Low Ir-content Ir/Fe@NCNT bifunctional catalyst for efficient water splitting

Abstract

In order to reduce the cost of electrocatalysts and increase the exposure of the Ir active sites while ensuring the stability of the catalyst, a N-doped carbon nanotube (NCNT) is applied as a conductive support to confine the Ir clusters for avoiding them growing up via a modified method based on pyrolysis of a mixture of melamine, ferric chloride and iridium trichloride. It is found that Ir species in the as-obtained Ir(20)/[email protected] composite exist in two forms, Ir nanoclusters (1–2 nm) dotted on the wall of NCNT and the Ir atomically scattered on the Fe nanoparticles wrapped in the NCNT. Although the Ir content of Ir(20)/[email protected] is extremely low (∼4 wt% Ir), the composite catalyst delivers excellent activity for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) with an exceptionally low overpotential of 4.7 mV/11 mV for HER and 300 mV/270 mV for OER to drive 10 mA cm−2 in 0.5 M H2SO4/1.0 M KOH electrolyte respectively, which exceeds the commercial Pt/C (20 wt% Pt) and IrO2 benchmarks. In addition, it has much higher mass activity for OER at 1.55 V (1.78 A mg−1Ir) than those of the referenced catalysts in acid. The cell voltage of the two-electrode system assembled by Ir(20)/[email protected] for total water splitting in acidic and alkaline media are only 1.520 V and 1.510 V to afford 10 mA cm−2 separately, lower than that of Pt/C||IrO2 and with a good stability. Our work provides a construction method of low-content precious metal composite catalysts which can be applied in OER and overall water splitting field.