Insights into active species of ultrafine iridium oxide nanoparticle electrocatalysts in hydrogen/oxygen evolution reactions

Heteroatom doping is a potent strategy to regulate electronic structures and improve electrocatalytic performances, which has been extensively applied in fabricating carbon-based composite catalysts. Here, we report an ultrafine iridium oxide supported on boron-doped carbon nanotubes with rich defects for high-efficiency hydrogen/oxygen evolution reactions and overall water splitting at all pH values. Theoretical study shows that the excellent OER and HER activities of ultrafine IrO₂ nanoparticles can be attributed to their enhanced redox abilities comparing to those of bulk IrO₂ catalysts. Under OER conditions, the O-excessive surface of ultra-fine IrO₂ nanoparticles weakens the binding strengths of oxygenated species, leading to enhanced OER activity. Under HER conditions, the surface of the IrO₂ nanoparticle will be reduced to an intermediate state between Ir oxide and Ir metal, which greatly enhances the H binding energy and thus improves HER activity (even higher than Pt(1 1 1)).