Publications
Life Cycle Assessment and Life Cycle Costing of Hydrogen Production from Biowaste and Biomass in Sweden
Jun 2023
Publication
In this study an environmental and economic assessment of hydrogen production from biowaste and biomass is performed from a life cycle perspective with a high degree of primary life cycle inventory data on materials energy and investment flows. Using SimaPro LCA software and CML-IA 2001 impact assessment method ten environmental impact categories are analyzed for environmental analysis. Economic analysis includes capital and operational expenditures and monetization cost of life cycle environmental impacts. The hydrogen pro duction from biowaste has a high climate impact photochemical oxidant and freshwater eutrophication than biomass while it performs far better in ozone depletion terrestrial ecotoxicity abiotic depletion-fossil abiotic depletion human toxicity and freshwater ecotoxicity. The sensitivity analysis of LCA results indicates that feedstock to biogas/pyrolysis-oil yields ratio and the type of energy source for the reforming process can significantly influence the results particularly climate change abiotic depletion and human toxicity. The life cycle cost (LCC) of 1 kg hydrogen production has been accounted as 0.45–2.76 € with biowaste and 0.54–3.31 € with biomass over the plant’s lifetime of 20 years. From the environmental impacts of climate change photo chemical oxidant and freshwater eutrophication hydrogen production from biomass is a better option than biowaste while from other included impact categories and LCC perspectives it’s biowaste. This research con tributes to bioresources to hydrogen literature with some new findings that can be generalized in Europe and even globally as it is in line with and endorse existing theoretical and simulation software-based studies.
Advancing Energy Management Strategies for Hybrid Fuel Cell Vehicles: A Comparative Study of Deterministic and Fuzzy Logic Approaches
Aug 2025
Publication
The increasing depletion of fossil fuels and their environmental impact have led to the development of fuel cell hybrid electric vehicles. By combining fuel cells with batteries these vehicles offer greater efficiency and zero emissions. However their energy management remains a challenge requiring advanced strategies. This paper presents a comparative study of two developed energy management strategies: a deterministic rule-based approach and a fuzzy logic approach. The proposed system consists of a proton exchange membrane fuel cell (PEMFC) as the primary energy source and a lithium-ion battery as the secondary source. A comprehensive model of the hybrid powertrain is developed to evaluate energy distribution and system behaviour. The control system includes a model predictive control (MPC) method for fuel cell current regulation and a PI controller to maintain DC bus voltage stability. The proposed strategies are evaluated under standard driving cycles (UDDS and NEDC) using a simulation in MATLAB/Simulink. Key performance indicators such as fuel efficiency hydrogen consumption battery state-of-charge and voltage stability are examined to assess the effectiveness of each approach. Simulation results demonstrate that the deterministic strategy offers a structured and computationally efficient solution while the fuzzy logic approach provides greater adaptability to dynamic driving conditions leading to improved overall energy efficiency. These findings highlight the critical role of advanced control strategies in improving FCHEV performance and offer valuable insights for future developments in hybrid-vehicle energy management.
Quantum-Inspired MoE-Based Optimal Operation of a Wave Hydrogen Microgrid for Integrated Water, Hydrogen, and Electricity Supply and Trade
Feb 2025
Publication
This research explores the optimal operation of an offshore wave-powered hydrogen system specifically designed to supply electricity and water to a bay in Humboldt California USA and also sell it with hydrogen. The system incorporates a desalination unit to provide the island with fresh water and feed the electrolyzer to produce hydrogen. The optimization process utilizes a mixture of experts in conjunction with the Quantitative Structure-Activity Relationship (QSAR) algorithm traditionally used in drug design to achieve two main objectives: minimizing operational costs and maximizing revenue from the sale of water hydrogen and electricity. Many case studies are examined representing typical electricity demand and wave conditions during typical summer winter spring and fall days. The simulation optimization and results are carried out using MATLAB 2018 and SAM 2024 software applications. The findings demonstrate that the combination of the QSAR algorithm and quantum-inspired MoE results in higher revenue and lower costs compared to other current techniques with hydrogen sales being the primary contributor to increased income.
A Comparison of Low-carbon Gas-turbine Power Generation Cycles
Sep 2025
Publication
This study investigates potential solutions for low-carbon power generation with hydrogen firing and carbon capture. Multi-dimensional system modeling was used to assess the effects on plant performance size and cost. The examined cycles include advanced dry- wet- bottoming- oxyfuel cycles with air-separation units and post-combustion carbon capture with exhaust gas recirculation. The results identify three distinct lowcarbon technology pathways. While conventional combined-cycle plants are suitable for hydrogen retrofits hydrogen firing (both blue and green) results in levelized costs of electricity 50%–300% higher than carbon capture solutions making carbon capture more attractive for long-term energy storage. When carbon capture is applied to conventional combined cycles they become suboptimal compared to alternative solutions. The intercooled-recuperated (ICR) gas turbine cycle integrated with post-combustion carbon capture offers superior performance: over 3% higher efficiency 12% lower capital costs and 70% smaller physical footprint compared to conventional combined cycles with carbon capture. The Allam cycle represents a third pathway achieving 100% CO2 capture with efficiency comparable to combined cycles at 90% capture. Gas separation units emerge as the dominant source of both capital costs and efficiency penalties across all carbon capture configurations representing the key area for future optimization to reduce overall electricity costs.
Progress in Carbon Capture and Impurities Removal for High Purity Hydrogen Production from Biomass Thermochemical Conversion
Nov 2024
Publication
Renewable hydrogen production from biomass thermochemical conversion is an emerging technology to reduce fossil fuel consumptions and carbon emissions. Biomass-derived hydrogen can be produced by pyrolysis gasification alkaline thermal treatment etc. However the removal of impurities from biomass thermochemical conversion products to improve hydrogen purity is currently technical bottleneck. It is important to assess and investigate the types and properties of impurities the difficulty of separation and the impact on downstream utilization of hydrogen in the biomass-derived hydrogen production process. The key objectives of this comprehensive review are: (1) to reveal the current status and necessity of developing biomass-derived hydrogen production; (2) to evaluate the types devices and impurities distribution of biomass thermochemical conversion; (3) to explore the formation pathways and removal technologies of typical impurities of tar CO2 sulfides and nitrides in hydrogen production process; and (4) to propose future insights on the separation technologies of typical impurities to promote the gradual substitution of biomass-derived hydrogen for fossil-derived energy.
Underground Hydrogen Storage in Sandstone Reservoirs: Effects of Geochemical Reactivity of Hydrogen on Reservoir Performance
Jan 2025
Publication
Underground hydrogen storage in porous rocks is a promising method to stabilize renewable energy fluctuations. However data on the geochemical reactivity of hydrogen with reservoir rocks and its potential effects on reservoir performance are limited. This study investigates the geochemical reactivity of hydrogen with Bunt sandstein reservoir sandstones from northern Germany collected at a depth of about 2.5 km. Experiments were performed at 100 ◦C and 150 bar hydrogen partial pressure for four weeks examining scenarios with dry hydrogen synthetic saline fluid with hydrogen synthetic saline fluid with helium (as a control) and an oxidation environment (air). We measured permeability porosity magnetic susceptibility and fluid element concentration before and after the experiments. Results showed no significant mineral changes attributed to hydrogen. Mag netic susceptibility indicated no formation of magnetic minerals such as magnetite and pyrrhotite. Minor var iations in permeability and porosity were attributed to anhydrite dissolution from fluid chemistry nonequilibrium. Overall our findings suggest hydrogen interactions with Buntsandstein sandstone (no pyrite content) at temperatures up to 100 ◦C do not risk hydrogen loss or reservoir performance degradation.
Evaluating the Hydrogen Storage Potential of Shut Down Oil and Gas Fields Along the Norwegian Continental Shelf
Apr 2023
Publication
The underground hydrogen storage (UHS) capacities of shut down oil and gas (O&G) fields along the Norwegian continental shelf (NCS) are evaluated based on the publicly available geological and hydrocarbon production data. Thermodynamic equilibrium and geochemical models are used to describe contamination of hydrogen loss of hydrogen and changes in the mineralogy. The contamination spectrum of black oil fields and retrograde gas fields are remarkably similar. Geochemical models suggest limited reactive mineral phases and meter-scale hydrogen diffusion into the caprock. However geochemical reactions between residual oil reservoir brine host rock and hydrogen are not yet studied in detail. For 23 shut down O&G fields a theoretical maximum UHS capacity of ca. 642 TWh is estimated. We conclude with Frigg Nordost Frigg and Odin as the best-suited shut down fields for UHS having a maximum UHS capacity of ca. 414 TWh. The estimates require verification by site-specific dynamic reservoir models.
Electrochemical Devices to Power a Sustainable Energy Transition—An Overview of Green Hydrogen Contribution
Mar 2024
Publication
This work discusses the current scenario and future growth of electrochemical energy devices such as water electrolyzers and fuel cells. It is based on the pivotal role that hydrogen can play as an energy carrier to replace fossil fuels. Moreover it is envisaged that the scaled-up and broader deployment of the technologies can hold the potential to address the challenges associated with intermittent renewable energy generation. From a sustainability perspective this synergy between hydrogen and electricity from renewable sources is particularly attractive: electrolyzers convert the excess energy from renewables into green hydrogen and fuel cells use this hydrogen to convert it back into electricity when it is needed. Although this transition endorses the ambitious goal to supply greener energy for all it also entails increased demand for the materials that are essential for developing such cleaner energy technologies. Herein several economic and environmental issues are highlighted besides a critical overview regarding each technology. The aim is to raise awareness and provide the reader (a non-specialist in the field) with useful resources regarding the challenges that need to be overcome so that a green hydrogen energy transition and a better life can be fully achieved.
Assessment of the Role of the Green Hydrogen as the Commodity Enabling a New Green Dialogue Among the Mediterranean Shores
Apr 2024
Publication
The Mediterranean basin has been characterized by a net flow of fossil commodities from the North African shore to Southern Europe and the Middle East for decades; however decarbonizing the energy system implies to substantially modify this situation turning the current “black dialogue” into a “green dialogue” (i.e. based on the exchange of renewable electricity and green hydrogen). This paper presents a feasibility study conducted to estimate the potential green hydrogen production by electrolysis in three Tunisian sites. It shows and compares several plant layouts varying the size and typology of renewable electricity generators and electrolyzers. The work adopts local weather data and technical features of the technologies in the computations and accounts for site specific topographical and infrastructural constraints such as land available for construction and local power grid connection capacities. It shows that configurations able to produce large quantities of green hydrogen may not be compliant with such constraints basically nullifying their contribution in any hydrogen strategy. Finally results show that the LCOH lies in the range 1.34 $/kgH2 and 4.06 $/kgH2 depending on both the location and the combination of renewable electricity generators and electrolyzers.
Research on Hydrogen Production System Technology Based on Photovoltaic-Photothermal Coupling Electrolyzer
Dec 2023
Publication
Solar hydrogen production technology is a key technology for building a clean low-carbon safe and efficient energy system. At present the intermittency and volatility of renewable energy have caused a lot of “wind and light.” By combining renewable energy with electrolytic water technology to produce high-purity hydrogen and oxygen which can be converted into electricity the utilization rate of renewable energy can be effectively improved while helping to improve the solar hydrogen production system. This paper summarizes and analyzes the research status and development direction of solar hydrogen production technology from three aspects. Energy supply mode: the role of solar PV systems and PT systems in this technology is analyzed. System control: the key technology and system structure of different types of electrolytic cells are introduced in detail. System economy: the economy and improvement measures of electrolytic cells are analyzed from the perspectives of cost consumption efficiency and durability. Finally the development prospects of solar hydrogen production systems in China are summarized and anticipated. This article reviews the current research status of photovoltaic-photothermal coupled electrolysis cell systems fills the current research gap and provides theoretical reference for the further development of solar hydrogen production systems.
The Emerging Role of Artificial Intelligence in Enhancing Energy Efficiency and Reducing GHG Emissions in Transport Systems
Dec 2024
Publication
The global transport sector a significant contributor to energy consumption and greenhouse gas (GHG) emissions requires innovative solutions to meet sustainability goals. Artificial intelligence (AI) has emerged as a transformative technology offering opportunities to enhance energy efficiency and reduce GHG emissions in transport systems. This study provides a comprehensive review of AI’s role in optimizing vehicle energy management traffic flow and alternative fuel technologies such as hydrogen fuel cells and biofuels. It explores AI’s potential to drive advancements in electric and autonomous vehicles shared mobility and smart transportation systems. The economic analysis demonstrates the viability of AI-enhanced transport considering Total Cost of Ownership (TCO) and cost-benefit outcomes. However challenges such as data quality computational demands system integration and ethical concerns must be addressed to fully harness AI’s potential. The study also highlights the policy implications of AI adoption underscoring the need for supportive regulatory frameworks and energy policies that promote innovation while ensuring safety and fairness.
Assessing the Carbon Intensity of e-fuels Production in European Countries: A Temporal Analysis
Nov 2024
Publication
The transport sector heavily relies on the use of fossil fuels which are causing major environmental concerns. Solutions relying on the direct or indirect use of electricity through efuel production are emerging to power the transport sector. To ensure environmental benefits are achieved over this transition an accurate estimation of the impact of the use of electricity is needed. This requires a high temporal resolution to capture the high variability of electricity. This paper presents a previously unseen temporal analysis of the carbon intensity of e-fuels using grid electricity in countries that are members of the European Network of Transmission System Operators (ENTSO-E). It also provides an estimation of the potential load factor for producing low-carbon e-fuels according to the European Union legislative framework. This was achieved by building on top of the existing EcoDynElec tool to develop EcoDynElec_xr a python tool enabling—with an hourly time resolution—the calculation visualisation and analysis of the historical time-series of electricity mixing from the ENTSO-E. The results highlight that in 2023 very few European countries were reaching low carbon intensity for electricity that enables the use of grid electricity for the production of green electrolytic hydrogen. The methodological assumptions consider the consumption of the electricity mix instead of the production mix and the considered time step is of paramount importance and drastically impacts the potential load factor of green hydrogen production. The developed tools are released under an open-source license to ensure transparency result reproducibility and reuse regarding newer data for other territories or for other purposes.
Green Hydrogen Energy Systems: A Review on Their Contribution to a Renewable Energy System
Jun 2024
Publication
Accelerating the transition to a cleaner global energy system is essential for tackling the climate crisis and green hydrogen energy systems hold significant promise for integrating renewable energy sources. This paper offers a thorough evaluation of green hydrogen’s potential as a groundbreaking alternative to achieve near-zero greenhouse gas (GHG) emissions within a renewable energy framework. The paper explores current technological options and assesses the industry’s present status alongside future challenges. It also includes an economic analysis to gauge the feasibility of integrating green hydrogen providing a critical review of the current and future expectations for the levelized cost of hydrogen (LCOH). Depending on the geographic location and the technology employed the LCOH for green hydrogen can range from as low as EUR 1.12/kg to as high as EUR 16.06/kg. Nonetheless the findings suggest that green hydrogen could play a crucial role in reducing GHG emissions particularly in hard-to-decarbonize sectors. A target LCOH of approximately EUR 1/kg by 2050 seems attainable in some geographies. However there are still significant hurdles to overcome before green hydrogen can become a cost-competitive alternative. Key challenges include the need for further technological advancements and the establishment of hydrogen policies to achieve cost reductions in electrolyzers which are vital for green hydrogen production.
Wind–Photovoltaic–Electrolyzer-Underground Hydrogen Storage System for Cost-Effective Seasonal Energy Storage
Nov 2024
Publication
Photovoltaic (PV) and wind energy generation result in low greenhouse gas footprints and can supply electricity to the grid or generate hydrogen for various applications including seasonal energy storage. Designing integrated wind–PV–electrolyzer underground hydrogen storage (UHS) projects is complex due to the interactions between components. Additionally the capacities of PV and wind relative to the electrolyzer capacity and fluctuating electricity prices must be considered in the project design. To address these challenges process modelling was applied using cost components and parameters from a project in Austria. The hydrogen storage part was derived from an Austrian hydrocarbon gas field considered for UHS. The results highlight the impact of the renewable energy source (RES) sizing relative to the electrolyzer capacity the influence of different wind-to-PV ratios and the benefits of selling electricity and hydrogen. For the case study the levelized cost of hydrogen (LCOH) is EUR 6.26/kg for a RES-to-electrolyzer capacity ratio of 0.88. Oversizing reduces the LCOH to 2.61 €/kg when including electricity sales revenues or EUR 4.40/kg when excluding them. Introducing annually fluctuating electricity prices linked to RES generation results in an optimal RES-to-electrolyzer capacity ratio. The RES-to-electrolyzer capacity can be dynamically adjusted in response to market developments. UHS provides seasonal energy storage in areas with mismatches between RES production and consumption. The main cost components are compression gas conditioning wells and cushion gas. For the Austrian project the levelized cost of underground hydrogen storage (LCHS) is 0.80 €/kg with facilities contributing EUR 0.33/kg wells EUR 0.09/kg cushion gas EUR 0.23/kg and OPEX EUR 0.16/kg. Overall the analysis demonstrates the feasibility of integrated RES–hydrogen generation-seasonal energy storage projects in regions like Austria with systems that can be dynamically adjusted to market conditions.
The Effect of Natural Ventilation through Roof Vents Following Hydrogen Leaks in Confined Spaces
Sep 2023
Publication
Hydrogen energy is gaining global popularity as a green energy source and its use is increasing. However hydrogen has a rapid diffusion rate and a broad combustion range; thus it is vital to take safety precautions during its storage. In this study we examined the change of hydrogen concentration in a confined space exposed to a hydrogen leak according to the size of the leakage hole and the leakage flow rate assuming an extreme situation. In addition we investigated rectangular vents (that serve as explosion panels in the event of an explosion) to assess their ventilation performance according to the area of the vent when used for emergency natural ventilation. The vent areas tested represented 12% 24% and 36% of the floor area and they were installed in the ceiling of the test enclosure. When exposed to a simulated hydrogen leak the enclosure acquired a hydrogen concentration of 1% which is 25% of the lower flammability limit (LFL) in less than 6 s across all test cases. The time to LFL varied from approximately 4–81 s. In an assessment of the emergency ventilation duration the ventilation time required to reach safe hydrogen concentrations decreased and showed less deviation as the vent size was increased. For the largest vent size tested the LFL was reached in <1 min; it took 145.6 s to acquire a 1 vol% of hydrogen which is relatively fast. However there were no significant differences between the performance of large and medium-sized vent areas. Therefore through the results we found that it is reasonable to apply the area Kv = 3.31 (24% of the floor area) or less when considering the design of a roof vent that can serve as both an emergency ventilation and an explosion vent. This suggests that it is difficult to expect an improvement in ventilation performance by simply increasing the area of the vent beyond a certain area. Through these results this study proposes a practical and novel method for future design and parameters of safety functions that protect areas where hydrogen is present.
Carbon Dioxide Removal Potential from Decentralised Bioenergy with Carbon Capture and Storage (BECCS) and the Relevance of Operation Choices
Mar 2022
Publication
Bioenergy with carbon capture and storage (BECCS) technology is expected to support net-zero targets by supplying low carbon energy while providing carbon dioxide removal (CDR). BECCS is estimated to deliver 20 to 70 MtCO2 annual negative emissions by 2050 in the UK despite there are currently no BECCS operating facility. This research is modelling and demonstrating the flexibility scalability and attainable immediate application of BECCS. The CDR potential for two out of three BECCS pathways considered by the Intergovernmental Panel on Climate Change (IPCC) scenarios were quantified (i) modular-scale CHP process with post-combustion CCS utilising wheat straw and (ii) hydrogen production in a small-scale gasifier with pre-combustion CCS utilising locally sourced waste wood. Process modelling and lifecycle assessment were used including a whole supply chain analysis. The investigated BECCS pathways could annually remove between − 0.8 and − 1.4 tCO2e tbiomass− 1 depending on operational decisions. Using all the available wheat straw and waste wood in the UK a joint CDR capacity for both systems could reach about 23% of the UK’s CDR minimum target set for BECCS. Policy frameworks prioritising carbon efficiencies can shape those operational decisions and strongly impact on the overall energy and CDR performance of a BECCS system but not necessarily maximising the trade-offs between biomass use energy performance and CDR. A combination of different BECCS pathways will be necessary to reach net-zero targets. Decentralised BECCS deployment could support flexible approaches allowing to maximise positive system trade-offs enable regional biomass utilisation and provide local energy supply to remote areas.
Levelised Cost of Hydrogen Production in Northern Africa and Europe in 2050: A Monte Carlo Simulation for Germany, Norway, Spain, Algeria, Morocco, and Egypt
May 2024
Publication
The production of green hydrogen through electrolysis utilizing renewable energies is recognized as a pivotal element in the pursuit of decarbonization. In order to attain cost competitiveness for green hydrogen reasonable generation costs are imperative. To identify cost-effective import partners for Germany given its limited green hydrogen production capabilities this study undertakes an exhaustive techno-economic analysis to determine the potential Levelized Cost of Hydrogen in Germany Norway Spain Algeria Morocco and Egypt for the year 2050 which represents a critical milestone in European decarbonization efforts. Employing a stochastic approach with Monte Carlo simulations the paper marks a significant contribution for projecting future cost ranges acknowledging the multitude of uncertainties inherent in related cost parameters and emphasizing the importance of randomness in these assessments. Country-specific Weighted Average Cost of Capital are calculated in order to create a refined understanding of political and economic influences on cost formation rather than using a uniform value across all investigated nations. Key findings reveal that among the evaluated nations PV-based hydrogen emerges as the most cost-efficient alternative in all countries except Norway with Spain presenting the lowest Levelized Cost of Hydrogen at 1.66 €/kg to 3.12 €/kg followed by Algeria (1.72 €/kg to 3.23 €/kg) and Morocco (1.73 €/kg to 3.28 €/kg). Consequently for economically favorable import options Germany is advised to prioritize PV-based hydrogen imports from these countries. Additionally hydrogen derived from onshore wind in Norway (2.24 €/kg to 3.73 €/kg) offers a feasible import alternative. To ensure supply chain diversity and reduce dependency on a single source a mixed import strategy is advisable. Despite having the lowest electricity cost Egypt shows the highest Levelized Cost of Hydrogen primarily due to a significant Weighted Average Cost of Capital.
A Survey on Hydrogen Tanks for Sustainable Aviation
Aug 2024
Publication
The aviation industry is facing challenges related to its environmental impact and thus the pressing need to develop aircraft technologies aligned with the society climate goals. Hydrogen is emerging as a potential clean fuel for aviation as it offers several advantages in terms of supply potential and weight specific energy. One of the key factors enabling the use of H2 in aviation is the development of reliable and safe storage technologies to be integrated into aircraft design. This work provides an overview of the technologies currently being investigated or developed for the storage of hydrogen within the aircraft which would enable the use of hydrogen as a sustainable fuel for aviation with emphasis on tanks material and structural aspects. The requirements dictated by the need of integrating the fuel system within existing or ex-novo aircraft architectures are discussed. Both the storage of gaseous and liquid hydrogen are considered and the main challenges related to the presence of either high internal pressures or cryogenic conditions are explored in the background of recent literature. The materials employed for the manufacturing of hydrogen tanks are overviewed. The need to improve the storage tanks efficiency is emphasized and issues such as thermal insulation and hydrogen embrittlement are covered as well as the reference to the main structural health monitoring strategies. Recent projects dealing with the development of onboard tanks for aviation are eventually listed and briefly reviewed. Finally considerations on the tank layout deemed more realistic and achievable in the near future are discussed.
Hydrogen and Fuel Cell Technology: Progress, Challenges, and Future Directions
Sep 2012
Publication
The Department of Energy’s (DOE) hydrogen and fuel cell activities are presented focussing on key targets and progress. Recent results on the cost durability and performance of fuel cells are discussed along with the status of hydrogen-related technologies and cross-cutting activities. DOE has deployed fuel cells in key early markets including backup power and forklifts. Recent analyses show that fuel cell electric vehicles (FCEVs) are among the most promising options to reduce greenhouse gas emissions and petroleum use. Preliminary analysis also indicates that the total cost of ownership of FCEVs will be comparable to other advanced vehicle and fuel options.
The Impact of Impurity Gases on the Hydrogen Embrittlement Behavior of Pipeline Steel in High-Pressure H2 Environments
May 2024
Publication
The use of hydrogen-blended natural gas presents an efficacious pathway toward the rapid large-scale implementation of hydrogen energy with pipeline transportation being the principal method of conveyance. However pipeline materials are susceptible to hydrogen embrittlement in high-pressure hydrogen environments. Natural gas contains various impurity gases that can either exacerbate or mitigate sensitivity to hydrogen embrittlement. In this study we analyzed the mechanisms through which multiple impurity gases could affect the hydrogen embrittlement behavior of pipeline steel. We examined the effects of O2 and CO2 on the hydrogen embrittlement behavior of L360 pipeline steel through a series of fatigue crack growth tests conducted in various environments. We analyzed the fracture surfaces and assessed the fracture mechanisms involved. We discovered that CO2 promoted the hydrogen embrittlement of the material whereas O2 inhibited it. O2 mitigated the enhancing effect of CO2 when both gases were mixed with hydrogen. As the fatigue crack growth rate increased the influence of impurity gases on the hydrogen embrittlement of the material diminished.
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