Corrosion is an inevitable and persistent issue that affects various metallic infrastructures, leading to significant economic losses and safety concerns, particularly in areas near or in contact with saline solutions such as seawater. Green corrosion inhibitors are compounds derived from natural sources that are biodegradable in various environments, offering a promising alternative to their conventional counterparts. Despite their potential, green corrosion inhibitors still face several limitations and challenges when exposed to NaCl environments. This comprehensive review delves into these limitations and associated challenges, shedding light on the progress made in addressing these issues and potential future developments as tools in corrosion management. Explicitly the following aspects are covered: (1) attributes of corrosion inhibitors, (2) general corrosion mechanism, (3) mechanism of corrosion inhibition in NaCl, (4) typical electrochemical and surface characterization techniques, (5) theoretical simulations by Density Functional Theory, and (6) corrosion testing standards and general guidelines for corrosion inhibitor selection. This review is expected to advance the knowledge of green corrosion inhibitors and promote further research and applications.

Hydrogen has emerged as a promising energy carrier, offering a viable solution to meet our current global energy demands. Solar energy is recognised as a primary source of renewable power, capable of producing hydrogen using solar cells. The pursuit of efficient, durable, and cost-effective photocatalysts is essential for the advancement of solar-driven hydrogen generation. Copper slag, a by-product of copper smelting and refining processes, primarily consists of metal oxides such as hematite, silica, and alumina. This composition makes it an attractive secondary resource for use as a photocatalyst, thereby diverting copper slag from landfills and generating 0.113 μmol/g h of hydrogen, as noted by Montoya. This review aims to thoroughly examine copper slag as a photocatalytic material, exploring its chemical, physical, photocatalytic, and electrochemical properties. Additionally, it evaluates its suitability for water treatment and its potential as an emerging material for large-scale solar hydrogen production.

The increasing demand for sustainable energy and clean water has prompted the exploration of alternative solutions to reduce reliance on fossil fuels. In this context, hydrogen production through water electrolysis powered by solar energy presents a promising pathway toward a zero-carbon footprint. This study investigates the potential of copper slag, an abundant industrial waste, as a low-cost electrocatalyst for the hydrogen evolution reaction (HER) in contact with saline water such as 0.5 M NaCl and seawater, comparing the electrochemical response when in contact with geothermal water from El Tatio (Atacama Desert). The physicochemical characterisation of copper slag was performed using XRD, Raman, and SEM-EDS to determine its surface properties. Electrochemical evaluations were conducted in 0.5 M NaCl and natural seawater using polarisation techniques to assess the corrosion behaviour and catalytic efficiency of the copper slag electrodes. The results indicate that copper slag exhibits high stability and promising HER kinetics, particularly in seawater, where its mesoporous structure facilitates efficient charge transfer processes. The key novelty of this manuscript lies in the direct revalorisation of untreated copper slag as a functional electrode for HER in real seawater and geothermal water, avoiding the use of expensive noble metals and aligning with circular economy principles. This innovative combination of recycled material and natural saline electrolyte enhances both the technical and economic viability of electrolysis, while reducing environmental impact and promoting green hydrogen production in coastal regions with high solar potential. This research contributes to the value of industrial waste, offering a viable pathway for advancing sustainable hydrogen technologies in real-world environments.

Solar saline water splitting is a promising approach to sustainable hydrogen production, harnessing abundant solar energy and the availability of brine resources, especially in the Atacama Desert. Bischofite salt (MgCl₂·6H₂O) has garnered significant attention due to its wide range of industrial applications. Efficient hydrogen production in arid or hyper arid locations using bischofite solutions is a novel and revolutionary idea. This work studied the electrochemical performance of Mn₂O₃ electrodes using a superposition model based on mixed potential theory and evaluated the superficial performance of this electrode in contact with a 0.5 M bischofite salt solution focusing on the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) that occur during saline water splitting. The application of the non-linear superposition model provides valuable electrochemical kinetic parameters that complement the understanding of Mn₂O₃, this being one of the novelties of this work.

Copper slag, produced in pyrometallurgical processes, has the potential to generate hydrogen through thermolysis, depending on its composition. This manuscript explores the use of copper slag as a highly abundant and low-cost material for thermochemical water splitting using concentrated solar power. Copper slag can undergo endothermic reactions with water vapor at high temperatures, conditions which are favorable for activating hydrogen evolution reactions which can be a potential resource for metal recovery such as magnetite and hematite in the circular economy. While research on copper slag and its components has primarily focused on the recovery of valuable metals and material reuse, its direct application in hydrogen production remains largely unexplored, partly due to historically low interest in hydrogen as an energy source. The vast deposits of copper slag in the Atacama Desert, combined with the growing demand for renewable energy, present a unique opportunity to develop sustainable and cost-effective hydrogen production technologies.

Hydrogen has emerged as a promising energy carrier, offering a viable solution to address our current global energy demands. Solar energy stands out as a primary source of renewable power and has the potential to produce hydrogen through the utilization of solar cells. The quest for efficient, durable, and cost-effective photocatalysts is imperative for the advancement of solar-driven hydrogen generation. Copper slag, a by-product stemming from copper smelting and refining processes, primarily consists of metal oxides like hematite, silica, and alumina. This composition renders it a compelling secondary resource for deployment as a photocatalyst, thereby diverting copper slag from landfills. This review aims to comprehensively examine copper slag as a photocatalytic material, exploring its chemical, physical, photocatalytic, and electrochemical properties. Furthermore, it assesses its suitability for water treatment and its potential as an emerging material for large-scale solar hydrogen production.