Electrochemical growth of CoNi and Pt–CoNi soft magnetic composites on an alkanethiol monolayer-modified ITO substrate

Abstract

CoNi and Pt-CoNi magnetic layers on indium-tin oxide (ITO) substrates modified by an alkanethiol self-assembled monolayer (SAM) have been electrochemically obtained as an initial stage to prepare semiconducting layer-SAM-magnetic layer hybrid structures. The best conditions to obtain the maximum compactness of adsorbed layers of dodecanethiol (C12-SH) on ITO substrate have been studied using contact angle, AFM, XPS and electrochemical tests. The electrochemical characterization (electrochemical probe or voltammetric response in blank solutions) is fundamental to ensure the maximum blocking of the substrate. Although the electrodeposition process on the SAM-modified ITO substrate is very slow if the blocking of the surface is significant, non-cracked metallic layers of CoNi, with or without a previously electrodeposited seed-layer of platinum, have been obtained by optimizing the deposition potentials. Initial nucleation is expected to take place at the pinhole defects of the C12-SH SAM, followed by a mushroom-like growth regime through the SAM interface that allows the formation of a continuous metallic layer electrically connected to the ITO surface. Due to the potential of the methodology, the preparation of patterned metallic deposits on ITO substrate using SAMs with different coverage as templates is feasible.

Enhancement of the Hydrogen Evolution Reaction from Ni-MoS2 Hybrid Nanoclusters

“…%). The fresh S 2p spectrum can be deconvoluted into two components at ∼160.7 eV and ∼161.9 eV, corresponding to the spin–orbit S 2p 3/2 :2p 1/2 doublet characteristic of the S 2– oxidation state, 23 and we observe that an additional broad signal at ∼167 eV related to oxidized sulfur species such as sulfites or sulfates 24 is also found on (MoS 2 ) 300 nanoclusters (Figure S3 SI). Quantification of the Mo 4+ :S 2– peak areas confirmed the S-deficient nature of (MoS 2 ) 300 nanoclusters (1:0.90 ± 0.02), while (Ni-MoS 2 ) 1000 nanoclusters present a 1:1.8 ± 0.1 ratio similar to the Mo:S ratio expected in MoS 2 (1:2).…”

Electrocatalytic Water Splitting and CO2 Reduction: Sustainable Solutions via Single‐Atom Catalysts Supported on 2D Materials

“…Linear sweep voltammetry at a range from 0 to −1.2 V (vs NHE) with a scan rate of 25 mV s −1 in 2 × 10 −3 m HClO 4 /0.1 m NaClO 4 aqueous electrolyte was tested for all samples; pristine MoS 2 nanoclusters exhibit an onset potential of 650 mV and an overpotential of 770 mV reaching a half‐maximum current density. These experimental values are ≈400 mV higher than those of 2H‐phase MoS 2 nanosheets due to the fabrication method of MoS 2 with S enrichment . A substantial increase in both HER overpotential and Tafel slope in chalcogen‐deficient TMDs can be ascribed in the case of MoS 2 to a deficiency of active sites and the formation of oxide species MoO 2 /MoO 3 at the S‐deficient sites unstable to cathodic potential in acidic media .…”

“…Tafel slope analysis was also carried out to provide insights into the HER efficiency of the catalysts and the HER reaction mechanisms. According to the previous literature, the noble metals follow the Volmer–Tafel mechanism, which is the chemical hydrogen desorption from the catalyst surface and is a rate‐determining step . The lowest Tafel slope (94 mV per decade) was calculated from the 14 h air‐exposed MoS 2 nanoclusters, which follows the Volmer mechanism; monoatomic hydrogen adsorption is the limiting step.…”

“…These experimental values are ≈400 mV higher than those of 2H-phase MoS 2 nanosheets due to the fabrication method of MoS 2 with S enrichment. [113] A substantial increase in both HER overpotential and Tafel slope in chalcogen-deficient TMDs can be ascribed in the case of MoS 2 to a deficiency of active sites and the formation of oxide species MoO 2 /MoO 3 at the S-deficient sites unstable to cathodic potential in acidic media. [106,114] Electrochemical testing of the MoS 2 nanoclusters after 14 h air exposure clearly shows an enhancement in their electrocatalytic performance to the HER, with enhanced current density and overpotential values.…”

“…According to the previous literature, the noble metals follow the Volmer-Tafel mechanism, which is the chemical hydrogen desorption from the catalyst surface and is a ratedetermining step. [113] The lowest Tafel slope (94 mV per decade) was calculated from the 14 h air-exposed MoS 2 nanoclusters, which follows the Volmer mechanism; monoatomic hydrogen adsorption is the limiting step. Comparing the undoped MoS 2 and Ni-doped MoS 2 in terms of Tafel slopes, the Ni doping could not decrease the Tafel slope value significantly, leaving the HER mechanism unchanged as reported previously.…”