A newly synthesized single crystal zinc complex as molecular electrocatalyst for efficient hydrogen generation from neutral aqueous solutions |
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Authors: | Mohammed A. Amin Mohamed M. Ibrahim Adil A. Gobouri Gaber A.M. Mersal Nasser Y. Mostafa Tariq Altalhi Salih Al-Juaid |
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Affiliation: | 1. Chemistry Department, Faculty of Science, Taif University, 888 Hawiya, Saudi Arabia;2. Chemistry Department, Faculty of Science, Ain Shams University, 11566 Abbassia, Cairo, Egypt;3. Chemistry Department, Faculty of Science, Kafrelsheikh University, Kafr El-Sheikh 33516, Egypt;4. Chemistry Department, Faculty of Science, South Valley University, Qena, Egypt;5. Chemistry Department, Faculty of Science, Suez Canal University, Egypt;6. Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia |
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Abstract: | A new chlorobis(2-aminomethylbenzimidazole)zinc(II) perchlorate complex [Zn(AMB)2Cl](ClO4) 1 has been synthesized and characterized. Spectral and X-ray structural features led to the conclusion that the zinc(II) complex has a square-pyramidal environment around zinc(II) center with coordination chromophore ZnN4Cl. Different amounts of complex 1 were supported on glassy carbon (GC) electrode yielding three GC-supported complex 1 electrodes with different loading densities (0.2, 0.4, and 0.8 mg cm?2). These electrodes were tested as molecular electrocatalysts for the hydrogen evolution reaction (HER) in phosphate buffer aqueous solutions (pH 7), employing linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). Results showed that GC-complex 1 catalysts are highly active for the HER, and this catalytic activity enhances with the loading density. The one with the highest loading density (0.8 mg cm?2) exhibited high HER catalytic activity with low onset potential of ?140 mV vs. RHE and a high exchange current density of 0.22 mA cm?2. It required an overpotential of 240 mV to achieve a current density of 10 mA cm?2. It also recorded a turnover frequency (TOF) of 1722 mol of hydrogen per mole of catalyst per hour at overpotential 500 mV, which is comparable with the most active molecular electrocatalysts reported in the literature for H2 generation from aqueous neutral solutions. A catalytic cycle is proposed for the generation of hydrogen by complex 1 and the mechanism of the HER is discussed based on the measured Tafel slope (140 mV dec?1). |
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Keywords: | Electrocatalysis Hydrogen evolution reaction Single crystal zinc complex Glassy carbon electrode |
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