Abstract
The given research was driven by prospects to design Mo-rich coatings with iron group metals electrodeposited from a highly saturated ammonium acetate bath. The obtained coatings could be employed as prominent electrodes for the hydrogen evolution reaction (HER). It was found that the Mo content in Ni–Mo alloys can be tuned from 30 to 78 at.% by decreasing the molar ratio [Ni(II)]:[Mo(VI)] in the electrolyte from 1.0 to 0.25 and increasing the cathodic current density from 30 to 100 mA/cm2. However, dense cracks and pits are formed due to hydrogen evolution at high current densities and that diminishes the catalytic activity of the coating for HER. Accordingly, smoother and crack-free Ni–54 at.% Mo, Co–52 at.% Mo and Fe–54 at.% Mo alloys have been prepared at 30 mA/cm2. Their catalytic behavior for HER has been investigated in a 30 wt.% NaOH solution at temperatures ranging from 25 to 65 °C. A significant improvement of electrocatalytic activity with increasing bath temperature was noticed. The results showed that the sequence of electrocatalytic activity in alkaline media decreases in the following order: Co–52 at.% Mo > Ni–54 at.% Mo > Fe–54 at.% Mo. These peculiarities might be linked with different catalytic behavior of formed intermetallics (and active sites) in electrodeposited alloys. The designed electrodeposited Mo-rich alloys have a higher catalytic activity than Mo and Pt cast metals.
Highlights
Hydrogen is a clean fuel and an energy carrier that can be used for energy conversion and storage and is considered as a possible substitute for fossil fuels [1]
The ability of a given metal to catalyze the hydrogen evolution reaction (HER) is estimated based on the exchange current density (ECD), i.e., the current density in the absence of net electrolysis at zero overpotential
Where F is Faradays constant (96485 C); m is the weight of the electrodeposit (g); I is an applied current (A); t is the time of electrodeposition (s); xi, ni, Mi is the content, electrons transferred per ion, and molecular weight (g/mol) of Ni, Co or Fe, respectively; xMo, nMo, MMo is the content, wt.%, electrons transferred per particular ion, respectively; molecular weight of Mo
Summary
Hydrogen is a clean fuel and an energy carrier that can be used for energy conversion and storage and is considered as a possible substitute for fossil fuels [1]. A considerable part of research on the design of effective cathode materials for HER has been focused on Mo alloys with iron group metals (Ni, Co, Fe) due to their superior catalytic performance in alkaline media [3,4,5], stability at elevated temperatures [6] and reasonable corrosion and oxidation resistance [7,8,9,10]. In order to determine the influence of the nature of the iron group metal on the catalytic activity of target coatings (Ni-, Co- and Fe- Mo-rich alloys) the electrochemical conditions were tuned in such way to ensure deposition of alloys with similar content of Mo. The catalytic activity of the electrochemically fabricated Mo-based alloy electrodes for the HER was explored in a 30 wt.% NaOH solution. In order to compare the electrochemical activity with other typical electrode materials, experiments were performed using bare platinum electrode (same geometrical area) under the same conditions
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