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.
Bibliographical noteFunding Information:
This research was supported by the National Research Foundation of Korea (NRF) grant funded by the Ministry of Science, ICT and Future Planning (NRF-2017R1A2A2A1400-1137 and 2016R1D1A1B03934962) and by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2018R1A6A1A03025340).
Copyright © 2019 American Chemical Society.
- DFT calculation
- Hydrogen evolution reaction
- Iridium metal
- Iridium oxide