Hydrogen gained momentum as a viable alternative to crude-derived fuels. Scalable production of green hydrogen harnessing solar energy emerged as one of the promising sustainable options that can be facilitated by photocatalyst-assisted water splitting. One-step and two-step photoexcitation systems for overall water splitting (OWS) processes gained much importance because of the ease with which they can be scaled up. This chapter gives a profound insight into the fundamental aspects of these systems, along with a broader picture regarding their possible pathway for commercial implementation. Thermodynamic and kinetic requisites of these novel systems have been described in detail and a critical appraisal of the selectivity of co-catalysts in the photocatalytic OWS process is presented. Subsequently, this chapter provides a comprehensive focus on various novel scalability studies like thin film systems, baggie reactors and the solar hydrogen farm project. The ultimate motive of this chapter is to summarize the current state-of-the-art strategies for producing green hydrogen through heterogeneous photocatalysis and the various limitations it possesses that preclude the system from reaching the market so far. By this it will motivate people to develop innovative pathways that would rectify the problems associated with it.@en

The reliability of battery performance is crucial for the implementation of long-term large-scale energy storage. The promising Iron-Air battery is known for its suitable properties relying on its advantageous iron-based anode, characterized by its high volumetric energy density, robustness, material abundance, low cost and scalability. The anode does however present drawbacks, such as self-discharge, hydrogen evolution reaction (HER) and initial- and gradual surface passivation. In previous studies the effect of porosity and specific additives have been presented as important factors in tackling these drawbacks. This multidisciplinary research aimed to study porosity and additive effects on the electrochemical behaviour and performance of iron-based mechanically-stable anodes, manufactured at elevated temperature and pressure. Specifically, the effect of 10wt% pore former K2CO3 on the initial capacity and on the passivation behaviour was studied by galvanostatic charge-discharge, with prior investigation on pore formation. In addition, the effect of high-performance additives (Bi2S3, Bi2O3, ZnS and FeS) was investigated on HER kinetics and the passivation behaviour, by cyclic voltammetry (CV) and galvanostatic cycling, respectively. Surface characterization was performed by optical microscopy, scanning
electron microscopy (SEM), and profilometry. Post-test analysis was carried out by optical microscopy and X-ray Photoelectron Spectroscopy (XPS). An intensification of surface cracks was observed for the K2CO3-rich sample before testing and its initial discharge capacity is 27 mAh/g less than a sample without pore former, but passivated later than the pristine sample in the full cell. Amongst the additives, the highest cycle of 100% capacity retention was marked at cycle 41 for FeS and for Bi2S3 at cycle 29 in the full cell, both showing 100% retention in the half cell up to 36 cycles. FeS might benefit from its readily available soluble reservoir of S2− ions. Bi2O3 showed the lowest capacity retention which might be explained by low conductivity, low solubility and/or lack of beneficial role of S2− ions. However, the additive Bi2O3 showed great reversibility of discharge products in the CV, confirmed by the lower O1s peaks and the lower respective Fe2O3 and FeOOH peak in XPS spectra. The pristine sample showed in the CV over the cycles increased current density and slope near the HER potential, with low reversibility. Apart from Bi2O3 and ZnS, the pristine sample showed lower capacity retention than FeS and Bi2S3, confirming the effective working of these additives. This systematic study portrays a good starting point for further studying porosity and additive effects on the electrochemical behaviour in hot-pressed anodes for the upcoming Iron-Air battery. Improvements can be assigned to cell design, electrolyte control and further detailed porosity characterization. Another type of current collector
might withstand higher current densities and anode thickness reduction can lead to higher discharge capacities over its lifespan.

Functional oxide nanoparticles are extensively utilized in the last decades for biomedical purposes due to their unique functional properties. Nevertheless, their biodegradation mechanism by biological species, particularly by proteins at oxide/protein interfaces, still remains limited. Here, a systematic approaches is provided to investigate electrochemical behavior, electronic properties, and biodegradation mechanism of cobalt ferrite (CFO) and cobalt ferrite-bismuth ferrite (CFO-BFO) core-shell nanoparticles in apoferritin-containing media. Scanning Kelvin probe force microscopy results indicate that the presence of a thin shell (≈5 nm) of BFO on CFO causes a significant increase in surface potential. The potentiodynamic polarization measurements in different solutions showed higher anodic current densities for both samples when decreasing pH and increasing apoferritin concentration. Notably, CFO-BFO exhibits lower anodic current densities than CFO due to a slightly higher flat band potential and lower donor density distribution on CFO-BFO than on CFO, which results in lower electrochemical activity. Long-term monitoring reveals that biodegradation of both nanoparticles is accelerated by high apoferritin concentrations and acidic media, resulting in the decrease of electrochemical potentials and impedance values, and enhancement of metal ion release. Thus, this systematic biodegradation study can help to predict the lifespan and toxicity of these functional nanoparticles in biological environments.

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Electrochemical reduction of carbon dioxide (CO₂) to useful products is an emerging power-to-X concept, which aims to produce chemicals and fuels with renewable electricity instead of fossil fuels. Depending on the catalyst, a range of chemicals can be produced from CO₂ electrolysis at industrial-scale current densities, high Faraday efficiencies, and relatively low cell voltages. One of the main challenges for up-scaling the process is related to (bi)carbonate formation (carbonation), which is a consequence of performing the reaction in alkaline media to suppress the competing hydrogen evolution reaction. The parasitic reactions of CO₂ with the alkaline electrolytes result in (bi)carbonate precipitation and flooding in gas diffusion electrodes, CO₂ crossover to the anode, low carbon utilization efficiencies, electrolyte carbonation, pH-drift in time, and additional cost for CO₂ and electrolyte recycling. We present a critical review of the causes, consequences, and possible solutions for the carbonation effect in CO₂ electrolyzers. The mechanism of (bi)carbonate crossover in different cell configurations, its effect on the overall process design, and the economics of CO₂ and electrolyte recovery are presented. The aim is to provide a better understanding of the (bi)carbonate problem and guide research directions to overcome the challenges related to low-temperature CO₂ electrolysis in alkaline media.

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Due to global warming, there is a rising demand for green energy storage and green fuels. $CO_2$ reduction can help mitigate these demands by storing energy in chemical bonds, thereby creating fuels that are relatively easy to use and store. In this way, a new carbon cycle can be created. Catalyst materials play a key role in improving the selectivity, productivity and stability of the $CO_2$ reduction reaction ($CO_2RR$). MOFs are an interesting catalyst material for this, as their porosity enables large surface areas and their structure allows for tunable selectivity. 2D-MOFs are especially beneficial due to their higher conductivity and mass permeability compared to 3D-MOFs. Carbonization can be used to improve the limited conductivity and stability of MOFs making them more suitable for $CO_2RR$. This is why this study investigates the effects of carbonization on the catalytic capabilities of 3D and 2D-MOFs for the $CO_2RR$. Therefore, Cu-BTC was carbonized using different parameters. The resulting materials were investigated via a multitude of electrochemical techniques to further understand their catalytic capabilities. The 2D-MOFs Cu-THQ and Cu-HAB were then carbonized and the $CO_2RR$ products of the resulting catalysts were investigated. The analysis of the $CO_2RR$ products created by the different MOF derived catalysts shows that the main influence on the selectivity of these catalyst materials is the size and distribution of the Cu-cluster formed during carbonization. Since SEM and EDS results showed that the Cu-cluster formation is influenced by the applied carbonization parameters, this shows that these parameters can affect the selectivity of the resulting catalyst. A reasoning for why the Cu-clusters influence selectivity is discussed, however this remains to be proven by future work.

In recent decades, there has been increasing concern about the impact of climate change on the earth. Various countries are actively developing sustainable energy technologies, of which solar cell is one of the new energy sources with the most attention. This thesis is based on poly−Si(O_x) cells consisting of SiO_x/poly−Si(O_x) passivating contact. Various methods have been investigated to mitigate the TCO (IWO) deposition induced passivation degradation and to optimize the screen printing process.

First, approaches to reduce the passivation degradation due to IWO deposition were explored. The power density and working pressure in IWO deposition were optimized. With utilizing 1.23 W/cm² power density and 5×10⁻³ mbar working pressure, the 𝑖𝑉_𝑂𝐶 degradation was reduced to 4.7 mV for 𝑛⁺ sample (NAOS-SiO_x) and to 7.9 mV for 𝑝⁺ sample after deposition of 75 nm IWO. Besides, hydrogenated amorphous silicon and AZO were used as buffer layers for the 𝑝⁺ SiO_x/poly−Si(O_x) samples, finding that they were effective in reducing sputtering damage. Then, the optimal post-annealing condition was investigated, which turned out to be vacuum annealing at 400 ^◦𝐶 for 30 min, recovering the 49 mV and 60 mV 𝑖𝑉_𝑂𝐶 for 𝑛⁺ sample (thermal-SiO_x) and 𝑝⁺ sample, respectively. Based on the above experiments, the first cells were prepared with a maximum efficiency of 17.4%.

Second, the existing screen printing process in the lab was optimized. The 0.37% organic solvent was added into the silver paste, reducing the viscosity of paste. The snap-off distance was changed to 0.02 mm in order to improve the continuity of printed grids. Moreover, the squeegee speed was optimized to 30 mm/s, limiting the spreading of silver paste to 57.3 𝜇m, much narrower than the initial spreading distance of 155.3 𝜇m.

Finally, a batch of poly−Si(O_x) cells were prepared by applying the above various optimized conditions. The cell with optimized IWO and optimized screen printing process performed best with an champion efficiency of 18.9%.

The often used simplistic correlations between molecular electronic parameters and experimentally determined corrosion inhibition efficiencies are critically evaluated for a set of 24 heterocyclic organic compounds, tested as corrosion inhibitors for copper in 3 wt.% NaCl aqueous solution. Twelve different molecular electronic descriptors—such as ionization potential, electron affinity, HOMO–LUMO gap, dipole moment—are tested and it is shown that none of them displays any noticeable correlation with the inhibition efficiency. Our results, therefore, cast serious doubt on reported correlations between such parameters and inhibition efficiency, obtained for only a few inhibitors, which are abundant in the literature. We also discuss some pros and cons of inhibition efficiency as a metric for evaluating the performance of corrosion inhibitors, and introduce a new metric termed inhibition power that uses the universal logarithmic scale and dimensionless decibel (dB) units.

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The initiation of corrosion can be triggered by defects in the adsorbed layer of organic inhibitors. A detailed knowledge of the intermolecular forces between the inhibitor molecules and the interfacial bonding will be decisive to unravel the mechanisms driving the corrosion initiation. In this work, adsorbed organic layers of 2-mercapto-5-methoxybenzimidazole (SH-BimH-5OMe) and 5-amino-2-mercaptobenzimidazole (SH-BimH-5NH2) were compared regarding their performance mitigating copper corrosion. Atomic force microscopy was used to address the stability and intermolecular forces of the self-assembled monolayers, using imaging and force measurement modes. For a film formed by amino-derivative molecules, a gold-coated tip frequently picked up individual molecules (molecular fishing) in force-distance measurements. For layers of the methoxy-derivative, no fishing events were observed, pointing to a constant functional layer. X-ray photoelectron spectroscopy revealed that SH-BimH-5OMe molecules form a stronger bond with the surface and more stable SAM layers on Cu surfaces as compared to SH-BimH-5NH2 molecules. Results of computational density functional theory modeling and electrochemical corrosion tests are in line with the microscopy and spectroscopy results. In particular, with aid of computational modeling the less ordered structure of the SH-BimH-5NH2 monolayer is attributed to dual bonding ability of SH-BimH-5NH2 that can adsorb with either S or NH2 groups.

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Microstructure-corrosion property correlation is an open question in the field of materials science. The microstructure of metals and alloys consists of several features with different individual corrosion response. The corrosion behavior of the macroscopic system is an outcome of the complex interaction of the components of microstructure. Hence, a definitive understanding of the corrosion response of the microstructural features is needed for improving the material durability and design.In the present work, the effect of grain size  on the active corrosion behavior of pure iron is investigated. Samples with different grain sizes are obtained by annealing heat-treatment. The microstructure of samples is characterized by optical microscopy, electron backscatter diffraction and X-ray diffraction. Electrochemical characterization using potentiodynamic polarization and electrochemical impedance spectroscopy are performed on the samples in deaerated 0.1 M and 0.01 M H₂SO₄ solutions. The surface topography of the corroded sample surface is characterized by atomic force microscopy. Following the experiments, a numerical corrosion model is attempted to replicate the observations. The results reveal an aggregate effect of grain size and crystallographic orientation of grains on the corrosion behavior of the samples.

Rapid industrialization and use of carbon based fuels has caused a drastic increase in the atmospheric CO₂ levels in the last few decades. The rising anthropogenic CO₂ levels pose a significant threat to the environment as evidenced by the increase in the mean global temperature levels, and the rising ocean levels. To mitigate the challenges associated with rising CO₂ levels, there is an urgent need to move towards carbon neutral sources of energy and to curb carbon emission from large scale point emitters such as industries. Additionally, emitted CO₂ could be converted into energy dense organic fuels using carbon-neutral forms of energy. This not only helps in reducing the carbon emissions but also balances the intermittent nature of renewable energy supply. CO₂ could also be converted into platform chemicals such as ethylene/CO, which can be further up-converted or directly used in industry. Ethylene is particularly interesting due to its high
energy density and wide industrial usage as a precursor in the polymer industry. Electroreduction of CO₂ provides one such approach to electrochemically convert CO₂ produced at large scale emitters to useful organic compounds. Different metallic catalysts are known to catalyse the electrochemical reduction towards different products, which follows from Sabatier’s principle. In this study copper is used as the model catalyst due to its unique ability to electrochemically convert CO₂ to multi-carbon products, such as ethylene. From a cell design perspective conventional electrochemical reduction of CO₂ in aq. media suffers from low production rates due to the low solubility of CO₂ in aq. electrolytes which makes it not feasible from an industrial standpoint. To overcome the low production rates, this study was carried out on novel gas diffusion electrodes. Another factor limiting the implementation of CO₂ electrolysers on an industrial scale, is the scalability of the catalyst synthesis. To improve this, electrodeposition of copper catalysts was employed. Electrodeposition is a well-established industrial technique and integrable within the existing infrastructure. Electrodeposition facilitates in-situ growth of the catalyst on gas diffusion layers, thereby providing a facile alternative to the conventional multi-step process for catalyst synthesis. Different morphologies of copper were synthesized by varying the electrodeposition process parameters. Copper nanowires were also synthesized by using templated electro-deposition techniques. The catalysts were characterised before and after the CO₂ reduction experiments by Scanning ElectronMicroscopy, and X- Ray Diffraction. CO₂ reduction experiments using the synthesised copper catalysts were carried out over a range of potentials. A peak Faradaic Efficiency (FE%) of 15% was measured at -1.5 V vs RHE (uncompensated) for ethylene, 19% FE at -1.1 V vs RHE for formic acid, and 13% FE at -1.5 V vs RHE for methane. It was also seen that the catalyst suffered from stability issues which were overcome by using pulsed electrolysis. Using pulsed electrolysis the lifetime of the catalyst was increased from 30 minutes to 15 hours.

This paper investigated a failure in a ventilated disc brake in an automobile. The failed brake disc had been in service for approximately 10 years. The observed failure was in the form of radial cracks that appeared to have initiated at the outer edge of the disc brake. The cracks were rather straight with no branching. Optical microscope, scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDS) were used to study the microstructure of the failed disc. Vickers microhardness test was also used to evaluate the hardness of the samples. Results showed that the root cause of crack formation, in this case, was related to the excessive wear in the brake disc. Different wear mechanisms, namely abrasive and adhesive wear, were recognized in the failed specimen. Moreover, the worn surface in some areas was covered with fine oxide particles. These particles appeared to have a significant contribution toward abrasion. To further understand the wear mechanisms, pin-on-disc experiments were also conducted on the samples. Results of the pin-on-disc experiments were compared and correlated to the results obtained from the failed brake disc.@en

The influence of silane treated nano zinc oxide (nZnO) on the protection, photocatalytic properties and interfacial interactions in acrylic/carbon steel systems was investigated. For this purpose, nZnO particles have been synthesized using microwave irradiation method. The morphology of synthesized zinc oxide nanoparticles was studied by scanning electron microscopy (SEM). The nZnO were treated by 3(2-amino ethyl amino) propyl trimethoxysilane. Fourier transforms infrared spectroscopy (FTIR) and thermogravimetry (TGA) techniques have been used to prove success of nZnO surface modification. In the next step, nanocomposites were prepared and coated on carbon steel by dip-coating method. Corrosion resistances of coatings were evaluated by electrochemical impedance spectroscopy (EIS). Field emission scanning electron microscopy (FE-SEM) has been carried out to study morphology of cross section of films. Moreover, to study the hydrophillicity and photocatalytic properties of coating surface, contact angle of the nanocomposites coating surface have been measured. Finally interfacial adhesion and their mechanisms have been studied by molecular dynamics (MD) and first principle quantum mechanics (QM) simulation method.

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