Comparative Study on Hydrogen Evolution Reaction Activity of Electrospun Nanofibers with Diverse Metallic Ir and IrO₂ Composition Ratios

Hydrogen evolution reaction (HER) is of importance in energy conversion processes. This paper reports the facile synthesis of iridium/iridium oxide nanofibers (Ir/IrO₂NFs) with diverse Ir and IrO₂ relative composition ratios and their electrocatalytic HER activities. Highly porous Ir/IrO₂NFs are simply synthesized via electrospinning and the following calcination at various temperatures (300-900 °C). Different calcination temperature alters the actual composition of Ir/IrO₂NFs: The higher the temperature, the greater IrO₂ content exists. The HER activity of Ir/IrO₂NFs is examined in 1 M H₂SO₄. Ir/IrO₂NF calcined at 300 °C exhibits the best HER activity in terms of the onset potential, overpotential generating 50 mA cm^-2, turnover frequency, Tafel slope along with the decent stability for 5 h; the HER performance of this material even exceeds that of platinum, a benchmark HER catalyst. As the IrO₂ content in Ir/IrO₂NFs increases with a higher calcination temperature, the HER activity decreases. Ir/IrO₂NF calcined at 900 °C consists of only IrO₂ and presents the worst activity. DFT calculations show that hydrogen atom adsorption on metallic Ir (not IrO₂) resembles that on Pt: similar adsorption energy and adsorbate-substrate distance. Both the experimental and theoretical results clearly demonstrate that metallic Ir rather than IrO₂ is a good HER catalytic platform.