Atmospheric-pressure plasma seawater desalination: Clean energy, agriculture, and resource recovery nexus for a blue planet

Water connects every aspect of life. Only 4% of the world's water is fresh water, as most water sources have different degrees of salinity. As a result, billions of people face water scarcity, which is a global challenge. Desalination technologies that separate fresh water from solvated salt ions in saline water are attracting major attention. However, conventional desalination processes including thermally and pressure driven processes are highly energy intensive. To address this issue we demonstrate that the atmospheric-pressure plasma (APP) treatment of saline water can be a new potential alternative low-energy and green desalination route. Valuable salts are recovered by direct salt crystal precipitation within a short plasma processing time. During desalination and salt precipitation, plasma activated desalinated water (PADW) is generated and can be used for clean energy processes such as water electrolysis and sustainable agriculture by enhanced plant seed germination. In addition, functional nanomaterials can be extracted from the precipitated salt. The PADW exhibited a low salinity of 5.6 mS/cm with a low pH value of 2.1. The unique intrinsic PADW chemistries enabled electrochemical water splitting for both the hydrogen evolution reaction (HER) at a Pt electrode and the oxygen evolution reaction (OER) at a RuO2 electrode. Moreover, the feasibility of using PADW in sustainable agriculture was demonstrated by enhancing mungbean seed germination using tap water mixed with PADW. At optimum mix concentration, both seed germination rates and germination percentages increased. Finally, we demonstrated the feasibility of synthesizing high-value 2D nanomaterials exemplified by Mg(OH)2 nanosheets via a single step thermal process using the salt precipitated from the seawater by the plasma process. Combined with straightforward use of renewable electricity to generate APPs, this study reveals the plasma potential for sustainable recovery of clean water, clean energy applications, sustainable agriculture, and manufacturing of advanced functional nanomaterials – all from the greatest treasure of our blue planet – seawater.</p

2D MXenes: A New Family of Promising Catalysts for the Hydrogen Evolution Reaction

Developing highly conductive, stable, and active nonprecious hydrogen evolution reaction (HER) catalysts is a key step for the proposed hydrogen economy. However, few catalysts, except for noble metals, meet all the requirements. By using state-of-the-art density functional calculations, herein we demonstrate that 2D MXenes, like Ti2C, V2C, and Ti3C2, are terminated by a mixture of oxygen atoms and hydroxyl, while Nb2C and Nb4C3O2 are fully terminated by oxygen atoms under standard conditions [pH 0, p(H2) = 1 bar, U = 0 V vs standard hydrogen electrode], findings in good agreement with experimental observation. Furthermore, all these MXenes are conductive under standard conditions, thus allowing high charge transfer kinetics during the HER. Remarkably, the Gibbs free energy for the adsorption of atomic hydrogen (ΔGH∗0) on the terminated O atoms (e.g., Ti2CO2) is close to the ideal value (0 eV). Our results demonstrate terminated oxygens as catalytic active sites for the HER at these materials and highlight a family of promising two-dimensional catalysts for water splitting. (Chemical Equation Presented)

Conducting Polymer Based Ammonia and Hydrogen Sulfide Chemical Sensors and Their Suitability for Detecting Food Spoilage

Food security is critical for the sustainability of society. The spoilage of stocked food is an ongoing problem that causes significant losses to the global economy. Novel portable analytical platforms that provide timely information on the condition of food stock can support informed decision-making on the safety of food consumption as well as on maximization of food storage lifetime. Ammonia (NH3) and hydrogen sulfide (H2S) are two of the major harmful gases that are produced due to bacteria activity during the food spoilage process. The timely detection of these gases in food stocks has vital importance to human health. In this review article, the recent progress of conducting polymer based NH3 and H2S gas sensors including sensor device prototypes, their sensing mechanisms, materials and methodologies for sensor fabrication, and their suitability for the development of consumer electronic devices for food spoilage detection are highlighted.Full Tex

Investigating the influence of amorphous/crystalline interfaces on the stability of IrO2 for the oxygen evolution reaction in acidic electrolyte

A major challenge with water splitting technology is to develop highly active and stable electrocatalysts for the oxygen evolution reaction (OER). IrO2 – based electrocatalysts are one of the most active electrocatalysts for proton exchange membrane (PEM) electrolysers, due to their excellent activity for the OER in acidic conditions. However, IrO2 often suffers from dissolution during electrolysis due to phase transitions into more soluble forms. Herein, a range of electrodeposited IrO2 films annealed to different temperatures of up to 500°C are prepared to understand the influence that crystalline/amorphous interfaces have on performance during accelerated degradation tests in concentrated acidic solutions. This study showed that an IrO2 film annealed at 300 °C exhibited the highest catalytic activity with a low overpotential of 150 mV at 10 mA cm−2, the smallest Tafel slope of 51 mV dec−1, with a less progressive decay in activity over a period of 8 h of accelerated degradation testing. This contrasts with both fully amorphous or more crystalline IrO2 films that decayed much more rapidly within 1 h of testing indicating the role that amorphous/crystalline regions have on OER performance.</p

Probing the surface oxidation of chemically synthesised gold nanospheres and nanorods

In this study, the electrochemical behaviour of commercially available gold spheres and rods stabilised by carboxylic acid and cetyl trimethyl ammonium bromide (CTAB) moieties, respectively, are investigated. The cyclic voltammetric behaviour in acidic electrolyte is distinctly different with the nanorods exhibiting unusual oxidative behaviour due to an electrodissolution process. The nanospheres exhibited responses typical of a highly defective surface which significantly impacted on electrocatalytic activity. A repetitive potential cycling cleaning procedure was also investigated which did not improve the activity of the nanorods and resulted in deactivating the gold spheres due to decreasing the level of surface defects

Electrocatalytic and SERS activity of Pt rich Pt-Pb nanostructures formed via the utilisation of in-situ underpotential deposition of lead

The controlled synthesis of nanostructured materials remains an ongoing area of research, especially as the size, shape and composition of nanomaterials can greatly influence their properties and applications. In this work we present the electrodeposition of highly dendritic platinum rich platinum-lead nanostructures, where lead acetate acts as an inorganic shape directing agent via underpotential deposition on the growing electrodeposit. It was found that these nanomaterials readily oxidise at potentials below monolayer oxide formation, which significantly impacts on the methanol electrooxidation reaction and correlates with the incipient hydrous oxide adatom mediator (IHOAM) model of electrocatalysis. Additionally these materials were tested for their surface enhanced Raman scattering (SERS) activity, where the high density of sharp tips provides promise for their application as SERS substrates

Activating iron based materials for overall electrochemical water splitting via the incorporation of noble metals

Although the presence of iron in mixed metal oxide based catalysts has shown significant performance improvement in the oxygen evolution reaction (OER), iron oxides themselves demonstrate much poorer activity. In this study, we investigate improving the performance of iron catalysts via surface decoration with gold or platinum for not only the OER but also the hydrogen evolution reaction (HER) for overall water splitting in an alkaline electrolyte. Two types of iron catalysts were synthesised, iron nanocubes and iron oxide via electrochemical deposition methods which were decorated with either Au or Pt via galvanic replacement. It was found that the presence of Au significantly enhanced the OER performance of iron oxide and the HER performance of iron nanocubes. The presence of Pt resulted in moderate improvement in the OER but significant improvement for the HER but did not surpass the performance of gold decorated iron nanocubes. This indicates that the speciation of the iron catalyst and the decorating metal was important for tuning the activity to the OER and the HER. For the OER, the formation of iron oxide/Au interfaces was determined to be an important component for high activity whereas the metallic nature of metal decorated iron nanocubes was important for the HER. Therefore, iron based catalysts can be modified to demonstrate bifunctional behaviour for overall water splitting via the inclusion of gold nanoparticles.</p

Impact of fuel cells on hydrogen energy pathways in a sustainable energy economy

The drive to decarbonise the electricity and transport industries when transitioning from a fossil fuel economy to a hydrogen economy requires careful consideration of techno-environmental implications. National and regional strategies for adopting hydrogen energy highlight an overarching objective to use hydrogen for electrification that requires a concomitant transition to fuel cell technologies. We therefore examine the impact of emergent fuel cell technologies on the sustainability of various hydrogen energy pathways. Using a technology neutral framework, we show that hydrogen derived from fossil fuels for use in fuel cells (i.e., blue hydrogen), is techno-environmentally unviable in a future economy. We propose that a narrative focused on a sustainable energy economy, rather than a hydrogen economy, shifts the debate to meet the requirements of national and regional strategies with key implications for the energy industry and policy maker.</p

Electrochemical synthesis of a multipurpose Pt−Ni catalyst for renewable energy-related electrocatalytic reactions

Renewable energy driven electrochemical processes are becoming increasingly important in the transition away from fossil fuels. One of the key reactions is electrochemical water splitting to generate green hydrogen which ideally could be directly integrated with a wind or solar electricity source. However, alkaline electrolysers suffer from significant degradation in performance if they are rapidly powered down under reduced sunlight conditions when directly coupled with a solar cell due to reverse current flow. In this work we address this issue by creating a truly bifunctional electrode material that is switchable between the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). The synthesis method is simple whereby a Pt electrode is electrochemically activated and then immersed in a nickel nitrate solution to electrolessly deposit Ni on the surface. When this electrode is electrochemically cycled, it creates an active Pt−Ni alloy at the Pt surface. Importantly, this electrocatalyst is switchable between both reactions without loss of activity as evidenced by an accelerated stress test over a 24 h period. An added advantage is that this Pt−Ni electrocatalyst is also more active than Pt for the oxygen reduction reaction which opens up its applicability in fuel cells. Finally, to demonstrate the multifunctionality of this Pt−Ni material, ethanol and ammonia oxidation is demonstrated which also shows better performance than Pt.</p

Conducting Polymer Based Ammonia and Hydrogen Sulfide Chemical Sensors and Their Suitability for Detecting Food Spoilage

Food security is critical for the sustainability of society. The spoilage of stocked food is an ongoing problem that causes significant losses to the global economy. Novel portable analytical platforms that provide timely information on the condition of food stock can support informed decision-making on the safety of food consumption as well as on maximization of food storage lifetime. Ammonia (NH3) and hydrogen sulfide (H2S) are two of the major harmful gases that are produced due to bacteria activity during the food spoilage process. The timely detection of these gases in food stocks has vital importance to human health. In this review article, the recent progress of conducting polymer based NH3 and H2S gas sensors including sensor device prototypes, their sensing mechanisms, materials and methodologies for sensor fabrication, and their suitability for the development of consumer electronic devices for food spoilage detection are highlighted