High Corrosion Stability Research Articles

Controlled electrochemical hydridation of Ti surfaces – optimisation and electrochemical properties

Ti is used as a construction material in many applications including electrodes in various electrochemical technologies due to its high corrosion stability provided by the stable oxide layer on the surface. However, this oxide layer is also the reason for its resistivity causing high interfacial resistance between components and energy losses. This problem can be solved by various surface modifications such as acid etching or coating with a layer of precious metals. In this study, we present a novel method for controlled hydridation of Ti materials based on a combination of acid etching and cathodic hydridation aimed primarily for surface modification of Ti components for proton exchange membrane water electrolyser. Cathodic polarisation represents the means to increase the amount of Ti hydride and to tune its properties to obtain a Ti surface with low interfacial resistance and preserved corrosion stability. The study investigated the effects of concentration, temperature, time, and current density on cathodic polarization in H2SO4 electrolytes. The resulting samples were characterized by X-ray diffractometry, X-ray photoelectron spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, Kelvin probe and temperature-programmed desorption. This allowed finding interesting correlations between the surface composition of the Ti samples and their electrochemical properties.

Activating and stabilizing Co sites in CoP for triggering oxygen electrocatalysis in zinc-air battery

Catalysts with high activity and corrosion-resistance are desirable for oxygen reduction and evolution reactions (ORR/OER) in rechargeable zinc-air batteries (ZABs). Herein, via an etching-phosphating-annealing strategy, CoP is in situ formed in hollow carbon-nanobox, both of which are wrapped by a thin nitrogen-doped carbon layer (CoP/HNBs@NCL). Tannic acid etches ZIF-67 nanobox to release Co2+ and 2-methylimidazole to generate hollow structure. As-marked CoP/HNBs@NCL-2 (271.9 m2 g−1) exhibits robust activities towards ORR (half-wave potential of 0.88 V) and OER (overpotential of 0.36 V), which outperforms many non-precious metal catalysts due to the strong interactions between CoP and N-species and the smooth mass transfer via the porous hollow structure. Even at high potentials (OER), HNBs@NCL framework can still relieve the leaching of Co species (leaching ratio of 15.5 % after 6 h) to obtain high corrosion resistance and stability. Theoretical calculations reveal that N atoms enhance the electron delocalization degree of Co sites in CoP to lower energy barriers and balance adsorption free-energies of O-intermediates to enhance oxygen electrocatalysis. Notably, ZAB with CoP/HNBs@NCL-2 air-electrode exhibits high peak power density (139.8 mW cm−2) and charge–discharge cycling stability (132 h). This work presents a reliable protocol to design hollow electrocatalysts with desirable bifunctional activity and stability for ZABs.

The Coating Effect on Interconnect Materials After >10 Years of Furnace Exposures

One of the key components in the SOFC stack is the interconnect which requires versatile material properties for a proper functioning, e.g., high temperature corrosion stability, low ASR degradation and low chromium evaporation. At the same time, a high production capacity needs to be reached in order to fulfil the supply demand required for GW levels. The high production capacity is realized through Alleima AB’s production line with coil-coil physical vapor deposition of coated interconnects for SOFC and SOEC applications [1].More specifically, Sanergy HT 441 is the standard material intended to be used as an SOC interconnect. The substrate is a ferritic stainless steel (ASTM 441) which is coated with thin layers of Ce and Co (<1 µm). The material can be coated on both sides using the same coating or with a different coating. At elevated temperatures the Co coating forms a protective (CoMn)3O4 spinel layer which drastically reduces Cr evaporation while the Ce layer improves the corrosion resistance by reducing the chromia scale growth at the coating/substrate interface and thereby maintaining a low and stable ASR over time.Since long-term stability is a critical property for interconnects, Alleima has over the years gathered data from furnace samples and can thus present results where some samples have been exposed at elevated temperatures during >10 years. The main results include the effect of Ce thickness or choice of substrate on mass gain and subsequent chromia growth. Selected samples with coating elements different than Co have also been investigated. Samples have been further investigated using scanning electron microscopy for cross-sections, x-ray diffraction for characterization of phases and residual stresses as well as glow discharge optical emission spectroscopy for elemental analysis.

Oxygen reduction stability of graphene-supported electrocatalyst: Electrochemical and morphological evidences

Graphene has been proposed as support or as co-support for Proton Exchange Membrane Fuel cells (PEMFCs) electrocatalysts due to its high electronic conductivity, corrosion stability and high specific surface area compared to common carbon blacks, such as Vulcan. Despite such outstanding properties, comprehensive studies on long-term stability of graphene-supported Oxygen Reduction Reaction (ORR) catalysts are still unavailable or limited.The stability of graphene as support is now studied and compared with carbon black in terms of electrochemical performance and degradation mechanisms. Catalytic layers with Pt/G were prepared and subjected to a set of three different Accelerated Stress Tests (ASTs): cycling at high potentials, Open Circuit Potential (OCP) holding and cycling at low potentials. This study aims to assess if and why graphene is a better candidate as support.The Pt/G catalyst outperformed the reference catalyst in all ASTs, delivering both higher electrochemical active surface area (ECSA) and ORR mass-specific activity. Such electrochemical performance was correlated with morphological evidences associated to the support itself and with Pt nanoparticles.

Carbon nanotubes doped with nitrogen, modified with platinum or platinum-free for alkaline H2-O2 fuel cell

A series of cathodic and anodic catalysts for alkaline H 2 -O 2 fuel cells (FC) deposited on the surface of functionalized and nitrogen-doped carbon nanotubes (CNT) was synthesized and studied by various structural and electrochemical methods. It was established that, due to the minor defect structure, CNT NaOH (functionalized in alkali) exhibit high corrosion stability. A further increase in the activity in the oxygen reduction reaction (ORR) and the stability of CNTs is observed following their doping with nitrogen. The high activity of CNT NaOH+N is attributed to pyridine groups and the increased electrical conductivity of this catalyst. It was shown that CNT NaOH comprise effective substrates for hydrogen oxidation reaction catalysts. The PtMo/CNT NaOH system containing 12 wt.% Pt at a molar ratio of PtMo=1:1 is characterized by the highest catalytic activity among investigated anode platinum and non-platinum catalysts. The use of this catalyst made it possible to reduce the content of platinum to 0.1-0.2 mg/cm 2 , while preserving the characteristics that significantly exceed those of the active layer containing 60Pt/C (HiSPEC 9100) catalyst (0.6 mgPt/cm 2 ).

Ti-Rich Mg1-X Ti2+X O5: A Highly Conductive and Acidic-Stable Ternary Oxides

Searching for a material that simultaneously satisfies highly conductive and corrosion-stable properties is crucial for various energy conversion applications, particularly for catalyst-supporting materials in polymer electrolyte membrane fuel cells (PEMFC). Here, we suggest the Mg-Ti-O chemical space as promising ternary compounds with high electrical conductivity and corrosion stability in acidic conditions to be potentially used in such applications. A high electrical conductivity (6.09 × 10-1 S/cm) and a good corrosion stability (1.2 × 10-4 mA cm-2 at pH = 1) are achieved at room temperature, by tuning the chemical compositions of Mg1-x Ti2+x O5 (MTO). We found that the corrosion stability of suggested MTO is two orders of magnitude higher than that of conventional carbon supporters used for PEMFC while providing high electrical conductivity. Furthermore, our combined computational and experimental works elucidate that the reducing gas environment during the solid-state synthesis ensures the higher Ti solubility in MTO, i.e., a reduced valence state of Ti, thus promoted the electrical conduction.

(Invited) Towards the Development of High-Performance Crystalline Rutile Iridium Dioxide Electrocatalysts for the Oxygen Evolution Reaction

Proton exchange membrane water electrolysis (PEMWE) offers a promising route for the production of green hydrogen from renewable energy sources and could be the master key to unlocking a future sustainable energy system (1). One of the main barriers delaying the wide-spread adoption of PEMWE technologies is the slow kinetics of the oxygen evolution reaction (OER) occurring at the anode and the need for high-cost, low-abundance precious metal electrocatalysts. Iridium-based oxides are still considered the only feasible option for practical applications due to their high activity and considerable corrosion stability under the harsh electrochemical reaction conditions. To improve the overall efficiency of PEMWEs, future electrocatalyst development strategies must concomitantly address performance metrics in terms of activity, stability and material cost.Towards enhancing iridium utilisation, efforts are aimed at increasing the electrochemical surface area of the catalyst per mass of iridium, thereby increasing the number of available electrocatalytic surface sites. In this regard, amorphous iridium oxide (IrOx) nanoparticles have been shown to achieve a high intrinsic activity (2). However, this comes at the expense of catalyst stability (3) and a loss of intrinsic electronic conductivity (4) associated with the lower degree of crystallinity. By maximising the dispersion of Ir-based nanoparticles, the use of high surface area support materials have also been shown to improve OER performance (5, 6).However, to address long-term stability concerns for Ir-based OER catalysts, highly crystalline rutile iridium dioxide (IrO2) materials may still offer the best prospects. The drawback of using this approach is that the formation of crystalline IrO2 nanoparticles often involves high temperature thermal oxidative treatment causing particle growth and loss of surface area, ultimately leading to decreased OER activities (7). Therefore, novel synthesis methods that retain a high degree of crystallinity without a loss of surface area for IrO2 nanoparticles are required.In this talk, we discuss two synthesis strategies geared towards the preparation of highly crystalline IrO2 nanoparticles with high OER performance. Firstly, we present a novel wet-chemistry synthesis method that avoids the use of reducing agents and eliminates the need for high temperature thermal oxidative treatment. The resultant nano-sized IrO2 nanoparticles were found to have excellent Ir mass-specific OER activity and durability attributed to the small nanoparticle size and high degree of crystallinity.Secondly, we present a novel metalorganic chemical deposition process as a simple, one-step preparation method for highly crystalline IrO2 nanoparticles supported on Sb-doped tin oxide (ATO) (8). The superior OER performance was attributed to the epitaxial anchoring of well dispersed, crystalline IrO2 nanoparticles onto the ATO support. We further discuss the versatility of the method to the application of other conductive oxide support materials such as indium tin oxide and F-doped tin oxide, with the ability of tuning the chemical state of the Ir-based nanoparticles by changing the reaction conditions, i.e., temperature and gas environment as well as the nature of the support.Finally, using a series detailed physico-chemical characterisation techniques to elucidate the nature the iridium phase, composition, morphology and structure, we relate these properties to the electrochemical activity and stability of the prepared materials for the OER. Herein, we highlight some of the challenges often encountered with the analysis of physical and electrochemical characterisation data for IrO2 nanoparticles, particularly when supported on other oxide materials. Acknowledgements This work is funded by the Department of Science and Innovation (DSI, South Africa) Impala Platinum Holdings Limited (Implats) and the Federal Minister of Education and Research (BMBF, Germany). References K. Ayers, Current Opinion in Electrochemistry, 18, 9 (2019). T. Reier, I. Weidinger, P. Hildebrandt, R. Kraehnert and P. Strasser, ECS Transactions, 58, 39 (2013). T. Binninger, R. Mohamed, K. Waltar, E. Fabbri, P. Levecque, R. Kötz and T. J. Schmidt, Scientific Reports, 5, 12167 (2015). M. Bernt, C. Schramm, J. Schröter, C. Gebauer, J. Byrknes, C. Eickes and H. A. Gasteiger, Journal of The Electrochemical Society, 168, 084513 (2021). H.-S. Oh, H. N. Nong, T. Reier, A. Bergmann, M. Gliech, J. Ferreira de Araújo, E. Willinger, R. Schlögl, D. Teschner and P. Strasser, Journal of the American Chemical Society, 138, 12552 (2016). A. Hartig-Weiss, M. Miller, H. Beyer, A. Schmitt, A. Siebel, A. T. S. Freiberg, H. A. Gasteiger and H. A. El-Sayed, ACS Applied Nano Materials, 3, 2185 (2020). J. Quinson, Advances in Colloid and Interface Science, 303, 102643 (2022). Z. S. H. S. Rajan, T. Binninger, P. J. Kooyman, D. Susac and R. Mohamed, Catalysis Science & Technology, 10, 3938 (2020).

Microstructural evolution in S31042 heat-resistant steel after service and the effect on hardness

The ultra-supercritical power generation technology with high energy efficiency and low emissions is one of the important ways to solve the current increasingly prominent energy problems in the context of international development requirements for carbon neutrality and the increasingly prominent energy shortage. Because of its excellent resistance to high temperature corrosion and organizational stability, S31042 is commonly employed in the most severe working environment of ultra-supercritical units. Due to its great resistance to high-temperature corrosion and organizational stability, S31042 is commonly employed in the most demanding components of ultra-supercritical units such as high-temperature reheaters and high-temperature superheaters. Various characterisation approaches were employed in this research to reflect the microstructure of S31042 heat-resistant steel in service under various time length conditions, and the hardness of S31042 heat-resistant steel was assessed under the corresponding service conditions. The results showed that the hardness of S31042 increased significantly with increasing service time, from around 160 Hv at the time of non-service to nearly 220 Hv after 75360 hours of service. The continuous distribution of uniformly sized M23C6 phase on the grain boundaries of S31042 developed toward grain coarsening after service, but the precipitation strengthening effect produced by the nanoscale secondary NbCrN phase appearing in the grains was the main reason for the increase of the hardness value of S31042, according to the microstructure of the material.

Development of a New AuCuZnGe Alloy and Determination of Its Corrosion Properties

In this paper, we present the idea and development of a new gold-copper-zinc-germanium (AuCuZnGe) alloy, which is related to the method of production and research of its key properties, so that the new Au alloy could be used for jewelry production and in dental technology. The research design was associated with the determination of appropriate chemical composition, manufacturing technology, and performing the characterization. Melting and casting technologies were used to cast the AuCuZnGe alloy while rolling was used to prepare the cylinders and cutting to make square plates with a = 10 mm and thickness of 1 mm. Such plates were provided for corrosion testing. Observation of the plate′s microstructure was performed with Scanning Electron Microscopy (SEM) equipped by Energy-Dispersive X-ray spectrometry (EDS) and X-ray diffraction (XRD). Corrosion testing involved performing the following measurements: Polarization, the open circuit potentials, and linear polarization resistance. Based on the SEM, EDS, XRD, and results of corrosion testing it can be concluded that the new AuCuZnGe alloy possesses high corrosion stability and can be classified as a high noble alloy.

Catalyst Dissolution Analysis in PEM Water Electrolyzers during Intermittent Operation

Sustainable development of the global energy sector requires a transition from fossil fuels to renewable energies. Considering the continuously increasing energy demand, effective utilization of intermittent output from the renewable sources will depend on the efficiency of energy storage and utilization processes. Low chemical complexity and high energy density and efficiency make hydrogen produced via proton exchange membrane water electrolysis (PEMWE) a prominent solution for the mentioned challenges.Acidic conditions and high potentials at the anode side of PEM water electrolyzers, where the oxygen evolution reaction (OER) takes place, demand for materials with high catalytic activity and corrosion stability. The state-of-the-art platinum and iridium (oxide) catalysts in the cathode and anode catalyst layers (CLs), respectively, demonstrate relatively good activity and stability during steady operation at low and moderate electrical loads. Indeed, it is anticipated that a significant decrease in the noble metal amount may be achieved without sacrificing the cell performance [1]. An intermittent operation of PEMWE, however, represents a considerable risk factor as both CLs may degrade with time. The extent of such degradation, especially at low catalyst loadings and high current densities, alternated with numerous off cycles is still not well understood and hence, difficult to predict and mitigate.Recent results from our group indicate a severe discrepancy between OER catalyst dissolution in aqueous model systems (AMS) and membrane electrode assemblies (MEA), with the main reasons being a suggested discrepancy between estimated and real pH in MEA and stabilization occurring over time [2]. In this work, CLs degradation during dynamic electrolyzer operation in a specially designed PEMWE test station was studied via ex-situ inductively coupled mass spectrometry analysis (ICP-MS) and its influence on the cell’s overall performance was analyzed. The S number, a new metric for OER catalyst lifetime estimation [3], was also used to compare catalyst stability properties within the two systems.

Electronic structure manipulation via composition tuning for the development of highly conductive and acid-stable oxides

Our combined computations and experiments suggest the Mg-Ti-O chemical spaces for novel ternary oxide compounds that can offer high conductivity and corrosion stability to be used in fuel cell applications.

Metal Substitution in Rutile TiO2: Segregation Energy and Conductivity

State-of-the-art acidic oxygen evolution reaction catalysts are mainly based on mixed oxides of titanium and iridium or ruthenium. Because of its high chemical corrosion resistance and stability in acid, $${\hbox {TiO}_2}$$ is a promising support material, yet with poor electrical conductivity. We herein theoretically examined the stability and the electronic properties of substituted rutile-phase titania, in which Ti is partly replaced by elements of the fourth, fifth and sixth period. For negative values of the calculated segregation energy, we conclude that the heteroelement M forms a solid solution for 25% or 50% substitution. For these heteroelements, we calculate the electrical conductivity. Since it is known that the electronic structure of transition metal oxides strongly depends on the applied theoretical method, we performed self-consistent optimizations of the Hartree-Fock contribution to the exchange functional in a hybrid functional for every compound. Experimentally, two favorable and two unfavorable elements were synthesized with 25% foreign metal concentration. The most promising candidates to improve the electronic properties of titania are Ta and Nb.

Surface pre-treatments of Ti-Nb-Zr-Ta beta titanium alloy: The effect of chemical, electrochemical and ion sputter etching on morphology, residual stress, corrosion stability and the MG-63 cell response

Pre-treatment methods for titanium alloys are of great importance, both as regards the treatment of the surfaces of the implant and as regards the pre-deposition phase of the coating processes and the surface modifications. We have investigated the impact of chemical, electrochemical and ion sputter etching on the surface properties, the corrosion stability and the MG-63 cell response of Ti-35Nb-7Zr-5Ta alloy. In the initial state, the samples have a mechanically polished surface. The pre-treatments that were applied led to significant morphological changes in microscale and also in nanoscale. The wettability of the pre-treated surfaces varied from hydrophilicity to hydrophobicity. Changes in contact angle were controlled by surface chemistry rather than changes in morphology and roughness. Native oxides and suboxides of alloying elements with a predominant amount of Nb2O5 were found to provide high corrosion stability of Ti-35Nb-7Zr-5Ta alloy after mechanical polishing, after chemical etching and after electrochemical etching. Significantly reduced corrosion resistance in a physiological saline solution was observed for the ion sputtered surface. A decreasing trend in the cell spreading area correlated with increasing surface roughness and decreasing polarization resistance. There is discussion of the causes of the changes in surface properties and cell behaviour.

Fabrication of functionalized coating with a unique flowery-flake structure for an effective corrosion performance and catalytic degradation

• Inorganic coating layers are hybridized with organic corrosion inhibitors. • Flowery-flake structures are formed by heterogeneous nucleation. • Crystal growth is formed via Layer by Layer self-assembly process. • Formation of stable coordination complexes via molecular orbital interactions. • Functionalized coating with catalytic activity and corrosion protection. The hybridization of organic compounds with inorganic layers would lead to the discovery of novel organic–inorganic hybrid materials with desired functional properties, which could open new avenues toward their state-of-the-art applications. In the present work, therefore, a hybrid organic–inorganic functionalized coating with unique flowery-flake structures was successfully deposited on the defective surface of plasma electrolysis (PE) coating via layer-by-layer self-assembly process of 1-azanaphthalene-8-ol molecules. Herein, two types of defective coatings obtained via PE treatments of AZ31 Mg alloy using either silicate or phosphate-based electrolyte systems were sealed additionally by ethanoic solution of 1-azanaphthalene-8-ol for 24 h. Although the formation level of unique flowery-flake structures has relied on the composition of the defective surface of PE coating, an organic–inorganic hybrid functionalized coating exhibiting high corrosion stability with a trade-off catalytic activity has been successfully obtained. Detailed analysis of the surface morphology of this coating suggested that the formation of stable coordination complexes, due to the molecular orbital interactions of azanaphthalene-8-ol molecules with the PE coating layer, would be the main reason for such performance. The roles of lone pairs and net charges of heteroatoms within 1-azanaphthalene-8-ol molecules during initial physisorption and chemisorptions are computationally analyzed. The mechanism underlying the heterogeneous nucleation and crystal growth of unique flowery-flake structures was discussed by impedance and computational analyses.

Enhanced photoelectrochemical response and stability of hydrogenated ZnO nanorods decorated with Fe2O3 nanoparticles

We report the nucleation-controlled fabrication of randomly oriented hetero-structure of pristine and hydrogen treated ZnO nanorods decorated with Fe2O3 nanoparticles grown via a simple solution-based deposition process. An ∼18-fold improvement (∼6.8 mA/cm2 at 1.23 VRHE) is observed in hydrogen treated ZnO nanorod decorated with Fe2O3 nanoparticles array as compared to the pristine (0.39 mA/cm2 at 1.23 VRHE) photoanode samples along with lowering of onset potential from 0.50 to 0.25 V w.r.t RHE. A detailed energy band diagram of the heterojunction derived from experimental investigations clearly shows staggered energy band alignment favouring photoelectrochemical performance. In addition to this, the enhanced surface area, suppressed recombination, effective charge separation/transport of photogenerated charge carriers and improved visible light absorption due to hydrogenation results in a noticeable high current density and photo corrosion stability.

Feasibility of Ni/Ti and Ni/ GF cathodes in microbial electrolysis cells for hydrogen production from fermentation effluent: A step toward real application

The low cost, low over-potential loss, good catalytic properties for hydrogen evolution reaction (HER), high corrosion stability, commercially available, and could be applied in pH-neutral solution and ambient temperature are important properties for the cathode materials when it is applied in microbial electrolysis cell (MEC) technology. This study has two-pronged objectives: the first is to investigate the feasibility of titanium (Ti) and graphite felt (GF) coated with nickel (Ni), and the second is to generate hydrogen from the fermentation effluent (FE). The electrodeposition (ED) method was used to deposit Ni catalyst onto Ti (Ni/Ti) and GF (Ni/GF) surfaces. The scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy were used to characterize the cathode morphology and element composition. The catalytic properties of Ni/Ti and Ni/GF could be evaluated using the linear sweep voltammetry tests. The maximum volumetric H2 production rates of MEC using Ni/Ti and Ni/GF cathodes were obtained at 0.39 ± 0.01 and 0.33 ± 0.03 m3 H2 m−3 d−1 respectively. The Ni/Ti and Ni/GF cathodes could be used as alternative cathodes while producing hydrogen from FE.

Mathematical modelling of heat-resistant nickel alloys high temperature corrosion

The mathematical modelling of the average corrosion rate () or nickel alloys with different alloying systems (for mono-, directed- and equilibrium crystallization) under synthetic ash conditions at different temperatures has been carried out. Since modern heat-resistant nickel alloys have complex multicomponent compositions, in which all the elements influence on corrosion complexly, the high temperature corrosion (HTC) stability was evaluated by the value of the known parameter Pks(surface resistance coefficient). This made it possible to compare the level of stability of alloys with different alloying schemes. However, this parameter does not cover all the alloying elements that are present in the heat-resistant nickel alloys. Therefore, as a result of analysis and processing of experimental data, the ratio of alloying elements to assess the corrosion resistance has been proposed; this ratio considers the complex influence of the main components of the alloy. Since high temperature corrosion (HTC) is related to the presence of certain elements in the alloy and their concentration, the ratio Kps (surface resistance coefficient) makes it possible to evaluate more adequately the average corrosion rate at different temperatures for multi-component nickel systems. The dependence of the average corrosion rate on Kps for monocrystalline alloys is straightforward, due to the specific character of the alloying systems of this class materials. Characteristic for them is a significantly less amount of chromium (up to 10% by weight) is characteristic of them and a decrease in the content (and in some alloys, absence) of titanium as well, which results in a significant reduction in the high temperature corrosion (HTC)-stability of the material. It has been established that to ensure the required level of high temperature corrosion (HTC) stability of alloys of directed and equilibrium crystallization, the value of the ratio should be not less than Kps ≥ 2, which will provide a non-destructive dense film of corrosion products. So, for the alloys with Kps ≤ 2 the formation of a thick layer of corrosion products, which is easily separated during the operation is characteristic. The obtained regression models give an opportunity to predict the average speed of corrosion depending on the alloying system, both for the development of new heat- resistant nickel alloys for directed crystallization, and in improving the composition of the known industrial alloys within the brand composition. The obtained correlation dependencies are exponential in nature

Study the Activity of a Novel Ni-Based Electrocatalyst for Oxygen Evolution Reaction in Alkaline Media

Electrocatalytic water splitting into hydrogen and oxygen has a great potential to produce hydrogen as a carbon neutral source of energy. However, the sluggish kinetics of oxygen evolution reaction (OER) leads to an inefficient process prohibiting industrial application [1]. Therefore, highly efficient OER electrocatalysts are needed to reduce the energy barrier and enhance the efficiency of water electrolysis cell [2]. IrO2 and RuO2 are the most efficient electrocatalysts for OER, however their commercial industrial applications are limited due to their high cost and low earth abundance. To address this issue, several non-noble metal based OER electrocatalysts including transition metal oxide/hydroxides, perovskite, and molecular electrocatalysts have been developed [3]. Among them, Ni-based materials attract substantial attention owing to their low cost, high corrosion stability, and remarkable catalytic activity in alkaline media. The present work aims to evaluate and compare the electrochemical activity of a novel Ni-based electrocatalyst prepared from two different plating baths toward OER. Electrochemical measurements including cyclic voltammetry (CV), quasi-steady state polarization (QSSP), electrochemical impedance spectroscopy (EIS), and chronopotentiometry (CP) were carried out to study and compare the activity, charge transfer resistance and stability of different electrocatalysts developed in this study toward OER in alkaline media.

Long-term Stable Electrodes Based on Platinum Electrocatalysts Supported on Titanium Sintered Felt for the Use in PEM Fuel Cells

In this work a long-term stable electrode structure, suitable for polymer electrolyte membrane fuel cell (PEMFC) applications is presented. Investigated electrodes are prepared by using sintered titanium felt as porous and current conducting gas diffusion layer, due to its corrosion resistance in acidic environment. Platinum is deposited onto the surface of the titanium fibres by an electrochemical method. This carbon-free electrode structure has been studied regarding stability and performance ex-situ and in-situ by cyclic voltammetry, corrosion tests, i-U polarisation measurements, and accelerated stress tests. Furthermore, the electrode morphology of the catalytic layer on titanium sintered felt has been investigated by means of scanning electron microscopy. Results of this study claim high corrosion stability for the use of these electrodes in PEMFCs. A small-scale laboratory prototype has been realised, which is also presented in this work.

Corrosion resistance of silicon-infiltrated silicon carbide (SiSiC)

Silicon carbide ceramics have found widespread use due to their high corrosion stability. Both solid state-sintered silicon carbide, which has an extremely high corrosion resistance, and silicon-infiltrated silicon carbide are used for various applications. The latter material contains SiC as well as free silicon, which is less stable. Hence, in the present work, the corrosion behavior of silicon-infiltrated silicon carbide ceramics was investigated in NaOH solutions. Long-term corrosion experiments were conducted, and a method for analyzing the corrosion behavior in short-term experiments was developed. The short-term method is based on the accurate measurement of the corrosion depth by laser scanning microscopy on polished surfaces. The results of both methods were in good agreement. The advantage of the short-term method is that it provides information on changes in corrosion mechanisms and corrosion rates in the initial period and as a function of the impurities present. Preferential corrosion of Si at the interface to SiC was observed. TEM investigations revealed that this enhanced corrosion was caused by the segregation of impurities.