Roelof J Kriek

Roelof J Kriek
North-West University | NWU · School of Physical and Chemical Sciences

PhD Chemistry
My current research focuses on electron transfer process related to electrocatalysis and photo-electrocatalysis.

About

46
Publications
6,194
Reads
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689
Citations
Citations since 2016
22 Research Items
588 Citations
2016201720182019202020212022020406080100120
2016201720182019202020212022020406080100120
2016201720182019202020212022020406080100120
2016201720182019202020212022020406080100120
Introduction
Skills and Expertise
Additional affiliations
October 2004 - present
North-West University
Position
  • Professor (Associate)

Publications

Publications (46)
Article
One drawback of alkaline water electrolysis is the sluggish oxygen evolution reaction kinetics at the anode of the electrolyser and improvement of the anode material is still a necessity. Various Ir1-yNiyOx electrocatalyst combinations were prepared by reactive sputtering and subjected to high-throughput electrochemical screening using a Au/SiO2 wa...
Article
Full-text available
The electrodeposition of platinum from hexachloroplatinic acid solutions, on glassy carbon, was studied by developing multiple cyclic voltammetry transients. The development of an isopotential point, only observed under hydrogen‐evolution conditions, is postulated to be associated with the reduction of [PtCl4]2− to Pt0 and the oxidation of the adso...
Article
This work highlights the fact that the activity of an already active metal/surface, i.e. Ni, can be increased even further by combining it with metals/surfaces that exhibit low activity, i.e. Pt and Al, when used on their own. Combinatorial screening was conducted on plasma vapour deposited PtxNiyAlz thin-film ratios for the oxygen evolution reacti...
Article
Three perovskite‐type nanocomposites, i. e. Ce0.8Sr0.2CoxFe1‐xO3‐δ (x=0.2, CSCF1; 0.5, CSCF2; 0.8, CSCF3), were synthesized employing the sol‐gel technique, subsequent to which they were physically and electrochemically evaluated for their electrocatalytic activity towards the oxygen evolution reaction (OER) in alkaline medium (0.1 M KOH) at room t...
Article
Full-text available
We report on nanocomposite materials that are both active and stable for the oxygen evolution reaction (OER) in alkaline media. Ce0.8Sr0.2Co0.6Ni0.2Fe0.2O3-δ (CSCNF1), Ce0.8Sr0.2Co0.3Ni0.2Fe0.5O3-δ (CSCNF2), and Ce0.8Sr0.2Co0.2Ni0.1Fe0.7O3-δ (CSCNF3) that contain a lanthanide, in the form of Cerium (Ce) in the A site and varied compositions of Co,...
Article
Full-text available
The development of effective electrocatalysts for the oxygen evolution reaction (OER) is of great importance to combat energy-related concerns in the environment. Herein, we report a one-step solvothermal method employed for the fabrication of nickel selenide hybrids (NiSe-Ni3Se2) and a series of nickel selenide hybrid/multiwalled carbon nanotube c...
Article
Full-text available
The development of support structures for electrocatalysts has received a great deal of attention over the last decade, with carbon structures (i.e. nanostructures, Vulcan carbon (VC)) having been studied extensively. Carbon support structures increase the surface area, stability and activity of electrocatalysts in most cases, and can be used to ov...
Article
Nickel-based oxides and (oxy)hydroxides are known to be electrocatalytically active for the oxygen evolution reaction (OER) in an alkaline medium. However, the aforementioned materials would be more auspicious, especially for photo-electrocatalysis, if their optical properties fell within the range of the solar spectrum. These properties could be a...
Article
Full-text available
A new type of perovskite, i.e. Sm0.8Sr0.2Fe0.8Co0.2O3-δ (SSFC1), Sm0.8Sr0.2Fe0.5Co0.5O3-δ (SSFC2), and Sm0.8Sr0.2Fe0.2Co0.8O3-δ (SSFC3) were (i) synthesised by employing a sol gel method with subsequent calcination at 1000 °C for 10 h and (ii) investigated for its activity towards the oxygen evolution reaction (OER) in alkaline medium. The synthesi...
Article
Full-text available
The influence of sputtered Pt40Pd57Al3 thin films of varying thickness, in the as-deposited (AD) and annealed (AN) state, was investigated for the electro-oxidation of aqueous SO2. From physical characterisation (scanning electron microscopy (SEM) and grazing incidence X-ray diffraction (GIXRD)), significant differences were found in the morphology...
Article
This work reveals that Eu2TeO6, as a photo-electrocatalyst, exhibits a sustained photo-charging effect that results in an enhanced and ‘sustained’ dark current (subsequent to the termination of illumination), which is greater than the current obtained through applied electrical potential alone. Samples of europium tellurium oxide, prepared through...
Article
Complex formation of mixed palladium (II) chloro-hydroxo and palladium(II) bromo-hydroxo complexes have been investigated employing spectrophotometry at 25 °C and an ionic strength of 1.0 M. Hyperquad Simulation and Speciation (HySS) was employed to determine the ideal titration conditions and an autotitrator (equipped with a flow-through cell) was...
Article
Titanium dioxide thin films were deposited by the reactive ion-assisted sputtering method from titanium targets at various partial pressures and deposition parameters. The films were deposited onto substrates at temperatures ranging from room-temperature conditions to 722 K. A selection of thin films was post-deposited annealed at temperatures up t...
Article
By incorporating all positive design criteria developed to date, to improve on performance and gas purities, a scalable and simplistic Mono-Circular Filter Press (MCFP) reactor has been developed and tested for the Divergent Electrode-Flow-Through (DEFT™) membraneless alkaline electrolysis technology. An improved gas/liquid separation methodology w...
Article
Full-text available
A series of Ag/NiO nanocomposite electrocatalysts, with a general molecular formula of AgxNi1 − xO, was synthesised employing the citrate sol-gel route and tested for the oxygen evolution reaction (OER) in 0.1 M KOH solution. Crystal structure, morphology and stoichiometry of the catalysts were evaluated by X-ray diffraction (XRD), scanning electro...
Article
Full-text available
This work investigates the viability and outlines the current challenges in electrochemical quartz crystal nanobalance (EQCN) experiments on supported Pt catalysts. EQCN experiments involving Pt supported on 2-D “surface-treated graphite sputtered onto quartz crystal” (Pt/MFG-H) catalysts were compared to standard polycrystalline Pt (Ptpoly), which...
Article
The effect of thermal treatment on the morphology (crystalline phase and size) and photocatalytic activity of freshly prepared TiO2 nano-powder is communicated. TiO2 nano-powders, prepared by hydrolyzing titanium tetraisopropoxide at room temperature, were all dried at 382 K and subsequently calcined at different temperatures, for 1 h, up to 1172 K...
Article
A membraneless Divergent Electrode-Flow-Through (DEFT™) alkaline electrolyser, for unlocking profitable hydrogen production by combining a simplistic, inexpensive, modular and durable design, capable of overcoming existing technology current density thresholds, is ideal for decentralised renewable hydrogen production, with the only requirement of e...
Article
As the speciation of metal species, especially the noble metals, are crucial for recovery and separation purposes, the complex formation of Pd(II), with chloride and bromide respectively, has been investigated employing spectrophotometry at 25 °C and an ionic strength of 1.0 M Hyperquad Simulation and Speciation (HySS) was employed to determine the...
Article
Full-text available
A co-sputtered PtxPdyAlz ternary system was investigated for potential use as anode catalyst for the electro-oxidation of aqueous sulphur dioxide (SO2), a key reaction in the hybrid sulphur (HyS) process for splitting water into hydrogen and oxygen. Combining the noble metals Pt and Pd with Al resulted in no significant improvement in onset potenti...
Article
Full-text available
Polycrystalline Rh and Pt were studied to ascertain their electrocatalytic activity for the electro-oxidation of SO2, an important reaction in sulfur dioxide depolarized electrolyzers used to produce hydrogen. Cyclic voltammetry and linear polarization methods were employed to evaluate the catalytic activity of these surfaces. Rh exhibited 25-fold...
Article
A membraneless divergent electrode-flow-through (DEFT) alkaline electrolysis design and operating principle is investigated, which allows for the ohmic drop contribution and performance threshold limitations of a conventional membrane barrier to be overcome. Employing mesh electrodes of 30 mm diameter, operation of the electrolyser at an electrolyt...
Article
Full-text available
Insight into the effect that rapid thermal annealing (RTA) has on the structural and electrochemical characteristics of sputtered Pt and Pt3Pd2 thin film electrocatalysts is communicated. The DC magnetron sputtered thin films were rapidly annealed at temperatures ranging from 600 to 900 °C under an Ar atmosphere. The microstructural changes and ele...
Article
Full-text available
Carbon dioxide electroreduction (CO2ER) was studied on 35 gold-based thin film catalysts sputtered on glassy carbon disks. A sputter-down setup was used for the deposition of these thin films in a combinatorial manner. Zinc and silver were employed in combination with gold in order to obtain new catalysts. Linear sweep voltammetry was employed to o...
Article
Full-text available
A combinatorial sputtering system, based on magnetron enhanced plasma sputtering, was employed in the syntheses of PtxPdy thin film catalysts, and a multi-channel potentiostat allowed for high-throughput parallel screening of the deposited electrocatalysts towards the electro-oxidation of aqueous sulphur dioxide (SO2). Employing onset potential as...
Article
The photocatalytic reduction of rhodium(III) chloro–aqua complexes, [RhCln(H2O)6−n]3−n (n = 0–6), was carried out employing formic acid, ethanol and sucrose as hole scavengers or sacrificial reducing agents (SRA). The investigation was conducted in air equilibrated titanium dioxide (TiO2) suspensions at 25 °C and pH 1employing UV light within a clo...
Article
A spectrophotometric investigation into the complexation of palladium(II) with thiocyanate revealed the existence of five coordinated palladium(II) complexes. Molar absorbance spectra as well as formation constants were calculated for all five complexes. Complex-formation of Pd(II) with thiocyanate has been investigated by spectrophotometry at 25 d...
Article
Sulphur dioxide (SO2), a known industrial pollutant and pulmonary irritant, is emitted to the atmosphere in excess of 120 Mt per annum. Great strides have been taken to reduce SO2 emissions, but with the growth of specifically China, and to a lesser extent India, it is on the rise again. The electrolysis of aqueous solutions of dissolved SO2 holds...
Article
The thermodynamics and surface chemistry affecting the photocatalytic reduction of chloro aqua platinum(II) and platinum(IV) complexes as means of platinum recovery from solution are communicated. The photocatalytic reduction rate trends of the cationic, neutral and anionic chloro complexes under acidic conditions in the TiO2 aqueous suspension in...
Article
The photocatalytic production of hydrogen from water as well as from an aqueous methanol solution employing pre-treated TiO2 and various Pt-TiO2 photocatalysts was studied by using an Nd:YAG laser as irradiation source. The photocatalysts (0.5, 1.0, 1.5 and 2.0 wt% Pt-TiO2) were prepared by utilizing a photocatalytic reduction method upon which cha...
Article
The photocatalytic reduction of chloro-aqua palladium(II) complexes, [PdCln(H2O)(4-n)](2-n) (n = 0-4), as a means of palladium metal recovery and waste water purification, was investigated employing four different titanium dioxide samples in a batch reactor. These suspensions were subjected to UV irradiation in the absence of an added sacrificial r...
Article
A new dithiocarbamate ligand, para-methylphenyl dithiocarbamate (L), has been synthesized at room temperature. The ligand was reacted with a cadmium salt to give bis(N-para-methylphenyl dithiocarbamate) Cd(II) (CdL2). The compounds were characterized by elemental analysis, NMR (1H and 13C), scanning electron microscopy (SEM), EDS and FTIR spectrosc...
Article
Full-text available
In continuation to our previous work with composite polyaniline-zirconium (IV)- arsenate (PZA), we further extended with the conductivity measurements in this report. All the calculations reported in here were extracted from the experiments carried out in the temperature range of (25-50)±0.1°C and at different concentrations (0.01C(M)1) of KCl, N...
Article
Full-text available
Global sulphur dioxide (SO2) emissions peaked around the mid-1970s, after which they declined. However, with the growth of specifically China, emissions are on the rise again. In 2008, global anthropogenic SO2 emissions totalled 127 Mt, with energy production accounting for 63.2 Mt and metal-related processes 12.8 Mt. As a well-known gaseous pollut...
Article
Full-text available
A new crystalline organic-inorganic nano-composite nylon-6,6 nickel phosphate membrane was synthesised subsequent to which (a) the physico-chemical characteristics of the membrane were evaluated employing FTIR, SEM, EDX, TEM, XRD and porosity measurements, and (b) membrane potential measurements were conducted employing different concentrations (0....
Conference Paper
Full-text available
A comparative investigation with regards to the activity of an industrial manufactured polycrystalline platinum (PolyPt) electrode and platinum deposited glassy carbon (Pt/GC) electrodes, prepared by sputtering with a pulsed vapour depostion system, towards the oxidation of aqueous sulfur dioxide, has been conducted using a combination of stationar...
Article
The photocatalytic reduction trends of palladium chloride aqua complexes, [PdCln(H2O)4−n]2−n (n = 0–4), have been investigated employing titanium dioxide (TiO2) as photocatalyst in the absence of an added sacrificial reducing agent (SRA). Solutions were prepared at those Cl−-concentrations that coincide with the maximum of each species and the phot...
Article
Full-text available
Ionic potentials were measured across polystyrene based titanium–vanadium (1:2) phosphate membranes with 1:1 electrolytes at different concentrations. These observed values are found to compare well with membrane potentials calculated from theoretical equations derived by Teorell–Meyer–Sievers (TMS). Membrane parameters have been used to examine th...
Chapter
In May 2007 the South African Cabinet approved a National Hydrogen and Fuel Cell Technologies R&D and Innovation Strategy. The strategy will focus on research, development and innovation for: i) wealth creation through high value-added manufacturing and developing platinum group metals catalysis; ii) building on the existing knowledge in high tempe...
Article
Complex formation of Pd(II) with chloride and hydroxide has been investigated by spectrophotometry at 25°C and ionic strength 1.0 M. For the chloride complexes [PdCln(H2O)4−n] (n = 0–4), the formation constants, βn, have been determined and the values are: log β1 = 4.47, log β2 = 7.80, log β3 = 10.18 and log β4 = 11.53. The formation of mixed chlor...
Article
In-house manufactured tubular ceramic supports prepared by centrifugal casting have a smooth inside surface and are ideal for thin defect-free coatings. The aim of this study was to directly coat a thin defect-free titania membrane in the anatase crystal structure on a ceramic support. The membrane preparation was successful. By means of XRD it was...
Article
Full-text available
Synopsis Selective photore-duction, using the semiconductor TiOz under UV irradiation, has been investigated as a possible recovery and/or separation methodfor the PGM's rhodium, palladium and platinum. The dfect qf pH value and concen-tration qf the sacrljidal redudng agent (ethanol) on the rate qf reducdon qfRh(Ill), Pd(ll) and Pt(IV) ions have b...

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