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/IrO(2)NFs) with diverse Ir and IrO2 relative composition ratios and their electrocatalytic HER activities. Highly porous Ir/IrO(2)NFs are simply synthesized via electrospinning and the following calcination at various temperatures (300-900 degrees C). Different calcination temperature alters the actual composition of Ir/IrO(2)NFs: The higher the temperature, the greater IrO2 content exists. The HER activity of Ir/IrO(2)NFs is examined in 1 M H2SO4. Ir/IrO2NF calcined at 300 degrees 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/IrO(2)NFs increases with a higher calcination temperature, the HER activity decreases. Ir/IrO2NF calcined at 900 degrees 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.