Johnson Matthey Technology Review - Volume 66, Issue 1, 2022

Adsorption is a fundamental process which takes place on a catalyst surface before it dissociates, diffuses over the surface and recombines with other adsorbed species to form the final product. Therefore, in theoretical chemistry understanding of the local geometrical and electronic properties of the adsorbed species on the catalyst surface has been a topic of core focus. In this short review we briefly summarise some of the important developments on theoretical studies related to the adsorption properties of transition metal (TM) catalysts on graphene and graphene-related carbon materials. Prior to this, we will present a discussion on various forms of carbon materials used as catalyst supports, which will be followed by a brief discussion of the fundamentals of the density functional theory (DFT).

Photoelectrocatalysis offers a way to generate hydrogen and oxygen from water under ambient light. Here, a series of hydrogen evolving photocatalysts based on a ruthenium(II) bipyridyl sensitiser covalently linked to platinum or palladium catalytic centres were adsorbed onto mesoporous nickel oxide and tested for hydrogen evolution in a photoelectrochemical half-cell. The electrolyte buffer was varied and certain catalysts performed better at pH 7 than pH 3 (for example, PC3 with photocurrent density = 8 μA cm^–2), which is encouraging for coupling with an oxygen evolving photoanode in tandem water splitting devices. The molecular catalysts were surprisingly robust when integrated into devices, but the overall performance appears to be limited by rapid recombination at the photocatalyst|NiO interface. Our findings provide further insight towards basic design principles for hydrogen evolving photoelectrochemical systems and guidelines for further development.

This study assesses the use of short wavelength radiative heating techniques such as near infrared (NIR), intense pulsed light (IPL) and ultraviolet (UV) heating for processing coatings in energy applications. It concentrates on the importance of investigating different radiative wavelengths to advance these technologies as scalable processes via reduced heating times. It illustrates the mechanisms by which these techniques can transform thin film materials: sintering, binder removal, drying and chemical reactions. It focuses on successful research applications and the methods used to apply these radiative mechanisms in solar energy, battery storage and fuel cells, while considering the materials suitable for such intentions. The purpose of this paper is to highlight to academics as well as industrialists some of the potential advantages and applications of radiative heating technologies.

In recent years, sodium-ion batteries (NIBs) have been explored as an alternative technology to lithium-ion batteries (LIBs) due to their cost-effectiveness and promise in mitigating the energy crisis we currently face. Similarities between both battery systems have enabled fast development of NIBs, however, their full commercialisation has been delayed due to the lack of an appropriate anode material. Hard carbons (HCs) arise as one of the most promising materials and are already used in the first generation of commercial NIBs. Although promising, HCs exhibit lower performance compared to commercial graphite used as an anode in LIBs in terms of reversible specific capacity, operating voltage, initial coulombic efficiency and cycling stability. Nevertheless, these properties vary greatly depending on the HC in question, for example surface area, porosity, degree of graphitisation and defect amount, which in turn are dependent on the synthesis method and precursor used. Optimisation of these properties will bring forward the widespread commercialisation of NIBs at a competitive level with current LIBs. This review aims to provide a brief overview of the current understanding of the underlying reaction mechanisms occurring in the state-of-the-art HC anode material as well as their structure-property interdependence. We expect to bring new insights into the engineering of HC materials to achieve optimal, or at least, comparable electrochemical performance to that of graphite in LIBs.

Since the early 2010s, less than a handful of studies have been communicated to the hydrogen and fuel cell communities that special care should be adopted, and a systematic approach should be applied, when homogenising catalyst ink slurries using ultrasound in the form of either a laboratory-grade ultrasonic cleaning bath, or an ultrasonic probe (sonifier). In these studies, it was demonstrated that the use of power ultrasound for the homogenisation of catalyst inks can be detrimental if not used appropriately. Unfortunately, and to this day, literature still indicates that ultrasound is still used for the homogenisation of fuel cell and electrolyser catalyst ink slurries and little or even no experimental conditions are given. To what extent is this approach acceptable? This short review paper discusses the importance of using ultrasound adequately to avoid catalyst dissolution and ionomer degradation induced by acoustic cavitation as well as metallic contamination originating from the ultrasonic probe. It also sheds some light on the important aspects and effects of power ultrasound in liquids and surfaces and presents some recommendations on how to use ultrasound adequately for mixing catalyst ink formulations.

In this work, seven different extracts from pomegranate (Punica granatum L., cv. Hicaz nar) peel were prepared by using different solvents (ethanol, methanol, either alone or in combination with acid, acetone and water). The phenolics (punicalagins and ellagic acid), organic acids (citric acid and malic acid) and sugars of pomegranate peel extracts (PPEs) were determined. The highest amounts of punicalagins and ellagic acid were detected by ethanol-acid extract as 13.86% and 17.19% w/v respectively, whereas the lowest levels were obtained with acetone and water extracts. Moreover, the methanol-acid (3.19% malic acid) and ethanol-acid (1.13% citric acid) extracts contained the highest levels of organic acids. The antimicrobial activities of extracts were investigated by agar well diffusion method. Methanol-acid and ethanol-acid extracts exhibited the highest antimicrobial effects on all tested microorganisms, giving inhibition zones ranging in size from 17 mm to 36 mm. Although similar antimicrobial activities were observed by ethanol, methanol and acetone extracts (up to 24 mm), the lowest antimicrobial activities were attained by water extract (0–15 mm). All extracts were generally more effective against Gram-positive bacteria: Enterococcus faecalis, Bacillus subtilis, Bacillus cereus than Gram-negative ones: Escherichia coli and Enterobacter aerogenes (Klebsiella aerogenes). It was shown that extracts from pomegranate peels represent a good source of bioactive compounds.

The aim of this study was to prepare microcapsules and transfer them to denim and non-denim trousers using different application methods. For this purpose, shea butter as active agent was encapsulated in an ethyl cellulose shell using the spray dryer method, and capsule optimisation was studied. A morphological assessment showed that the capsules had a smooth surface and were spherical in shape. The homogenous size distribution of the capsules was supported by laser diffraction analysis. The capsules showed a narrow size distribution, and the mean particle size of optimum formulations of shea butter was 390 nm. Denim fabrics were treated with shea butter capsules using the methods of exhaustion and spraying in order to compare these application methods. The presence of capsules on the fabrics was tested after five wash cycles. The comparison of application methods found similar preferred characteristics for both the exhaustion and spraying methods. However, the spraying method was found to be more sustainable, because it allows working with low liquor ratios in less water, with lower chemical consumption and less waste than the exhaustion method, which requires working with a high liquor ratio. This study showed that the spraying method can be used as an alternative to other application methods in the market for reducing energy consumption, and shea butter capsules can provide moisturising properties to the fabrics.

Electronic textiles (e-textiles) hold the key for seamless integration of electronic devices for wearable applications. Compared to other flexible substrates, such as plastic films, textiles are, however, challenging substrates to work with due to their surface roughness. Researchers at the University of Exeter, UK, demonstrated that using different coating techniques as well as different types of graphene coatings is the key to overcome this challenge. The results of coating selected monofilament textile fibres and woven textiles with graphene are discussed here. These conductive textiles are fundamental components in e-textiles, and some applications will be reviewed in this paper. That includes light-emitting devices, touch and position sensors, as well as temperature and humidity sensors. The possibility of triboelectric energy harvesting is also discussed as the next step to realise self-powered e-textiles.