Abstract
Active and durable electrocatalysts for the oxygen evolution reaction (OER), capable of replacing noble metal catalysts, are required to develop efficient and competitive devices within the frame of the water electrolysis technology for hydrogen production. In this work, we have investigated tantalum based catalysts supported on carbon nanofibers (CNF) for the first time. The effect of CNF characteristics and the catalyst annealing temperature on the electrochemical response for the OER have been analyzed in alkaline environment using a rotating ring disc electrode (RRDE). The best OER activity and oxygen efficiency were found with a highly graphitic CNF, despite its lower surface area, synthesized at 700 °C, and upon a catalyst annealing temperature of 800 °C. The ordering degree of carbon nanofibers favors the production of oxygen in combination with a low oxygen content in tantalum oxides. The most active catalyst exhibited also an excellent durability.
Highlights
Hydrogen (H2) is widely considered as an ideal candidate to replace fossil fuels and solve the associated problems of pollution and a theoretical future energy crisis
Both carbon nanofibers (CNF) present a similar X-ray diffraction (XRD) pattern (Fig. S.1) with the characteristic peak for graphitic structures (002) at 2q 1⁄4 26 (CuKa), which corresponds to a value for lattice parameter c of around 6.8 Å and the signals for face-centered cubic (FCC) structure of Ni, mainly the peak at around 45 (111)
Nitrogen adsorption-desorption isotherms were obtained at À196 C (Fig. S.2) revealing a larger surface area (SBET) and mesopore volume for CNF600 (SBET 1⁄4 136 m2 gÀ1; VBJH 1⁄4 0.49 cm3 gÀ1) than for CNF700 (SBET 1⁄4 60 m2 gÀ1; VBJH 1⁄4 0.23 cm3 gÀ1), while micropore volume is negligible in both samples
Summary
Hydrogen (H2) is widely considered as an ideal candidate to replace fossil fuels and solve the associated problems of pollution and a theoretical future energy crisis. Different kinds of catalysts have been developed such as oxides and oxyhydroxides of transition metals (e.g. Mn, Co, Ni, Fe) alone or in combination with carbonaceous materials [14e21], and metal-free carbon-based electrocatalysts [22e24] These electrocatalysts present great benefits such as relatively low cost and high OER activity. Their main drawback is related to a poor corrosion and oxidation resistance, of carbonbased materials, which limits their use in a water electrolyzer. To overcome this problem, the design and development of durable and highly active transition metal-based electrocatalysts need to be studied. The effects of temperature in the CNF growth and the catalyst annealing have been studied in order to understand how they impact on the electrochemical response of the catalysts for the OER in alkaline environment
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