Found 19 results
Open Access
Article
25 October 2024Supply Chain of Grey-Blue Hydrogen from Natural Gas: A Study on Energy Efficiency and Emissions of Processes
Hydrogen energy offers a significant potential for reducing carbon emissions and integrating clean energy across sectors such as heavy-duty vehicles, energy-intensive industries, and building heating. This study analyzes the energy efficiency and emissions of grey and blue hydrogen supply chains, identifying key issues such as high energy consumption and losses in transportation, steam methane reforming, and liquid hydrogen storage. Truck transportation emerges as the highest emitter, with emissions ranging from 0.140 to 0.150 kg CO2e per kg of hydrogen. Using a bi-objective Dijkstra Algorithm, the study identifies the most energy-emissions-efficient pathways and reveals a trade-off between energy efficiency and greenhouse gas emissions. Grey hydrogen shows higher energy efficiency (38.0%) but higher emissions (0.1689 kg CO2e per kg of hydrogen). In contrast, with 60% and 90% carbon capture and storage, blue hydrogen has slightly lower energy efficiencies (37.5% and 36.9%) but reduced emissions (0.1564 and 0.1514 kg CO2e per kg of hydrogen). Liquefied natural gas and hydrogen offer high energy efficiency but increase emissions, while compressed natural gas and hydrogen slightly reduce efficiency but nearly halve emissions. Hence, compressed options are preferable for an energy-emissions-efficient shortest path.
Open Access
Review
22 October 2024Engineering of Cu-Based Quaternary Sulfide Nanomaterials for Photocatalytic Applications
Semiconductor nanomaterials have been widely used as light-responsive photocatalysts for solar-to-fuel conversion over the past decade. However, the wide band gap of the most reported photocatalysts stems from light absorption in the visible region and results in low solar conversion efficiency. Therefore, it is necessary to develop new semiconductor nanomaterials with high absorption coefficients over the visible region as photocatalysts. The most promising candidates include Cu-based quaternary sulfide nanomaterials (CQSNs), such as Cu-II-III-S (e.g., CuZnInS, CuZnGaS), Cu-II-IV-S (e.g., Cu2ZnSnS4, Cu2ZnGeS4), and I-III-IV-S (e.g., CuInSnS4, Cu3GaSnS5). This review provides a comprehensive overview of the recent progress in developing CQSNs for various photocatalytic applications. Firstly, we present an overview of the synthesis of CQSNs with precise control over crystal phase, composition, size, and shape using solution-based methods. Then, the enhancement of photocatalytic performance was presented via the engineering of CQSNs, which included surface engineering, elemental doping, cocatalyst loading, vacancy engineering, and interface engineering. Subsequently, we further introduce the photocatalytic applications in the fields of photocatalytic and photoelectrochemical hydrogen conversion, CO2 reduction, organic synthesis, and pollutant degradation. Lastly, this review ends with views on the current challenges and opportunities of CQSNs in future studies.
Open Access
Communication
22 August 2024Mixed Matrix Membranes Produced from a Fluorinated MOF and Pebax for CO2/H2 Separation
Hydrogen (H2) emerges as a promising clean energy source, but its efficient purification from various sources needs advanced separation technologies. This study explores the use of CO2-selective membranes, especially mixed matrix membranes (MMM) incorporating KAUST-7 metal-organic framework (MOF), for hydrogen purification. The MMM was fabricated with various KAUST-7 content in a polymer matrix (Pebax 1657) and characterized via Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and gas permeation tests. The XRD analysis confirms the incorporation of KAUST-7 into the MMM, while SEM reveals a homogeneous particle distribution at low content (below 10%) but agglomeration at higher ones (above 10%). FTIR confirms good interfacial interactions between the MOF and polymer matrix. TGA results show that the MMM thermal stability slightly decreases with increasing MOF content. Gas permeation results reveal improved CO2 permeability (79%) and CO2/H2 selectivity (19%) for MMM compared to neat Pebax membranes, with an optimal performance observed at 10 wt.% KAUST-7. Beyond this threshold, the performance deteriorates, possibly due to polymer rigidity and MOF agglomeration. Overall, the study highlights the potential of KAUST-7/Pebax MMM for enhanced hydrogen purification.
Open Access
Article
26 July 2024Current and Future Costs of Storage for Electricity in a Decarbonized Electricity System
As power systems globally are transitioning from fossil fuels to renewable sources, integrating energy storage becomes imperative to balance variable renewable electricity generation. The core objective of this paper is to conduct a comprehensive cost assessment of selected energy storage technologies from 2023 to 2050, focusing on the Austrian electricity market. Our method combines techno-economic assessment with the technological learning method to integrate various storage technologies into a renewable electricity system, using scenarios that account for decarbonization goals. Results indicate that pumped storage hydro exhibits none or negative learning effects, while lithium-ion batteries demonstrate significant investment cost decreases. Despite investment cost reductions, underground hydrogen storage continues to incur high total costs per kWh discharged due to low roundtrip efficiency, suggesting its future outlook depends on seasonal storage needs in fossil-free power systems. An important finding of this analysis underscores the importance of optimizing the ratio of electricity demand, renewable generation expansion and storage deployment for cost-effectiveness. Excessive storage deployment leads to lower utilization and higher costs, emphasizing the necessity of at least 1500 full-load hours for profitable operation across all storage systems. Strategic planning for optimal storage deployment is emphasized to optimize utilization and minimize costs.
Open Access
Case Report
26 February 2024‘Greening’ an Oil Exporting Country: A Hydrogen and Helium Closed-cycle Gas Turbines Case Study
Holistic decarbonisation requires collaborative efforts and substantial investments across diverse economic sectors. This study introduces an innovative national approach, blending technological insights and philosophical considerations to shape decarbonization policies and practices. Libya is the case study. The proposed framework involves submersible power stations with continuous-duty helium closed-cycle gas turbines to supply electricity demand and hydrogen. Extensive national data is analysed, incorporating factors such as sectoral consumption, sea temperature, and port locations. An analytical model is developed, providing a valuable foundation for realistic decarbonization scenarios. The model aims to maintain the benefits of current energy consumption, assuming a 2% growth rate, while assessing changes in a fully green economy. The results offer qualitative and quantitative insights on hydrogen use and an expected rise in electricity demand. Two scenarios are examined: self-sufficiency and replacing oil exports with hydrogen exports. This study provides a quantitative perspective on decarbonization, focusing on a submersible helium closed cycle gas turbine concept resistant to natural disasters and proliferation. Findings underscore the substantial changes and investments needed for this transition, identifying primary needs of 27 GW or 129 GW for self-sufficiency and exports, respectively. This foundational analysis marks the start of research, investment, and political agendas toward decarbonization.
Open Access
Article
23 January 2024Analysis of a σ54 Transcription Factor L420P Mutation in Context of Increased Organic Nitrogen Tolerance of Photofermentative Hydrogen Production in Cereibacter sphaeroides Strain 2.4.1 Substrain H2
Photofermentative hydrogen production with non-sulfur purple bacteria like Cereibacter sphaeroides (formerly Rhodobacter sphaeroides) is a promising and sustainable process to convert organic waste into the energy carrier hydrogen gas. However, this conversion is inhibited by elevated organic nitrogen concentrations in the substrate, which limits its applicability to nitrogen-poor organic waste. We present genomic and transcriptomic insights into a substrain of Cereibacter sphaeroides strain 2.4.1 that shows unexpected high levels of photofermentative hydrogen evolution when fed with glutamate. Genome sequencing revealed 222 single nucleotide variances (SNVs) between the reference genome of C. sphaeroides strain 2.4.1 and the analyzed substrain H2. These affect 61 protein coding genes. A leucine-proline exchange is present in the σ54 factor (rpoN2 gene), a global hydrogen and nitrogen metabolism regulator. We propose a model how this mutation alters DNA-binding properties that explain the unexpected organic nitrogen tolerance of hydrogen production. Transcriptomic analyses under varying glutamate concentrations support this finding. Thus, we present the first thorough genomic and transcriptomic analysis of a Cereibacter strain that shows promising metabolic characteristics for biotechnological hydrogen gas production from organic waste. These results suggest a potential target for strain optimization. Possibly, our key finding can be transferred to other hydrogen producing microorganisms.
Open Access
Article
05 January 2024Benzene Bridged Carbon Nitride for Efficient Photocatalytic Hydrogen Evolution
Turing the electronic structure by inserting certain functional groups in graphitic carbon nitride (g-C3N4, CN for short) skeleton through molecular doping is an effective way to improve its photocatalytic performance. Herein, we prepare a benzene bridged carbon nitride (BCN) by calcining urea and 1,3,5-tribromobenzene at elevated temperature. The introduction of benzene ring in g-C3N4 layers improves the separation efficiency and lifetime of photogenerated carriers, inhibits the recombination rate of electron/hole pairs, thus the performance of photocatalytic hydrogen evolution improves. The optimal hydrogen evolution rate of 1.5BCN reaches 1800 µmol/h·g, which is nine times that of the pure g-C3N4. DFT calculation proved the benzene bridged CN increased the distance of charge transfer (DCT) and the push-pull electronic effect of intramolecular electrons. This work may provide a pathway for preparing molecular doped g-C3N4 with improved photocatalytic performance.
Open Access
Article
19 September 2023Advancing Green Hydrogen Production in Saudi Arabia: Harnessing Solar Energy and Seawater Electrolysis
The transition to clean and sustainable energy sources is crucial for combating the challenges posed by climate change. Green hydrogen, produced through renewable energy-driven electrolysis, holds significant promise as a viable clean energy carrier. The study introduces a system that leverages abundant solar energy and utilizes seawater as the feedstock for electrolysis, potentially offering a cost-effective solution. A comprehensive mathematical model, implemented in MATLAB, is employed to simulate the design and operational efficiency of the proposed green hydrogen production system. The system’s core components include solar panels as a clean energy source, an advanced MPPT charge controller ensuring optimal power delivery to the electrolyzer, and a seawater tank serving as the electrolyte source. The model combines these elements, allowing for continuous operation and efficient hydrogen production, addressing concerns about energy losses and cost-effectiveness. Results demonstrate the influence of solar irradiance on the system’s performance, revealing the need to account for seasonal variations when designing green hydrogen production facilities. Theoretical experiments are conducted to evaluate the behavior of a lithium battery, essential for stabilizing the system’s output and ensuring continuous operation during periods of low solar radiation.
Open Access
Article
03 March 2023SnS2 Quantum Dots Decorated MoS2 Nanosheets Enabling Efficient Photocatalytic H2 Evolution in CO2 Saturated Water
SnS2/MoS2 heterojunction nanocomposite was prepared by a one-step hydrothermal synthesis method. The nanocomposite exhibited much improved photocatalytic hydrogen evolution performance in CO2 saturated solution compared with pure MoS2 and SnS2 samples. The improved photocatalytic activity was attributed to the S-scheme heterojunction structure between SnS2 quantum dots and MoS2 nanosheets which facilitate electron-hole separation both in MoS2 and SnS2. In the S-scheme structure, the strong reduction ability of SnS2 quantum dots was well maintained for the improved H2 evolution. In situ DRIFT studies allowed us to suggest reaction pathways from CO2 and H2O to photocatalytic H2, CO, and CH4 generation.
