Electrodeposited tungsten-rich Ni-W, Co-W and Fe-W cathodes for efficient hydrogen evolution in alkaline medium

Abstract

The search of active, stable and cost-effective non-noble electrocatalysts for hydrogen evolution reaction (HER) is essential for sustainable energy systems. In this study, the electrodeposited Ni-W, CoW and FeW coatings having 5e30 at.% of W were examined as an alternative electrocatalysts for hydrogen evolution. The electrocatalytic efficiency of the electrodes was investigated on the basis of electrochemical data obtained from steady-state polarization technique in 30 wt% NaOH solution. It was found that with increasing of tungsten content in the deposits up to ~30 at.% a crystal-to-ultra-nanocrystalline transition takes place and the crystal grain size decreases up to 2e4 nm. The high content of W leads to course-grained coatings. These morphological and structural changes showed remarkable impact on the catalytic activity. The maximum catalytic performance was obtained for ultra-nanocrystalline W coatings. Among them the Ni-29at.%W demonstrated the highest apparent exchange current density (ECD) at the room temperature, i.e. 0.55 mA cm À2 , thus indicating more favorable hydrogen reduction. A significant improvement of catalytic activity of all tested cathodes with increasing the temperature of NaOH solution was noticed. Among investigated Co-33at.%W, Fe-30at.%W and Ni-29at.%W cathodes, the last one showed the best performance towards HER (ECD ¼ 14.5 mA cm À2 at 65 C).

Tribocorrosion properties of nanocrystalline W-rich Co–W, Ni–W and Fe–W coatings

“…It is well known, that the broadening of the XRD peak is related to the refinement of the crystallite size that typically occurs with increasing the W content in the deposit. Indeed, the TEM analysis supported [5] that W-rich alloys have ultra-nanocrystalline structure composed of the grains with the size around 2-5 nm which is consistent with the grain size estimated from XRD results.…”

“…The mapping of elements, both iron group metal (Co, Ni, Fe) and W, indicated that metals are distributed almost evenly onto entire surface even at nanometric scale [5]. However, there are some regularly located spots with higher W amount.…”

“…The structure and crystallite size of the electrodeposited W-rich alloy coatings with Co, Ni and Fe was evaluated earlier by XRD analysis [5]. The broad peaks at 2θ ~ 43-44° which are characteristic to an "amorphous-like" structure were observed for Co-32W, Ni-29W and Fe-31W (in at.%) alloys.…”

“…Nanocrystalline W-rich alloys with iron group metals (Co, Ni, Fe) are of special interest in the materials science due to their enhanced strength, superior hardness [2,3] and corrosion resistance [4]. Furthermore, such alloys have become an important component in catalytic hydrogen evolution reaction [5], microelectromechanical systems (MEMS), for wear protection of cutting tools and for the reduction of friction in sliding parts [6].…”

The Influence of Sodium Tungstate Concentration on the Electrode Reactions at Iron–Tungsten Alloy Electrodeposition

“…Recently, electrochemical studies were concentrated preferentially on Fe alloys, whereas the use of Ni, Co and their salts were discouraged due to environmental and health issues. Thus, Fe-W alloys as "eco-friendly" deposits are investigated for multipurpose applications: protective coatings [8], recording media [9,10], catalysts [11], and fuel cells [12].…”