Trifunctional iridium-based electrocatalysts for overall water splitting and Zn-air batteries

Abstract

• 3%IrO x /NCNT shows an ultra-low overpotential of 8 mV for HER. • 3%IrO x /NCNT exhibits an ultra-low overpotential of 241 mV for OER. • 3%IrO x /NCNT can deliver overall water splitting current density of 10 mA•cm −2 at 1.487 V. • 3%IrO x /NCNT-based Zn-air battery exhibits a peak power density of 59.3 mW cm −2 . • The cooperation effect between IrO 2 and NCNT promotes these reactions. Abstract Development of high-efficiency multifunctional catalysts is pivotal to cut down the fabricating cost and complicacy of energy conversion and storage devices. Here, we fabricate ultrafine iridium-based nanoparticles onto nitrogen-doped carbon nanotubes (IrO x /NCNT) for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). As a representative sample, the 3%IrO x /NCNT with 2.82 wt% Ir loading exhibits superior electrocatalytic HER activity, showing ultra-low overpotentials of 8 mV, 35 mV, 44 mV, and 82 mV at 10 mA•cm −2 in 0.5 M H 2 SO 4 , 1 M KOH, 0.1 M KOH, and 1 M PBS (pH =7), respectively. Additionally, it shows outstanding OER performance with low overpotentials of 241 mV, 285 mV, and 376 mV at 10 mA•cm −2 in 1 M KOH, 0.5 M H 2 SO 4 , and 1 M PBS, respectively. Due to excellent multifunctional properties, it can be used for overall water splitting, showing potentials of 1.487 V, 1.523 V, and 1.854 V to reach 10 mA•cm −2 in 0.5 M H 2 SO 4 , 1 M KOH, and 1 M PBS, respectively. In addition, the 3%IrO x /NCNT-based Zn-air battery displays a maximal power density of 59.3 mW cm −2 . The IrO x should be the main active site for HER, OER and ORR, while cooperation mechanisms between IrO x and NCNT facilitate these reactions. TOC Ultrafine iridium oxide supported onto nitrogen-doped carbon nanotubes exhibits trifunctional HER, OER and ORR performance due to the synergistic effect between IrO 2 and NCNT.