About the journal The journal Energy Conversions is an international, peer-reviewed open-access journal that aims to advance the science, engineering, and policy aspects of sustainable energy systems. The journal focuses on the transformation, integration, utilization, and management of energy in its various forms to improve efficiency, reduce environmental impact, and accelerate the transition toward decarbonized systems. View full aims & scope Article publishing options Open Access Article Publishing Charge (APC): USD 200 (excluding taxes). The amount you pay may be reduced during submission if applicable. Subscription No publication fee charged to authors, and published articles are immediately available to subscribers. <table class="MsoNormalTable" style="border-collapse: collapse; border: none; mso-border-left-alt: solid windowtext .5pt; mso-border-right-alt: solid windowtext .5pt; mso-yfti-tbllook: 1184; mso-padding-alt: 0in 5.4pt 0in 5.4pt; mso-border-insideh: 1.5pt solid #76923C; mso-border-insideh-themecolor: accent3; mso-border-insideh-themeshade: 191; mso-border-insidev: 1.5pt solid #76923C; mso-border-insidev-themecolor: accent3; mso-border-insidev-themeshade: 191;" border="1" cellspacing="0" cellpadding="0"> 1 day Time to first decision 6 days Review Time 7 days Submission to acceptance 1 day Acceptance to publication View all insights Editor-in-chief l View Full editorial board Dr. Malcolm D. Hartwell Professor of Thermal Systems Engineering Midwestern Institute of Energy Innovation, USA Articles Research article lOpen access Evaluating Solar Tracking System Efficiency in Dusty and Humid Environments Anwar H. Al-Assaf 23 July 2025 Research article lOpen access Desalination in the Anthropocene: Technologies, Energy, Brine Management, and Pathways to Ultra-Low-Carbon Water Laila M. Alhumaydi 23 July 2025 Research article lOpen access Cooling Efficiency in Thermal Systems: Metrics, Drivers, and Pathways to Ultra-Low Energy Cooling Jazmynn K. Haffez 23 July 2025 Research article lOpen access Built Environment 2050: Integrating Efficiency, Health, and Carbon Neutrality Across Buildings Jaalaa M. El-Shamyy 23 July 2025 Research article lOpen access A Comprehensive Review of Air Quality Science, Measurement, Health Impacts, and Policy Pathways for Clean Air Narriam A. El Dayd 23 July 2025 Research article lOpen access Advances and Challenges in Solar Energy Conversion: Technologies, Integration Pathways, and Future Prospect Shen Zei 15 Aug 2025 Research article lOpen access Geothermal Energy: Pathways, Technologies, and Prospects for Sustainable Power Generation Hmeed Karm 23 July 2025 Research article lOpen access Hydrogen Energy: Pathways, Technologies, and Global Prospects for a Decarbonized Future Markcus Vogar 23 July 2025 Read latest issue
Multi-Objective Generative Design for Energy-Efficient Heat Sinks: Integrating Constructal Theory with Manufacturing Constraints for Industrial Thermal Management
Thermal management inefficiencies contribute significantly to global energy consumption, with data centers alone using 200+ TWh annually for cooling. While constructal theory predicts optimal branching geometries that minimize thermal resistance, these designs typically violate fundamental manufacturing constraints, preventing industrial implementation. This study presents a Physics-Informed Graph Diffusion Network (PI- GDN) that simultaneously optimizes thermal performance, manufacturing feasibility, production cost, and material efficiency. The framework encodes heat transfer physics and process-specific constraints for metal additive manufacturing, investment casting, and die casting into a unified multi-objective optimization. Computational validation across 500 generated designs demonstrates Pareto-optimal solutions spanning Rth = 0.24–0.39 K/W at 0.7–1.3× baseline manufacturing costs. Experimental testing of 12 fabricated prototypes confirms <4% deviation from computational predictions, with best-performing designs achieving Rth = 0.247 K/W — a 42% reduction compared to conventional extruded-fin heat sinks. A data center case study demonstrates 1.3 GWh/year energy savings across 10,000 servers, yielding a net 5-year benefit of \$1.21M. The framework includes an intelligent manufacturing method recommender that selects optimal production processes based on volume and performance targets, enabling automated design-to-production workflows.
Energy efficiency; Thermal management; Constructal theory; Additive manufacturing; Multi- objective optimization; Heat sinks; Generative design; Deep learning
Enhanced Room-Temperature Transesterification of Palm Oil Using a DES K2CO3–Glycerol Catalyst with Acetone as Co-Solvent
Biodiesel production conventionally requires elevated temperatures (65–70 ℃), resulting in high energy consumption. This study investigates a low-energy alternative by employing a deep eutectic solvent (DES) catalyst based on K2CO₃–glycerol for transesterification of palm cooking oil at room temperature (27-28 oC), assisted by acetone as a co-solvent to enhance phase miscibility. The effects of methanol concentration (25–35%), DES K2CO₃–glycerol catalyst loading (4–6%), and reaction time (2 and 4 h) were examined. Biodiesel properties—including density, viscosity, acid value, total glycerol, methyl ester content, and yield—were evaluated with reference to SNI 7182-2015 and ASTM D6751 standards. Increasing catalyst loading, methanol concentration, and reaction time generally reduced density, viscosity, and total glycerol while increasing methyl ester content. The most favorable operating conditions were obtained at 6% catalyst, 35% methanol, and 4 h reaction time, producing biodiesel with a density of 0.866 g/cm³, viscosity of 3.73 cSt, total glycerol of 0.404%, and methyl ester content of 95.7004%. While density and viscosity met SNI and ASTM specifications, the acid value and total glycerol did not fully comply, indicating the need for further catalyst and purification optimization. This work demonstrates the potential of DES K2CO3–glycerol for room-temperature (27-28 oC) biodiesel synthesis and highlights key factors governing fuel quality in low-energy production routes.
Biodiesel, Palm Cooking Oil, DES K2CO3-Glycerol, Room Temperature, Co-solvent acetone
Hybrid Renewable Energy System Design and Economic-Environmental Analysis for Isolated Islands using HOMER Pro and Pareto-Fuzzy Optimization
Remote islands in Malaysia currently rely heavily on diesel generators for electricity supply, resulting in high operational costs, significant carbon dioxide (CO2) emissions, and fuel supply insecurity. Despite the abundance of solar and wind resources, improper system sizing and limited consideration of energy storage capacity frequently restrict renewable energy penetration in these regions. This study aims to develop a multi-objective sizing optimization framework to design a cost-effective and low-emission hybrid renewable energy system (HRES) comprising photovoltaic (PV) panels, wind turbines (WT), a diesel generator (DG), and a battery energy storage system (BESS). While HOMER Pro is a robust tool for generating sizing combinations, it is inherently limited to single-objective optimization based on cost minimization. To overcome this limitation, a Pareto–Fuzzy decision-making method was integrated into the analysis to perform multi-objective optimization considering both cost minimization and CO2 emission reduction. The performance of these configurations was then compared against a conventional diesel-only baseline to evaluate their overall effectiveness. Results demonstrate that the Pareto-Fuzzy optimized HRES achieves a 49% reduction in CO₂ emissions and increases the renewable fraction to 91.8% compared to the HOMER cost-optimal configuration, while incurring only marginal increases of 1.45% in Net Present Cost (NPC) and 1.44% in Levelized Cost of Energy (LCOE), highlighting an effective trade-off between economic and environmental performance. Critically, the Pareto-Fuzzy solution outperforms the diesel-only baseline in terms of cost-effectiveness while delivering significantly lower annual CO₂ emissions. Consequently, this research confirms that the integration of Pareto-Fuzzy multi-objective optimization provides a superior and more sustainable pathway for isolated HRES by achieving substantial environmental gains with negligible economic impact.
CO₂ emission reduction, Hybrid renewable energy system (HRES), Multi-objective optimization, Net Present Cost, Pareto-Fuzzy
Towards Net-Zero Aviation: A Critical Review of Sustainable Aviation Fuel Pathways and Scale-Up Constraints
Aviation is one of the most difficult sectors to decarbonize because long-range flight still depends on high-energy-density liquid fuels. Sustainable aviation fuel (SAF) has therefore emerged as the principal near-term decarbonization option, but its real climate value depends on feedstock origin, conversion route, energy inputs, and deployment scale. This review synthesizes the state of knowledge on the major SAF pathways—including hydroprocessed esters and fatty acids (HEFA), Fischer–Tropsch (FT), alcohol-to-jet (ATJ), and power-to-liquid (PtL)—and compares their feedstocks, fuel yields, lifecycle greenhouse gas performance, production costs, certification status, and infrastructure readiness. Particular attention is given to the trade-offs among technological maturity, resource availability, land and water pressures, hydrogen demand, and electricity carbon intensity. The analysis also examines how policy instruments such as CORSIA and regional blending mandates shape investment signals and market formation. The review shows that no single pathway can satisfy future aviation demand on its own: mature lipid-based routes can support near-term growth, whereas deep long-term decarbonization will require large-scale expansion of residue-based and synthetic fuels. Progress in certification, feedstock governance, and industrial scale-up will be decisive for meaningful SAF penetration
Sustainable Aviation Fuel; Aviation Decarbonization; Hydroprocessed Esters and Fatty Acids; Fischer–Tropsch
Catalytic Strategies for Low-Carbon Fuel Production: Progress, Constraints, and Future Directions
Catalytic materials determine how efficiently carbonaceous, biogenic, and fossil-derived feedstocks can be upgraded into practical fuels. This review reassesses progress in fuel-oriented catalysis by comparing the influence of active metals, supports, promoters, pore architecture, and operating conditions on conversion, selectivity, and durability. Thermochemical routes such as Fischer–Tropsch synthesis, reforming, hydrodeoxygenation, and CO₂ hydrogenation are considered alongside emerging electrochemical pathways. The analysis highlights how transport limitations, acidity/basicity, metal dispersion, and interfacial chemistry govern performance, while coking, sintering, poisoning, and structural reconstruction continue to limit industrial deployment. Special attention is given to mesostructured supports, bifunctional catalysts, single-atom active sites, and data-driven screening approaches that can shorten development cycles. Across the surveyed literature, high initial activity alone is not a sufficient metric of quality; catalysts must also maintain selectivity, tolerate realistic feeds, and remain regenerable over extended operation. The review therefore emphasizes integrated design strategies that couple rational synthesis, operando characterization, kinetic interpretation, and machine-learning-assisted discovery to support cleaner and more resilient fuel production technologies.
Catalysis; Green fuel production; Fischer–Tropsch synthesis; CO₂ hydrogenation; Hydrodeoxygenation; Biofuels; Zeolite catalysts; Catalyst deactivation
Bridging Simulation and Deployment in Numerical Energy Modeling
Numerical modeling now underpins the analysis, design, and optimization of contemporary energy systems. This review examines the development and application of major numerical approaches, including computational fluid dynamics (CFD), finite element analysis (FEM), and transient system-level simulation, across representative technologies such as solar thermal collectors, fuel cells, wind turbines, heat exchangers, buildings, and electrochemical reactors. The paper outlines the governing equations, discretization routes, solver strategies, validation practices, and uncertainty-handling methods that shape model credibility. Selected case evidence is used to show how mesh density, physical assumptions, and boundary conditions influence solution accuracy, cost, and interpretability. The review also highlights the increasing integration of optimization routines, machine learning surrogates, and digital-twin architectures with physics-based models. Despite major progress, persistent limitations remain in numerical stability, data availability, computational expense, and multiphysics coupling. The overall trajectory points toward faster, more adaptive, and more operationally connected simulation environments for next-generation energy systems.
Numerical modeling; Energy systems; Computational fluid dynamics (CFD)
Green Hydrogen for Deep Decarbonization: Technology Progress, Cost Evolution, Infrastructure, and Global Deployment Pathways
Green hydrogen is increasingly viewed as a strategic option for decarbonizing energy- and carbon-intensive sectors while improving long-term energy system flexibility. Produced by water electrolysis powered by renewable electricity, it offers a low-emission alternative to fossil-derived hydrogen and a potential bridge between variable renewable generation, industrial fuel demand, and emerging clean-fuel markets. This review synthesizes recent progress in electrolyzer technologies, national deployment strategies, cost trajectories, infrastructure development, and market formation. Comparative discussion is provided across major regions including the European Union, North America, Australia, China, and the Gulf, highlighting differences in resource endowment, policy support, and export orientation. The assessment shows that the economics of green hydrogen remain highly location-dependent, but declining electrolyzer costs, larger project scales, and access to low-cost solar and wind resources are expected to narrow the gap with conventional hydrogen. Key barriers persist in water availability, transport logistics, storage, certification, and manufacturing supply chains. Overall, the literature indicates that levelized green hydrogen costs could approach or fall below about $2/kg in favorable settings by 2030, provided that policy support, infrastructure build-out, and technology scale-up advance in parallel. The paper concludes by identifying research and governance priorities needed to accelerate robust and equitable market growth.
Green hydrogen; Water electrolysis; Energy transition
Optimizing Flight Operations for Lower Emissions: A Review of Wind-Aware Routing, AI, and SAF-Linked Strategies
Commercial aviation remains a significant emissions source, while fuel continues to dominate airline operating costs. For that reason, operational efficiency is one of the most immediate levers available for lowering both climate impact and expenditure. This review examines aviation route optimization through four interacting dimensions: wind-aware and altitude-aware trajectory design, airspace-level congestion management, artificial intelligence (AI)-assisted planning, and the coupling of routing decisions with sustainable aviation fuels (SAFs). Literature published between 2010 and 2024 was screened from major scientific databases, producing a final set of 50 studies for detailed synthesis. Across the reviewed work, wind-informed routing commonly delivers fuel savings of about 1-4.2% on long-haul missions, while congestion mitigation and collaborative flow management add a further 2-5% at network level. AI-based methods report the largest operational improvements, with several studies indicating fuel-burn reductions approaching 14% under data-rich conditions. SAF deployment mainly affects lifecycle emissions, but several studies also point to favorable combustion and efficiency characteristics that can reinforce optimized routing. The review identifies the principal synergies, practical barriers, and research priorities associated with these approaches, including certification, explainability, digital data sharing, and equitable global deployment. Overall, integrated optimization emerges as a credible pathway for reducing the energy and carbon intensity of flight.
Aviation route optimization, sustainable aviation fuel, fuel efficiency
Theoretical Frameworks for Estimating Internal Combustion Engine Power
This review examines the principal theoretical routes used to estimate engine power without relying exclusively on full-scale dynamometer testing. The analysis spans ideal cycle formulations, zero-dimensional and quasi-dimensional combustion models, one-dimensional gas-exchange simulations, high-fidelity CFD, and emerging data-driven surrogates. Particular attention is given to how heat release, in-cylinder pressure evolution, volumetric efficiency, friction, pumping work, and fuel properties influence the prediction of indicated and brake output. Representative figures are used to compare modeling hierarchies, visualize fuel-energy partitioning, track pressure and heat-release phasing, map parameter sensitivity, and illustrate the dependence of brake power on engine speed and mean effective pressure. The review shows that low-order thermodynamic methods remain effective for screening and preliminary design, whereas combustion-resolved and CFD-based approaches are better suited to calibration, abnormal-combustion assessment, and fuel-flexibility studies. Machine-learning models can accelerate prediction, but their reliability improves when they are anchored to physics-based constraints. Overall, the most appropriate framework depends on the intended application, the level of fidelity required, the availability of input data, and the acceptable computational cost.
Engine power quantification, Thermodynamic and combustion modeling, Heat-release and pressure-based analysis
Alternative Fuels for Power Generation: Conversion Pathways, Performance Trade-Offs, and Deployment Readiness
Decarbonizing power generation requires fuel options that can complement variable renewable electricity while reducing dependence on fossil resources. This review critically compares biofuels, hydrogen, ammonia, synthetic hydrocarbon fuels, and alcohol-based fuels with emphasis on production pathways, fuel properties, lifecycle greenhouse gas performance, infrastructure demands, and economic viability. The analysis shows that no single pathway dominates across all criteria. Biofuels benefit from comparatively high technological maturity and easier integration into existing assets, but sustainable feedstock availability constrains long-term scale-up. Green hydrogen offers the lowest carbon intensity among the reviewed options and can support flexible generation, yet storage penalties, supply-chain development, and current production cost remain major barriers. Synthetic fuels retain the strategic advantage of compatibility with legacy engines and handling systems, although their multi-step conversion routes impose significant efficiency and cost penalties. Ammonia is promising for large-scale storage and dispatchable power applications, but toxicity, combustion stability, and NOx mitigation must be addressed before broad deployment. Overall, future fuel selection should be guided by integrated assessments that simultaneously consider emissions, cost, energy density, infrastructure readiness, and sector-specific performance requirements
Alternative fuels, power generation, fuel production pathways, lifecycle emissions, techno-economic assessment, infrastructure compatibility
Solid Biomass Energy Pathways: Feedstock Resources, Conversion Routes, Sustainability Implications, and Deployment Prospects
Solid biomass remains one of the few renewable resources capable of delivering dispatchable energy while also supporting waste valorization and rural economic activity. This review re-examines the role of solid biomass in low-carbon energy systems by synthesizing evidence on feedstock availability, thermochemical conversion routes, environmental performance, and techno-economic feasibility. The discussion covers agricultural residues, forestry by-products, dedicated energy crops, and the organic fraction of municipal waste, emphasizing how calorific value, moisture level, ash content, and logistics shape technology selection. Combustion, pyrolysis, and gasification are compared in terms of operating conditions, conversion efficiency, emissions, and product flexibility, with additional attention to co-benefits such as biochar generation and combined heat and power integration. The review also evaluates life-cycle emissions, policy support, feedstock supply chains, and scale-up barriers that determine whether biomass systems deliver genuine climate benefits or simply shift burdens to land, air quality, and food systems. Across the surveyed literature, the strongest performance is observed when biomass is locally sourced, properly pretreated, and deployed within robust sustainability frameworks. Although solid biomass cannot serve as a universal replacement for fossil fuels, it can make a meaningful contribution to distributed heat and power generation, circular waste management, and regional decarbonization. Continued progress will depend on cleaner conversion technologies, better resource governance, digital process monitoring, and stronger integration with bio-refinery and circular-economy models.
Solid biomass energy; Biomass conversion; Combustion; Gasification
Food Waste-to-Energy Conversion: A Critical Review of Pathways, Performance and Deployment Constraints
Food waste constitutes a major biodegradable fraction of municipal refuse and is increasingly viewed as a recoverable energy resource rather than a disposal burden. This review critically examines the principal routes for converting food waste into useful energy, including anaerobic digestion, gasification, pyrolysis, hydrothermal liquefaction, and direct combustion. The analysis compares process severity, feedstock tolerance, energy yield, environmental performance, and downstream utilization options such as combined heat and power and solid oxide fuel cells. Across the literature, anaerobic digestion remains the most mature option for wet, source-separated waste because it tolerates high moisture content and enables simultaneous biogas and digestate production. Thermochemical pathways provide broader product flexibility and higher energy-density intermediates, but they generally require tighter feedstock conditioning and more complex gas-cleaning or upgrading steps. Life-cycle and techno-economic evidence indicates that food waste valorization can outperform landfilling when collection logistics, pretreatment, and policy support are adequately addressed. The review also highlights recurring commercialization barriers linked to feedstock heterogeneity, contamination, pretreatment cost, and fragmented regulation. Overall, the evidence favors integrated food waste-to-energy systems that combine robust preprocessing, appropriate conversion selection, and digital process control to improve recovery efficiency while limiting environmental impacts.
Food waste valorization; Waste-to-energy; Anaerobic digestion; Pyrolysis
Energy-Efficient Flight Path Optimization: A Review of Wind-Aware Routing, AI Planning, and SAF Integration
Decarbonizing commercial aviation requires measures that can be deployed before large-scale fleet renewal, and flight-route optimization is one of the most actionable levers available today. This review examines how wind-aware routing, congestion management, artificial intelligence, and sustainable aviation fuels (SAF) can be combined to reduce fuel use and emissions across different operating contexts. A structured survey of literature published between 2010 and 2024 was conducted using major academic databases and technical-report sources; more than 300 records were screened, and 50 studies with quantitative operational or energy outcomes were retained for detailed analysis. The evidence shows that trajectory optimization commonly delivers about 1-4% fuel savings on long-haul operations, network-level traffic measures contribute roughly 2-5%, and AI-assisted planning can achieve larger reductions when supported by high-quality operational data. Studies involving SAF further indicate that route optimization can amplify efficiency and emissions benefits by matching fuel properties, aircraft operating points, and atmospheric conditions. The review also identifies the main barriers to deployment, including certification of data-driven tools, fragmented governance of airspace data, unequal regional access to digital infrastructure, and limited SAF availability. Overall, the literature indicates that the strongest gains arise from integrated implementation rather than isolated interventions, positioning route optimization as a core component of aviation's broader energy-transition strategy.
Aviation route optimization; fuel-efficient trajectory planning; sustainable aviation fuel.
Recent Progress in Microbiological Energy Systems: Microbial Pathways, Reactor Design, and Scale-Up Challenges
Microbiological energy systems exploit the metabolic activity of microorganisms to transform organic and inorganic feedstocks into useful energy carriers such as electricity, hydrogen, methane, and reduced carbon products. Their appeal lies in the simultaneous recovery of energy and treatment of waste streams, which makes them relevant to low-emission and circular resource systems. This review examines the principal microbiological energy routes—anaerobic digestion (AD), microbial fuel cells (MFCs), microbial electrolysis cells (MECs), and microbial electrosynthesis (MES)—with emphasis on extracellular electron transfer, biofilm development, reactor architecture, and materials selection. The discussion also addresses operating variables including pH, temperature, loading rate, hydraulic retention time, and electrode properties, all of which strongly influence conversion efficiency and operational stability. The evidence reviewed indicates that AD remains the most mature and economically established option, whereas MFCs, MECs, and MES offer important opportunities for decentralized treatment, renewable hydrogen generation, and carbon utilization. Advances in metabolic engineering, omics-based microbial analysis, and electrode design have improved performance, but low power density, electron-transfer resistance, membrane fouling, and scale-up losses still limit deployment. Overall, microbiological energy represents a promising platform for integrating energy recovery, waste valorization, and environmental remediation within future sustainable infrastructure.
Microbial fuel cells, Anaerobic digestion, Bioelectrochemical energy recovery
Carbon Capture at Scale: Materials, Process Platforms, and Integration Strategies
Carbon capture has become a central element of decarbonization strategies because it can reduce emissions from concentrated industrial sources while also enabling atmospheric CO₂ removal. This review re-examines the field through the combined lenses of process route, material performance, and system integration. Post-combustion, pre-combustion, oxy-fuel, and direct air capture pathways are compared alongside absorption, adsorption, membrane, and cryogenic separation technologies. The synthesis brings together bibliometric evidence, technology-readiness screening, and benchmarking of energy demand, cost, and environmental constraints reported in the literature. Particular attention is given to sorbent chemistry, structured contactors, humid operating conditions, and low-partial-pressure CO₂ capture. The results show that mature solvent systems remain dominant at industrial scale, whereas advanced solids, hybrid flowsheets, and intensified regeneration strategies are reshaping the performance frontier. The review also identifies integration with low-grade heat, renewable electricity, transport and storage networks, and carbon utilization pathways as decisive factors for scale-up. Overall, carbon capture is best viewed not as a single technology, but as an interconnected portfolio whose future depends on coordinated advances in materials, process engineering, infrastructure, and policy.
Carbon capture, Direct air capture, Process integration
Biomass Energy in the Low-Carbon Transition: Pathways, Performance, and Limits
Biomass is one of the few renewable resources capable of supplying dispatchable heat, power, and transport fuels while also valorizing agricultural, forestry, and municipal residues. This review synthesizes biomass feedstock classes, dominant conversion routes, environmental performance, and techno-economic trends using literature published between 2000 and 2025. Agricultural residues, forestry by-products, energy crops, algae, and the biodegradable fraction of municipal solid waste are assessed against conversion suitability, efficiency, cost, and lifecycle greenhouse-gas performance. Thermochemical routes such as combustion, gasification, and pyrolysis are compared with biochemical routes including anaerobic digestion and fermentation. The analysis shows that residue- and waste-derived feedstocks generally offer the strongest sustainability case, whereas dedicated crops remain sensitive to land and water constraints. Mature options such as combustion and anaerobic digestion are already commercially relevant, while gasification, pyrolysis, and biorefinery concepts offer higher product flexibility but still face capital and scale-up barriers. Biomass can make a meaningful contribution to decarbonization when deployment prioritizes sustainable sourcing, logistics optimization, and integration with carbon capture. Future progress depends on region-specific feedstock strategies, stable policy support, and system configurations that couple energy production with waste management and negative-emission potential
Biomass energy; waste-to-energy; carbon neutrality.
Global Green Hydrogen Scale-Up: Technology and Infrastructure
Green hydrogen is increasingly regarded as a strategic option for decarbonizing industrial processes, long-distance transport, and energy systems that cannot be fully electrified. Produced from water electrolysis supplied by renewable electricity, it offers a route to low-carbon hydrogen, but its large-scale deployment remains constrained by cost, infrastructure, and governance. This review synthesizes recent literature, policy roadmaps, and project databases to assess the status of green hydrogen across technology, economics, trade, and regulation. The analysis compares major regional pathways in Europe, North America, Australia, China, and the Gulf, with attention to electrolyzer scale-up, renewable integration, hydrogen logistics, and certification frameworks. The reviewed evidence shows that strong renewable resource bases and manufacturing growth could push levelized green hydrogen costs toward the $2/kg range in favorable regions by 2030, whereas higher-cost markets are likely to remain above that threshold without sustained policy support. The paper also highlights unresolved issues related to water demand, critical materials, storage and transport infrastructure, and the absence of globally aligned standards. Overall, the review positions green hydrogen as an important but context-dependent pillar of future energy systems, whose success will depend on coordinated technology development, market design, and international cooperation.
Comparative Assessment of Sustainable Aviation Fuel Pathways: Performance, Sustainability, Certification, and Scale-Up Constraints
Sustainable aviation fuel (SAF) is widely regarded as the most practical near-term route to lower aviation emissions without replacing today’s aircraft and airport fuel systems. This review synthesizes the current state of SAF development across biomass-derived and synthetic pathways, with emphasis on feedstock sustainability, conversion performance, lifecycle greenhouse-gas mitigation, production cost, certification status, and deployment readiness. Certified routes such as HEFA, Fischer–Tropsch, and Alcohol-to-Jet are assessed alongside emerging Power-to-Liquid systems that couple renewable hydrogen with CO₂. The comparison shows that no single pathway simultaneously maximizes yield, scalability, cost competitiveness, and climate benefit. Waste-based HEFA is commercially mature but feedstock-limited; FT and ATJ broaden the resource base but require stronger process and capital optimization; PtL offers the deepest long-term decarbonization potential but remains highly dependent on renewable electricity, low-cost hydrogen, and supportive policy. The review concludes that accelerated certification, durable market incentives, and region-specific supply-chain strategies will be essential if SAF is to move from niche deployment to meaningful global scale.
Sustainable aviation fuel; lifecycle assessment; aviation decarbonization.
Desalination at Scale:Technology Choices, Energy Pathways, and Circular Brine Management for Low-Carbon Water
Growing water stress, stricter discharge regulations, and the need to decarbonize utilities are pushing desalination from a niche option to a core component of resilient water portfolios. This review synthesizes the fundamentals and current best practice of thermal desalination (MSF, MED), membrane routes (SWRO/BWRO, electrodialysis), and emerging systems (membrane distillation and electro‑sorption) through a unified lens of thermodynamic limits, practical losses, and plant-level integration. We compare specific energy consumption (SEC), recovery ratio, and permeate quality using harmonized assumptions representative of contemporary operation, emphasizing the roles of high‑efficiency pumps, isobaric energy‑recovery devices, pretreatment robustness, and flexible dispatch under renewable-rich grids. Because concentrate handling is now a dominant sustainability constraint, we map brine pathways spanning engineered marine outfalls, inland MLD/ZLD trains, and targeted valorization (salts, magnesium products, and acid/base generation), highlighting when circular options are credible versus when they add avoidable complexity. New scenario visualizations are provided to summarize (i) sector capacity growth, (ii) technology SEC ranges, (iii) energy-supply shares, (iv) the salinity–recovery trade space, (v) permeate TDS variability, and (vi) the fleet distribution of SWRO energy use. We conclude with design guidelines that connect technology selection, controls, and brine strategy to cost, reliability, and ultra‑low‑carbon targets for site-specific constraints.
Desalination; Reverse osmosis; Thermal desalination; Energy efficiency; Brine valorization; Hybrid systems; Zero-liquid-discharge; Membrane materials; Renewable desalination; Life-cycle assessment
Toward Net-Zero Flight: Scaling Sustainable Aviation Fuel Pathways and Policy
Aviation contributes a meaningful share of global climate forcing and its fuel demand is expected to grow substantially toward mid-century. Sustainable Aviation Fuel (SAF) is widely viewed as the most practical near-term decarbonization lever for long-haul fleets because it can be blended with Jet A-1 and used within existing aircraft and airport infrastructure. This review synthesizes the state of SAF feedstocks and conversion routes, spanning lipid-based hydroprocessing (HEFA), gasification and Fischer-Tropsch synthesis (FT), Alcohol-to-Jet (ATJ), and emerging Power-to-Liquid (PtL) e-fuels produced from CO₂ and renewable hydrogen. We compare indicative yields, lifecycle greenhouse-gas performance, and cost drivers, and we summarize policy and certification enablers including CORSIA and the EU Fit for 55 package. The analysis highlights a central deployment tension: near-term volume growth is constrained by sustainable feedstock availability, while the deepest long-term abatement hinges on scaling low-carbon electricity and green hydrogen. We conclude with priority research and market-structuring actions to accelerate credible, scalable SAF deployment.
Sustainable Aviation Fuel (SAF), Conversion pathways (HEFA, FT, ATJ, PtL), Policy and certification (CORSIA, EU Fit for 55)
Solar Energy Conversion at Scale: Performance Progress, Integration Strategies, and the Next Technology Frontiers
Solar energy is increasingly central to decarbonization because it can be deployed at multiple scales—from rooftops to utility-scale plants—and coupled to storage and sector-coupling pathways. This review synthesizes progress across photovoltaics (PV), concentrated solar power (CSP), photothermal conversion, and solar-driven fuel production, with an emphasis on integration options that improve reliability and system value. We compare technology pathways using conversion performance, levelized cost of electricity (LCOE), storage compatibility, and life-cycle indicators, complemented by case-study evidence from diverse climates and grid contexts. Reported trends show large cost declines for PV since 2010, dispatchability advantages for CSP when paired with molten-salt thermal storage, and fast-rising laboratory efficiencies for emerging absorbers such as perovskites and tandem architectures. We also discuss intermittency management through batteries, thermal storage, and hydrogen as a long-duration option, alongside sustainability challenges including land-use trade-offs, water constraints for steam-cycle CSP, and end-of-life recycling and critical-material recovery for PV modules. The analysis highlights that the next phase of solar deployment depends less on proving technical feasibility and more on scaling integrated, circular, and equitable energy-system designs.
Solar photovoltaics, Concentrated solar power, Energy storage, Photothermal conversion, Hybrid systems, Solar fuels, Sustainability, Smart grids, Solar integration, Renewable energy
Bioelectrochemical and Anaerobic Pathways for Microbial Energy Recovery: Progress, Performance Metrics, and Deployment Challenges
Microbial energy technologies convert organic matter and carbon dioxide into useful energy carriers by exploiting microbial metabolism and electron-transfer networks. This review compares four representative platforms—anaerobic digestion (AD), microbial fuel cells (MFCs), microbial electrolysis cells (MECs), and microbial electrosynthesis (MES)—using a unified lens of biochemical pathways, reactor/electrode design, microbial ecology, and scalability. We highlight how extracellular electron transfer (EET), biofilm structure, and electrode surface chemistry govern bioelectrochemical performance, while syntrophic consortia and retention time control AD conversion. Recent advances in omics-enabled community management, non-precious cathode catalysts, and structured/3D electrodes have improved efficiency and robustness, yet major barriers remain: internal resistance, membrane fouling, product selectivity, and scale-up losses. We close by outlining practical integration routes with wastewater treatment and carbon-management infrastructure, clarifying where each technology is best positioned—from mature centralized biogas to decentralized treatment-power co-benefits, renewable hydrogen coupling, and carbon-to-chemicals conversion.
Microbial fuel cells (MFCs), Anaerobic digestion, Wastewater-to-energy integration
From Blend Limits to Net-Zero Flight: Comparing SAF Pathways, Costs, and the Scale-Up to 2050
Aviation’s reliance on energy-dense liquid fuels makes deep decarbonization challenging, and Sustainable Aviation Fuel (SAF) remains the most immediately deployable lever because it can be used within existing aircraft and fueling infrastructure. This paper reviews SAF as a portfolio of routes rather than a single solution, synthesizing the techno-performance, lifecycle impacts, certification status, and deployment constraints of today’s leading pathways. We compare lipid-based HEFA, waste/residue-enabled Fischer–Tropsch (FT), Alcohol-to-Jet (ATJ), and Power-to-Liquid (PtL) e-kerosene, highlighting how yield/efficiency, upstream energy inputs, and feedstock availability jointly determine climate benefit and cost. Reported performance spans high HEFA yields (80–90%) versus lower FT yields (35–45%) and PtL electricity-to-liquid efficiencies (35–45%), while lifecycle GHG reductions vary from ~40–70% (ATJ) to ~90–100% for PtL under fully renewable electricity and atmospheric CO2 sourcing. Economic barriers persist: SAF costs commonly exceed fossil jet fuel, with pathway-dependent ranges that can reach multiple dollars per liter, especially for PtL dominated by hydrogen cost. Finally, we frame deployment as a scale problem: moving from today’s sub-billion-liter production to hundreds of billions of liters by 2050 requires sustained, policy-backed capacity growth and rapid infrastructure learning curves.
Sustainable Aviation Fuel (SAF), Conversion pathways (HEFA, FT, ATJ, PtL), Lifecycle greenhouse gas (GHG) emissions
From Molecules to Megatons: Materials, Process Intensification, and Infrastructure Integration for Scalable CO₂ Capture
Carbon capture is moving from single-unit demonstrations toward integrated, multi-sector deployment—yet scale-up remains constrained by the coupled limits of materials performance, regeneration energy, and infrastructure readiness. This review synthesizes advances across post-combustion, pre-combustion, oxy-fuel, and direct air capture routes, with a comparative focus on adsorption, absorption, membrane separation, and cryogenic methods under realistic operating conditions. Emphasis is placed on how humidity, trace impurities, and low CO₂ partial pressure reshape sorbent/solvent selection and dictate practical process windows. We consolidate reported benchmarks for capacity, kinetics, cyclic stability, heat duties, and cost ranges, and connect these metrics to process intensification strategies such as structured contactors, hybrid solvent–sorbent concepts, and low-grade heat utilization. In parallel, we assess integration pathways—industrial clusters, renewable coupling, and CO₂ transport/storage networks—highlighting how shared infrastructure and heat/power integration can reduce energy penalties and improve technoeconomic feasibility. Finally, we outline research and deployment priorities for the next decade, including standardized testing protocols, durability-focused material design, and system-level optimization that links capture performance to downstream utilization or permanent storage.
Carbon Capture, CCS, CCUS, Direct Air Capture, Adsorption, Absorption, Membranes, Climate Change Mitigation, Energy Systems, Decarbonization
Combustion-to-Work Conversion: A Cross-Platform Review of Thermo‑Chemical Pathways, Cycles, and Emerging Low‑Carbon Directions
Combustion-to-work systems convert fuel chemical energy into mechanical power through coupled thermo‑chemical processes and heat‑engine cycles. This review synthesizes the pathway across reciprocating internal combustion engines, gas turbines, and combined cycles, emphasizing how irreversibilities accumulate from mixing and finite‑rate chemistry to component aerodynamics, heat transfer, friction, and auxiliary loads. A loss‑based framework is used to compare platforms on a consistent lower-heating-value basis and, where informative, through exergy destruction localization. The synthesis highlights that efficiency gains increasingly require coordinated improvements—heat‑release shaping, effective expansion, minimized pressure drops, and recovery of high‑quality exhaust exergy—rather than isolated component upgrades. Emissions are treated as intrinsic constraints that reshape the achievable optimum, with NOx, soot/PM, CO, and unburned hydrocarbons responding differently to temperature–mixture distributions, dilution, and residence time. Emerging directions are reviewed, including lean and staged combustors, low-temperature compression‑ignition modes, hybridized operation, supercritical CO₂ bottoming cycles, and pressure‑gain combustion. Finally, the review discusses fuel transitions (hydrogen, ammonia, sustainable and synthetic fuels) and the implications for stability, materials, and net climate benefit.
combustion, heat engines, Otto cycle, Diesel cycle, Brayton cycle, combined cycle, exergy analysis, emissions, low‑carbon fuels, pressure‑gain combustion
Thermal Energy Storage for Flexible, Low-Carbon Energy Systems: Materials, Architectures, Design Metrics, and Deployment Pathways
Thermal energy storage (TES) is a cornerstone technology for decarbonizing heating and cooling, increasing renewable penetration, and improving grid flexibility by shifting thermal demand in time. This review consolidates TES fundamentals and deployment practice across sensible, latent, and thermochemical pathways, emphasizing how material properties and system architectures translate into practical metrics such as energy density, power density, round-trip efficiency, cycling durability, and levelized cost. Sensible TES remains the most mature and widely deployed, ranging from chilled-water tanks and ice storage in buildings to packed-bed rock, concrete, and molten-salt systems for industrial heat and concentrating solar power. Latent TES (phase change materials, PCMs) enables quasi-isothermal operation and compactness but is constrained by low thermal conductivity, phase segregation, subcooling, and packaging complexity. Thermochemical TES offers the highest theoretical energy density and the possibility of long-duration storage with limited standing losses, yet faces challenges in reactor/contactor design, kinetics, cycling stability, and integration. The review proposes a consistent framework for material screening, component sizing, and system-level evaluation, and summarizes emerging enhancement strategies including encapsulation, finned heat exchangers, metal foams, graphite additives, and cascading temperature stages. Six illustrative figures and three design-oriented tables are provided to connect key concepts: technology classification, energy-density ranges, temperature signatures, PCM property trade-space, suitability scoring, and multi-criteria comparison.
Thermal energy storage; sensible heat; phase change materials; thermochemical storage; district cooling; concentrating solar power; underground thermal energy storage; heat exchangers; energy flexibility; techno-economic metrics
Hybrid Cooling–Desalination Systems for Water–Energy Co-Production: Architectures, Integration Strategies, Performance Metrics, and Research Needs
Cooling and desalination increasingly co-locate in arid coastal regions, creating an opportunity for hybrid systems that co-produce chilled water (or conditioned air) and freshwater while improving total resource utilization. This review surveys hybrid cooling–desalination architectures including absorption cooling integrated with thermal desalination or membrane distillation, adsorption desalination cycles that inherently co-generate cooling and freshwater, seawater air conditioning coupled with reverse osmosis, and solar-assisted multigeneration configurations. The synthesis emphasizes integration mechanisms such as heat cascading from chillers to desalination modules, shared heat rejection, coupling through seawater intake and brine management, and operational coordination under variable ambient conditions. Performance metrics are harmonized across studies using specific electricity consumption, gain-output ratio, cooling COP, exergy efficiency, and water–energy productivity indicators, with attention to constraints like scaling/fouling, intake temperature, and environmental discharge. Recent reviews on synergistic desalination/cooling and on hybrid membrane–thermal desalination underscore both near-term integration benefits and the need for robust, validated designs that can be deployed at scale.
Hybrid desalination, absorption cooling, adsorption desalination, membrane distillation, reverse osmosis, trigeneration, seawater air conditioning, waste heat utilization, solar-driven systems
Organic Rankine Cycle for Low-to-Medium Temperature Heat Recovery: Working Fluids, Architectures, Expanders, Control, and Deployment Pathways
Organic Rankine cycles (ORCs) have matured into a leading technology for converting low-to-medium temperature heat into electricity in applications spanning industrial waste heat, geothermal, biomass, and solar thermal systems. Their competitiveness stems from the ability to match diverse heat-source temperature profiles using organic fluids, flexible architectures (subcritical, recuperated, regenerative, transcritical, and supercritical variants), and compact turbomachinery or volumetric expanders. This review consolidates the state of the art across (i) working-fluid selection under simultaneous thermodynamic, environmental, safety, and cost constraints; (ii) plant architectures and heat-exchanger design that govern pinch losses and off-design behavior; (iii) expander choices from radial turbines to scroll, screw, and piston machines; and (iv) modeling, control, and techno-economic assessment frameworks for robust deployment. The paper synthesizes performance trends drawn from experimental surveys and system demonstrations, highlighting that heat exchangers dominate irreversibilities and dynamic response, while expander efficiency and stable condensation strongly shape net output in small-to-mid scale systems. Recent advances in off-design optimization, moving-boundary dynamics, and supervisory control improve annual energy production and operational reliability. Remaining bottlenecks include fluid regulation transitions, high-temperature stability of “dry” fluids, cost-effective scaling below ~100 kWe, and integration constraints (cooling availability, fouling, and transient heat-source behavior).
Organic Rankine cycle; waste heat recovery; working fluid selection; expander technology; recuperated ORC; supercritical ORC; thermo-economic optimization; dynamic control; exergy analysis
A Comprehensive Review of Air Quality Science, Measurement, Health Impacts, and Policy Pathways for Clean Air
Air pollution remains the leading environmental risk factor for premature mortality worldwide, driven primarily by fine particulate matter (PM₂.₅) and ozone exposure. This review synthesizes advances in atmospheric science, exposure assessment, health evidence, and policy design to inform effective clean‑air strategies. We summarize the physical and chemical formation pathways of key pollutants, evaluate the expanding measurement toolkit from regulatory reference monitors to satellite remote sensing and dense low‑cost sensor networks, and compare modeling architectures that convert emissions and meteorology into concentration fields and population exposure. We assess the strength of the epidemiological evidence linking air pollution to cardiovascular, respiratory, and metabolic outcomes, emphasizing developments in causal inference, non‑linear concentration–response relationships, and the global transferability of risk functions. The review highlights source apportionment insights that prioritize action on residential solid fuel use, traffic, industry, power generation, agriculture, and natural sources. We discuss policy architectures—ambient standards, emission controls, market instruments, and integrated climate‑air frameworks—and quantify health, climate, and economic co‑benefits of mitigation. Six original illustrative figures and three methodological tables are provided to aid teaching and practice. We conclude with a research and policy agenda centered on equity, transparency, sensor fusion, accountability, and sustained implementation
ambient air quality; PM₂.₅; NO₂; ozone; health burden; source apportionment; exposure assessment; low cost sensors; policy; co benefits ambient air quality; PM₂.₅; NO₂; ozone; health burden; source apportionment; exposure assessment; low cost sensors; policy; co benefits
Built Environment 2050: Integrating Efficiency, Health, and Carbon Neutrality Across Buildings and Cities
The built environment accounts for a substantial share of global energy demand, greenhouse gas emissions, and time spent indoors, positioning buildings and urban form at the center of climate mitigation and human well-being. This review synthesizes advances across building physics, systems engineering, and urban design to identify coordinated strategies that lower operational energy, reduce embodied carbon, improve indoor air quality and thermal comfort, and enhance resilience. We map evidence from laboratory studies, field monitoring, and city-scale modeling to show that demand reduction through envelopes, efficient and electrified HVAC, lighting, and controls remains the least-cost pathway in most contexts, particularly when sequenced with grid-interactive demand flexibility and onsite renewables. We highlight the convergence of materials science (low-carbon materials, phase change media), mechatronics (heat pumps, active façades), and data science (digital twins, AI-based controls), and we discuss trade-offs between air quality, ventilation energy, and filtration. Finally, we frame a research agenda around climate-appropriate design, performance verification, and equity-centered retrofits that deliver persistent emissions reductions and healthier indoor environments. Six original figures and three tables summarize trends, correlations, performance distributions, and adoption barriers for decision-makers and researchers.
built environment; building energy; retrofits; HVAC; indoor air quality; thermal comfort; embodied carbon; digital twins; urban morphology; resilience