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 ultrafine 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)).