Global Decarbonization Research Articles

The Role of Hydrogen in Achieving Sustainable Energy Systems: Challenges and Opportunities

Hydrogen has emerged as a crucial element in the pursuit of sustainable energy solutions due to its versatility and its ability to combust without emitting greenhouse gases. This research examines hydrogen's multifaceted role as an energy carrier, emphasizing its methods of production, storage, and utilization. Recent technological advancements, such as enhanced electrolysis efficiency and innovative storage materials, are explored to tackle existing challenges such as high production costs and energy inefficiencies. Case studies in transportation, industrial applications, and power generation illustrate hydrogen's potential to significantly reduce carbon emissions, supporting global decarbonization endeavors. Strategic investments and supportive policies are identified as an essential to fully capitalize on hydrogen's capabilities, emphasizing the necessity for ongoing innovation and cross-sector collaboration to achieve a sustainable, decarbonized energy future. With the increasing attention of the whole society to climate change, hydrogen energy will play an increasingly important role in creating a green and low-carbon world.

Water Status Detection Method Based on Water Balance Model for High-Power Fuel Cell Systems

With the gradually accelerating pace of global decarbonization, highly efficient and clean proton exchange membrane fuel cells (PEMFCs) are considered to be an energy solution for the future. During the operation of a fuel cell, it is necessary to keep the internal proton exchange membrane in a good state of hydration, so an appropriate method of detecting the hydration state is essential. At present, fuel cell systems are rapidly developing towards high power, but methods for detecting the hydration state of high-power fuel cell systems are still relatively lacking. Therefore, this paper studies the hydration state of high-power fuel cell systems and builds a condensation tail-gas water collection device for calculating the water flow out of a fuel cell system, deriving the hydration status inside the high-power fuel cell system. To verify the proposed water balance model, a series of experiments were conducted based on controlled variables such as working temperature, air metering ratio, and load current. Experiments were conducted on a 100 KW fuel cell system to collect water flow from the fuel cell system. Finally, based on the experimental data, the change rate of the internal water content of the fuel cell system under different conditions was calculated. The results show that, under the same load current, as the working temperature and air metering ratio increase, the change rate of the internal water content of the fuel cell system gradually decreases. Therefore, at low power, it is necessary to maintain an appropriate working temperature, while at high power, maintaining an appropriate air metering ratio is more important.

On The Relationship Between Swirl And Unsteadiness Within Turbine Rim Seals

Abstract Unravelling the flow physics pertaining to hot gas ingress in turbines is crucial in enabling designers to realise global decarbonisation targets in aerospace. A turbine rim seal is fitted at the periphery of the rotor-stator cavity to minimise the ingress of annulus gas, which detrimentally affects cycle efficiency. The inherent unsteadiness in rim seal flows, arising from shear gradients between contiguous flow paths, introduces a consequential, yet presently unestablished, influence on sealing characteristics. A single-stage axial turbine facility in conjunction with an aeroengine architecture is employed to assess the steady and unsteady sealing characteristics of a range of industrially-relevant rim seals. Time-averaged measurements of gas concentration and swirl, acquired over a range of flow coefficients (CF), exhibited an inverse relationship between sealing performance and the purge-mainstream swirl difference (Δβ). Spectral analysis of unsteady pressure signals revealed an associated unsteadiness, induced by the strength of the annulus-cavity interaction. Across all CF, a low-frequency harmonic range consistently displayed proportionality between spectral activity and Δβ. Thus, a relationship between steady and unsteady characteristics was established. Examining a series of rim seal configurations with varying radial clearances signified that sealing performance was predominantly influenced by the radially outermost clearance. The configurations exhibiting superior performance presented heightened spectral activity, ascribed to an increased radial purge mass flux and establishing a definite relationship with concurrent steady measurements.

Hydrogen Storage Materials: Promising Materials for Kazakhstan’s Hydrogen Storage Industry

Hydrogen, widely recognized as an efficient and clean energy carrier, holds significant promise for transforming future energy systems. Despite advances in hydrogen production and cost reduction, challenges in hydrogen storage continue to impede its widespread adoption. Traditional storage methods, such as high-pressure tanks and liquid hydrogen, have limitations related to high energy and resource costs. Solid-state materials offer a safer and more reliable alternative for hydrogen storage under various operating conditions. This review article provides an in-depth analysis of hydrogen storage materials, focusing on metal hydrides, complex hydrides, and carbon-based materials, with particular attention to their thermodynamic, structural, and kinetic properties. Additionally, the article explores the potential application of certain materials in Kazakhstan's hydrogen market, highlighting the country's rich mineral resources and existing industrial infrastructure. By leveraging these resources, Kazakhstan can play a crucial role in advancing hydrogen storage technologies and contributing to global decarbonization efforts. The review aims to offer comprehensive insights into the current state and prospects of solid-state hydrogen storage materials, emphasizing their relevance and potential impact on Kazakhstan's energy sector.

Trace element contamination biomonitoring: A comparative study between the polychaetes Alitta virens and Hediste diversicolor

Trace elements (TEs) remain of significant toxicological concern as many are critical for global decarbonisation. TEs accumulate in sediments so benthic polychaetes (e.g. Hediste diversicolor and Alitta virens) are highly relevant for ecotoxicology. However, ecological/biological differences could influence TE accumulation and biomonitoring suitability. Exploiting multiple sympatric populations (Solent, UK), we measure sediment and tissue concentrations generating EFs (enrichment factors), AEIs (Adverse Effects Indexes) and tissue bioaccumulation factors. We also assess stable isotope compositions to elucidate diet influences. Despite diverse anthropogenic activity in the Solent, the majority of TEs present low levels of sediment contamination at the sites. For Ni, Pb and As, a combination of mean AEIs >1 and some sediment concentrations exceeding SQVs (Sediment Quality Values) indicate a slight toxicological risk. For Cu and Hg, high EFs and AEI scores confirm they are the greatest risk, thus requiring source identification/control. However, only mean As tissue concentrations reflect contaminated sites, therefore, identifying the As-source(s) is also a priority. Sediment and tissue concentration relationships were generally negative and not significant for both species. Although a significant negative relationship for Cd for A. virens requires further investigation, the lack of evidence for TE bioaccumulation from sediment may limit both species' biomonitoring suitability for low-contamination sites. Species differences in tissue concentration were also TE specific: H. diversicolor had significantly higher concentrations for Ag, Cu, Hg, Ni and Zn, whilst the reverse was true for Cd, Fe, Cr and As. Whilst ecological differences and that feeding sources are site and species-specific (as evidenced by C, N and S stable isotopes analysis) cannot be ignored, the diverse tissue concentrations strongly suggest different TE regulation strategies per species. Together these data will be important for ecotoxicologists and regulators to select the ‘best’ polychaete biomonitor and assess TE toxicity under future global decarbonisation trajectories for TE inputs.

Energy transition in the oil and gas sector: Business models for a sustainable future

The global energy landscape is undergoing a significant transformation as industries shift towards more sustainable practices, driven by environmental regulations, societal pressure, and technological advancements. The oil and gas sector, traditionally dependent on fossil fuels, is at the forefront of this energy transition. This review explores the evolving business models that facilitate the industry's transition to a low-carbon economy, focusing on strategies for achieving sustainability while maintaining profitability. Key approaches include diversifying energy portfolios by investing in renewable energy sources such as wind, solar, and hydrogen, as well as enhancing operational efficiency through digital technologies like artificial intelligence and the Internet of Things (IoT). The transition is also marked by an increased focus on carbon capture, utilization, and storage (CCUS) technologies, which mitigate the environmental impact of traditional oil and gas operations. Business models are being reshaped to incorporate circular economy principles, where waste and emissions are minimized through innovation and resource optimization. Furthermore, partnerships between oil and gas companies and renewable energy firms are emerging as a critical pathway for mutual growth and sustainability. This energy transition also involves rethinking the workforce and reskilling employees for emerging sectors, emphasizing the need for adaptability in business models. Regulatory frameworks play a pivotal role in shaping these models, as policies increasingly favor green investments and low-carbon initiatives. As oil and gas companies diversify their portfolios, they are creating new revenue streams that align with global decarbonization goals while ensuring financial resilience. This study highlights how these innovative business models are setting the foundation for a sustainable future in the oil and gas sector, ensuring that the industry remains relevant in a rapidly changing energy ecosystem. Keywords: Energy Transition, Oil and Gas, Business Models, Sustainability, Renewable Energy, Carbon Capture, Circular Economy, Digital Transformation, Decarbonization, Low-Carbon Economy.

Estimating electrical distribution network length and capital investment needs from real-world topologies and land cover data

Green technologies such as solar photovoltaic systems and electric vehicles play a fundamental role in the global decarbonization effort. To enable their diffusion, electricity distribution networks need to be upgraded, which is a complex and expensive endeavor. However, utilities face budgetary constraints and seek to reduce planning uncertainty. Here, we utilize 7,527 real-world grid topologies and land cover data to develop a model for estimating conductor and capital investment needs for electrifying a specific area. Our work yields three main contributions: First, we demonstrate the important role of land cover data in power line planning. We show that, for medium and large networks, distinct methodologies are needed due to the significant impact of land cover, particularly buildings and roads. Second, we introduce a parsimonious model of power line length and identify the number of consumption points as the primary determinant of network investment costs. Third, we present a cost assessment model tailored for regulators and investors, offering valuable insights for network planning, policymaking, due diligence, and research. Our work highlights the importance of combining land cover data and operations research algorithms in distribution network planning and provides policymakers with a tool to ensure cost-efficient network expansion.

Decarbonization In the Steel Industry, Resource Management and Environmental Impact Assessment

The steel industry, as one of the basic global industries, plays a very important role in the production of carbon dioxide and greenhouse gases. Considering the necessity of the global decarbonization process and the big challenges facing the steel sector in Iran, the stakeholders must discover ways to achieve the decarbonisation of the Iranian steel sector. In this context, we present an initial exploration of this perspective, where the general focus is towards using suitable substitute materials, using more scrap steel and changing existing recycling methods to remove more impurities (e.g., vehicle disassembly). instead of crushing them, which challenges material separation). better design and material substitution; increasing energy efficiency; Changing carbon-intensive technologies to net zero; etc., which have the potential to accelerate the transition towards decarbonization of steel and thus strengthen and promote the vital process of decarbonization in the steel sector. New technologies are being developed that will significantly reduce carbon emissions in the iron and steel sector. Ways in which the uptake of more sustainable technology can be stimulated, including their orientation.

Perspectives on NO X Emissions and Impacts from Ammonia Combustion Processes.

Climate change and global warming necessitate the shift toward low-emission, carbon-free fuels. Although hydrogen boasts zero carbon content and high performance, its utilization is impeded by the complexities and costs involved in liquefaction, preservation, and transportation. Ammonia has emerged as a viable alternative that offers potential as a renewable energy storage medium and supports the global economy's decarbonization. With its broader applicability in large power output applications, decentralized energy sources, and industrial locations off the grid, ammonia is increasingly regarded as an essential fuel for the future. Although ammonia provides a sustainable solution for future low-carbon energy fields, its wide-scale adoption is limited by NO X emissions and poor combustion performance under certain conditions. As research on ammonia combustion expands, recent findings reveal factors impacting the chemical reaction pathways of ammonia-based fuels, including the equivalence ratio, fuel mixture, pressure, and temperature. Investigations into ammonia combustion and NO X emissions, at both laboratory and industrial scales, have identified NO X production peaks at equivalence ratios of 0.8-0.9 for ammonia/hydrogen blends. The latest studies about the NO X emissions of the ammonia flame at different conditions and their generating pathways are reviewed in this work. Effective reduction in NO production from ammonia-based flames can be achieved with richer blends, which generate more NH i radicals. Other advanced NO X mitigation techniques such as plasma-assisted combustion have been also explored. Further research is required to address these challenges, reduce emissions, and improve efficiencies of ammonia-based fuel blends. Finally, the extinction limit of ammonia turbulent flame, its influential factors, and different strategies to promote the ammonia flame stability were discussed. The present review contributes to disseminating the latest advancements in the field of ammonia combustion and highlights the importance of refining reaction mechanisms, computational models, and understanding fundamental phenomena for practical implications.

Global carbon transition in the passenger transportation sector over 2000–2021

The high-emitting and hard-to-abate passenger transport sector plays a crucial role in global deep decarbonization. To lead an equitable and rapid transition in the passenger transportation, this work is the first to develop a bottom-up modeling framework integrated with the latest decomposing structural decomposition methodology to assess and compare historical emission patterns and decarbonization efforts of 28 countries over the past two decades. Results indicate: (1) Carbon emissions from the global passenger transport sector increased between 2000 and 2021, peaking in 2019, with GDP per capita and population size being key drivers of rising carbon emissions across countries. (2) The decarbonization efforts of the global passenger transport sector varied by traffic mode. The largest contributors were passenger buses [−0.46 megatons of carbon dioxide per year (Mt CO2/yr)], followed by trains (−0.4 Mt CO2/yr), and airplanes (−0.28 Mt CO2/yr), while passenger cars (1.04 Mt CO2/yr) hindered the decarbonization process. (3) Although the global passenger transport sector has cumulatively decarbonized 3005.9 Mt CO2 and achieved a decarbonization rate of 5.1 %, regional performance varied significantly, exhibiting uneven and inadequate progress. Overall, the study provides an effective data-driven assessment framework for reviewing and comparing global and national passenger transport decarbonization performance, which will facilitate the planning of decarbonization pathways by global emitters and the early achievement of zero-carbon transport.

From fertilizer to fuel: Ammonia's evolution and role in global decarbonization

Green ammonia is gaining traction as a hydrogen carrier and decarbonization vector, particularly for maritime fuel, power generation, and energy storage—sectors that face significant challenges with electrification on their path to decarbonization. While green hydrogen could also play a key role in decarbonizing these sectors, many regions lack the capital or resources to produce it at scale. Additionally, green hydrogen has limitations that green ammonia is well-positioned to overcome. Rather than competing with electrification and green hydrogen, green ammonia complements the energy transition by replacing fossil-fuel-based grey ammonia, acting as a hydrogen carrier, and serving as a carbon-free fuel. Its high energy density, widespread use as a manufacturing feedstock, and carbon-free composition make it a practical decarbonization solution for regions with impediments to renewable electricity and green hydrogen production. There is a need for a nuanced understanding on ammonia’s role in energy systems decarbonization to determine where it best fits in the puzzle.

Fiscal decentralisation and renewable energy development: Inhibition or promotion?

In line with global green development and decarbonisation initiatives, China has prioritized renewable energy advancement in recent decades. Given the critical role of financial support, scholarly attention has increasingly focused on the impact of fiscal decentralisation (FD) within this sector. This study investigates FD's effect on renewable energy development, analyzing data from 30 Chinese provinces between 2008 and 2022. Findings reveal that FD tends to impede renewable energy progress. Specifically, a one-standard-deviation increase in FD leads to a decrease of 23.1775 % of a standard deviation in renewable energy development. However, this hindrance can be mitigated by foreign direct investment and central transfer payments, while research and development intensity exacerbates the negative impact. Notably, regions with limited natural resources, weaker environmental regulations, fiscal transparency, high marketisation, energy demand, and vertical fiscal imbalances experience a more pronounced decentralisation-renewable-energy relationship. Anti-corruption campaigns in China can alleviate but not reverse this effect. Furthermore, the diffusion of technology and cooperative efforts in nearby regions positively influence renewable energy development. Nonetheless, overall effects still turn out negative due to competition among local governments under the FD framework. Based on these findings, policy recommendations for accelerating renewable energy development are summarized.

Bioinspired smart dual-layer hydrogels system with synchronous solar and thermal radiation modulation for energy-saving all-season temperature regulation

All-season thermal management with zero energy consumption and emissions is more crucial to global decarbonization over traditional energy-intensive cooling/heating systems. However, the static single thermal management for cooling or heating fails to self-regulate the temperature in dynamic seasonal temperature condition. Herein, inspired by the dual-temperature regulation function of the fur color changes on the backs and abdomens of penguins, a smart thermal management composite hydrogel (PNA@H-PM Gel) system was subtly created though an “on-demand” dual-layer structure design strategy. The PNA@H-PM Gel system features synchronous solar and thermal radiation modulation as well as tunable phase transition temperatures to meet the variable seasonal thermal requirements and energy-saving demands via self-adaptive radiative cooling and solar heating regulation. Furthermore, this system demonstrates superb modulations of both the solar reflectance (ΔR = 0.74) and thermal emissivity (ΔE = 0.52) in response to ambient temperature changes, highlighting efficient temperature regulation with average radiative cooling and solar heating effects of 9.6 °C in summer and 6.1 °C in winter, respectively. Moreover, compared to standard building baselines, the PNA@H-PM Gel presents a more substantial energy-saving cooling/heating potentials for energy-efficient buildings across various regions and climates. This novel solution, inspired by penguins in the real world, will offer a fresh approach for producing intelligent, energy-saving thermal management materials, and serve for temperature regulation under dynamic climate conditions and even throughout all seasons.

Деятельность российских нефтегазовых компаний в Арктике: теория и практика резильентности в эпоху декарбонизации

Addressing global climate change presents a shared challenge, particularly for the development of the Arctic Zone of the Russian Federation (AZRF) and for industrial companies operating in the region, including oil and gas producers. Given the strategic role of hydrocarbon development in the AZRF for ensuring Russia’s energy security and the responsibility of oil and gas companies in reducing greenhouse gas emissions, it is critical to examine their role in enhancing the resilience of the AZRF amidst global decarbonization efforts. This article aims to provide a theoretical and practical analysis of the relationship between organizational and territorial resilience in the context of climate change. It focuses on the measures taken by Russian oil and gas companies to reduce greenhouse gas emissions and minimize the anthropogenic impact of their operations in the AZRF. The empirical basis for this study is drawn from the corporate reports of the largest Russian oil and gas companies. Through a review of contemporary Russian and international research, key risks to the resilience of economic systems in the AZRF are identified. A conceptual framework is proposed, highlighting the role of oil and gas companies in supporting the resilience of the AZRF, particularly through decarbonization initiatives aimed at mitigating the effects of climate change, such as permafrost thawing. Content analysis has been used to categorize the environmental and industrial safety measures, as well as decarbonization efforts, undertaken by Russian oil and gas companies in the AZRF. The study concludes by outlining the various decarbonization scenarios and strategies implemented by these companies in the AZRF.

Towards net zero: Comprehensive approach for voluntary carbon trading among microgrids

In the context of growing focus over climate changes and promoting sustainability across a various range of fields, microgrids can play a significant role in global decarbonization endeavors, contributing to carbon neutrality and ultimately attaining net-zero emissions in the energy sector. The objective of this paper is to address the integration of voluntary carbon trading within microgrid communities, in the perspective to mitigate greenhouse gas (GHG) emissions and boost the integration of renewable energy sources (RES). Introducing five modular algorithms managing key aspects of carbon trading, the study engineers a comprehensive framework aiming to optimally orchestrate the Voluntary Carbon Market (VCM) within microgrids. Particularly, the developed algorithms address aspects such as market enrollment decision, optimal energy dispatch, managing the market transactions, sellers-buyers matching as well as the dynamic adjustment of carbon credit prices and emission taxes. The framework has been rigorously tested across three distinct scenarios. Results show that the developed VCM, with adequate configurations, has the potential to incentivize microgrids to curtail their GHG emissions, encourage the integration of more RES into their generation mix, and rewards the more proactive microgrids with substantial financial incentives.

Accelerating decarbonized economic growth through net-zero entrepreneurship: Low-carbon economic development perspective

Net-zero entrepreneurship is a novel concept introduced in the context of carbon neutrality, and exploring whether it can catalyze decarbonized economic growth is a worthy pursuit. This study constructs a comprehensive, low-carbon endogenous economic growth model to scrutinize the intricate nexus between net-zero entrepreneurship and decarbonized economic growth. Empirical validation employs a series of multiple regression models to rigorously test the hypotheses derived from the theoretical framework using an extensive dataset spanning Chinese provinces. The results reveal a nuanced landscape. (i) Net-zero entrepreneurship plays a remarkable role in promoting decarbonization growth, with considerable regional heterogeneity. (ii) Green technology progress exhibits a notable mediating effect. (iii) Environmental regulation and industrial structure optimization have positive moderating effects. (iv) The results passed alternative dependent variable and one-phase lag regression robustness tests. In a distinct contribution to entrepreneurship literature, this study augments the discourse on strategies to steer low-carbon transitions. The research findings indicate that net-zero entrepreneurship can accelerate the global decarbonization process, and green technology progress is a significant driving mechanism in this process. Additionally, it is essential to strengthen environmental agencies’ regulatory oversight and optimize industrial structures to pave the way for transformative sustainable growth. In the future, more entrepreneurs should be encouraged to engage in green technology and business model innovation to contribute to global decarbonization efforts.

Techno-economic and environmental assessment of green hydrogen and ammonia production from solar and wind energy in the republic of Djibouti: A geospatial modeling approach

This study conducts a thorough economic and technical analysis to assess the viability of green hydrogen and green ammonia production using renewable energy sources in the Republic of Djibouti. We explore the economic competitiveness of utilizing wind and solar power for sustainable energy production through various measures including levelized cost of energy (LCOE), hydrogen (LCOH), and ammonia (LCOA). Our analysis incorporates sensitivity assessments and Monte Carlo simulations to predict financial feasibility and environmental impact, focusing on CO2 emission reductions. A cost mapping of electricity, green hydrogen, and green ammonia from solar and wind resources was created to find Djibouti's most cost-effective production sites. The feasibility of exporting green ammonia to neighboring countries with high fertilizer demand was also evaluated using rail and truck transport scenarios. Key findings demonstrate that Moulouhlé, endowed with robust wind and solar resources, presents a strategic site for deploying renewable energy technologies. Wind energy, with a lower LCOE of 0.066 $/kWh compared to solar's 0.093 $/kWh, emerges as a more cost-effective solution for both hydrogen and ammonia production. Notably, wind-powered hydrogen production costs are 2.25 $/kgH2, significantly lower than solar-powered costs at 4.17 $/kgH2. In terms of green ammonia, wind power achieves production costs of 399.76 $/tonNH3, outperforming solar power which stands at 537.11 $/tonNH3. Additionally, our study evaluates the logistics of exporting green ammonia, determining rail transport as a more economically viable option than trucking. This research not only underscores Djibouti's potential as a leader in green energy exportation but also aligns with global decarbonization efforts, showcasing significant CO2 savings—154.94 Mt annually from wind. This work emphasizes the importance of strategic resource utilization in Djibouti, offering insights critical for stakeholders in making informed decisions about investing in renewable energy infrastructures. The outcomes suggest a promising future for regional energy sustainability and economic resilience, fostering a transition towards low-carbon energy systems.

International cooperation for the decarbonization of energy-intensive industries: unlocking the full potential

ABSTRACT This article investigates the state of global governance for the deep decarbonization of energy-intensive industries (EIIs) and identifies key options for mobilizing the so far underexploited potential of this global governance. Focusing on four main EIIs (i.e. iron and steel, cement and concrete, chemicals, and aluminium) the analysis is advanced in three steps. First, we establish the theoretical potential of international institutions to address the main barriers to EII decarbonization focusing on six main governance functions. Second, the article provides an up-to-date account of the global governance landscape for EII decarbonization and the contribution it has made to addressing the main barriers. This assessment also identifies major gaps and underexploited potentials of global governance. Finally, we systematically appraise key options for advancing global governance for EII decarbonization based on clear assessment criteria (membership, institutional capacity, legitimacy, feasibility). The major findings are that: (a) global governance has advanced significantly in the 2020s across all governance functions, in particular through the emergence of several initiatives focused on industrial decarbonization, including the recent Climate Club; (b) key priorities for advancing global EII decarbonization concern rules for collective action, means of implementation, landscape orchestration/coordination, and a more equal coverage of different sub-sectors and regions. We argue that the main barrier to addressing these priorities is rooted in (geo)politics rather than a lack of suitable institutions. Consequently, the global governance for EII decarbonization may best be advanced through incrementally developing existing rather than creating major new institutions.

Global primary aluminum smelters' CO2 mitigation potential and targeted carbon-neutral pathways

The expansion of aluminum smelter capacity generates high CO2 emissions, exhibiting spatiotemporal diversity due to diverse processing routes and technologies. Despite extensive discussions on macro abatement options, facility-specific mitigation potentials and decarbonization strategies remain unclear, which cumulatively affects the progress towards global 1.5 °C and 2 °C warming control targets. This study develops a carbon footprint inventory of 163 primary aluminum smelters in 2022 and analyzes current emission structures concerning location, age, production, and input-output. Then adjust available technologies and efficiencies to match global plant-level decarbonization routes. The potential contributions of each strategy are finally quantified, accounting for significant geographic variations in emissions, thereby supplementing tailored technology transformation pathways for smelters across nine focus regions. The results show that: (1) Young smelters, predominantly in developing regions, are crucial for abatement. Rapid retrofits ahead could save CO2 budgets by 0.6–28.56 Gt, potentially delaying excess emissions under climate targets, particularly with comprehensive retrofits. (2) The paramount technical retrofitting for carbon neutrality differs regionally and evolves. Smelters in developing countries should prioritize renewable energy investment in the immediate future, succeeded by the optimization of power generation infrastructures. To liberate more emission allowances, developed countries ought to contemplate the decommissioning of aged smelters or upgrading through emerging supply-side technologies. (3) Available retrofits can facilitate the aluminum industry's contribution to the 2 °C climate target, whereas addressing the 1.5 °C target will necessitate the adoption of more innovative technologies and materials. This paper endeavors to assist global and regional smelters in developing more targeted decarbonization pathways.

Biohydrogen production from wastewater: Production technologies, environmental and economic aspects

Biohydrogen (bio-H2) production from wastewater can be a sustainable and innovative approach that uses biotechnological processes to convert organic waste into hydrogen, a clean energy source. Technologies such as dark fermentation, photo-fermentation, microbial electrolysis cells, and biophotolysis are widely utilized, with emerging technologies like anaerobic membrane bioreactors and microalgae processes also gaining prominence. Integration between these systems aims to enhance process efficiency. This study reviews the hydrogen production from wastewater, analyzing its potential as a source for bio-H2 production and evaluating environmental and economic issues. The performance of various processes in bio-H2 production from different wastewater sources is discussed, focusing on challenges, opportunities, and trends. Wastewater, including cassava (225.2 mL H2/gVS) and corn (265 mL H2/gVS) processing, dairy (54.5 mL H2/gVS), domestic (154–180 mL H2/gVS), fruit (104.9 mL H2/gVS) and starchy (153–200 mL H2/gVS), show promising potential for bio-H2 production. Economically, indirect biophotolysis is the most cost-effective technology per kg of bio-H2 produced, followed by microbial electrolysis cells, photo-fermentation, dark fermentation, and direct biophotolysis. Furthermore, from an environmental and sustainability perspective, bio-H2 production presents a strategic tool for global decarbonization efforts, reducing CO2 emissions and facilitating transformation towards clean energy solutions. Bio-H2 generation during wastewater treatment holds potential by concurrently producing clean fuel and enabling safe disposal of wastewater. Continued research and development efforts are essential to overcoming current challenges. Achieving this will require targeted investments, policy support, and technological innovations to make biohydrogen a viable and sustainable energy solution.