for 6 h exhibited only a slight increase in the applied potential during a chronopotentiometry measurement at a current density of 5 mA cm –2 over 100 h. Graphical Abstract