Effect of ZrO2 on the performance of Co–CeO2 catalysts for hydrogen production from waste-derived synthesis gas using high-temperature water gas shift reaction

In this study, highly active and stable CeO₂, ZrO₂, and Zr_(1-x)Ce_(x)O₂-supported Co catalysts were prepared using the co-precipitation method for the high-temperature water gas shift reaction to produce hydrogen from waste-derived synthesis gas. The physicochemical properties of the catalysts were investigated by carrying out Brunauer-Emmet-Teller, X-ray diffraction, CO-chemisorption, Raman spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and H₂-temperature-programmed reduction measurements. With an increase in the ZrO₂ content, the surface area and reducibility of the catalysts increased, while the interaction between Co and the support and the dispersion of Co deteriorated. The Co–Zr_0.4Ce_0·6O₂ and Co–Zr_0.6Ce_0·4O₂ catalysts showed higher oxygen storage capacity than that of the others because of the distortion of the CeO₂ structure due to the substitution of Ce⁴⁺ by Zr⁴⁺. The Co–Zr_0.6Ce_0·4O₂ catalyst with high reducibility and oxygen storage capacity exhibited the best catalytic performance and stability among all the catalysts investigated in this study.     

Expected impacts on greenhouse gas and air pollutant emissions due to a possible transition towards a hydrogen economy in German road transport

Transitioning German road transport partially to hydrogen energy is among the possibilities being discussed to help meet national climate targets. This study investigates impacts of a hypothetical, complete transition from conventionally-fueled to hydrogen-powered German transport through representative scenarios. Our results show that German emissions change between ?179 and +95 MtCO₂eq annually, depending on the scenario, with renewable-powered electrolysis leading to the greatest emissions reduction, while electrolysis using the fossil-intense current electricity mix leads to the greatest increase. German energy emissions of regulated pollutants decrease significantly, indicating the potential for simultaneous air quality improvements. Vehicular hydrogen demand is 1000 PJ annually, requiring 446–525 TWh for electrolysis, hydrogen transport and storage, which could be supplied by future German renewable generation, supporting the potential for CO₂-free hydrogen traffic and increased energy security. Thus hydrogen-powered transport could contribute significantly to climate and air quality goals, warranting further research and political discussion about this possibility.     

Renewable-powered hydrogen economy from Australia's perspective

This article broadly reviews the state-of-the-art technologies for hydrogen production routes, and methods of renewable integration. It outlines the main techno-economic enabler factors for Australia to transform and lead the regional energy market. Two main categories for competitive and commercial-scale hydrogen production routes in Australia are identified: 1) electrolysis powered by renewable, and 2) fossil fuel cracking via steam methane reforming (SMR) or coal gasification which must be coupled with carbon capture and sequestration (CCS). It is reported that Australia is able to competitively lower the levelized cost of hydrogen (LCOH) to a record $(1.88–2.30)/kg_H2 for SMR technologies, and $(2.02–2.47)/kg_H2 for black-coal gasification technologies. Comparatively, the LCOH via electrolysis technologies is in the range of $(4.78–5.84)/kg_H2 for the alkaline electrolysis (AE) and $(6.08–7.43)/kg_H2 for the proton exchange membrane (PEM) counterparts. Nevertheless, hydrogen production must be linked to the right infrastructure in transport-storage-conversion to demonstrate appealing business models.     

Improving inter-plant integration of syngas production technologies by the recycling of CO2 and by-product of the Fischer-Tropsch process

This paper deals with the emission reduction in synthesis-gas production by better integration and increasing the energy efficiency of a high-temperature co-electrolysis unit combined with the Fischer-Tropsch process. The investigated process utilises the by-product of Fischer-Tropsch, as an energy source and carbon dioxide as a feedstock for synthesis gas production. The proposed approach is based on adjusting process streams temperatures with the further synthesis of a new heat exchangers network and optimisation of the utility system. The potential of secondary energy resources was determined using plus/minus principles and simulation of a high-temperature co-electrolysis unit. The proposed technique maximises the economic and environmental benefits of inter-unit integration. Two scenarios were considered for sharing the high-temperature co-electrolysis and the Fischer-Tropsch process. In the first scenario, by-products from the Fischer-Tropsch process were used as fuel for a high-temperature co-electrolysis. Optimisation of secondary energy sources and the synthesis of a new heat exchanger network reduce fuel consumption by 47% and electricity by 11%. An additional environmental benefit is reflected in emission reduction by 25,145 tCO₂/y. The second scenario uses fossil fuel as a primary energy source. The new exchanger network for the high-temperature co-electrolysis was built for different energy sources. The use of natural gas resulted in total annual costs of the heat exchanger network to 1,388,034 USD/y, which is 1%, 14%, 116% less than for coal, fuel oil and LPG, respectively. The use of natural gas as a fuel has the lowest carbon footprint of 7288 tCO₂/y. On the other hand, coal as an energy source has commensurable economic indicators that produce 2 times more CO₂, which can be used as a feedstock for a high-temperature co-electrolysis. This work shows how in-depth preliminary analysis can optimise the use of primary and secondary energy resources during inter-plant integration.     

Preparation of gas standards for quality assurance of hydrogen fuel

This study has developed traceable standards for evaluating impurities in hydrogen fuel according to ISO 14687. Impurities in raw H₂, including sub μmol/mol levels of CO, CO₂, and CH₄, were analyzed using multiple detectors while avoiding contamination. The gravimetric standards prepared included mixtures of the following nominal concentrations: 1, 2, 3–5, 8–11, 17–23, and 47–65 μmol/mol for CO₂, CH₄ and CO, O₂, N₂, Ar, and He, respectively. The expanded uncertainty ranges were 0.8% for Ar, N₂, and He, 1% for CH₄ and CO, and 2% for CO₂ and O₂. These standards were stable, while that for CO varied by only 0.5% during a time span of three years. The prepared standards are useful for evaluating the compliance of H₂ fuel in service stations with ISO 14687 quality requirements.     

Co-generation of hydrogen and electricity from biodiesel process effluents

In this study, we apply a short-term voltage (0.2–0.8 V) to both crude glycerol (CG) and an anaerobic digestion (AD) effluent in a single-chamber microbial fuel cell (MFC) for power production. This improves the bioelectrogenesis in both CG (in MFC-1) and the AD effluent (in MFC-2), but higher power generation is attained in MFC-2. The use of domestic and synthetic wastewaters in the AD process leads to the generation of 195 and 350 mL H₂/L-medium, respectively. MFC-2 performs better than MFC-1 in terms of both voltage generation and chemical oxygen demand (COD) reduction. The application of 0.8 V yields a power density of 311 mW/m² (1.94 times higher than that of the control (160 mW/m²)). In addition, MFC-2 exhibits a 70% COD removal at 0.8 V, which decreases to 56% at 0.2 V. Thus, the application of a short-term voltage in MFC can stimulate both bioelectrogenesis and COD removal.     

Review of hydrogen economy in Malaysia and its way forward

Heavy fossil fuels consumption has raised concerns over the energy security and climate change while hydrogen is regarded as the fuel of future to decarbonize global energy use. Hydrogen is commonly used as feedstocks in chemical industries and has a wide range of energy applications such as vehicle fuel, boiler fuel, and energy storage. However, the development of hydrogen energy in Malaysia is sluggish despite the predefined targets in hydrogen roadmap. This paper aims to study the future directions of hydrogen economy in Malaysia considering a variety of hydrogen applications. The potential approaches for hydrogen production, storage, distribution and application in Malaysia have been reviewed and the challenges of hydrogen economy are discussed. A conceptual framework for the accomplishment of hydrogen economy has been proposed where renewable hydrogen could penetrate Malaysia market in three phases. In the first phase, the market should aim to utilize the hydrogen as feedstock for chemical industries. Once the hydrogen production side is matured in the second phase, hydrogen should be used as fuel in internal combustion engines or burners. In the final phase hydrogen should be used as fuel for automobiles (using fuel cell), fuel-cell combined heat and power (CHP) and as energy storage.     

Novel sonochemical synthesis of Zn2V2O7 nanostructures for electrochemical hydrogen storage

Although utilization of diverse classes of metal oxides as hydrogen storage materials has been reported, but there is still a major need to introduce efficient materials. Herein, mesoporous Zn₂V₂O₇ nanostructures were produced by a new sonochemical method using hydrazine, zinc nitrate, and ammonium vanadate as the starting reagents and then annealed at 700 °C. Prior to annealing, Zn₃V₃O₈ was produced in the presence of ultrasonic waves, whereas in the absence of ultrasonic waves, Zn₂(VO₄)₂ was the major product. In fact, ultrasonic waves interfered with the reaction mechanism and reduced V⁵⁺ to V⁴⁺ and V³⁺. Because of the proper composition and structure of these nanostructures, they were used for electrochemical storage of hydrogen. Storage of over 2899 mAh/g after 20 cycles by flower-like nanostructures revealed their high capability. The results also showed that morphology affects efficiency such that three-dimensional spherical nanostructures had a storage capacity of 2247 mAh/g after 20 cycles.     

Evaluating influences of impurities on hydrogen production in the reaction of Si with water using Si sludge

Hydrogen has attracted much attention as a next-generation energy resource. Among various technologies, one of the promising approaches for hydrogen production is the use of the reaction between Si and water, which does not require any heat, electricity, and light energy as an input. Notwithstanding the usefulness of Si as a prospective raw material of hydrogen production, the manufacturing process of Si requires a significant amount of energy. Therefore, as an alternative to pure Si, this study used a wasted Si sludge, generated though the manufacturing process of Si wafer, for the direct reuse. Thus, the Si-water reaction for the hydrogen generation was investigated in comparison with pure Si and Si sludge by employing X-ray absorption near edge structure (XANES) to evaluate the feasibility of hydrogen production with the use of Si sludge and to identify the influence of impurities contained in Si sludge. As a result, hydrogen was not produced with the use of Si sludge because of containing Al compound as the impurity. Through the XANES analysis, the formation of SiO(OH)₂ was found as core-shell structure, which potentially would hinder the hydrogen generation.     

Economic valuation of green hydrogen charging compared to gray hydrogen charging: The case of South Korea

The South Korean government promotes hydrogen-powered vehicles to reduce greenhouse gas (GHG) emissions but these vehicles use gray hydrogen while charging, which causes GHG emissions. Therefore, converting this fuel into green hydrogen is necessary to help reduce GHG emissions, which will incur investment costs of approximately USD 20 billion over a decade. In this study, a contingent valuation method is applied in an analysis to examine the extent to which consumers are willing to pay for green hydrogen charging compared to gray hydrogen charging. The results indicate that the monthly mean of willingness to pay per driver is 51,674 KRW (USD 45.85), equivalent to 4302 KRW per kg (USD 3.82). Additionally, consumers accept a 28.5% increase in the monthly average fuel expenses when converting to green hydrogen. These findings can be used in the development of pricing and energy use plans to finance the expansion of green hydrogen infrastructure.     

Effects of hydrogen enrichment of methane on diffusion flame structure and emissions in a back-pressure combustion chamber

In the present study, the effects of hydrogen enrichment of methane are investigated numerically from the diffusion flame structure and emissions aspect. Fluent code is utilised as the simulation tool. In the first part of the study, four experiments were conducted using natural gas as fuel. A non-premixed burner and a back-pressure boiler were utilised as the experimental setup. The natural gas fuel consumption rate was changed between 22 Nm³/h and 51 Nm³/h. After the experimental studies, the numerical simulations were performed. The non-premixed combustion model with the steady laminar flamelet model (SFM) approach was used for the calculations. The methane-air extinction mechanism was utilised for the calculation of the chemical species. The numerical results were verified with the experimental results in terms of the flue gas emissions and flue gas temperature values. In the second part of the study, four different hydrogen-enriched methane combustion cases were simulated using the same methane-air extinction mechanism, which included the hydrogen oxidation mechanism as a sub mechanism. The same energy input (432 kW) was supplied into the boiler for all the studied cases. The obtained results show that the hydrogen addition to methane significantly change the diffusion flame structure in the combustion chamber. The hydrogen-enriched flames become broader and shorter with respect to the pure methane flame. This provides better mixing of the reactants and combustion products in the flame regions due to the use of a back-pressure boiler. In this way, the maximum flame temperature values and thermal NO emissions are reduced in the combustion chamber, when the hydrogen addition ratio is less than 15% by mass. The maximum temperature value is calculated as 2030 K for the case with 15% hydrogen addition ratio by mass, while it is 2050 K for the case without hydrogen enrichment. Therefore, it is determined that the hydrogen-enriched methane combustion in a back-pressure combustion chamber has the potential of reducing both the carbon and thermal NO emissions.     

The role of oxygen vacancies in the CO2 methanation employing Ni/ZrO2 doped with Ca

The Ni/ZrO₂ catalyst doped with Ca and Ni/ZrO₂ were employed in the CO₂ methanation, a reaction which will possibly be used for storing intermittent energy in the future. The catalysts were characterized by X-ray photoelectron spectroscopy (XPS, reduction in situ), X-ray diffraction (XRD, reduction in situ and Rietveld refinement), electron paramagnetic resonance (EPR), temperature-programmed surface reaction, cyclohexane dehydrogenation model reaction, temperature-programmed desorption of CO₂ and chemical analysis. The catalytic behavior of these catalysts in the CO₂ methanation was analyzed employing a conventional catalytic test. Adding Ca to Ni/ZrO₂, the metallic surface area did not change whereas the CO₂ consumption rate almost tripled. The XRD, XPS and EPR analyses showed that Ca⁺² but also some Ni²⁺ are on the ZrO₂ surface lattice of the Ni/CaZrO₂ catalyst. These cations form pairs which are composed of oxygen vacancies and coordinatively unsaturated sites (cus). By increasing the number of these pairs, the CO₂ methanation rate increases. Moreover, the number of active sites of the CO₂ methanation rate limiting step (CO and/or formate species decomposition, rls) is enhanced as well, showing that the rls occurs on the vacancies-cus sites pairs.     

Hydrofluoroolefin-based mixed refrigerant for enhanced performance of hydrogen liquefaction process

Hydrogen has the highest gravimetric energy density of all fuels; however, it has a low volumetric energy density, unfavorable for storage and transportation. Hydrogen is usually liquefied to meet the bulk transportation needs. The exothermic interconversion of its spin isomers is an additional activity to an already energy-intensive process. The most significant temperature drop occurs in the precooling cycle (between ?150 °C and up to ?180 °C) and consumes more than 50% of the required energy. To reduce the energy consumption and improve the exergy efficiency of the hydrogen liquefaction process, a new high-boiling component, Hydrofluoroolefin (HFO-1234yf), is added to the precooled mixed refrigerant. As a result, the specific energy consumption of precooling cycle reduces by 41.8%, from 10.15 kWh/kg_LH2 to 5.90 kWh/kg_LH2, for the overall process. The exergy efficiency of the proposed case increases by 43.7%; however, the total equipment cost is also the highest. The inflated cost is primarily due to the added ortho-to-para hydrogen conversion reactor, boosting the para-hydrogen concentration. From the perspective of bulk storage and transportation of liquid hydrogen, the simplicity of design and low energy consumption build a convincing case for considering the commercialization of the process.     

HRT control as a strategy to enhance continuous hydrogen production from sugarcane juice under mesophilic and thermophilic conditions in AFBRs

The objective of this study was to evaluate the effects of hydraulic retention time (HRT) (8–1 h) on H₂ production from sugarcane juice (5000 mg COD L⁻¹) in mesophilic (30 °C, AFBR-30) and thermophilic (55 °C, AFBR-55) anaerobic fluidized bed reactors (AFBRs). At HRTs of 8 and 1 h in AFBR-30, the H₂ production rates were 60 and 116 mL H₂ h⁻¹ L⁻¹, the hydrogen yields were 0.60 and 0.10 mol H₂ mol⁻¹ hexose, and the highest bacterial diversities were 2.47 and 2.34, respectively. In AFBR-55, the decrease in the HRT from 8 to 1 h increased the hydrogen production rate to 501 mL H₂ h⁻¹ L⁻¹ at the HRT of 1 h. The maximum hydrogen yield of 1.52 mol H₂ mol⁻¹ hexose was observed at the HRT of 2 h and was associated with the lowest bacterial diversity (0.92) and highest bacterial dominance (0.52).     

Pollutant emissions,performance and combustion behaviour assessment of an Si gas engine fuelled with Lcv gas containing carbon monoxide and hydrogen diluted by nitrogen

This paper includes the experimental test data of an SI engine fuelled with simulated LCV gas (Low Calorific Value), which resembles synthesis gas in composition. The LCV gas was simulated by a mixture of carbon monoxide, hydrogen and nitrogen. During the experiment, the lower heating value of the LCV gas was altered by dilution with nitrogen. A single-cylinder Honda GX270 engine was adopted in the experiment to assess the impact of LCV gas on the system performance. This engine is typically used to power various machines and for electrical energy production in small generator sets. A modified engine was connected to an electric generator, which was loaded with an electric resistor. Engine operation was controlled using a microprocessor controller. All tests were performed at constant engine speed (3000 rpm). The engine was working at wide-open throttle for all mixtures. All mixtures were burned at stoichiometric conditions and with fixed value of ignition timing (30 deg bTDC). The indicated performance of the SI engine was evaluated based on the in-cylinder pressure measurements. No significant impact on the main internal parameters of the tested SI engine fuelled with simulated LCV gas diluted by nitrogen was observed. The experimental tests showed that the combustion duration increased for the mixtures with higher content of inert gas. Increase in the LHV raised the specific emissions of NO_x and decreased specific emissions of CO and HC.     

A novel approach to ammonia synthesis from hydrogen sulfide

There are a number of shortcomings for currently-available technologies for ammonia production, such as carbon dioxide emissions and water consumption. We simulate a novel model for ammonia production from hydrogen sulfide through membrane technologies. The proposed production process decreases the need for external water and reduces the physical footprint of the plant. The required hydrogen comes from the separation of hydrogen sulfide by electrochemical membrane separation, while the required nitrogen is obtained from separating oxygen from air through an ion transport membrane. 10% of the hydrogen from the electrochemical membrane separation along with the separated oxygen from the ion transport membrane is sent to the solid oxide fuel cell for heat and power generation. This production process operates with a minimal number of processing units and in physical, kinetic, and thermal conditions in which a separation factor of ~99.99% can be attained.     

Hydrogen sulphide to hydrogen via H2S methane reformation: Thermodynamics and process scheme assessment

Hydrogen Sulphide Methane Reformation (HSMR) represents a valid alternative for the simultaneous H₂S valorisation and hydrogen production at the industrial scale, without direct CO₂ emissions. The major concerns about the process commercialization are the possible coke formation in the reaction zone and the lack of active and selective catalysts. The study of the thermodynamics is the essential preliminary step for the reaction phenomena understanding. In this work, a deep thermodynamic analysis is performed to explore the system behaviour as a function of temperature, pressure, and inlet feed composition, using the Aspen Plus RGibbs module. In this way, the optimal process operating conditions to avoid carbon lay down can be identified.Assessed the system's thermodynamics, a preliminary process scheme is developed and simulated in Aspen Plus V11.0®, considering hydrogen production and its distribution in pipeline with methane. The process performances are discussed in terms of products' purity and process energy consumptions.     

Economic viability assessment of sustainable hydrogen production,storage, and utilisation technologies integrated into on- and off-grid micro-grids: A performance comparison of different meta-heuristics

In recent years, there has been considerable interest in the development of zero-emissions, sustainable energy systems utilising the potential of hydrogen energy technologies. However, the improper long-term economic assessment of costs and consequences of such hydrogen-based renewable energy systems has hindered the transition to the so-called hydrogen economy in many cases. One of the main reasons for this is the inefficiency of the optimization techniques employed to estimate the whole-life costs of such systems. Owing to the highly nonlinear and non-convex nature of the life-cycle cost optimization problems of sustainable energy systems using hydrogen as an energy carrier, meta-heuristic optimization techniques must be utilised to solve them. To this end, using a specifically developed artificial intelligence-based micro-grid capacity planning method, this paper examines the performances of twenty meta-heuristics in solving the optimal design problems of three conceptualised hydrogen-based micro-grids, as test-case systems. Accordingly, the obtained numeric simulation results using MATLAB indicate that some of the newly introduced meta-heuristics can play a key role in facilitating the successful, cost-effective development and implementation of hydrogen supply chain models. Notably, the moth-flame optimization algorithm is found capable of reducing the life-cycle costs of micro-grids by up to 6.5% as compared to the dragonfly algorithm.     

TiO2 photocatalyst with single and dual noble metal co-catalysts for efficient water splitting and organic compound removal

Photocatalysts can be used both for air cleaning and solar energy harvesting through water splitting. However, pure TiO₂ photocatalysts are often inefficient and therefore co-catalysts are needed to improve the yield. To achieve this goal, we prepared TiO₂ and deposited Pt, Ir and Ru co-catalysts on its surface. Two base TiO₂ nanoparticles were used: P25 and rutile TiO₂ synthesized via hydrothermal method. Co-catalysts were deposited by wet impregnation technique using single element and a combination of two elements (Pt and Ir or Pt and Ru), followed by annealing in either air or H₂/Ar. Annealing in reducing atmosphere increased the photocatalytic activity of oxidation of isopropanol compared to annealing in air. We demonstrated a clear influence of the co-catalysts on the photocatalytic degradation of isopropanol and on electrochemical water-splitting reaction. The platinum-containing samples showed the best HER activity.     

A comprehensive review on water management strategies and developments in anion exchange membrane fuel cells

In spite of significant achievements in alkaline exchange membrane fuel cells (AEMFCs) in recent years, they are still lagging behind proton exchange membrane fuel cells (PEMFCs) due to performance instability. Among the relevant operational parameters of AEMFC, the researchers have found that poor water management within the cell was the main reason for failure of the system. In the past five years, numerous modeling and experimental works were reported proposing different strategies to improve water management of AEMFC. With proper water management, the achievable power output in AEMFCs is comparable with that of PEMFCs or even more. Efforts have to be continued, but AEMFCs can become a strong competitor in the market place. This review paper discusses the strategies and developments impacting water management of AEMFCs providing knowledge source for upcoming studies.