Ni and Ni-doped with transition metals (TM) such as Fe and Co represent the most suitable electrodes for hydrogen evolution reaction (HER) in alkaline media. Various compositions of co-precipitated ...Ni1 + xFe2 − xO4 and Ni1 + yCo2 − yO4 nanoparticles were investigated. The intrinsic HER catalytic activity is the same for all the catalysts, which we relate to similar values of the iso-electric point (IEP). However, the mass catalytic activity of the catalysts changes through a modification of the electrochemical surface area. Fractional reaction orders for hydrogen evolution revealed in all catalyst compositions are due to double layer effects and surface acid-base equilibria. Reaction order and Tafel slope of the catalysts are compatible with electrochemical adsorption as the rate-determining step for the HER. Tafel slopes were also evaluated independently from impedance spectroscopy, in good agreement with the polarization curves. Electrodes prepared from catalyst inks containing an anion-exchange ionomer displayed inferior catalytic activity for the HER as compared to electrodes prepared with Nafion in the ink. Chronoamperometry confirmed the sustained superior hydrogen kinetics over time of NiFe2O4 and NiCo2O4 composition over that of NiO.
Titanium based BiPolar Plates (BPPs) are commonly used in Proton Exchange Membrane Water Electrolyzers (PEMWEs) today as they can withstand the harsh operating conditions experienced inside an ...operating PEM water electrolyzer. In particular, the high anode potential and acidic nature of the PEM is crucial for BPP performance. In this work we expand the investigation of non-coated materials at relevant operating conditions to include molybdenum, 254 SMO, tungsten, AISI 316L, AISI 304L, Inconel 625, niobium and tantalum, in addition to Titanium gr. 2. Pre-designed potentiostatic and potentiodynamic tests at potentials up to 2.0 VSHE were performed in addition to Interfacial Contact Resistance (ICR) and weight loss measurements. Scanning Electron Microscopy (SEM) imaging was conducted to observe morphology changes during the electrochemical tests. Titanium, tantalum and niobium experienced little or no weight change during potentiostatic polarization, while for AISI 304L, AISI 316L and tungsten the measured weight loss was much lower than the weight loss calculated from currents produced. When the potentiostatic test was prolonged for titanium, the ICR was found to increase with time. Auger Electron Spectroscopy measurements confirmed that the increase in ICR for titanium, tantalum and niobium is related to an increased thickness of surface oxides.
•Several of the materials have never been polarized up to 2 V before.•A selection of non-coated metals for use as BPP in PEM water electrolysis were tested.•Niobium, tantalum and titanium showed good corrosion resistance.•AES confirmed that the increase in ICR for niobium, tantalum and titanium was caused by oxide growth.•At 2 V the interfacial contact resistance of titanium increased with time.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Anion exchange membrane water electrolysis (AEMWE) is an efficient, cost-effective solution to renewable energy storage. The process includes oxygen and hydrogen evolution reactions (OER and HER); ...the OER is kinetically unfavourable. Studies have shown that nickel (Ni)- iron (Fe) catalysts enhance activity towards OER, and cerium oxide (CeO2) supports have shown positive effects on catalytic performance. This study covers the preliminary evaluation of Ni, Ni90Fe10 (at%) and Ni90Fe10/CeO2 (50 wt%) nanoparticles (NPs), synthesized by chemical reduction, as OER catalysts in AEMWE using commercial membranes. Transmission electron microscopy (TEM) images of the Ni-based NPs indicate NPs roughly 4–6 nm in size. Three-electrode cell measurements indicate that Ni90Fe10 is the most active non-noble metal catalyst in 1 and 0.1 M KOH. AEMWE measurements of the anodes show cells achieving overall cell voltages between 1.85 and 1.90 V at 2 A cm−2 in 1 M KOH at 50 °C, which is comparable to the selected iridium-black reference catalyst. In 0.1 M KOH, the AEMWE cell containing Ni90Fe10 attained the lowest voltage of 1.99 V at 2 A cm−2. Electrochemical impedance spectroscopy (EIS) of the AEMWE cells using Ni90Fe10/CeO2 showed a higher ohmic resistance than all catalysts, indicating the need for support optimization.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Anion exchange membrane (AEM) electrolysis is hampered by two main issues: stability and performance. Focusing on the latter, this work demonstrates a highly active NiMo cathode for hydrogen ...evolution in AEM electrolysis. We demonstrate an electrolyzer performance of 1 A cm−2 at 1.9 V (total cell voltage) with a NiMo loading of 5 mg cm−2 and an iridium black anode in 1 M KOH at 50 °C, that may be compared to 1.8 V for a similar cell with Pt at the cathode. The catalysts developed here will be significant in supporting the pursuit of cheap and environmentally friendly hydrogen fuel.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Maintaining nanoparticle properties when scaling up a chemical synthesis is challenging due to the complex interplay between reducing agents and precursors. A sonochemical synthesis route does not ...require the addition of reducing agents as they are instead being continuously generated in-situ by ultrasonic cavitation throughout the reactor volume. To optimize the sonochemical synthesis of nanoparticles, understanding the role of radical scavengers is paramount. In this work we demonstrate that optimum scavenger concentrations exist at which the rate of Ag-nanoparticle formation is maximized. Titanyl dosimetry experiments were used in conjunction with Ag-nanoparticle formation rates to determine these optimum scavenger concentrations. It was found that more hydrophobic scavengers require lower optimum concentrations with 1-butanol < 2-propanol < ethanol < methanol < ethylene glycol. However, the optimum concentration is shifted by an order of magnitude towards higher concentrations when pyrolytic decomposition products contribute to the reduction. The reduction rate is also enhanced considerably.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Optimizing the surface area of nanoparticles is key to achieving high catalytic activities for electrochemical energy conversion devices. In this work, the frequency range (200 kHz–500 kHz) for ...maximum sonochemical radical formation was investigated for the sonochemical synthesis of Pt-nanoparticles to assess whether an optimum frequency exists or if the entire range provides reproducible particle properties. Through physical and electrochemical characterization, it was found that the frequency dependent mechanical effects of ultrasound resulted in smaller, more open agglomerates at lower frequencies with agglomerate sizes of (238 ± 4) nm at 210 kHz compared to (274 ± 2) nm at 326 kHz, and electrochemical surface areas of (12.4 ± 0.9) m2g−1 at 210 kHz compared to (3.4 ± 0.5) m2g−1 at 326 kHz. However, the primary particle size (2.1 nm) and the catalytic activity towards hydrogen evolution, (19 ± 2) mV at 10 mA cm−2, remained unchanged over the entire frequency range. Highly reproducible Pt-nanoparticles are therefore easily attainable within a broad range of ultrasonic frequencies for the sonochemical synthesis route.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Large scale production of electrocatalysts for electrochemical energy conversion devices such as proton exchange membrane fuel cells must be developed to reduce their cost. The current chemical ...reduction methods used for this synthesis suffer from problems with achieving similar particle properties such as particle size and catalytic activity when scaling up the volume or the precursor concentration. The continuous production of reducing agents through the sonochemical synthesis method could help maintain the reducing conditions (and also the particle properties) upon increasing the reactor volume. In this work we demonstrate that the reducing conditions of Pt-nanoparticles are indeed maintained when the reactor volume is increased from 200 mL to 800 mL. Similar particle sizes, 2.1(0.3) nm at 200 mL and 2.3(0.4) nm at 800 mL, and catalytic activities towards the oxygen reduction reaction (ORR) are maintained as well. The reducing conditions were assessed through TiOSO4 dosimetry, sonochemiluminesence imaging, acoustic power measurements, and Pt(II) reduction rate measurements. Cyclic voltammetry, CO-stripping, hydrogen evolution measurements, ORR measurements, and electron microscopy were used to evaluate the catalytic activity and particle size. The similar particle properties displayed from the two reactor volumes suggest that the sonochemical synthesis of Pt-nanoparticles is suitable for large scale production.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The effect of Fe‐containing alkaline electrolyte, on the oxygen evolution reaction (OER) activity of Ni electrocatalysts, has long been of interest as Fe increases the OER activity of Ni ...electrocatalysts. However, controversy exists as to whether it is surface or bulk Fe that is responsible for the increased activity. In this study, magnetron sputtering was employed to sputter Ni, NiO and NiNiO thin film electrocatalysts to study the effect that different concentrations of Fe in the electrolyte have on their OER activities. It was found that increasing concentrations of Fe increasingly enhanced the OER activity of these thin film electrocatalysts until the electrolyte was saturated with Fe. The lowest overpotential achieved is 279 mV (at 10 mA cm−2) for NiNiO cycled in KOH containing 1 mM Fe, with all three thin film electrocatalysts exhibiting overpotentials within the same range after 30 voltammetry cycles in 0.9 ppm Fe and 1 mM Fe. All Tafel slopes are between 36 and 45 mV dec−1 indicating similar kinetics for the samples cycled in different Fe concentrations. Energy‐dispersive X‐ray spectroscopy and X‐ray photoelectron spectroscopy results show that Fe is found in the top layers of the electrocatalysts after cycling.
Activity‐enhancing Fe in the top layers of Ni thin films: The oxygen evolution reaction (OER) activity of magnetron sputtered Ni, NiO and NiNiO thin films increases with increasing Fe concentration in the KOH in which they are cycled. Activity‐enhancing Fe is found in the top layers of the films.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Reducing the amount of noble metals in catalysts for electrochemical conversion devices is paramount if these devices are to be commercialized. Taking advantage of the high degree of particle ...property control displayed by the sonochemical method, we set out to synthesize Cu@Pt bimetallic nanocatalysts in an effort to improve the mass activity towards the hydrogen evolution reaction. At least 17 times higher mass activity was found for the carbon supported Cu@Pt bimetallic nanocatalyst (737 mA mg−1, E = −20 mV) compared to carbon supported Pt nanocatalysts prepared with the same ultrasound conditions (44 mA mg−1, E = −20 mV). The synthesis was found to proceed with the sonochemical formation of Cu and Cu2O nanoparticles with the addition of PtCl4 leading to galvanic displacement of the Cu-nanoparticles and the formation of a Pt-shell around the Cu-core.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Electrocatalyst support affects not only catalytic activity of a catalyst, but also mass transportation and electron transfer in the catalyst layers of an electrode for proton exchange membrane fuel ...cells. Multi-dimensional and combined carbon materials such as Vulcan XC-72, carbon nanotubes (CNTs), and home-made coiled carbon nanotubes (CCNTs) are applied to enhance the catalyst activity and utilization. Three-dimensional CCNTs with large specific surface area and graphitic characteristic are synthesized by solid-state catalytic method. This obtained CCNTs and commercial CNTs are used as support to prepare platinum catalysts via modified ethylene glycol method, respectively. And the electrochemical surface areas (ECSAs) of the as-prepared Pt/CNTs, Pt/CCNTs and commercial Pt/C (JM) catalyst are evaluated by cyclic voltammetry. Then each two and three kinds of above catalysts mixed with different mass ratios are investigated. The ECSAs of Pt/C–Pt/CCNTs (95:5) and Pt/C–Pt/CNTs–Pt/CCNTs (80:10:10) are calculated to be 106 m2 gPt−1 and 111 m2 gPt−1, with respect to 70 m2 gPt−1 of Pt/C (JM) catalyst. And these mixed catalysts also demonstrate improved oxygen reduction reaction activities. This is mainly attributed to the unique structure of CCNTs, which can construct a multi-dimensional network to facilitate the mass transportation and electrons/protons transfer.
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•CCNTs with large specific surface area and graphitic characteristic were synthesized.•Pt/C, Pt/CNTs, and Pt/CCNTs were mixed with different mass ratios and evaluated.•The ECSA of Pt/C–Pt/CNTs–Pt/CCNTs (80:10:10) were calculated to be 111 m2 gPt−1.•Improved ORR activity of Pt/C–Pt/CNTs–Pt/CCNTs was obtained.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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