Martin Paidar

Electrochemical reduction of nitrate in weakly alkaline solutions

The electrocatalytic activity of several materials for the nitrate reduction reaction was studied by cyclic voltammetry on a rotating ring disc electrode in solutions with different concentrations of sodium bicarbonate. Copper exhibited highest catalytic activity among the materials studied. Nitrate reduction on copper was characterized by two cathodic shoulders on the polarization curve in the potential region of the commencement of hydrogen evolution. In this potential range an anodic current response was observed on the Pt ring electrode identified as nitrite to nitrate oxidation. This indicates that nitrite is an intermediate product during nitrate reduction. These conclusions were verified by batch electrolysis using a plate electrode electrochemical cell. Copper and nickel, materials representing the opposite ends of the electrocatalytic activity spectra, were used in batch electrolysis testing.

Polymer anion-selective membranes for electrolytic splitting of water. Part II: Enhancement of ionic conductivity and performance under conditions of alkaline water electrolysis

An attempt was made to increase the ionic conductivity of novel, heterogeneous, anion-selective membranes by increasing the porosity of their surface skin. This was based on the addition of a water-soluble component, namely poly(ethylene-ran-propylene glycol), to an inert polymer matrix, based on low-density polyethylene, while mixing it with the ion-exchange particles. A series of membranes was prepared, consisting of 66 wt% of anion-exchange phase represented by a styrene-divinyl benzene copolymer matrix with quaternary ammonium functional groups and an inert polymer matrix in a mixture with variable amounts of water-soluble component added. The membranes were subsequently tested with respect to their morphology, mechanical properties, apparent ion-exchange capacity, ionic conductivity, and performance under conditions of alkaline water electrolysis. When added in the appropriate amount, the addition of a water-soluble component was found to improve the electrochemical properties of the resulting membrane efficiently, while at the same time not reducing its mechanical properties to below a critical level.

Study of mass transfer in a vertically moving particle bed electrode

AbstractA study was made of the influence of process parameters on the mass-transfer coefficient in a flow-through cell with a cascade of rotating drums partially filled with conductive particles (called the ‘vertically moving particle bed’). Copper deposition from an acidic sodium sulphate solution was used as the model reaction. To evaluate the experimental data a macrohomogeneous mathematical model of potential and current density distribution inside the cell was developed. The electrolyte flow distribution between the empty space above the particle bed and through the bed was evaluated. On the basis of these results the following correlation is proposed:

Effect of the MEA design on the performance of PEMWE single cells with different sizes

Sh = \frac{{1.09}}{\varepsilon }Re_{\text{p}}^{1/3} Sc^{1/3} + \frac{{52.8Re_r }}{{2498 + Re_r }}\{ 1 - {\text{exp[ - 125(1}}{\text{.04}} \times {\text{10}}^{{\text{ - 6}}} Re_r {\text{ + }}Re_{\text{p}} {\text{)]}}\}

Non-conductive TiO2 as the anode catalyst support for PEM water electrolysis

where the first term corresponds to the packed bed electrode and the second term represents the contribution of bed rotation. It is valid for bed porosity of 45%, cathode drum rotation rates between 0.047 and 0.120 Hz (i.e., 2.8 to 7.2 rpm) and a Rep range of 0.003 to 0.013.

Ion-conductive polymer membranes containing 1-butyl-3-methylimidazolium trifluoromethanesulfonate and 1-ethylimidazolium trifluoromethanesulfonate

A microporous layer represents an important element of the gas diffusion electrodes used in polymer electrolyte membrane (PEM) fuel cells and water electrolysers. It forms an interface between the nanostructured catalyst layer and the macrostructured electrode body. In the case of PEM water electrolysis such a layer has only been applied to the cathode to date. On the other hand, it is typically absent on the anode side of the cell. In the present study, such a layer was integrated into the anode of a PEM water electrolyser. It was based on antimony-doped tin oxide placed on titanium felt forming the electrode backing. Using an in-house synthesised IrO2, gas diffusion anodes were manufactured with and without the microporous layer and their performance compared in a laboratory PEM water electrolyser. Current–voltage curves and electrochemical impedance spectra were recorded. The results revealed that the microporous layer is only advantageous in a range of low current densities, while at higher current densities the ohmic resistance of the microporous layer significantly reduces the efficiency of electrolysis.Graphical Abstract

The effect of surface modification by reduced graphene oxide on the electrocatalytic activity of nickel towards the hydrogen evolution reaction

In the field of polymer electrolyte membrane water electrolysis (PEMWE), a significant amount of excellent scientific results has been generated during the past decades. However, the comparability and reproducibility of these results between different cell types and different laboratories is not always straightforward. In this contribution, an exemplary ring experiment on the single-cell level compares the performances of three cell types: the differential cell (