Crystalline ZnO and ZnO / TiO ₂ nanoparticles derived from tert ‐butyl N‐(2 mercaptoethyl)carbamatozinc( II ) chelate: Electrocatalytic studies for H ₂ generation in alkaline electrolytes

Abstract

Summary A newly synthesized zinc(II) complex, namely tert‐butyl N‐(2 mercaptoethyl)carbamatozinc(II) complex [Zn(Boc‐S)2] (Boc = tert‐butyl N‐[2‐mercaptoethyl]carbamate), has been used as an organozinc precursor for the production of crystalline ZnO and ZnO/TiO2 nanoparticles. The synthesized complex and the obtained nanomaterials were fully characterized using various spectroscopic and surface analysis techniques. Their surface morphology, chemical purity and stoichiometry have been investigated by scanning electron microscopy (SEM), energy dispersive X‐ray analysis (EDX) as well as X‐ray fluorescence. The synthesized Zn(II) molecular complex, ZnO and ZnO/TiO2 nanomaterials have been tested in alkaline aqueous solution (1.0 MNaOH) for the hydrogen evolution reaction (HER) using various electrochemical techniques. The results revealed high HER catalytic performance of ZnO and ZnO/TiO2 cathode materials, with the latter exhibiting higher catalytic activity recording an exchange current density (jo) of 0.3 mA cm−2. This current value, which approaches that of Pt wire (0.5 mA cm−2), cross‐sectional area ~0.008 cm2, is about 11 and 100 times greater than those measured for ZnO alone (0.028 mA cm−2) and TiO2 alone (0.0032 mA cm−2), respectively. Moderate catalytic activity was recorded for the complex catalyst, namely GC‐Zn(Boc‐S)2 with jo value of (0.01 mA cm−2). Tafel slope values of 130 and 122 mV dec−1 were calculated for ZnO and ZnO/TiO2, respectively. Such Tafel slope values, which are close to that of the Pt wire (120 mV dec−1), referred to a Volmer‐controlled HER kinetics. Other important electrochemical parameters describing the kinetics of the HER, such as roughness factor (Rf) and turnover frequency (TOF) were also estimated and discussed. The high numerical values of the various HER kinetic parameters recorded for the ZnO/TiO2 catalyst, in addition to its high stability and durability (stable for up to 10 000 continuous cathodic polarization cycles), besides maintaining its morphology and chemical composition after stability test (confirmed from SEM/EDX and XRD examinations), located it in a privileged position among the most efficient HER electrocatalysts reported in the literature.

Enhanced Alkaline Hydrogen Evolution on Gd1.0/Ndx (x = 0.5, 1.0, 3.0, and 6.0%)-Doped TiO2 Bimetallic Electrocatalysts

“…The Kubelka-Munk equation αhν = A(hν −E g ) 2 , where α, h, ν, and E g and A are the absorption coefficient, Plank constant, light frequency, band gap, and the proportionality constant, respectively, was used for band gap determination, Figures 11 and 12. For pure TiO 2 , a band gap energy of 3.18 eV was determined, which is in accordance with that of other reports [52][53][54], while for RE-doped TiO 2 , the band gap energy decreased due to the red-shift of absorbance (see Figures 11 and 12 and Table 9), suggesting that gadolinium and neodymium improved the visible light absorbance of TiO 2 .…”

“…Catalysts 2023, 13, x FOR PEER REVIEW 14 of 2 determined, which is in accordance with that of other reports [52][53][54], while for RE-doped TiO2, the band gap energy decreased due to the red-shift of absorbance (see Figures 11 and 12 and Table 9), suggesting that gadolinium and neodymium improved the visible light absorbance of TiO2. Catalysts 2023, 13, x FOR PEER REVIEW 14 of 26 determined, which is in accordance with that of other reports [52][53][54], while for RE-doped TiO2, the band gap energy decreased due to the red-shift of absorbance (see Figures 11 and 12 and Table 9), suggesting that gadolinium and neodymium improved the visible light absorbance of TiO2. 13a presents the cathodic polarization plots of our synthesized catalysts, namely, Gd x /TiO 2 and Nd x /TiO 2 with various RE doping percentages (0.5, 1, 3, and 6%).…”

Enhancing the Electrical and Photoelectrical Efficacy with the Synergistic SrO–ZnO Nano‐Heterosystem

“…While ZnO as an isolatory oxide had the Tafel slope of 130 mV dec À1 . [68] The Tafel slopes obtained for SrO-ZnO nanocomposite and ZnO/ TiO 2 have a closer proximity with the Tafel slope value of the commercially used Pt wire, i.e., 120-130 mV dec À1 . These values reveal the Volmer-Heyrovsky type of the HER kinetics for SrO-ZnO nanocomposite resulting in an excellent pure H 2 generation.…”

Cathodic Activation of Titania-Fly Ash Cenospheres for Efficient Electrochemical Hydrogen Production: A Proposed Solution to Treat Fly Ash Waste

“…Table S1: Comparison of HER activity of our synthesized FA-TiO2 catalyst (before and after cathodic activation*) with Pt/C and some other, highly effective titania and titania-based electrocatalysts reported in the literature. References [10,11,[51][52][53][54][55][56][57][58][59][60][61][62] are cited in the Supplementary Materials.…”