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• Promising chlorine- and sulfur-based thermochemical water-splitting cycles are investigated. • Challenges related to safe and efficient thermochemical cycles are discussed in detail. • Key factors for thermodynamic, economic, and environmental evaluation are classified. • Future prospects of research and engineering activities in this field are discussed. • Different strategies to reduce energy and economic/environmental parameters are recommended. Thermochemical water-splitting (TWS) processes are regarded as one of the most environmentally friendly strategies, capable of harnessing high-temperature waste heat from industries, renewable energy, and nuclear power sources to produce clean hydrogen (H 2) on a large scale. This review investigates and discusses the thermodynamic, economic, and environmental aspects of promising TWS cycles based on chlorine and sulfur. The TWS cycles discussed in this study include copper-chlorine (Cu-Cl), magnesium-chlorine (Mg-Cl), iron-chlorine (Fe-Cl), vanadium-chlorine (V-Cl), cobalt-chlorine (Co-Cl), cerium-chlorine (Ce-Cl), hybrid sulfur (HyS), sulfur-iodide (S-I), and zinc-sulfur-iodine (Zn-S-I) cycles. Challenges associated with the safe and efficient production of H 2 using the TWS cycles, operating conditions, and potential applications are recognized and discussed in detail. The economic, safety, and environmental aspects of the TWS cycles based on different energy sources (e.g., renewable and nuclear) are thoroughly examined. Enhancing the capacity of thermochemical cycles, employing pinch analysis, and utilizing cutting-edge optimization strategies based on state-of-the-art machine learning techniques and feasible optimization frameworks to reduce energy consumption can effectively reduce the TWS-based H 2 production costs. In a short-term strategy, the primary sources of energy supply for thermochemical cycles can be provided from current nuclear power plants, waste energy from various chemical industries, and renewable energy sources. Advanced reactors and artificial geothermal energy sources can be considered to power thermochemical cycles in a long-term strategy. The outcomes of the current work demonstrate that four-stage Cu-Cl units and four-stage Mg-Cl with dry hydrochloric acid absorption cycles in chlorine-based TWS systems, and S-I and HyS cycles in sulfur-based TWS systems are promising in terms of technical viability, efficiency, economic feasibility, and environmental compatibility. The energy efficiency of the Cu-Cl, Mg-Cl, S-I, and HyS cycles are reported as 32–58.60, 30–63.63, 15.30–60, and 35–48.80%, respectively. The economically optimal cycles for H 2 production include Cu-Cl (1.28–15.56), S-I (2.25–11.65), and HyS (2.97–9.98 $/kg). The global warming potential and acidification potential for the nuclear-based Cu-Cl thermochemical cycles are categorized as 0.50–1.35 kgCO 2 eq/kgH 2 and 1.75–9.60 kgSO 2 eq/kgH 2 , respectively; they are suitable candidates for H 2 production from the environmental perspectives. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel system for production and storage of H 2 with net-zero carbon emissions is developed. • High-temperature fuel cells and biogas upgrading unit are efficiently integrated. • Waste heat of the fuel cells is recovered in the Cu-Cl unit for hydrogen production. • Integrated process can generate 108 kmol/h liquid hydrogen and 18.88 MW power. • A hybrid method of the GA and artificial intelligence tools is applied for optimization. Global energy consumption has been exponentially increasing, leading to the depletion of conventional energy sources and a considerable increase in greenhouse gas emissions. The exploitation of sustainable energy sources and the development of innovative methods for mitigation of CO 2 emissions is necessary. Hydrogen (H 2) as a versatile and green fuel can be produced and stored in liquid form using sustainable energy sources through innovative methods. In this paper, a novel optimal hybrid structure is proposed for hydrogen production and storage with net-zero CO 2 emissions. A high-temperature fuel cell is utilized to reduce CO 2 emissions and supply the heat and power needed to produce and liquefy hydrogen. The hybrid configuration employs an electro-thermochemical unit for hydrogen production, molten carbonate fuel cells, a hydrogen liquefaction process, and a biogas upgrading by water scrubbing. A robust combination of meta-heuristic algorithms and artificial intelligence is developed to optimize the investment return period and energy/exergy efficiencies. The fuzzy Bellman-Zadeh, LINMAP, and TOPSIS techniques are also used to make decisions in multi-objective optimization. This innovative configuration generates 108 kmol/h liquid hydrogen, 18.88 MW power, 54 kmol/h oxygen, and 3258 kmol/h hot water. Pinch, sensitivity, exergy, and economic assessments are implemented to evaluate the performance of the hybrid structure. The thermal and exergy efficiencies of the proposed configuration are obtained to be 78.21 % and 64.83 %, respectively. The greatest portions of destructed exergy are resulted from the fuel cells-gas turbine hybrid system (63.63 %), electro-thermochemical unit (25.96 %), and biogas upgrading technology (6.23 %). The returns period on investment, the prime price of electricity, and the net benefit are computed as 4.854 years, 0.0420 US$/kWh, and 15.73 million US$/years, respectively, based on the energy potentials of Newfoundland and Labrador, Canada. [ABSTRACT FROM AUTHOR]

[Display omitted] • The current status and future prospects of hydrogen production and utilization are discussed. • Challenges and government regulations for hydrogen production in North America are addressed. • High energy consumption and CO 2 emissions are the main challenges for conventional H 2 production. • Hydrogen storage materials are still lacking in both volumetric and gravimetric density. • Biohydrogen production needs further research and development before commercialization. Hydrogen is one of the most efficient and attractive energy carriers that can fulfill current and future energy requirements and address the drawbacks of conventional energy resources. Hydrogen as a fuel is nonmetallic, carbon-free, non-toxic, and has higher specific energy than gasoline (on a mass basis). Hydrogen production, storage, safety, and utilization are the four main aspects that should be considered in hydrogen energy-based systems. This review extensively analyzes the literature on fundamental, technological, and environmental aspects of various hydrogen applications and production techniques as well as theoretical and practical challenges. The global demand for hydrogen is mainly for its utilization in oil refineries (33%), chemical production (40%), metallurgical industries (3%), and the rest is in applications such as fuel, glass manufacturing, welding processes, and food industries. Natural gas, crude oil, coal, and electrolysis processes are the main feedstock sources for hydrogen production, with shares of 49, 29, 18, and 4%, respectively. Currently, hydrocarbon and alcohol reforming, gasification (coal and fossil fuels), and fossil fuel partial oxidation have the greatest shares of the hydrogen production methods. The main challenges for these methods are the high total energy consumption and carbon emissions to the environment. Water electrolysis technologies are still under development and can be combined with renewable energy resources, such as solar, geothermal, wind, and tidal to achieve eco-friendly technologies. Biohydrogen production through biological approaches such as direct and indirect biophotolysis, and photo and dark fermentation processes can be sustainable and promising technologies for bioenergy production worldwide. This review investigates the various thermochemical cycles for hydrogen production and presents the process flow diagram of each cycle. It discusses the different chemical and physical methods and materials for hydrogen storage. In fact, hydrogen storage materials are still lacking in both volumetric and gravimetric density, and in some cases, they do not have promising storage capacity. The current status of hydrogen production, available resources, various challenges in the field of hydrogen production, storage and transportation, and government regulations in North America are discussed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Vital parameters affecting control and utilization of co-culture systems are evaluated. • Utilization of microalgal microbial fuel cells in wastewater treatment is reviewed. • Microalgal co-cultivation systems for biomass/biofuel production are analyzed. • Techniques for biomass and lipid content measurement are comprehensively discussed. • Current challenges and future prospects in microalgal co-cultures progress are addressed. The adverse impacts of fossil fuels on the environment, specifically climate change, have intensified the need for finding a sustainable alternative source of energy. Numerous studies have postulated that biotechnology development, focusing on biofuel production processes, could be a suitable solution for sustainable energy production. The utilization of microorganisms, such as microalgae, is one of the basic strategies to produce biodiesel, pharmaceuticals, and nutraceuticals. Co-cultivation has overtaken mono-cultivation to improve the production of microalgae due to its endurance, foreseeability, and stability. However, further development of the co-cultivation process requires elaborate efforts to make it safe, practical, and optimal. Some dominant factors affecting the co-culture system control are the diversity of the cell groups, mass transfer, scale-up, population ratio, and time. In this review article, we will discuss some critical topics related to the co-cultivation process, such as data collection, modelling, cultivation methods, and interaction varieties. An overview of the quantification techniques for biomass concentration and lipid content is also provided. Moreover, the utilization of microalgal co-cultures will be analyzed, depicting the difficulties associated with their efficient control. As knowledge of the reactions and their entailing kinetics is elemental for analyzing the microalgal systems, which are used to synthesize intermediate products and chemicals, some studies focusing on the kinetics of microalgal biomass conversion into biofuels are presented. Since the microbial fuel cells (MFCs), as a new bioelectrochemical process, are utilized in the mixed-culture systems to treat wastewater and produce biofuels and other valuable by-products, a summary of the microalgal MFCs is also provided. Finally, arguments about the challenges and advantages of the co-cultivation systems are presented. [ABSTRACT FROM AUTHOR]

[Display omitted] • A comprehensive study on renewable energy resources in North America is conducted. • A detailed evaluation of renewable energy potentials is provided. • Important steps for better use of renewable energy resources are summarized. • Emerging technologies for development and management of renewable energy are addressed. • Theoretical and practical challenges in development of renewable energies are highlighted. Energy is an important drive for the economic development and social growth. The energy demand has remarkably escalated due to the technological developments in various governmental, industrial, and municipal activities. The fast growing rate of the energy demand as well as the fuel prices, along with the necessity to control the greenhouse gas emissions are the leading driving forces for effective exploitation of the renewable energy resources. In fact, satisfying the growing global energy demands and mitigating the climate change are of the utmost importance in the modern days. In this review paper, a detailed overview of the development and evolution of the renewable and sustainable energy sources is provided in terms of their types, characteristics, applications, production processes, advantages and disadvantages. Moreover, we discuss the impacts of the renewable energies on health and environment, along with the relevant policies and regulations. Further, the emerging technologies and theoretical and practical challenges in the development of the renewable energies are analyzed. Particularly, this review provides information on renewable and sustainable energies' status and prospects in North America. Central large-scale technology and distributed configurations of the renewable energies might be improved in the North American countries to effectively utilize the renewable energies for producing electricity, biomass-based fuels, and heating in both local/rural and industrial divisions. In addition to employment opportunities stemmed from manufacturing of the renewable energies, its significant impact on the economic development can be enhanced in the US, Canada, and Mexico through development of the renewable energy sources. [ABSTRACT FROM AUTHOR]