Cyclic Voltammetry In Aqueous Solution Research Articles

Electrocatalytic reduction of CO 2 on modified electrodes with alkylcyclam-metal complex Langmuir-Blodgett films

Two amphiphilic nickel(II) complexes with the long-alkyl-substituted 1,4,8,11-tetraazacyclodecane cyclam were synthesized, i.e. nickel tetrakis( N-hexadecyl)cyclam and nickel N-hexadecyclam. Monolayers of these complexes were immobilized onto glassy carbon (GC) disc electrodes using the Langmuir-Blodgett (LB) technique, and the electrocatalytic activities of these electrodes were examined by cyclic voltammetry in aqueous solutions saturated with nitrogen or carbon dioxide. The redox waves of the LB films of the nickel alkylcyclams observed in nitrogen were shifted in the anodic direction relative to those of nickel cyclams in a homogeneous solution. In carbon dioxide, the increase in the reduction current on these electrodes compared with that in nitrogen was observed at more negative potentials than - 1.3 V vs. a saturated calomel electrode in a solution with a constant pH value. This result shows that the LB films of these complexes possess sufficient electrocatalytic activity to reduce carbon dioxide despite their small amounts when compared with the amounts of homogeneous catalyst.

Mechanical and electrochemical properties of various tool steels implanted with nitrogen or NO ions

A study has been made of the tribological properties of various tool steels implanted with nitrogen or NO ions in order to investigate practical applications of nitrogen implantation for the improvement in durability of injection moulds for plastics. The substrates used were prehardened steels, maraging steels, alloy tool steels and stainless steels. The nitrogen or NO ion implantation was performed with doses of (1–5) × 10 17 ions cm −2 at 150 ke V. Surface analyses were carried out by means of secondary ion mass spectrometry, electron spectroscopy for chemical analysis, Auger electron spectroscopy and scanning electron microscopy. The near-surface hardness of implanted steels was measured with a Knoop hardness tester. Wear tests were carried out under unlubricated conditions in a pin-on-disc machine. Aqueous corrosion was estimated by means of cyclic voltammetry in aqueous solutions. The results are as follows. 1. (1) Implanted nitrogen atoms form a gaussian-like distribution and various nitrides. 2. (2) Nitrogen implantation causes the surface hardness to increase and the wear process to change from adhesive wear to oxidative wear. The change in wear process improves the wear resistance. 3. (3) NO implantation causes the corrosion to improve more than nitrogen implantation does. 4. (4) The surface hardness and wear resistance are correlated. This relationship may be useful in selecting material for practical applications.

Reduction of some acidopentaaquochromium(III) complexes at the mercury electrode: Effect of maximum suppressors and free ligand

The complexes [CrNCS(H 2O) 5] 2+, [CrCl(H 2O) 5] 2+, [Cr(H 2O) 5′ 2+ and [Cr(H 2O) 6] 3+ were studied by polarography and cyclic voltammetry in aqueous solution. It is shown that Triton X-100 and gelatine shift the polarographic waves to more negative potentials. In 1M NaClO 4HClO 4 the half-wave potentials in the absence of maximum suppressor are (in Volts vs. SCE): CrNCS 2+: −0·675; CrCl 2+:−0·62; CrF 2+:−1·105; Cr 3+:−0·90 (water omitted in the formula). All reductions are irreversible. Replacement of NaClO 4 by NaSCN makes the reduction of CrNCS 2+ and CrCl 2+ more reversible and shifts E 1 2 50 mV per log [SCN −] unit to more negative potentials for CrNCS 2+ and 66 mV for CrCl 2+. It is suggested that CrNCS 2+ and CrCl 2+ may be reduced via a mechanism analogous to the inner-sphere mechanism in homogeneous reductions.